TABLE 3.
Definitions of currently accepted indices for determination of quality carbohydrate-containing foods along with the pros and cons, discussion, and conclusion on including them in a future carbohydrate quality algorithm1
| Index | Definition | Pros | Cons | Discussion | Conclusion |
|---|---|---|---|---|---|
| Glycemic index (GI) and glycemic load (GL) | GI indicates the blood glucose response from consuming a particular carbohydrate-containing food as compared with a carbohydrate-containing reference food, typically glucose or white bread (38) | Beneficial for diabetes patients as a way to effectively control blood sugar (38).Potentially translatable for prevention and treatment of other diseases such as obesity, cancer, and heart disease (39).Potentially beneficial when used in combination with other nutritional quality indices to determine nutrient quality (29) | Labile marker that is alterable based on the effect of foods eaten together, preparation of that food, and time of day that the food is eaten (37, 40, 41).GI and GL are expressed in isolation while real-life dietary intake is not that of single nutrients, but food consumed within a matrix that involves interactions between different nutrients, the nutrients and the food form, and the foods and dietary patterns that contain those foods (42) | First publication on GI was introduced in 1981 as a ranking system of various carbohydrates based on their impact on postprandial glycemia and was originally intended for diabetes patients (41, 43).GL was developed shortly thereafter to describe the amount of carbohydrates in a portion of food and its corresponding increase in blood glucose concentrations. Although originally indicated for diabetes patients, GI and GL have been recommended for translation to other disease populations such as obesity, cancer, and heart disease for treatment and prevention of these diseases, with the need for impact assessment (39).The ICQC, an international summit held by experts in carbohydrate research, identified the important role that postprandial glycemia plays in health outcomes and therefore indicated GI as a valid index to measure carbohydrate quality (44).A review on a series of meta-analyses on GI and GL agrees with the ICQC, but with the caveat that many low-GI and -GL foods tend to be more energy dense and higher in undesirable fats, unfavorable nutritional characteristics for population health and therefore not indices to use in isolation of other factors (38). However, as exemplified by minimally processed and naturally occurring carbohydrates in grains, fruits, and vegetables, which are naturally low in GI and GL, the basis for their inclusion in reference diets is based on their additional qualities | A variety of systematic reviews and meta-analyses conclude that dietary fiber and whole-grain content would be more beneficial in determining carbohydrate quality over using GI or GL due to the mass quantity of studies correlating fiber and whole-grain content with improved health outcomes in comparison to GI and GL (35). It is noted that GI and GL can be useful for specific diseases such as T2D or as a complement to other carbohydrate quality markers but may not be as translatable to carbohydrate quality in isolation due to its reductionist approach (43, 45) |
| Whole grain (WG) and WG food | WGs are grain with specific components and proportions of endosperm, germ, and bran (46).WG food refers to the quantity of grain in a certain food product | The mechanisms of action by which WGs benefit human health is still debated, but the accolades of their quality are due to their provision of fiber, phytonutrients, vitamins, and minerals (47).Systematic reviews analyzing WGs effect on markers like weight loss/maintenance, improved glycemic control, blood lipids, and blood pressure show improvements in all of these markers but only when restricted to specifically oats and barley (48).Additional reviews have shown a positive effect of WGs on decreased cardiovascular disease incidence, diabetes incidence, and cardiovascular mortality, as well as all-cause mortality (34, 37) | Due to the variety in types of WGs as well as definitions of WG foods, it can be difficult to construct a consistent way to measure health outcomes from consumption and therefore elucidate correlations between health and WG consumption (49) | Since the rise of agriculture, WGs have been a key component of the human diet, with the most commonly consumed grains in the United States including wheat, oats, rice, maize, and rye, with wheat contributing the most to total intake (66–75%) (7).Recommendations around WGs were first implemented in the Dietary Guidelines in 2000 and have evolved over the years from “choose a variety of grains, especially whole grains” to “eat at least 3-ounce equivalents (oz-eq) of whole grain daily, and at least half of all grains consumed should be whole grains” in 2005–2010, with this messaging continuing in the 2020–2025 DGA guidelines (11, 50, 51).This messaging has seen a subsequent rise in WG consumption (52).There is debate about prioritization of fiber content over WG content as an indicator of quality and therefore health benefit, with research underway to determine the relation (46) | Despite the discrepancies in definitions of WGs, WG foods, and their corresponding health benefits, the knowledge of WG consumption as a benefit to human health is well established and therefore should be included as a carbohydrate quality index |
| Fiber | Total fiber consisting of dietary fiber and functional fiber, with dietary fiber composed of nondigestible carbohydrates and lignin that are intrinsic and intact in plants, and functional fiber as isolated, nondigestible carbohydrates that have beneficial physiological effects in humans (9, 53).Dietary fiber can be further broken down into soluble and insoluble fiber with different physiological benefits from each group | A series of systematic reviews have shown that high viscous soluble fiber from oats and barley has resulted in improved blood lipids, decreased systolic and diastolic blood pressure, and improved glycemic control, thereby decreasing the risk of various cardiometabolic diseases (54–56).Insoluble fiber consumption does not similarly result in lowered blood lipids, specifically from wheat bran, but diets rich in these insoluble fibers do benefit laxation (7, 39).An additional set of systematic reviews and meta-analyses indicated that fiber, irrespective of its food source, resulted in decreased incidence of diabetes and cardiovascular disease (34, 57, 58) | Due to debates about the labeling and measurement of fiber, as well as added fiber versus intact fiber, it can be difficult to consistently assess fiber content and type as related to health outcomes (7) | A recent paper examined a variety of carbohydrate ratios within carbohydrate-containing foods, with fiber as the consistent component to determine healthier foods and health outcome (37).While there is debate surrounding the specifics of fiber identities and therefore measurement and correlative abilities, fiber consistently appears to present itself as a valuable marker of quality | As a result, similar to WGs, fiber content seems to be an indicated and necessary metric to include in a quality carbohydrate formula |
| Added sugar | Added sugars are defined as those that are added to foods during processing, manufacturing, or preparation and therefore not naturally present in that food. This is in contrast to natural sugars, such as those found in whole fruit or dairy milk products | Epidemiologic and experimental evidence highlights added sugar and specifically sugar-sweetened beverages as a major public health concern when it comes to obesity (59, 60).The DGAC (61), a committee of nutrition science experts who analyze current data to make nutrition recommendations to the USDA and the HHS in their development of the DGAs, and additional studies further note that intake of added sugars, specifically sugar-sweetened beverages, also increases the risk of T2D, coronary heart disease, hypertension, elevated blood pressure, and stroke, and higher intakes of free sugars are linked to the development of dental caries in children and adults (59–63).An established added-sugar guideline allows for enforcement and regulation | Including added sugar as a metric is difficult for policy reasons due to the inability to analytically measure added sugar, as well as the differing standards between countries, and as a result, to attribute specific amounts to health outcomes (64) | Some studies suggest that, while sugar consumption is often correlated with these chronic diseases, this is not necessarily due to the sugar itself—for example, fructose in sugar-sweetened beverages—but rather the excessive consumption of sugar and other added-sugar–containing foods when compared with the same diets without excessive energy consumption from sugars (63). Therefore, studies suggest that it is not the presence of fructose or other added sugars themselves but rather the amount of added sugar consumed and the food matrix they are consumed within, highlighting this with the fact that whole fruit containing fructose often benefits health (65, 66).The DGA has taken different approaches over time to deal with empty calories or discretionary calories. Added sugars fit in this category as they add calories to food products but are not “intrinsic” in recommended carbohydrate foods. Thus, the sugars in fruits and milk are considered part of recommended dietary patterns, while added sugars are not. This has been a struggle over time to determine best practices to regulate and label added sugars as added sugars are always captured in total sugar chemical methods. So, if added sugars are required on a label, then those values must be calculated by established rules (64, 67, 68).The 2015 DGAC set a recommendation to limit intake of added sugars. The scientific basis of guideline recommendations of sugar intake has been extensively debated (67), with concerns about our inability to measure total sugar and added-sugar intakes in populations and in foods. But the 2015 DGA set a goal of 10% of calories coming from added sugars and the FDA included a DV for added sugars and a requirement for added-sugars labeling as part of the Nutrition Facts panel (67). The 2020 DGA are consistent with the 10% of calories as added sugars on its recommendation | Due to the agreed-upon stance regarding excessive consumption of added sugar and its impact on human health, percent added sugar seems a necessary indicator to include when developing a metric for quality carbohydrate designation |