Low-Carbohydrate DietsStephen Barrett, M.D.
Many promoters of dietary schemes would have us believe that a special substance or combination of foods will automatically result in weight reduction. That's simply not true. To lose weight, you must eat less, or exercise more, or do both.
There are about 3,500 calories in a pound of body weight. To lose one pound a week, you must consume about 500 fewer calories per day than you metabolize. Most fad diets, if followed closely, will result in weight loss -- as a result of caloric restriction. But they are invariably too monotonous and are sometimes too dangerous for long-term use. Moreover, dieters who fail to adopt better exercise and eating habits will regain the lost weight -- and possibly more.
The most drastic way to reduce caloric intake is to stop eating completely. After a few days, body fats and proteins are metabolized to produce energy. The fats are broken down into fatty acids that can be used as fuel. In the absence of adequate carbohydrate, the fatty acids may be incompletely metabolized, yielding ketone bodies and thus ketosis. Prolonged fasting is unsafe, because it causes the body to begin to digest proteins from its muscles, heart, and other internal organs.
Low-carbohydrate diets also produce ketosis. As it begins, large amounts of water will be shed, leading the dieter to think that significant weight reduction is taking place. However, most of the loss is water rather than fat; the lost water is regained quickly when eating is resumed. Appetite, often reduced during ketosis, also returns when a balanced diet is resumed.
Most low-carbohydrate diets do not attempt to limit the intake of proteins, fats, or total calories. (In other words, their fat content tends to be very high.) Promoters claim that unbalancing the diet will lead to increased metabolism of unwanted fat even if the calories are not restricted. This is not true, but calorie reduction is likely to occur because the diet's monotony tends to discourage overeating.
The most widely used low-carbohydrate diet is the one advocated by the late Robert C. Atkins, M.D., of New York City. His 1972 book Dr. Atkins' Diet Revolution sold millions of copies within the first two years. His 1992 update, Dr. Atkins' New Diet Revolution, has sold even more. The current plan has four steps: a 2-week "induction" period, during which the goal is to reduce carbohydrate intake to under 20 grams per day, and three periods during which carbohydrate intake is progressively raised but kept below what Atkins calls "your critical carbohydrate level" for losing or maintaining weight . The dieter is permitted to eat unlimited amounts of noncarbohydrate foods "when hungry," but ketosis tends to suppress appetite. The plan calls for checking one's urine for ketone bodies to ensure that the desired level of ketosis is reached. Atkins also recommended large amounts of nutritional supplements.
The AMA Council on Foods and Nutrition , Consumer Reports , and many individual experts have warned that the unlimited intake of saturated fats under Atkins' food plan can increase the dieter's risk of heart disease. In 2000, experts at the University of Kentucky did a computer analysis of a week's worth of sample menus and reported:
- The diet contained 59% fat.
- The diet provided fewer servings of grains, vegetables, and fruits than recommended by the U.S. Dietary Guidelines.
- Although the diet can produce short-term weight loss, long-term use is likely to increase the risk of both cardiovascular disease and cancer .
Another study was done by researchers at the Bassett Research Institute in Cooperstown, New York, who followed 18 Atkins dieters for a month. During the 2-week induction period, the dieters consumed 1,419 calories a day, compared with 2,481 calories a day before starting the diet, and lost an average of about 8 pounds. In the next phase, dieters averaged 1,500 calories a day and lost an additional 3 pounds in two weeks. Dieters in both phases cut back on carbohydrates by more than 90%, but the actual amounts of fat and protein they ate changed little. Some patients felt tired, and some were nauseated on the plan. Most indicated that they were eager to go back to their regular diet .
Another study found that (a) 41 overweight people who followed the Atkins diet for six months lost an average of 10% of their initial body weight; (b) most lowered their blood cholesterol level by 5%; (c) some increased their cholesterol level; and (d) 20 subjects who continued the program had maintained their weight loss at the end of a year .
In yet another study, researchers who compile the National Weight Control Registry analyzed the diets of 2,681 members who had maintained at least a 30-pound weight loss for a year or more. Because the Atkins diet has been used for more than 30 years, the researchers reasoned that, if it worked, its followers would be well represented. However, they found that fewer than 1% of these successful people had followed a diet with less than 24% or less of their daily calories in the form of carbohydrates. The mean duration of successful weight maintenance in this low-carbohydrate group was 19 months, whereas the mean duration of dieters who consumed more than 24% of their daily calories as carbohydrates was 36 months. Because so few Atkins dieters were found in the Registry, the researchers concluded that the Atkins diet may not create the favorable "metabolic advantage" claimed for it .
The nutrition committee of the American Heart Association has issued a science advisory warning that high-protein diets have not been proven effective and pose health risks. The report covered the Atkins, Zone, Protein Power, Sugar Busters, and Stillman diets. The committee stated:
- Such diets may produce short-term weight loss through dehydration.
- Weight loss may also occur through caloric restriction resulting from the fact that the diets are relatively unpalatable.
- The high fat content may be harmful to the cardiovascular system in the long run.
- Any improvement in blood cholesterol levels and insulin management would be due to weight loss, not the change in composition.
- A very high-protein diet is especially risky for patients with diabetes because it can speed the progression of diabetic kidney disease .
In 1999, Atkins set up a foundation to provide "funding for research and education on the role of controlled carbvohydrate utritional protocols in treating and preventing a wide range of medical conditions."  In 2002, a 6-month study funded by Atkins found that followers of the Atkins diet lost more weight than comparable people on a high-carbohydrate diet and improved their blood cholesterol and triglyceride levels . However, the dropout rate was much higher in the low-carbohydrate group and the improved lipid levels did not necessarily mean that the diet would have a cardioprotective effect in the long run . In response to publicity about the study, the American Heart Association cautioned:
- A high intake of saturated fats over time raises great concern about increased cardiovascular risk. The study did not follow participants long enough to evaluate this.
- The study did not actually compare the Atkins diet with the current AHA dietary recommendations .
In 2003, experts who evaluated reports indexed since 1966 in MEDLINE found that weight loss was associated with longer diet duration and calorie restriction but not with reduced carbohydrate content. The researchers concluded:
There is insufficient evidence to make recommendations for or against the use of low-carbohydrate diets, particularly among participants older than age 50 years, for use longer than 90 days, or for diets of 20 g/d or less of carbohydrates. Among the published studies, participant weight loss while using low-carbohydrate diets was principally associated with decreased caloric intake and increased diet duration but not with reduced carbohydrate content .
Atkins died in April 2003 of complications of a head injury .
In July 2003, researchers at the University of Pennsylvania reported the results of a controlled study of 63 people who were randomly assigned to either the Atkins diet or a conventional diet. The low-carbohydrate (Atkins) group lost about 4% more weight for the first 6 months, but there was no significant difference between two groups at 1 year. The low-carbohydrate diet appeared to improve risk factors for heart disease, but the authors concluded that more research is needed on the safety and effectiveness of this regimen .
The Bottom Line
Although short-range studies have found that low-carbohydrate diets can produce weight loss, no study has demonstrated that such diets are safe or effective for long-term use [11-16]. Atkins advocated his diet for more than 30 years and stated that more than 60,000 patients treated at his center have used his diet as their primary protocol. However, he never published any study in which people who used his program were monitored over a period of several years. Scorekeeping can be done simply and inexpensively by mailing an annual questionnaire and tabulating the results. Why do you suppose he never did this?
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