Popular diets, particularly those low in carbohydrates, have challenged current recommendations advising a low-fat, high-carbohydrate diet for weight loss. Potential benefits and risks have not been tested adequately.
This study compared 4 weight-loss diets representing a spectrum of low to high carbohydrate intake for effects on weight loss and related metabolic variables. The twelve-month randomized trial was conducted in the United States from February 2003 to October 2005 among 311 free- living, overweight/ obese (body mass index, 27-40) nondiabetic, premenopausal women. Intervention Participants were randomly assigned to follow the Atkins (n=77), Zone (n=79), LEARN (n=79), or Ornish (n=76) diets and received weekly instruction for 2 months, then an additional 10-month follow-up.
Weight loss at 12 months was the primary outcome.
Secondary outcomes included lipid profile (low-density lipoprotein, high-density lipoprotein, and non–high-density lipoprotein cholesterol, and triglyceride levels), percentage of body fat, waist-hip ratio, fasting insulin and glucose levels, and blood pressure.
Outcomes were assessed at months 0, 2, 6, and 12. The Tukey studentized range test was used to adjust for multiple testing.
Weight loss was greater for women in the Atkins diet group compared with the other diet groups at 12 months, and mean 12-month weight loss was significantly different between the Atkins and Zone diets (P .05). At 12 months, secondary outcomes for the Atkins group were comparable with or more favorable than the other diet groups.
In this study, premenopausal overweight and obese women assigned to follow the Atkins diet, which had the lowest carbohydrate intake, lost more weight and experienced more favorable overall metabolic effects at 12 months than women assigned to follow the Zone, Ornish, or LEARN diets. While questions remain about long-term effects and mechanisms, a low-carbohydrate, high-protein, high-fat diet may be considered a feasible alternative recommendation for weight loss.
Funding/Support: This investigation was supported by National Institutes of Health grant R21AT1098, by a grant from the Community Foundation of Southeastern Michigan, and by Human Health Service grant M01-RR00070, General Clinical Research Centers, National Center for Research Resources, National Institutes of Health.
-----------PROCOR member comments:
The recent publication of the results of the A TO Z trial of four weight-loss "diets" made headlines around the world, "ATKINS DIET TOPS". The group on the Atkins diet lost about 10 pounds, a few more pounds than the others, after one year of "dieting".
Did anyone, including the paper's reviewers, actually look at the numbers behind this conclusion?
Average BMI was about 32. One is considered to be obese above a BMI of 30. So most were obese. Note also the weights--about
Results were derived by SELF REPORTING of food consumption and exercise. The subjects could tell the investigators anything. There was no check on what they said. They were paid, so the subjects had an incentive to tell the investigators what the subjects thought the investigators wanted to hear. The subjects claimed to be eating about 1900 kcal/day at the outset of the trial.
Any adult who eats only 1900 kcal/day is UNLIKELY TO BECOME OBESE in the first place. During the trial they claimed to be eating only about 1500 kcal/day with no difference between groups. So even if they hadn't increased exercise they should have had a deficit of 400 kcal/day, 2800 kcal/wk. One pound of fat is about 3500 kcal. So, if we are to believe what they reported, they should have lost at least
3 pounds per month or 36 pounds per year. But even the Atkins group only lost 10 pounds. It gets worse. They reported total energy expenditure of about 35 kcal/kg/day. Why didn't the investigators report energy expenditure in kcal/day, like energy intake? Anyway, multiply by their weight and you get about 3000 kcal/day. But they claimed to be eating only 1500 kcal/day. So they should have lost two to three pounds per week, at least 100 pounds per year.
The First Law of Thermodynamics says energy cannot be created or destroyed. Any study of energy flows that cannot first show that energy is conserved should never be published. The methods employed by the study are fatally flawed. No conclusion can be drawn from this data. Many interpretations are possible.
So, if all groups ate the same REPORTED calories on the average and burnt the same REPORTED calories on average, why did the Atkins group lose a little more weight? Maybe the Atkins group did a little more
exercise: that group did do significantly less exercise at baseline.
Colin Rose MD
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