Month: May 2022

Peer-Reviewed Publication

THE ALLIANCE FOR POTATO RESEARCH AND EDUCATION (APRE)

A new study recently published in Frontiers in Nutrition has challenged the tendency in nutrition research to separate starchy vegetables from their non-starchy counterparts and categorize them with foods delivering lower nutritional value.

Whole grains, legumes, non-starchy vegetables, and fresh fruit are typically considered to be higher quality carbohydrate foods, yet starchy vegetables, including white potatoes, are typically categorized in nutrition studies with sweets, candy, and soda, when researchers assess subjects’ food intake and associations with health outcomes. This new study used five separate indices to assess carbohydrate quality to determine if this categorization of starchy vegetables is an accurate reflection of the foods’ nutritional value.

Four of those carbohydrate quality indices (CQIs), based on carbohydrate to fiber and sugar ratios, had been developed and validated in 2021 by researchers at Tufts University. The fifth index, the new carbohydrate food quality scoring system (CFQS-4) recently developed by scientists working with the Quality Carbohydrate Coalition, also incorporated potassium and sodium. All five indices had been previously published.

The new study screened more than 2,400 carbohydrate-containing foods for carbohydrate quality.  Recognizing that carbohydrates are present in a great variety of plant-based foods, the study expanded the range of food groups to include refined and whole grains, snacks and sweets, but also starchy and non-starchy vegetables, legumes and whole fruit. Starchy vegetables had not been tested before using the new carbohydrate quality metrics.

“Starchy vegetables are often not even viewed as vegetables and are routinely removed from high-quality food categories in nutrition research. That view is now challenged by the new nutrient profiling methods” said lead author Adam Drewnowski, PhD, researcher at the Center for Public Health Nutrition at the University of Washington. “Now that we have formal measures of carbohydrate quality that we can agree on, it is time to put starchy vegetables back where they belong.  There is no need to demonize ‘bad’ vegetables when the American diet could do with more produce of all kinds.”

“I certainly hope that the Dietary Guidelines Advisory Committee take note as they design a healthy diet at an affordable cost,” Dr. Drewnowski added

The four CQIs and the CFQS-4 had been published before but had not been applied to evaluating carbohydrate quality of legumes, vegetables and fruit.  The five indices were based on specific rations of carbohydrate, fiber, free sugar, potassium and sodium. Whereas potassium is under-consumed, sodium is consumed to excess. Both nutrients are recognized as ‘nutrients of public health concern’ in the Dietary Guidelines for Americans.

Based on the four CQI scores, nearly half of the 210 starchy vegetable foods analyzed in the study met the CQI definitions for high-quality carbohydrates, which were defined as those with evidence-based cut-off values for fiber and free sugar. Meanwhile, extremely few snacks and sweets (1-5%), candy and desserts (0-5%) and refined grain foods (10-12%) could be considered high-quality, according to the same CQI measures.

Based on the more comprehensive CFQS-4 model, which also accounts for foods’ potassium and sodium content, starchy vegetables scored most closely to non-starchy vegetables and fruit versus sweets and soda.

“I hope that this simple application of existing carbohydrate quality metrics to a wide spectrum of carb-containing foods will show that starchy vegetables belong with the high-quality carbohydrate foods” said Drewnowski. “Our application of other nutrient profiling has previously shown that potatoes and beans led the pack in terms of nutrients per penny. This latest demonstration clearly shows that all vegetables should remain together when it comes to both research and dietary guidance.”

Study Design, Strengths, and Limitations

More than 2,400 carbohydrate foods in the USDA Food and Nutrient Database for Dietary Studies were evaluated using four previously published CQIs, and one more recently created carbohydrate food quality scoring system (CFQS-4).

Specifically, the various CQI composites were:

• 10:1 Carbohydrate-to-Fiber model: at least 1 gram of fiber for every 10 grams of carbohydrate
• 10:1:1 Carbohydrate-to-Fiber-to-Free Sugars model: at least 1 gram of fiber and no more than 1 gram of free sugar for every 10 grams of carbohydrate 
• 10:1:2 Carbohydrate-to-Fiber-to-Free Sugars model: at least 1 gram of fiber and no more than 2 grams of free sugar for every 10 grams of carbohydrate
• 10:1|2:1 Carbohydrate-to-Fiber and Sugar-to-Fiber model: at least 1 gram of fiber for every 10 grams of carbohydrate and fewer than 2 grams of sugar per 1 gram of fiber
• The CFQS-4 model builds upon previous 10:1 and 10:1:1 ratios for fiber and free sugars relative to carbohydrate, but also assesses sodium (an over-consumed nutrient of concern) and potassium content (a shortfall nutrient of concern) according to the Dietary Guidelines for Americans.

Foods with at least 40% energy from carbohydrates per 100g dry weight were included in all analyses. The frequency and percentage of foods that met the CQI criteria were calculated for each food group. Carbohydrate quality scores were measured against the average energy densities of food groups and subgroups.

This study included a large, comprehensive data set using multiple nutrient profiling models. Further research to build upon these models, however, should continue to incorporate other vitamins and minerals in food quality assessments. Nonetheless, this study aligns with a broader, evolving body of literature showcasing the multi-dimensionality of carbohydrate foods and their role in human health. As Dr. Drewnowski explained, “Current efforts to inform dietary guidelines and regulatory frameworks would benefit from modern, comprehensive tools to define and assess carbohydrate food quality.”

This research was supported by the Alliance for Potato Research and Education (APRE) and by the Quality Carbohydrate Coalition (QCC), which is funded by Potatoes USA. Neither APRE nor Potatoes USA had an influence on the study design, conduct, execution, or data analysis after approving the initial proposal for funding. Dr. Adam Drewnowski is a member of the QCC-Scientific Advisory Council.

The article “Multiple metrics of carbohydrate quality place starchy vegetables alongside non-starchy vegetables, legumes, and whole fruit” is published in Frontiers in Nutrition (doi: 10.3389/fnut.2022.867378).

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JOURNAL

Frontiers in Nutrition

DOI

10.3389/fnut.2022.867378 

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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. 9^th 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

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DOI

10.3389/fnut.2022.896333 

Read the Full Study Summary