By Dónal P. O’Mathúna, PhD
The Atkins® diet is one of the most popular weight-loss programs people are embracing these days. Dr. Atkins’ New Diet Revolution, the book that the late Robert C. Atkins wrote to popularize the approach, has been on the New York Times bestsellers’ list continuously for five years.1 The low-carbohydrate, high-protein approach is not new, with Atkins himself having popularized the same basic principles in an earlier book in the 1970s. Several other best-selling diets use the same general approach (the Zone, Carbohydrate Addict’s, and Sugar Busters diets). Prior to these, similar diets have been promoted from time to time since William Banting first proposed it in the 1860s.2
The Atkins diet flies in the face of the conventional low-fat approach to dieting. Atkins pointed out that while Americans have decreased the proportion of fat in their diets from 40% to about 32%, obesity has become an epidemic.3 More than half of all U.S. adults and about a quarter of U.S. children are overweight, and the trend is moving in the wrong direction.4 The prevalence of obesity rose from 12% to 18% between 1991 and 1998, with increases in all states and for all ages, but most among the youngest and most educated.5 The problem is on the increase in affluent societies around the world.6
In response, many are turning to various weight-loss programs, now estimated to be a $33 billion industry.7 Among adult U.S. women, 43.6% are trying to lose weight and 34.4% are trying to maintain their current weight.8 For men, the respective numbers are 28.8% and 35.1%. Of concern also is that in addition to overweight women trying to lose weight, almost one-third of those women who are of normal weight are trying to lose weight.8
Mechanism of Action
According to Atkins, although the American diet has reduced its proportion of fat, it has been replaced by carbohydrates, including lots of simple sugars. The Atkins diet calls on people to avoid carbohydrates, initially recommending they constitute only 10% of one’s intake. People are allowed to eat unrestricted amounts of high-protein foods, like meat, eggs, fish, cheese, olives, and nuts. These foods include more fat, but the lack of carbohydrates mobilizes the body’s stored fat and uses it up. This leads to a metabolic condition called ketosis, in which elevated ketone levels result from fatty acid breakdown. Once the initial two-week period is completed, small amounts of complex carbohydrates are allowed (primarily vegetables and fruits), but breads, pastas, and starchy foods should be a thing of the past. The goal is to keep carbohydrate intake under 20 g/d.2 In addition, people feel quickly filled up by protein and are less likely to overeat or snack.
One of the problems with most weight-loss programs is a lack of controlled research on their effectiveness or safety. Given the popularity of low-carbohydrate, high-protein diets, a systematic review of research on these types of diets was published early in 2003.2 A total of 94 diets were revealed, 38 of which were described as lower-carbohydrate diets (> 60 g/d). Of these, 13 were lowest-carbohydrate diets of the type recommended by Atkins (> 20 g/d). People lost weight on all diets, although no controlled trials of lower-carbohydrate diets lasted longer than 90 days.
When comparing the effectiveness of the different diets, the many variables in the study designs presented difficulties for the reviewers. When comparing the most similar studies, weight loss did not differ significantly between the lower-carbohydrate and higher-carbohydrate diets, or between the lowest-carbohydrate and lower- carbohydrate diets. The 22 diets producing the largest weight losses varied widely in their carbohydrate content. The most important predictors of weight loss were restricted calorie intake, longer duration, and higher baseline body weight. The lower-carbohydrate diets were associated with reduced calorie intake. The authors concluded that "there is insufficient evidence to make recommendations for or against the use of these diets."2
The first randomized controlled trial (RCT) of the Atkins diet was published in 2003.9 The study randomly assigned 63 obese subjects (body mass index [BMI] = 34) to the Atkins diet or a conventional diet (high- carbohydrate, low-fat, low-calorie). Contact with health care professionals was kept to a minimum to simulate the self-help nature of these diets. Drop-out was high (41%) and not statistically different between the two diets. Those on the Atkins diet had significantly more weight loss at 3 months (P = 0.002) and 6 months (P = 0.03), but not after 12 months. The Atkins diet led to a loss, on average, of 7.3% of baseline weight, while the conventional diet led to a 4.5% loss (P = 0.26). Healthy changes in blood pressure and insulin sensitivity occurred in both groups, but were not significantly different. Ketone levels were significantly elevated for those on the Atkins diet for only the first three months. No correlation was found between weight loss and ketosis, in spite of this being the diet’s alleged mechanism of action.
Serum lipoprotein changes were more complicated. Total cholesterol and LDL levels initially increased for those on the Atkins diet (not desirable), but had returned to baseline after 12 months. The levels initially decreased for those on the conventional diet, but were not significantly lower after 12 months. In contrast, total triglycerides and HDL-cholesterol levels remained unchanged on the conventional diet, while the Atkins diet led to significant lowering of total triglycerides and elevation of HDL levels (both desirable).
A second RCT published at the same time involved 132 severely obese subjects (BMI = 43 kg/m2) but lasted only 6 months.10 Those on the low-carbohydrate diet (> 30 g/d) lost on average 5.8 kg while those on the conventional low-fat diet lost 1.9 kg (P = 0.002). Significant improvements were noted in the low-carbohydrate group for total triglyceride levels and insulin sensitivity. Significant differences did not occur in total cholesterol, HDL, LDL, or uric acid levels.
As the Atkins diet grew in popularity, health care professionals expressed concern about its potential adverse effects. The additional protein in these diets comes from animal sources that include higher fat content. This could increase serum lipid and cholesterol levels putting people at higher risk of heart disease. At the same time, dramatic reductions in carbohydrates leads to reductions in fruits and vegetables, which are high in fiber and vitamins essential for good health and disease prevention. The large amounts of protein that the body must break down may lead to increased uric acid levels (which causes gout) and stress on the liver and kidneys (especially problematic for people with diabetes). The American Heart Association, for example, concluded that, "High-protein diets are not recommended because they restrict healthful foods that provide essential nutrients and do not provide the variety of foods needed to adequately meet nutritional needs."11
The systematic review described above found no significant association between dietary carbohydrate levels and changes in serum lipids, fasting blood glucose levels, or systolic blood pressure. The two recent RCTs did not find changes consistent with concerns about adverse effects. However, these concerns would arise primarily with long-term use of high-protein diets and no studies have examined this issue.
The studies support the claim that low-carbohydrate, high-protein diets produce weight loss. However, this would appear to have more to do with the reduced calorie intake. It has been noted that foods and drinks containing high-fructose corn sweeteners were introduced into the food industry at exactly the same time as obesity started to become problematic (in 1970).12 These sweetened drinks and foods not only contain many calories, they stimulate the appetite, leading to over-consumption. Eliminating these will be highly beneficial.
Low-carbohydrate diets lead to the body using stored glycogen which can result in rapid weight loss, which is highly motivating. However, much of this weight loss is probably water being excreted. After the first week or two of the diet, the glycogen is used up and dieters enter the more difficult period of slower weight loss. The question then becomes whether people can tolerate the high-protein diet for very long. The two RCTs showed benefits over the first six months, but at the end of the second six months the low-carbohydrate diet was not significantly more beneficial.9,10
These results probably reflect the fact that although special diets can initiate a weight-loss program, sustained weight loss requires lifestyle adjustments. The rules of combating overweight have not changed. No pill or diet will replace the diligence necessary to maintain healthy body weight. Reducing calorie intake, increasing output through exercise, and enlisting the support and encouragement of friends and family must remain central to any weight-loss strategy.
O’Mathúna, BS (Pharm), MA, PhD, Visiting Professor of Bioethics, University of Ulster Coleraine, Northern Ireland, is on the Editorial Advisory Board of Alternative Therapies in Women’s Health.
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