Expert Answers to Readers’ Questions
- What is the difference between the glycemic index and glycemic load?
- Where can I get information about the glycemic index of foods?
- What is the glycemic index of sugar substitutes like NutraSweet?
- Are high-carbohydrate diets good for losing weight and weight control?
- Will going on a low-carbohydrate diet help me lose weight?
- Are sugar alcohol sweeteners like erythritol and xylitol good alternatives to sugar?
Glycemic index and glycemic load are two similar but different terms. Glycemic index indicates how rapidly a certain food increases blood sugar after eating, compared to the same amount of carbohydrate as white bread (50 grams of carbohydrate). Glycemic load, on the other hand, takes into account the glycemic index of a food multiplied by the carbohydrate content of the food. For most foods, the rule follows that a food with a high glycemic index will also have a high glycemic load. However, there are exceptions to the rule; carrots and watermelon have high glycemic index but a low glycemic load, due to the small amounts of carbohydrate found in these foods.
More information about the glycemic index of foods can be found in the Carbohydrate section of this Web site, in Dr. Walter Willett’s book Eat, Drink and Be Healthy, and on the University of Sydney’s Glycemic Index Web site.
Consuming foods made with NutraSweet-especially beverages-are a better option than consuming sugary drinks. Aspartame does not have a high glycemic index, since it is not a carbohydrate. However, foods and beverages with sugar substitutes should be limited since the lifelong effects of these products are unknown.
A high-carbohydrate diet is likely not advantageous to weight loss, and more importantly to long-term weight maintenance. This is because high-carbohydrate diets also tend to be low in fat. In the past two decades, there has been a tremendous focus on low-fat diets. In turn, food manufacturers have produced low-fat foods that are also high in refined carbohydrates and therefore tend to have a high glycemic index promoting more fat synthesis and storage. In addition, it is important to realize that fat is a vital component of a meal. Fat adds flavor to meals and can make them more satisfying. Furthermore, plant oils also contain “healthy” fats rich in monounsaturated and polyunsaturated fats.
Some people who go on a low-carbohydrate diet have managed to keep weight off in the short term, but the best studies show that on average the weight loss is small after one year. There has been much debate about the impact of low-carbohydrate diets on overall health. A recent 20-year study on 82,080 women found that that a low-carbohydrate eating pattern did not increase risk of heart disease; if the protein and fats mainly came from vegetable sources, a low carbohydrate eating pattern actually reduced heart disease. A controlled trial underway at the Harvard School of Public Health may give us a more definitive answer on the possible benefits of low-carbohydrate diets. The study is testing four diets with different amounts of carbohydrate, protein, and fat; it will follow 800 overweight volunteers for two years to see which type of diet is best for weight loss, weight maintenance, and overall good health.
Erythritol, xylitol, and other sugar alcohols have been used for decades to sweeten chewing gum, candy, fruit spreads, toothpaste, cough syrup, and other products. Newer, cheaper ways to make sugar alcohols from corn, wood, and other plant materials, along with their sugar-like taste, are fueling their use in a growing array of foods. Erythritol has even begun cropping up in beverages, on its own or combined with stevia in the “natural” calorie-free sweeteners Truvia™ and PureVia™. Other sugar alcohols you may see listed on food labels are mannitol, sorbitol, and hydrogenated starch hydrolysates. Sugar alcohols taste like sugar, with 50 to 70 percent of the sweetness of sucrose (table sugar). The body doesn’t break down or absorb sugar alcohols as easily as sucrose—you get four calories from a teaspoon of table sugar compared with 0.2 calories from erythritol and 2.4 calories from xylitol. There is a price to pay for the poor absorption of sugar alcohols: At high levels of intake, sugar alcohols can have a laxative effect. Erythritol’s manufacturers, however, say that erythritol is somewhat better absorbed than other sugar alcohols, and is therefore less likely to cause digestive discomfort.
The aim of the Harvard T.H. Chan of Public Health Nutrition Source is to provide timely information on diet and nutrition for clinicians, allied health professionals, and the public. The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site. The information does not mention brand names, nor does it endorse any particular products.