Americans are infatuated with low-carbohydrate dieting. In the quest to lose weight and improve their health, scores of men and women, and even adolescents and children, have jumped headfirst onto the low-carb bandwagon—often with little understanding of the benefits or drawbacks of this diet approach.
Is cutting carbs really a magic weight-loss formula? Scientific evidence backing the alleged health benefits of this eating style is limited. Low-carb supporters tell us to believe that carbohydrate-rich foods are the cause of weight gain and that if you eliminate carbohydrates, calories won't matter. Scientists are not convinced. Gary Foster, PhD, clinical director of the Weight and Eating Disorders Program at the University of Pennsylvania, and numerous others believe that weight loss on a low-carb diet results from eating fewer calories. If you eliminate any one food group and don't increase your intake of other food groups, you will lose weight.
Nevertheless, there is no way to ignore the appeal of any seemingly simple way to lose weight and the many claims of success with cutting carbs. "If it gets some people to eat fewer calories," says Foster, "then the dieting approach deserves attention." However, most health professionals and researchers, including Foster, are quick to point out that there remains a lack of solid evidence supporting the long-term safety and effectiveness of low-carb dieting.
Carbohydrates in Perspective
Much of the confusion over low-carb diets lies in the lack of understanding of what carbohydrates are and their role in the diet.
Carbohydrates make up one of the three major macronutrients found in food, and provide calories, or energy, for the body. In addition, many carbohydrate-rich foods such as whole grains, fruits, and vegetables also contain essential vitamins and minerals, plus fiber and phytonutrients important for health and disease prevention.
Carbohydrates come in two types, simple and complex. Although their chemical structures differ, the body treats them similarly and both types supply the same amount of calories. Fiber is also a form of carbohydrate, but it cannot be digested, so it does not supply calories. Simple carbohydrates occur naturally in fruits, dairy products, and some vegetables, and they make up the refined sugars, such as table sugar, used in sweet foods. Complex carbohydrates such as starch are the primary nutrient in grains (pasta, bread, and rice), potatoes, beans, and vegetables.
Popular low-carb diets suggest that in the initial phase dieters should eat no more than 20 to 30 grams of carbohydrates a day. This equates to half of a medium-sized bagel or a half cup of cooked pasta, leaving little room for whole grains, fruits, or vegetables. The Institute of Medicine (IOM), which is responsible for setting the recommended daily intake of nutrients in the United States, advises adults and children over the age of 1 year to consume at least 130 grams of carbohydrates a day, roughly six times what is recommended for the initial phases of low-carb diets. This minimum requirement is based on the brain's use of carbohydrates as its primary source of fuel by the central nervous system. The brain can only function on carbohydrates as no other nutrient reaches the brain. Nevertheless, most Americans on a regular diet easily meet this minimum amount.
Carbohydrates versus Calories Q&A
Q Does cutting carbohydrates lower blood sugar and insulin levels, leading to weight loss?
A In reality, weight loss on low-carb diets has little to do with the effects of blood sugar or carbohydrates' effects on the body. "It's more likely a result of cutting calories combined with the fact that high-protein foods tend to be more filling," says Foster. For instance, removing the bun from a burger, eating a salad instead of fries, and drinking a diet soda instead of a regular soda sounds like a "low-carb" meal, but it's also a lower calorie meal. "If you reduce calories, regardless of the source, for a long enough period of time, weight loss is inevitable," adds Foster. Add physical activity to the equation and success is even more likely.
Low-carb proponents would have you believe that eating carbs makes you want more carbs because of fluctuations in blood sugar levels. However, a decrease in blood sugar, which can occur an hour or two after eating a meal or snack consisting of mostly carbohydrates, has not been linked to hunger or desire for more carbohydrates. Unless you have diabetes or a pre-diabetes metabolic syndrome, the body keeps blood sugar in a stable range. Other body reactions and certain peptides and hormones play a much greater role in controlling hunger and satiety.
Q Is a low-carbohydrate diet more effective overall than a low-fat diet?
A Until recently, very little research on low-carb diets had been conducted. In the first year-long study comparing a low-carb diet to a conventional low-fat, high-carbohydrate diet, led by Dr. Foster, the results showed that after 12 months both groups had lost the same amount of weight. However, low-carb diets initially produced greater weight loss than conventional low-fat diets. The low-carb dieters lost nearly 7 percent of their body weight after 6 months whereas the traditional dieters lost about 3 percent of their body weight after the same amount of time. These findings have since been confirmed by similar studies. Foster and other researchers tend to agree that these comparisons simply show that any diet that reduces calories over time will work.
Q Does following a low-carb diet have possible cardiovascular benefits?
A These studies mentioned above also examined the effects of the different diets on lipid levels and glycemic control and found that after 6 months low-carbohydrate dieters experienced more favorable decreases in blood triglyceride levels, increased HDL-cholesterol levels, and improved glycemic control. Experts believe, however, that the reductions in blood cholesterol and glucose levels are a result of the weight loss.
Even so, the American Heart Association does not recommend this type of diet, objecting that it encourages people to eat foods high in saturated fats and cholesterol. Plenty of evidence points to an increased risk of heart disease and some forms of cancer from a diet consistently high in fat and saturated fat. The studies to date have not been conducted over a long enough period of time to determine whether low-carb diets may be linked to health problems that develop over many years, such as heart disease, cancer, bone disease, and kidney problems.
Q Do specially formulated products for people who are counting carbs make it easier to follow a diet with fewer carbohydrates?
A Most people find a low-carbohydrate diet gets boring after dining on mostly meat, eggs, and cheese. Food manufacturers are thus meeting this need by producing a variety of products for carb-conscious people.
These foods are designed for dieters who are counting carbohydrates (rather than calories) and have fewer net carbohydrates. These products may offer more variety, making it easier to stick to a low-carb diet. On the other hand, many of these products with reduced carbohydrates often have about the same number of calories along with a much higher price tag compared to their regular counterparts. Consumers should check the Nutrition Facts panel so they can choose the products that fit with their weight management goals.
Products for people interested in reducing carbohydrate intake often have label statements referring to "net carbs." The theory is that fiber, glycerin, and sugar alcohols used in these foods do not raise blood sugar as quickly or as high as regular carbohydrates, so they shouldn't be tallied when counting carbs.
Calories Still Count
Reducing carbohydrates may make sense as a calorie-cutting tactic for people whose diets largely comprise foods such as sweets, sweetened beverages, and baked goods. It makes little sense, however, to reject wholesome, nutrient-dense foods such as fortified and whole grains, fruits, and vegetables in favor of protein- and fat-rich foods or special foods low in carbohydrates. Obviously, not only the quantity, but also the quality of carbohydrates must be considered.
If there is one thing to learn from this latest lesson in dieting it is that calories still count. Although some foods are not reduced in calories, other products that are reduced in carbohydrate have fewer calories than their counterparts. To compare the caloric content of foods, consumers should check the Nutrition Facts Panel. The solution to the problem of overweight remains the same: maintaining a negative energy balance by a combination of eating fewer calories and increasing physical activity is the key to weight loss.
Lowdown on "Low-Carb" Labeling
Whether it's carb-smart, carb-wise, carb-fit, or just plain low-carb, no federal regulation defines these marketing terms used to sell the flood of new reduced-carbohydrate food products. In the absence of an official definition, "low-carb" can be interpreted in many ways. It may mean that the product has fewer carbohydrates than a comparable product or it may mean that it contains a specific amount of carbohydrates per serving. Even the labels of some foods that are naturally low in carbohydrates may be using label terms that call out to carb-conscious consumers.
To confuse matters further, some food labels refer to "net carbs" or "effective carbs." Again, no government or generally agreed-upon definition exists for this terminology but the terminology is typically used as the result when fiber and certain sweeteners, such as sugar alcohols and glycerin, are subtracted from the total carbohydrate content.
How Do They Do It? Reducing the Carbs in Traditional Foods
A variety of foods have been modified to meet the growing demands of low-carb consumers including bread, pasta, cereals, cookies, cakes, juice, soft drinks, and candy. The manufacturers of these traditionally carbohydrate-rich foods are using a variety of methods to reduce the net carbohydrate content per serving. The methods include:
- Increasing the amount of animal or vegetable protein, such as replacing wheat or corn flour with soy flour. Examples include soy-based chips, pasta, and breads.
- Increasing the amount of fiber. Examples include adding fiber, such as cellulose, to candy products, cereals, bread, and pasta.
- Using sugar substitutes or sugar alcohols in place of traditional sweeteners. Examples include soft drinks, fruit drinks, baked goods, and frozen desserts.
- Using smaller portions. Examples include baked goods, such as breads.
A word of caution: When food manufacturers make lower-carbohydrate products by replacing some of the sugar with sugar alcohols—sorbitol, mannitol, and maltitol are examples—a laxative effect may result. When these sugar alcohols are consumed in very large quantities they can cause cramping, diarrhea, or other digestive discomfort in sensitive individuals. Thus, foods that contain certain sugar alcohols and that are likely to be eaten in amounts that could produce such effects must bear the statement, "Excess consumption may have a laxative effect."
