Carbohydrate Quality vs. Quantity

Shift your focus from carb quantity to quality

Human populations have thrived eating widely disparate amounts of carbohydrates. Yet, the Western diet full of low-quality carbohydrates predicts greater risks of cardiometabolic diseases. Recent research suggests that the typical focus on carbohydrate quantity should shift to carbohydrate quality. For example, shift from low-quality carbs with high glycemic index or high glycemic load (causing higher post-meal blood sugar spikes) including refined grains, starchy vegetables, and added sugars to high-quality carbs in fruits, whole grains, legumes, nuts, seeds, and non-starchy vegetables.

Carb quality is key

A 2018 study published in the Journal of the American Medical Association provides a refreshing degree of clarity for what might seem problematic—how to eat better. The purpose of the study was to determine if a low-fat or a low-carbohydrate diet would lead to greater weight loss for overweight adults. It turned out that both diets were similarly effective. How could that be? The researchers advised all study participants, regardless of their assigned diet, to cut back on added sugar (as in sodas, energy drinks, and sweet teas), refined grain products (as in bread, chips, and crackers), and highly processed foods (as in microwaved meals, fast food, and margarine). In addition, participants were asked to ramp up their consumption of vegetables and whole foods. To top it off, the researchers told the participants not to worry about portion sizes or calories.

It’s harder to gain weight while eating lots of high-quality carbs, meaning foods with relatively high levels of fiber and low amounts of added sugar and refined grains. Eat more veggies, especially the non-starchy kinds, and fruits, beans, nuts, seeds, and whole grains, while minimizing added sugar, refined grain products, and junk food. I eat spinach, cabbage, carrots, Brussels sprouts, kale, onions, and garlic frequently. Swiss chard, celery, tomatoes, green peppers, zucchini, green beans, and parsley also help keep me going (in more ways than one). Brown rice and beans and perhaps some meat show up for dinner several times each week.

Ratios of total carbs to fiber and sugar

Researchers at Tufts University compared four measures of carbohydrate quality on a 10-gram of carbohydrate basis for carbohydrate-rich food products. The measures included 1) 10 grams carb to 1 or more grams of fiber (10:1), 2) 10 grams carb to 1 or more grams of fiber and less than 1 gram of free sugar (10:1:1), 3) 10 grams carb to 1 or more grams of fiber and to less than 2 grams of free sugar (10:1:2), and 4) 10 grams carb to 1 or more grams of fiber and per 1 gram of fiber less than 2 grams of free sugar (10:1|1:2). Confused already? Food intake data for 2013-2014 and 2015-2016 came from the National Health and Nutrition Examination Survey Food and Nutrient Databases for Dietary Studies. The nutritional status of 2,208 carbohydrate-rich food protects was classified in terms of 12 food categories and overall on the basis of a 100-gram serving. The categories included calories, total fat, saturated fat, protein, sugar, fiber, sodium, potassium, magnesium, folate, and 8 vitamins and minerals.

Only 23.2 percent of the food products met the 10:1 measure, while 16.4 percent met the 10:1:1 measure. The foods that met these two measures had relatively healthy nutrient profiles including fewer calories, and less fat, free sugars, and sodium but higher protein, fiber, magnesium, iron, vitamin B6, vitamin E, and zinc. Note that the health status of a particular food depends on the nutrients considered and their relative importance for a better diet. In addition, the foods that met the 10:1 and 10:1:1 measures were not necessarily healthy. Rather they appeared to be healthier than the foods that did not meet these measures.

Total carbs, cereal fiber

Researchers at Harvard used data from two large cohorts, the Nurses’ Health Study and the Health Professionals Follow-up Study, to understand links between measures of carbohydrate quality and quantity and risk of coronary heart disease (CHD) during up to 24 years of follow-up. Food intake data were reported every four years for both cohorts and averaged over the length of follow-up. For both men and women, compared to the lowest quintiles of total daily carbohydrate intake, the highest quintile did not increase the risk of CHD after adjusting for confounders. Higher levels of cereal fiber consistently showed lower risks of CHD for men and women. Higher ratios of carbohydrate to cereal fiber and carbohydrate to starch predicted significantly higher risks of CHD for both men and women. The negative effects of higher carbohydrate or cereal intake relative to cereal fiber were more pronounced for participants less than 60 years of age at baseline. The beneficial effect of higher cereal fiber intake on CDH risk occurred at median daily intakes of 7.6 and 10.3 grams of fiber for men and women, respectively. (Most Americana eat about 15 grams of fiber per day.) Boosting daily cereal fiber intake to 20 grams (my daily target) might provide greater benefits. Interestingly, increased consumption of fruit and vegetable fiber did not show significantly lower risk of CHD. The messages of this study: 1) Eat more cereal fiber, 2) Lower your ratio of carbs to fiber.

Eat more fiber

Recent research suggests that human health more strongly reflects carbohydrate quality than quantity. Researchers in New Zealand conducted a series of systematic reviews and meta-analyses of 185 published longitudinal studies and randomized controlled trials to evaluate links between aspects of carbohydrate quality and markers of human health. Observational studies showed 15-30 percent decreases in all-cause mortality, cardiovascular mortality, stroke mortality, and incidence of coronary heart disease, stroke, type 2 diabetes, and colorectal cancer for people who ate high compared to low levels of fiber. Clinical trials showed significantly lower body weight, systolic bold pressure, and total cholesterol for high- as opposed to low-fiber participants. The greatest reduction in various health risks occurred with fiber intakes between 25 and 29 grams per day. Additional fiber intake might result in greater health benefits. Higher intakes of whole grains in the form of foods (as opposed to supplements) predicted reduced risks of various health markers, although confidence in the predictions was lower than those for fiber. Low as opposed to high glycemic index carbohydrates appeared to confer some protective effects on health but generally with low or very low confidence. The clear take-home message: Eat more fiber from whole grain foods, vegetables, fruits, and legumes. Your body will thank you.

Carbohydrate Food Quality Score

Members of the Quality Carbohydrate Coalition’s Scientific Advisory Council, a group linked to the food industry, proposed the Carbohydrate Food Quality Score (CFQS). It expands the number of nutrients of existing carb quality approaches from two (total carbs, fiber) or three (total carbs, fiber, free sugar) to four (total carbs, fiber, free sugar, potassium) or five (total carbs, fiber, free sugar, potassium, whole grains). The two CFQS versions (based on 4 or 5 nutrients) were applied to 2,596 carbohydrate foods (1,561 for grain foods) in the Food and Nutrient Database for the Dietary Studies. Substantially lower percentages of foods in 6 of 15 food categories were rated as “Higher Quality Carbohydrate Foods” compared to results from using the 10:1:1 measure. For example, 1, 8, and 24 percent of breads passed the test using CFQS-4, CFQS-5, and 10:1:1 measures, respectively. Expanding the number of nutrients CFQS-4 and CFQS-5 aligns more closely with the 2005-2020 Dietary Guidelines for Americans.

Support for the 10:1 measure of carbohydrate quality

Carbohydrates have traditionally been classified as either simple (free) sugars (primarily glucose, fructose, and lactose that are readily digested by humans) or complex carbohydrates that resist digestion in the small intestine but can be partly metabolized by microbes in the large intestine. Research has revealed large, metabolically important differences among free sugars and complex carbohydrates. Thus, the amounts of carbohydrates eaten may be less informative with regard to human health than the specific types of carbohydrates. Researchers have developed ways to classify carbohydrates according to their health value.

One group of researchers proposed that carbohydrate quality can be evaluated conceptually with three factors: 1) the amount of a carbohydrate consumed, 2) fibers (relatively non-digestible complex carbohydrates), and 3) free sugars. High-quality carbohydrates would 1) reduce blood sugar response following consumption, 2) improve digestion, and 3) provide anti-oxidants with anti-inflammatory capabilities. With respect to carbohydrates, a high-quality diet would emphasize whole grains with lots of fiber and minimize products with added sugars and refined carbohydrates. More specifically, a ratio of digestible carbohydrate to fiber of 10:1 might be a relatively easy way for shoppers to gauge carbohydrate quality—simply  by dividing the number of grams of carbohydrates per serving by the number of grams of fiber per serving using information from Food Facts on food packages.

Which carbs predict less weight gain?

Controversy reigns regarding the role of carbohydrates, especially compared to dietary fat, in weight gain and overall health. But does the amount of carbohydrate matter less than the quality of carbohydrates? Researchers in Boston used data from women and men participants in three large, long-term studies (Nurses’ Health Study, Nurses’ Health Study II, Health Professionals Follow-up Study) to evaluate weight gain during successive 4-year periods over 24 years of follow-up. Carbohydrate intakes were classified as 1) non-starchy vegetables, 2) fiber, 3) added sugar, 4) starch, and 5) starchy vegetables (corn, peas, potatoes, sweet potatoes).

The average participant gained 1.5 kg (3.3 lbs) every four years for 24 years for a total of 8.8 kg (19.4 lbs). Increased consumption of carbs with higher glycemic index or higher glycemic load predicted higher weight gain. Carb groups that predicted greater weight gain for each 100 gram increase in daily intake over 4 years included starchy vegetables (2.6 kg), starch (1.5 kg), sugar (0.9 kg), and refined grains (0.8 kg). On the other hand, each 100 gram per day increase in the following predicted less weight gain over 4 years: non-starchy vegetables fiber (3.0 kg), fruit (1.6 kg), and whole grains (0.4 kg). Each 10-gram increase in fiber intake predicted 0.8 kg less weight gain over 4 years. Participants with overweight and obesity exhibited stronger links with each of these carb groups compared to normal weight participants.

What to do

A note of caution: High-carb food products that pass a carbohydrate quality measure might be promoted as healthy regardless of other nutritional aspects. Most food quality rating systems will likely be relative, that is, identifying certain foods as more or less healthy than others based on the rating criteria. The rating system may help distinguish among ultra-processed foods, which should not be the centerpiece of your daily diet. Regardless of what the rating system says, limit your consumption of ultra-processed foods. You don’t need a food rating system to tell you that frozen pizza is less healthy than Swiss chard.

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