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Author: Kelsey Cornell

Nutrition Today publishes expert commentary on high-quality carbohydrates and physical performance

Posted on by Kelsey Cornell

January 8, 2018

Peer-Reviewed Publication
Fleishman-Hillard, Inc.

Denver, CO. – A report about high-quality carbohydrates and physical performance was recently released in the peer-reviewed journal Nutrition Today. The report focuses on commentary that took place during an expert panel. The results of the report suggest that balanced diets high in natural, carbohydrate-rich foods, including nutrient-dense potatoes, may be optimal for improving performance among elite endurance athletes. The report is aligned with numerous studies conducted over the past 40-50 years, which have suggested that carbohydrates are a primary macronutrient for sustaining and improving athletic performance.

The expert commentary, “High-Quality Carbohydrates and Physical Performance,” was authored by Mitch Kanter, PhD, and is a summation of a meeting of five sports nutrition researchers and practitioners. The meeting and this published commentary were funded by the Alliance for Potato Research & Education (APRE), as part of its ongoing research efforts to understand the role of potatoes in healthful lifestyles. Panelists discussed the existing research surrounding the nutritional needs for optimal physical performance and provided their collective perspectives on how dietary recommendations for athletes have evolved over the years. The expert panel included Janet Rankin, PhD, Virginia Tech; Katherine Beals, PhD, RD, CSSD, University of Utah; Bob Murray, PhD, respected researcher and lecturer in sports nutrition; and Lawrence Spriet, PhD, University of Guelph. The session was moderated by Mitch Kanter, PhD, chief science officer, FoodMinds.

To learn more about the role of potatoes in athletic performance, visit PotatoGoodness.com/Performance.

About Potatoes USA

Potatoes USA is the nation’s potato marketing and research organization. Based in Denver, Colorado, Potatoes USA represents more than 2,500 potato growers and handlers across the country. Potatoes USA was established in 1971 by a group of potato growers to promote the benefits of eating potatoes. Today, as the largest vegetable commodity board, Potatoes USA is proud to be recognized as an innovator in the produce industry and dedicated to positioning potatoes as a nutrition powerhouse.

Journal

Nutrition Today

DOI

10.1097/NT.0000000000000238 

Are all sources of carbohydrates created equal?

Posted on by Kelsey Cornell

February 13, 2020

Daily potato intake leads to better diet quality compared to refined grains

Peer-Reviewed Publication
FoodMinds LLC

UNIVERSITY PARK, PA -Potatoes are often equated with refined grains due to their carbohydrate content. Yet, potatoes contain fiber, resistant starch, and key micronutrients that Americans need more of in their diet. A randomized crossover study that included 50 generally healthy adults directly compared the nutrient quality and impact on cardiometabolic risk factors of non-fried potatoes to refined grains. The study was conducted by researchers at Penn State and was recently published in the British Journal of Nutrition. Its findings demonstrate that potatoes can support a healthy diet; daily intake of one serving of non-fried potato did not affect markers of glycemia and was associated with better diet quality compared to refined grains.

“Clinical studies are important to contextualize observational findings,” say Penn State Researchers. “Some epidemiologic studies have suggested an association between potato intake and increased risk of cardiometabolic diseases. However, the context around how potatoes are eaten, such as their preparation method or other foods eaten alongside them, may be important factors in explaining why our clinical trial findings differ from those of observational studies.”

Participants were randomly assigned to eat either a refined grain side dish (e.g., pasta, rice, white bread) or a steamed/baked potato side dish of equal calories each day with a main meal for four weeks. After a two-week break, the same individuals ate the opposite side dish with a main meal for another four weeks. Aside from being required to consume either a potato or refined grain side dish, no other dietary restrictions were placed on participants. Several markers of cardiometabolic risk were measured including plasma glucose, serum insulin, cholesterol and other blood lipids, blood pressure, and participants’ reported diet quality.

While neither refined grains nor potatoes impacted cardiometabolic risk factors, participants’ potassium and fiber intake, total vegetable and starchy vegetable intake and Healthy Index Score – a sign of how well people are following the Dietary Guidelines for Americans were higher when they ate potatoes, compared to refined grains.

“Americans eat too many refined carbohydrates and not enough whole grains or starchy vegetables, according to the 2015-2020 Dietary Guidelines for Americans. Our study findings suggest that eating 1 serving of non-fried potatoes in place of refined grains can help individuals meet more dietary recommendations.”

The study had several strengths, such as the randomized crossover design and isocaloric dietary substitution. All dishes were prepared in a healthy way with limited added fat or sodium. However, the researchers noted a few limitations: the need for larger sample sizes, a longer intervention time and controlled dietary intake rather than self-reported diets. “It is important to replicate our findings in other groups, such as those at higher risk of cardiometabolic disease. These findings apply to the generally healthy population.”

The article, “Daily intake of non-fried potato does not affect markers of glycemia and is associated with better diet quality compared to refined grains: A randomized, crossover study in healthy adults,” is published in the British Journal of Nutrition (doi: 10.1017/S0007114520000252). Authors include Emily Johnston, Kristina Petersen and Penny Kris-Etherton of Penn State. Funding was provided by the Alliance for Potato Research and Education.

Journal

British Journal Of Nutrition

DOI

10.1017/S0007114520000252 

Potato nutrients can help reduce sodium retention, may help reduce risk of hypertension

Posted on by Kelsey Cornell

June 21, 2021

New study finds that individuals with higher cardiometabolic risk may benefit from adding more dietary potassium, via potatoes, to a typical American diet

Peer-Reviewed Publication
FoodMinds LLC

A new study published in Nutrients investigated the effect of increased dietary potassium from a whole food source–baked/boiled potatoes and baked French fries–or a potassium supplement on blood pressure and other cardiovascular disease risk factors compared to a ‘typical American’ control diet (lower potassium intake) among 30 pre-hypertensive to hypertensive men and women. Results showed that including baked/boiled potato consumption as part of a typical American diet had the greatest benefit on reducing sodium retention, even more than the supplement, and resulted in a greater systolic blood pressure reduction compared to the control diet. Further, despite commonly held misbeliefs about French fries and their role in heart-healthy lifestyles, the authors observed that a 330-calorie serving of baked French fries, when eaten as part of a typical American diet, had no adverse effect on blood pressure or blood vessel function.

“While significant emphasis is often placed on reducing dietary sodium intakes to better control for blood pressure and cardiovascular disease risk, that’s only half of the story,” says Connie Weaver, PhD, the primary investigator. “Potassium plays just as an important role, and perhaps the ratio of potassium to sodium is most important in the context of the entire food matrix, as the potato meal resulted in a greater reduction of sodium retention than the potassium supplement alone.”

Evidence on the effect of increased dietary potassium on blood pressure from clinical trials is extremely limited, and this is one of the first known controlled feeding interventions investigating dietary potassium as the primary variable of interest.

“It’s important to establish clinical trials that follow observational research to establish a causal link between diet and health,” notes Weaver. “For example, in this clinical study baked French fries had a null effect on blood pressure, which counters observational findings, at least in the short term, and helps to prioritize the importance of focusing on a total diet approach for maintaining health versus one that overemphasizes avoidance of any single food or food group.”

Potatoes comprise roughly 20 percent of the vegetable intake in the American diet and help fill several nutrient gaps, including dietary fiber and potassium.1 Eating just one medium potato meets approximately 10 percent of an adult’s daily potassium needs. According to the 2020-2025 Dietary Guidelines for Americans, potassium is an essential nutrient of concern, indicating most Americans aren’t consuming enough. The mineral has been linked to improvements in cardiovascular and other metabolic health outcomes – including decreased blood pressure in those with hypertension. Overall, potatoes and French fries represent about 7 percent and 3 percent of potassium intake, respectively, in the United States.1

“Considering Americans fall significantly short in meeting daily potassium intakes, these findings show the importance of promoting, not restricting, whole food good-to-excellent sources of potassium in Americans’ diets, like potatoes,” Weaver said.

A Closer Look at the Study Methodology, Strengths and Limitations

Participants were randomly assigned to one of four 16-day dietary potassium interventions:

  • Control diet including 2300 mg potassium/day (reflective of typical intake, considered to be ‘low potassium’)
  • Control diet + 1000 mg of potassium from potatoes (baked, boiled, or pan-heated with no additional fat)
  • Control diet + 1000 mg from baked French fries
  • Control diet + 1000 mg from a potassium-gluconate supplement

Each diet was tailored to participants’ specific caloric needs while all other nutrients were kept constant. Blood pressure was measured across multiple visits of each phase, and participants also collected daily urine/stool samples to assess potassium and sodium excretion and retention.

The strengths of the study include a highly controlled diet, cross-over design, and excellent compliance. However, the researchers note a few limitations as well, including the study’s relatively small sample size, poor retention in study participation and relatively short study duration.

“All clinical studies are faced with limitations; however, despite those found in this study, the rigor of the study design is strong and unlike any other studies that have investigated the effect of a whole food – and potassium – on high blood pressure,” Weaver notes. “Through our carefully controlled balance study, we could determine the mechanism by which potatoes reduced blood pressure. Overall, we concluded that boiled or baked potatoes can help reduce systolic blood pressure – and baked French fries have no adverse effects on blood pressure and can be included as part of an overall healthy diet.”

The research manuscript, “Short-term randomized controlled trial of increased dietary potassium from potato or potassium gluconate: effect on blood pressure, microcirculation, and potassium and sodium retention in pre-hypertensive-to-hypertensive adults,” is published in Nutrients (doi: https://doi.org/10.3390/nu13051610). Authors include Michael Stone, Berdine Martin and Connie Weaver of Purdue University. Funding was provided by the Alliance for Potato Research and Education.

Journal

Nutrients

DOI

10.3390/nu13051610 

The glycemic index may be counterproductive to helping Americans adopt healthier diets

Posted on by Kelsey Cornell

May 10, 2022

Newly published perspective examines the shortcomings of the glycemic index as a measure of carbohydrate food quality

Peer-Reviewed Publication
The Alliance for Potato Research and Education (APRE)

Today, many people struggle to make healthy food and beverage choices in line with the Dietary Guidelines for Americans (DGA). In fact, the average American under-consumes nutrient-dense fruits, vegetables, whole grains, beans and dairy foods – and more than half of American adults have at least one diet-related chronic disease.1 To improve overall diet quality, Jill Nicholls, PhD, asserts in a recently published perspective in Frontiers in Nutrition, people need tools that are relevant, reliable and applicable – and evidence suggests the glycemic index (GI) falls short on all of the above.

“The GI is increasingly used and interpreted as a measure of overall carbohydrate food quality, with some proponents advocating for its broader adoption as a public health tool. However, the GI model doesn’t address nutrient density or translate well to healthy dietary patterns, and its narrow focus on just one dimension of carbohydrate-containing foods may divert public attention away from approaches to improving health that are accessible, affordable, culturally appropriate and environmentally sustainable,” stated Nicholls, owner of Food Context, LLC. “At best, it’s an incomplete gauge of carbohydrate food quality. At worst, it may be counterproductive to achieving the dietary recommendations set forth in the DGA.”

Intended for People with Type 1 Diabetes – Not the General Public

Developed in the 1980s as a blood glucose management tool for people with type 1 diabetes, the GI is a comparative measure of glycemic impact. The GI measures the ability of the available carbohydrate in a food to increase blood glucose. It is determined by measuring blood glucose after consuming 50 grams of carbohydrate from a single test food and normalizing to a comparable portion of a control food, typically pure glucose or white bread.2

Carbohydrate-containing foods are quite varied and make important contributions to dietary patterns, yet the GI measures only glucose response. It does not account for overall nutrient content, and research has shown it may not be an accurate predictor of overall diet quality. And because low-GI foods are not necessarily high in essential nutrients, over-reliance on GI values may lead to food choices that are inconsistent with current dietary guidelines. Energy-dense choices such as ice cream and candy bars, for instance, can have low GI values, while nutrient-dense choices that support healthy dietary patterns can also be high-GI foods, including carrots, potatoes and grains.

An Unreliable and Highly Individualized Measure of Glycemic Response

“The reliability of the GI has been scrutinized since its introduction more than 40 years ago, including critiques about methodology and questions about the relationship between a food’s GI value and true post-meal glycemic response,” said Nicholls.

Because GI values are calculated based on foods consumed in isolation and analyzed under standard laboratory conditions, their real-world application may be limited. “Under the GI model, fat, protein and fiber are treated as entirely independent variables, but that assumption is at odds with current views about our understanding of how eating patterns influence health based on all food and beverage contributions,” Nicholls explained.

Much of the research has demonstrated significant variability in both inter- and intra-individual glycemic responses to the same food. Thus, it remains unclear whether the GI is a property of foods or a characteristic of each unique individual consuming those foods. Emerging studies have found that glycemic responses are more similar within individuals than between them, and an array of factors in addition to meal composition can influence individual carbohydrate metabolism, including, meal timing, physical activity and sleep habits. 4

A Questionable Predictor of Health Outcomes

Research also indicates that the GI may not be the best carbohydrate food quality metric to assess diets and chronic disease prevention. In a landmark series of systematic reviews and meta-analyses, Reynolds et al. found that the association between the GI and risk of non-communicable diseases was low to very low compared to fiber or whole grains.5 Meanwhile, the dietary patterns emphasized in the DGA contain more whole grains and fiber-containing foods than Americans usually eat, along with higher amounts of fruits, vegetables, and dairy foods. These patterns are associated with lower risk for NCDs. Eating nutrient-dense whole foods as part of balanced meals during the day is an easy way to improve glycemic responses and improve diet quality without monitoring the GI of foods.

“The Mediterranean Diet is one example of a dietary pattern that has been associated with reduced disease risk; yet, not every food in a Mediterranean eating pattern is low GI,” Nicholls added. In addition, clinical trials have shown compelling evidence that high GI foods eaten within the context of high-quality dietary patterns can yield improvements in cardiovascular disease risk factors, and weight loss regimens may be less reliant on glycemic responses than expected.6-7

“Evidence increasingly suggests that it’s the total diet that counts. Improving the overall quality of an individual’s dietary patterns can have beneficial effects on a variety of diet-related chronic disease, but the effect of any single food choice is mediated by the other foods and beverages eaten, physical activity and other lifestyle choices. While the GI may illuminate some narrow insights, it also keeps many of these relevant variables in the dark.”

The article, “Perspective: The Glycemic Index Falls Short as a Carbohydrate Food Quality Indicator to Improve Diet Quality,” is published in Frontiers in Nutrition (https://doi.org/10.3389/fnut.2022.896333). Funding was provided by the Alliance for Potato Research and Education.

References:

1U.S. Department of Agriculture and U.S. Department of Health and Human Services. Dietary Guidelines for Americans, 2020-2025. 9th Edition. December 2020. [Internet]. Available from: https://www.dietaryguidelines.gov/sites/default/files/2020-12/Dietary_Guidelines_for_Americans_2020-2025.pdf

2Wolever, T.M., Jenkins, D.J., Jenkins, A.L., & Josse, R.G. (1991). The glycemic index: methodology and clinical implications. The American journal of clinical nutrition, 54 5, 846-54

3Zazpe, I., Sánchez-Taínta, A., Santiago, S., De la Fuente-Arrillaga, C., Bes-Rastrollo, M., Martínez, J., & Martínez-González, M. (2014). Association between dietary carbohydrate intake quality and micronutrient intake adequacy in a Mediterranean cohort: The SUN (Seguimiento Universidad de Navarra) Project. British Journal of Nutrition, 111(11), 2000-2009. doi:10.1017/S0007114513004364

4Berry SE, Valdes AM, Drew DA, Asnicar F, Mazidi M, Wolf J, et al, Human postprandial responses to food and potential for precision nutrition. Nat Med. (2020) 26:964–73. doi: 10.1038/s41591-020-0934-0

5Reynolds A, Mann J, Cummings J, Winter N, Mete E, Te Morenga L. Carbohydrate quality and human health: a series of systematic reviews and meta-analyses. Lancet. (2019) 393:434–45. doi: 10.1016/S0140-6736(18)31809-9

6Sacks FM, Carey VJ, Anderson CAM, Miller ER III, Copeland T, Charleston J, et al. Effects of high vs. low glycemic index of dietary carbohydrate on cardiovascular disease risk factors and insulin sensitivity: the OmniCarb randomized clinical trial. J Am Med Assoc. (2014) 312:2531–41. doi: 10.1001/jama.2014.16658

7Gardner CD, Trepanowski JF, Del Gobbo LC, Hauser ME, Rigdon J, Ioannidis JPA, et al. Effect of low-fat vs. low-carbohydrate diet on 12-month weight loss in overweight adults and the association with genotype pattern or insulin secretion: the DIETFITS randomized clinical trial. J Am Med Assoc. (2018) 319:667–79. doi: 10.1001/jama.2018.0245

DOI

10.3389/fnut.2022.896333 

Which promote greater metabolic health, almonds or potatoes? Rigorous, randomized trial weighs in

Posted on by Kelsey Cornell

March 7, 2022

No short-term, statistically significant difference between calorie-matched fries and almonds on key health metrics

Peer-Reviewed Publication
The Alliance for Potato Research and Education (APRE)

White potatoes — especially French fries — are often described in nutrition research literature and dietary guidance statements as having associations with obesogenic diets and as increasing chronic disease risk based on observational research findings. However, there is limited evidence from randomized controlled trials (RCTs) testing cause-and-effect relationships. Now, an RCT published in the American Journal of Clinical Nutrition demonstrates that adding a 300-calorie serving of French fries to one’s typical diet every day for a month does not result in differential weight gain or other biomarker changes associated with impaired blood sugar regulation compared to adding an isocaloric daily serving of almonds, generally considered a healthy snack option.

“In our School of Public Health at Indiana University-Bloomington and in my own work, we adhere to a slogan: ‘It’s About Knowing.’ Because conjecture is good, but knowing is better,” says David Allison, PhD, the study’s principal investigator. “The way we come to know is through rigorous, randomized controlled trials. Based on our RCT findings, there is no statistically significant evidence of differential effects between consuming a typical 300-calorie serving of French fries daily and a 300-calorie serving of almonds daily when it comes to weight gain or markers of type 2 diabetes risk, at least in the short term.”

Changes in body composition (i.e., body fat mass), body weight, fasting glucose and fasting insulin levels at the end of the one-month trial were comparable across the French fry and almond intervention groups and were not clinically significant. As expected, given the difference in carbohydrate content between the French fries and almonds, acute peak blood glucose and insulin levels were higher after consuming the French fries. However, these levels were not elevated beyond a normal range, and this difference did not have an apparent impact on any other glucoregulatory biomarkers.

“Our results show two food items identified previously for opposite associations with health outcomes had no differences in effects on the health outcomes we measured,” notes study co-author Daniel Smith, PhD. “Nutrition recommendations that focus primarily on single foods in isolation may be missing the mark. A more effective approach to dietary guidance is likely one that takes total diet, lifestyle and individual needs and risk factors into account.”

Study Design, Strengths, and Limitations

A group of 180 adult men and women were randomized to one of three treatment groups for 30 days, with 165 completing the study. The three arms included an additional 300 kilocalories/day from one of the three food items (below) and participants were asked to add the specific food item into their “normal daily diet.”

  • Almonds: approximately 1/3 of a cup of almonds, roasted and salted
  • Standard French fries: approximately the size of a medium serving
  • French fries with herb/spice mix: approximately the size of a medium serving, prepared with oregano, basil, garlic, onion and rosemary

Instructions were provided regarding storage and preparation methods of food items for all participants. Participants were simply asked to incorporate the specific food item into their normal daily diet. They were not instructed to compensate for these added calories in any way.

Body composition (body fat mass), body weight, blood sugar, insulin and hemoglobin A1c were measured at baseline and at study completion. A subset of five participants also completed post-meal evaluations to assess short-term blood sugar response.

The study’s strengths include its randomized controlled trial design, considered the gold standard in identifying causal relationships, as well as the standardization of the study foods’ preparation, presentation and convenience. Its limitations include the fact that it was a free-living study, limiting researchers’ control over the participants’ diets; however, such a study design also allows for real-world data collection. It also excluded participants with type 2 diabetes, limiting the application of the findings to individuals without the disease. Additionally, the study did not include an analysis of energy (calorie) intake, nor were satiety data collected, making it unclear exactly how the varied snack intakes affected calorie intake overall.

The research article, “French-fried potatoes consumption and energy balance: a randomized controlled trial,” is published in The American Journal of Clinical Nutrition (https://doi.org/10.1093/ajcn/nqac045). Authors include David Allison, PhD, Indiana University and Daniel Smith, PhD, University of Alabama at Birmingham. Funding was provided by the Alliance for Potato Research and Education; however, APRE had no influence on the study design, conduct, execution or data analysis after approving the initial proposal for funding.

Journal

American Journal of Clinical Nutrition

DOI

10.1093/ajcn/nqac045 

Method of Research

Randomized controlled/clinical trial

Subject of Research

People

Article Title

French-fried potatoes consumption and energy balance: a randomized controlled trial

Article Publication Date

18-Feb-2022


New study illustrates that potato protein ingestion strongly increases muscle protein synthesis rates at rest and during recovery from exercise

Posted on by Kelsey Cornell

June 6, 2022

The latest findings challenge outdated assumptions about the anabolic effects of plant-derived proteins

Peer-Reviewed Publication
The Alliance for Potato Research and Education (APRE)

Exercise enthusiasts have long presumed animal protein to be superior to plant-derived options for muscle protein synthesis due to its essential amino acid profile. While many plant proteins are deficient in one or more essential amino acids necessary for optimal muscle growth and repair, a new randomized controlled study published in Medicine & Science in Sports & Exercise shows that plant-derived proteins can still induce strong anabolic responses. Researchers at Maastricht University, The Netherlands, found that consuming 30 grams of potato-derived protein concentrate following resistance exercise strongly increased muscle protein synthesis rates to levels that did not differ from the response following the ingestion of an equivalent amount of milk protein concentrate.

“The anabolic response to exercise depends on the exercise stimulus and the postprandial increases in circulating amino acids,” said lead study investigator Luc J.C. van Loon, PhD, a professor of physiology of exercise and nutrition at Maastricht University Medical Centre. “In general, plant-derived proteins are considered to have lesser anabolic properties, due to their lower digestibility and incomplete amino acid profile. Our results show that ingestion of 30 g potato-derived protein will support muscle growth and repair at rest and during recovery from exercise.”  

The findings from van Loon’s research group demonstrate that potato-derived protein concentrate powder can be used to increase muscle protein synthesis rates both at rest and during post-exercise recovery in healthy, young men, at rates that do not differ from the ingestion of an equivalent amount of milk protein.

“The potato’s amino acid profile has no apparent deficiencies and ingestion of 30 g protein was shown to strongly stimulate muscle protein synthesis during recovery from exercise,” explained van Loon.

These study results are part of a growing body of literature that demonstrate the benefits of potatoes in physical activity and exercise recovery.1-3 As van Loon explained, “Although further dose-response studies in broader populations are undoubtedly necessary, these data seem to support the use of potato-derived protein concentrate as an effective means to support muscle conditioning.”

Study Design, Strengths, and Limitations 

Twenty-four young, healthy males between the ages of 20-28 years volunteered to participate in this randomized, double blind, parallel group study.

  • Participants completed resistance exercise on a seated knee-extension machine (randomized to complete with either their dominant or non-dominant leg) following a warm-up on a supine leg press machine.
  • Participants rested for 10 minutes following their exercise session. Blood samples were drawn, and muscle biopsies were taken from each leg.
  • Immediately after the biopsies, 12 participants ingested 30 grams potato-derived protein while the other 12 ingested an equivalent amount of milk-derived protein. 
  • Blood samples were collected over a 5-hour period following ingestion to determine blood amino acid, glucose, and insulin concentrations.
  • Second and third muscle biopsies were taken to determine muscle protein synthesis rates at rest and during recovery from exercise.

The strategic use of a randomized double-blind study design with a unilateral exercise protocol allowed for assessment of postprandial muscle protein synthesis in both exercised and non-exercised muscle. Further studies will need to assess dose-response relationships between smaller and larger doses of protein on muscle protein synthesis. Future studies will also benefit from assessing the effects of plant-derived protein concentrates on muscle conditioning after repeated bouts of exercise in larger and more diverse populations.

Nonetheless, the current data show “there is ample room for high quality plant-derived proteins in sports nutrition, such as protein from nutrient-dense sources like potatoes,” stated van Loon.

This research was supported by the Alliance for Potato Research and Education (APRE). APRE had no influence on the study design, conduct, execution, or data analysis after approving the initial proposal for funding.

The article “Potato Protein Ingestion Increases Muscle Protein Synthesis Rates at Rest and during Recovery from Exercise in Humans” is published in Medicine & Science in Sports & Exercise (10.1249/MSS.0000000000002937).

References

  1. Oikawa SY, Bahniwal R, Holloway TM, Lim C, McLeod JC, McGlory C, Baker SK, Phillips SM. Potato Protein Isolate Stimulates Muscle Protein Synthesis at Rest and with Resistance Exercise in Young Women. Nutrients. 2020 Apr 27;12(5):1235. doi: 10.3390/nu12051235.
  2. Flynn S, Rosales A, Hailes W, Ruby B. Males and Females Exhibit Similar Muscle Glycogen Recovery with Varied Recovery Food Sources. Eur J Appl Physiol. 2020. doi: 10.1007/s00421-020-04352-2
  3. Salvador AF, McKenna CF, Alamilla RA, et al. Potato Ingestion is as Effective as Carbohydrate Gels to Support Prolonged Cycling Performance. J Appl Physiol. 2019;127(6):1651-1659. doi: 10.1152/japplphysiol.00567.2019

DOI

10.1249/MSS.0000000000002937 

Method of Research

Randomized controlled/clinical trial

Subject of Research

People

Is it time to rethink the glycemic index?

Posted on by Kelsey Cornell

May 18, 2022

The glycemic index gives some healthy carbohydrates a poor score, while elevating other, less-nutritious foods. Understanding the complexity of foods and their interaction with lifestyle would be far more helpful for health-care professionals who are advising their patients on what — and what not — to eat.

Over the past half-century, type 2 diabetes cases in the United States have risen precipitously. Just 1% of adults had the disease in 1958; by 2020 it was 13% — around 34 million people1.

“It’s a very serious public health problem, and we need to address it,” says Mindy Patterson, an Associate Professor of Nutrition at Texas Woman’s University, and dietitian.

One of the key tools that physicians draw on to manage or prevent diabetes in patients is the glycemic index (GI), which ranks the impact of carbohydrate-containing foods on blood glucose levels on a scale of one to 100. Since it was developed in 1981, awareness of the index has spread beyond clinicians. Many people now consider it to be a metric for healthy nutrition.

However, use of this 40-year-old paradigm has become controversial among nutrition scientists and medical practitioners, says Joanne Slavin, a dietitian and researcher at the University of Minnesota’s Department of Food Science and Nutrition. “The index ignores many factors that determine how quickly carbohydrates are digested and absorbed,” she explains. Key omissions include how foods are grown, manufactured, cooked and stored; serving size; and the combination of foods eaten as part of a meal2.

The GI also doesn’t account for substantial heterogeneity in blood-glucose responses to the same food by different people, or even by the same person on different occasions, Slavin adds.

These problems have incentivized researchers to search for more comprehensive ways to evaluate carbohydrates and personalize glycemic control — while incorporating other nutritional indicators such as fibre content. The goal is to help health-care professionals support their diabetes patients to choose the most appropriate foods. And these foods, Patterson adds, should be affordable, available, and respectful of cultural eating patterns so that recommendations work in the real world.

Carbs are complex

The GI, with its narrow focus on glucose, skews the health value of some carbohydrate foods, says Slavin. Fructose, she points out, ranks a healthy-sounding 19 on the GI, but its consumption is associated with diabetes and heart disease3 — another oversight because the GI does not consider chronic disease risk. A candy bar, which is loaded with sucrose but contains little glucose, gets a better GI score than a slice of whole-grain bread, she adds.

Furthermore, there are numerous rankings for the same food, making the GI confusing for physicians and patients. Patterson cites the example of rice, which has 126 different entries for various brands and regional varieties, further sub-divided by cooking method4. The GI scores range from 37 (for Chinese rice vermicelli, cooked for 8 min) to 116 (Jasmine rice, Reindeer brand, made in a rice cooker).

These differences can be compounded by how the GI score is determined. When seven different labs assessed the same type of rice, GI scores ranged from 55 to 875.

Serving temperature also affects a food’s score. Cooked rice, when eaten hot, causes a higher glycemic response than the same rice eaten cold6. The same is true of other starchy foods like potatoes. “Cooking and cooling starch alters the amylose content,” says Patterson. This process increases the content of ‘resistant starch’ in carbohydrates, which then acts more like dietary fibre — moderating the glycemic response, she says.

One of the biggest issues with the index, says Patterson, is that it tests carbohydrates alone to derive a GI score, but these foods are rarely eaten in isolation. Most are consumed as part of meals also containing fat, protein and fibre, which alter glucose absorption and blood-sugar levels. “Butter the bread,” she says, “and the glycemic index drops.”

Attempts have been made to modify the GI to better reflect real life. The glycemic load (GL) adjusts GI scores for portion sizes, but it creates some confusing scenarios. High-GI foods may have a low GL. Watermelon, for example, has a GI of 72, but the GL of a standard-sized portion is only 4. What’s more, the calculations are complicated: to find the glycemic load, the GI must be multiplied by the amount of carbohydrate in a serving size, then divided by 100. Not only does the GL suffer from the same issues as the GI, it is impractical for real world situations.

It’s not one size fits all

Ongoing research continues to highlight individualized glycemic responses to foods. One study monitored 800 people for a week, finding a five-fold difference in post-meal glucose levels between the top and bottom 10%, though all had eaten the same foods. Dietary habits, physical activity, body composition and gut microbiota were all important factors in response7.

A more recent study assessed the postprandial metabolic responses of more than 1,000 healthy adults, eating identical meals over a 2-week period. Continuous glucose monitors mapped blood sugar levels and revealed large inter-individual variability, even between identical twins — suggesting that genetics were not the main cause of the differences8.

Such is the variability that even the same person can exhibit different responses to the same food eaten on consecutive days9 or at different times of the day10.

Altogether, such studies have found that many biological and behavioural factors influence glycemic response, including age, stress, health status, baseline insulin levels, alcohol consumption and sleep.

The upshot is that people with type 2 diabetes, and their physicians are in need of more holistic dietary tools. “Current approaches that demonize staple carbohydrate foods do little to promote the recommended pattern of foods known to improve health status and reduce disease risk,” Slavin wrote in one recent analysis11.

In 2021, an expert panel report outlined ways to revamp carbohydrate assessment12. The authors — including Slavin — outlined the need for a more expansive, standardized, evidence-based way to evaluate carbohydrate quality.

The panel envisioned a single simple carbohydrate-food metric that melds multiple intrinsic properties, including total fibre content, nutrient density, food group designation and processing effects. While such a metric will not fully capture all of a food’s health effects, the panel believes that it would make the metric more realistic and better able to inform public health policies, including the 2025–2030 Dietary Guidelines for Americans.

By separating the intrinsic food values from the extrinsic effects, there is a clearer pathway to fully personalized nutrition, says Patterson. Research can then build by better understanding the effects that carbohydrate quality has on human health. Many labs are already working towards developing such predictive models.

A more expansive analysis of healthy carbohydrates that ends the confusion over ‘high-GI’ plant-based, fibre-rich foods will give people, particularly those with diabetes, better information to make dietary decisions.

References:

  1. CDC’s Division of Diabetes Translation. United States Diabetes Surveillance System April 2017. https://www.cdc.gov/diabetes/data/index.html
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The Need for Nuance: Carbohydrate Quality Is Much More Than the Glycemic Index

Posted on by Kelsey Cornell

There is no globally accepted definition of carbohydrate quality – no equation, algorithm, or succinct way of identifying the quality of a carbohydrate-containing food, meal, or diet. Unlike protein and fat – where deficiency can lead to serious and even life-threatening situations – the physiological impacts of carbohydrate food intake are much more complex and individualized. Effects can vary with one’s lifestyle, dietary habits, health status, and age – among many other factors. Despite this complexity, carbohydrate dietary guidance often heavily relies upon a single, simplistic marker – Glycemic Index (GI) – despite its notable flaws and application limitations.

The Alliance for Potato Research and Education interviewed a select group of carbohydrate experts to better understand how the carbohydrate quality debate got to where it is today. This is the second of two articles exploring this topic – read the first article here.

Glycemic Index is an oversimplified approach with unintended consequences

Since it was developed in the 1980’s, the GI has been used as a simple surrogate for glycemic response – which was then made a measure of carbohydrate quality. Yet, over the decades, numerous scientific studies and nutrition experts have indicated that although the GI has its utility in a clinical or laboratory setting, this metric has significant shortcomings that make it a less-than-optimal measure of carbohydrate quality for consumers.

For one, experts argue that GI is a narrow indicator. Jamie Baum, PhD from the University of Arkansas states that “GI alone is not the right tool to determine the quality of a carbohydrate food. Among other things, it fails to account for total nutrition – the vitamins, minerals, fiber, and protein – in a food.” According to Julie Miller Jones, PhD, professor emeritus from St. Catherine’s University, negative health consequences can arise from selecting foods solely based on GI. “Some low-GI foods are high in fat and fructose, and elevated intake of many of these foods is not advisable. Meanwhile, avoiding breads and cereals – especially whole-grain versions – based on their high GI value might lead to low intake of cereal fiber, a dietary component associated with lower risk of cardiovascular disease and obesity. While avoiding potatoes due to GI concerns means missing out on a food that has a high satiety value and is a low-cost source of fiber and potassium.”

Even as a research tool, GI has its limitations. Several studies suggest that the GI is difficult to replicate, even in the same person following the same protocol. While researchers have gotten better over the years with standardizing procedures to minimize variability, people in the real world don’t live in the regimented way of a laboratory setting. Human routines often differ from day-to-day or week-to-week. Consequently, the GI results gathered under rigid lab conditions rarely reflect the actual response in free-living situations. 

Dr. Brooke Devlin, PhD from Australian Catholic University pointed out several confounders that make reliance on GI a dubious endeavor. “In the laboratory, the GI of a food is assessed by testing that food in isolation, and not as part of a meal. This is not how people eat in the real world. In addition, GI is usually tested in healthy subjects in the morning, limiting its utility for people with type 2 diabetes or in assessing its effects when eaten at different times of the day, including before or after meals. Finally, GI in the lab is based on the body’s response to 50 grams of available carbohydrate in a food. In order to consume 50 grams of available carbohydrate, one would have to eat an entire mini watermelon or unreasonable quantities of many other foods. The volume of food required to obtain a GI value could certainly produce a false perspective of the food’s impact on the body in normal circumstances.” 

Nick Bellissimo, PhD from Ryerson University in Toronto further elaborates on the concern with applying the GI to real-life settings, where mixed meals are typically eaten, and different preparation techniques are used. He explains, “a small amount of butter or oil added to a high GI food can greatly reduce the glycemic response to that food and, consequently, its GI. Additionally, evidence shows that two forms of the same food can lead to highly different glycemic responses – such as choosing a store-bought frozen potato product versus a homecooked potato. This makes GI an inadequate tool for representing the highly varied food options chosen by consumers today.”

For all these reasons, Richard Bruno, PhD, RD – a nutrition scientist at The Ohio State University – says, “I don’t put too much stock in the GI as a marker of carbohydrate quality. In a research setting, including my own where we study acute hyperglycemia on vascular dysfunction, GI is a helpful tool to model responses to isolated foods or to induce a physiological effect. However, it is nearly impossible to predict the GI of a mixed food based on its macronutrient composition. There are too many variables in play including carbohydrate type, and interactions with other dietary constituents.”

Research and guidance must move beyond GI to consider other impacts on health – both glycemic and otherwise

While carbohydrate-containing foods have often been classified according to their GI value, this solitary and flawed focus needs to shift. According to Siddhartha Angadi, PhD, a cardiovascular exercise physiologist and assistant professor at the University of Virginia, carbohydrates may not even be the most concerning macronutrient for insulin resistance and impaired glucose tolerance. “Physiologists have known for close to a century that if you want to make someone insulin resistant or worsen glucose tolerance in a clinical laboratory setting, you feed them an excess amount of fat (especially saturated fat) – not carbohydrates,” explains Dr. Angadi. “The decades-long focus on defining carbohydrate foods based on GI therefore needs to shift to better health indicators, especially when considering outcomes related to chronic disease.”

Of course, it is important to note that the health impact of a carbohydrate-containing food is not just related to its nutritional components. Dr. Angadi explains that “factors such as genetics, physical activity, sex, age, and body mass index can have just as much of an impact on the body’s metabolic response as the food itself.” Meanwhile, individual choices such as food preparation techniques or specific meal combinations can also have a notable impact, as explained by Dr. Bellissimo.

Developing a new definition for quality carbohydrate-containing foods thus requires a shift away from the singular focus on GI towards a more holistic approach. While focusing on the nutritional value of a food is an important first step in defining quality, the approach must also recognize the need for individualistic adaptations based on personal lifestyle choice and genetic factors. Only then can a quality carbohydrate definition be a truly valuable tool in helping consumers choose the right foods that promote their health.

The Need for Nuance: Nutrition Researchers Dig into What’s Needed for Future Carbohydrate Guidance

Posted on by Kelsey Cornell

Carbohydrates are a diverse group of compounds, ranging from simple monosaccharides – such as glucose and fructose – to various types of polysaccharides, like starch and dietary fiber. And, the foods that contain them are even more diverse – from highly nutrient-dense and health-promoting, to energy-dense and potentially detrimental to human health. Despite this diversity, the role that carbohydrates play in human health and nutrition is often overly reduced to a source of calories, frequently assumed to have the same function in the body and the same impact on health – and without consideration of other important determinants of health like food access, cost and cultural acceptance.

The Alliance for Potato Research and Education interviewed a select group of carbohydrate experts to better understand how the carbohydrate debate got to where it is today, and what the research community and health professionals can do to provide clarity and enhance understanding of the nutritional role carbohydrates play in our diet.

Nuanced carbohydrate guidance is needed

According to Jamie Baum, PhD, a nutrition scientist from the University of Arkansas, “There is a wide knowledge gap between what nutritional scientists understand about carbohydrates, and what consumers believe about carbohydrates. There is a need to educate consumers about nutrient-dense carbohydrate foods that contain high amounts of fiber, vitamins and minerals, and food sources that contain a lot of added sugar and refined carbohydrates with little-to-no additional nutrients.”

Part of this knowledge gap stems from a lack of nuance in current carbohydrate guidance. While the Dietary Guidelines for Americans recommends people consume nearly two-thirds of calories from carbohydrates, with some advice around fiber and added sugar specifically, in general, the advice is simplistic. The research and public health communities have more nuanced recommendations for the other macronutrients (protein, fat), usually including specific guidance on the subtype of macronutrient (i.e., unsaturated vs. saturated fat, complete vs. incomplete protein) and the food sources of these macronutrients (i.e., plants, animals). Such detailed advice does not yet exist for carbohydrate-containing foods.

Dr. Baum suggests we think of carbohydrate quality in a similar way to how we think about protein – in terms of the nutritional value. Indeed, nutrition is a foundational pillar for any definition that identifies quality sources of carbohydrates, but other non-nutritive social determinants of food decisions and health should also be considered as well.

Current carbohydrate indicators need to be reexamined

Several different sources of data and contextualizing factors are required to understand carbohydrate’s role in the diet and provide dietary guidance. The current scientific dialogue focuses on just a few and, some would argue, flawed sources and indicators of carbohydrate quality. In fact, a recently published article outlines at least 20 factors that should be taken into consideration when defining carbohydrate quality, including the nutritional value of the food in question, the biological and metabolic changes it promotes, and the cost and accessibility of the food. Brooke Devlin, PhD, the clinical research officer at the Australian Catholic University in Australia, emphasized that she doesn’t “[think] there is necessarily one metric that is most meaningful in defining carbohydrate quality. We need to take into consideration several factors.”

However, carbohydrate dietary guidance often relies on a single metric, the measurement of a food’s Glycemic Index – which does not consider the multitude of ways a carbohydrate-containing food can impact health. Nick Bellissimo, PhD, a nutrition scientist at Ryerson University, questions the over-reliance on GI, a measurement of how one food consumed in isolation impacts glycemic changes in the hours following consumption of that food, to develop food-based guidance. “The field must move beyond a GI-based approach for judging carbohydrate quality,” suggests Dr. Bellissimo. Instead, he proposes we take a different approach. “Food and function studies (e.g., satiety, cognition, performance) are needed that investigate carbohydrates first in isolation, secondly within mixed meals, and then followed by studies investigating a dietary patterns approach on functional markers of interest.” See more detail on the limitations of GI here.

The current dialogue has created confusion about carbohydrate sources, like the potato

As one example, Dr. Devlin notes that potatoes are often the victim of reductionist carbohydrate guidance. “Despite being a vegetable, potatoes are sometimes associated negatively with carbohydrates.” Dr. Baum agrees, suggesting that the nutritional value of white potatoes is misunderstood, as is the myriad of ways that potatoes can be prepared and consumed. The white potato is a nutrient-rich vegetable, an excellent source of vitamin C and a good source of potassium. It is also a high-quality source of carbohydrates, like resistant starch, as well as a source of high-quality protein, on par with many animal proteins. While white potatoes have a reputation for negatively impacting glycemic response, Dr. Bellissimo explains that “recent experimental trials show benefits of consuming potatoes on many functional outcomes that are uncoupled from their glycemic response; and glycemic response to various forms of potatoes has been shown to be low-to-moderate in both young and elderly adults.”

Where do we go from here?

So how do we ensure that consumers know which carbohydrate-containing foods are the most nutritious and the highest quality? Adding more nuance to carbohydrate guidance while needed, is a big undertaking, requiring multi-stakeholder input and support. More importantly, it must be led by a multicultural diverse group of researchers who are experts in nutrition, carbohydrates and diverse populations so that realistic and relevant guidance is developed.

Recent Review Shows Potatoes are a Top Source of Resistant Starch

Posted on by Kelsey Cornell

A recent narrative review was published in the Journal of the Academy of Nutrition and Dietetics that identified food sources of resistant starch, an indigestible fiber linked with numerous health benefits.  Potatoes were identified as a top source, especially when cooked and then chilled. The authors also found that the enrichment of processed foods with resistant starch may be one way to improve intake and enhance a foods’ nutritional profile, without losing sensory appeal. The database the authors developed is intended to help health practitioners support patients who would benefit from increasing their resistant starch intake and to assist researchers in developing resistant starch dietary interventions.

Citation: Resistant Starch Content in Foods Commonly Consumed in the United States: A Narrative Review. Patterson, Mindy A. et al. Journal of the Academy of Nutrition and Dietetics, Volume 120, Issue 2, 230-244.