Summary
Diets that emphasize foods with higher glycemic index and higher glycemic load predict worse health. Find foods that you like to eat and which have lower glycemic loads. Increase your consumption of non-starchy vegetables (as in leafy green veggies), fruits (apples, berries), and whole grains, while reducing your intake of sugar (as in soft drinks) and products with refined grains (as in white bread).
What are glycemic index and glycemic load?
Glycemic index refers to the type of carbohydrate (how rapidly it can be digested and how much it elevates blood glucose), while glycemic load reflects the type and the amount of carbohydrate in a serving of food. Glycemic load represents the effect a serving of food has on blood glucose. A food, such as a raw carrot, can have a moderate glycemic index (the carbohydrate in a carrot is fairly readily digestible) and a low glycemic load (a raw carrot doesn’t contain digestible carbohydrate).
Why should you care about glycemic status of the foods you eat?
Diets that feature foods with high glycemic index or high glycemic load predict increased risks of bad health outcomes including larger post-meal blood glucose response, cardiovascular disease, type 2 diabetes, cancer, and weight gain.
Post-meal insulin response
Sharp rises in blood sugar immediately following a meal and sharp falls in blood sugar two hours later predict adverse health outcomes. Researchers at the University of Sydney in Australia developed a food insulin index that quantified the degree of insulin response for 120 individual foods commonly found in Western diets. The index was based on the glycemic load and energy content of each food. Their study then investigated how well the index values for individual foods predicted the insulin response for mixed-food meals. Twenty-one healthy college students (average age 24 years) ate 2,000 calorie test meals designed to mimic breakfast, lunch, dinner, and snacks. The meals had widely varying glycemic index and glycemic load values. On a unit-energy basis, meals that consisted of foods with a low glycemic load (< 50) predicted lower post-meal insulin levels than meals with high glycemic loads. The carbohydrate content of the meals did not predict insulin response. The meal (actually a snack) with the lowest insulin response (35 out of 100) included walnuts, raisins, and carrot juice. Meals that emphasize low-sugar, low-starch, and minimally processed foods may help keep post-meal blood insulin levels of the safe range.
Coronary heart disease
For years, medical authorities advocated a low-fat diet to reduce risk of cardiovascular disease. In fact, we Americans reduced our intake of fats but also increased our intake of sugary and starchy carbs. Researchers at Harvard used data from 75,521 female nurses aged 38-63 years in 1984 in the Nurses’ Health Study to see if the glycemic load of participants’ diets predicted risk of coronary heart disease.
Compared to participants in the lowest quintile of glycemic load, those in the highest quintile had a significant 57 percent higher risk of developing coronary heart disease during 10 years of follow-up. After adjusting for conventional coronary heart disease risk factors, the risk increased to 98 percent. Potatoes and cold-breakfast cereals (8 and 4 percent, respectively) held the top two spots in glycemic load contribution. Women with body-mass index values greater than 29 (in the overweight and obese categories) had 97 percent higher risk of coronary heart disease than women with body-mass index less than 23. Thus, diets rich in easily digestible and absorbed carbohydrates (including many low-fat diets) predict greater risk of coronary disease, regardless of coronary heart disease risk factors.
More on coronary heart disease
Consuming foods and meals with lower glycemic index and lower glycemic load may reduce risk of developing type 2 diabetes. Might the same be true for coronary heart disease? Two British researchers conducted a meta-analyses of longitudinal studies to find out. Based on 12 studies, researchers found a significant 44 percent higher risk of developing coronary heart disease over an average 11 years of follow-up for every 65 grams per day increase in glycemic load. Every 10-unit increase in glycemic index predicted a 24 percent increase in risk of coronary heart disease. The researchers concluded that the relationship between glycemic load and glycemic index and coronary heart disease is likely causal, not just coincidental. If you want to reduce your risk of coronary heart disease and other ills, increase your intake of low-glycemic load foods (non-starchy veggies, berries, beans, unsweetened dairy products) and reduce your intake of high-glycemic load and index foods (refined grain products such as most breads, cookies, cakes, as well as sugar-sweetened beverages).
Type 2 diabetes
Medications and lifestyle changes comprise the therapies for type 2 diabetes. The American Diabetes Association typically recommends weight loss complemented with lower intake of high-calorie foods and increased physical activity as the lifestyle changes. Alas, only a modest fraction of people are able to lose substantial weight permanently. Recent research suggests that improving diet through reducing intake of high-glycemic load carbs can help people with type 2 diabetes manage their blood sugar levels.
Researchers at the University of Virginia developed the Glycemic load, Exercise, and Monitoring (GEM) program as an alternative approach to managing type 2 diabetes. The monitoring portion of the program seeks to educate participants about how foods affect blood glucose levels, induce participants to learn which food choices raise or lower blood sugar, and motivate participants to eat better and engage in more physical activity. A preliminary randomized controlled trial included 55 people with an average age of 55 years and with type 2 diabetes diagnosed within the past 5 years. Participants were randomized to the experimental program or to routine care. Those in the GEM program were invited to five classes to orient them to the program, review a GEM manual, and to learn how to use a provided blood glucose monitoring unit.
At 6 months from baseline, participants in the GEM program had significantly lower and clinically meaningful HbA1c (1.0 percentage point) than participants in routine care (0.1 percentage point). GEM outperformed routine care in a number of ways: better knowledge of type 2 diabetes, lower intake of high-glycemic foods, fewer total carbs, fewer calories, lower weight, greater HDL-cholesterol, higher perceived quality of life, fewer concerns about diabetes, and greater diabetes empowerment. All this without increasing diabetes medications. Overall, the GEM program yielded better results medically and psychologically than routine care.
Visualizing the effects of foods on blood sugar
The message to cut back on added sugars, especially sugar-sweetened drinks, appears to have made its way into the public conscientiousness. But a trio of UK doctors lamented that the adverse effect of starchy carbohydrates on blood glucose levels seems to be ignored or misunderstood. Many patients and health professionals believe, erroneously, that table sugar has a stronger effect on blood sugar than a baked potato. It’s useful to consider the glycemic index and glycemic load of a food when gauging its effects on blood sugar.
Doctors and patients have a hard time visualizing glycemic load. The UK doctors addressed this problem by giving patients a handout that compared the blood sugar raising effect of foods in terms of a 4-gram teaspoon of table sugar. Most people can visualize a teaspoon of table sugar. The handout visually showed how many teaspoons of sugar correspond to one serving of a specific food. For example, a serving of boiled basmati rice equates to 10.1 teaspoons of table sugar. Ouch! A serving of boiled broccoli corresponds to one-fifth of a teaspoon. Much better. The trio of doctors gave 69 patients the handout and provided feedback from bi-monthly blood glucose, weight, and blood pressure measurements. Over 3 years, the cost of diabetes medications declined compared to patients in nearby general medical practices. In addition, the prevalence of obesity declined and blood glucose control improved. This effective approach could easily be adopted in other general medical practices.
Carbohydrate quality vs. carbohydrate quantity
Carbohydrate quality seems to be more important than carbohydrate quantity in terms of health value. Increased intake of high-glycemic load grains, potatoes, and added sugars (especially in drinks) seems to be causally related to obesity, diabetes, cardiovascular disease, and some cancers. However, increased consumption of non-starchy vegetables, whole fruits, legumes, and whole kernel grains seems to be healthful. Abundant fiber, both soluble and insoluble, may account for the much of the health value of higher-quality carbohydrate foods. People with insulin resistance or diabetes may especially benefit from increasing their intakes of higher-quality carbs.
Weight gain
Controversy reigns regarding the role of carbohydrates, especially compared to dietary fat, in weight gain and overall health. But does the quantity 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 a 24-year total of 8.8 kg (19.4 lbs). Increased consumption of carbs with higher glycemic index or glycemic load predicted greater 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 (3.0 kg less), fruit (1.6 kg less), and whole grains (0.4 kg less). 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. If you’re interested in reducing or avoiding weight gain, increase your intake of non-starchy vegetables, fruits, and whole grains, while reducing your intake of sugar-sweetened drinks, other sources of added sugar, refined grains in their many guises, and fried potatoes.
Soft drinks and white bread
Researchers at Brigham Young University created a database of glycemic index and glycemic load values of 7,976 different foods using data from 10 cycles of the National Health and Nutrition Examination Survey. Soft drinks and white bread topped the list of foods that contributed the most glycemic load. Other high glycemic load foods included fruit drinks, pizza, and French fries. On a positive note, the trend of glycemic load values for a typical American diet declined progressively from 1999-2000 to 2017-2018. One way to Eat Better is to lower the glycemic load of your diet. To do that, limit your intakes of soft drinks and white bread.
