It's Not Which Diet, It's How You Diet

Summarized by Robert W. Griffith, MD
February 25, 2005

Introduction

During the last two years a battle has raged between the Atkins (low-carb) diet and its rivals - low-fat and other approaches. The longest clinical study comparing low-carb and low-fat lasted 6 months, and was inconclusive. Given the role that faddism, rather than science, plays in the choice of diets, a comparison of the actual success of such diets over a longer period is overdue. Now the results of such a study have been reported in the Journal of the American Medical Association.

What was done

Overweight or obese adults living in the Boston area were recruited. They were known to have high blood pressure, abnormal blood lipids, or raised blood sugar levels, so that weight loss was desirable from a medical point of view.

The participants were randomly allocated to one of four diets:

• Dr Atkins diet (low-carbohydrate: maximum 20 gm daily initially, increasing to 50 gm daily)
• Zone (macronutrient balance with a carbohydrate-fat-protein ratio 40-30-30)
• Weight Watchers (counting calories to achieve between 1,200 and 1,600 kcal daily)
• Ornish (low-fat: vegetarian, with less than 10% of energy from fat)

Dietary advice was given for the first two months; after this time, participants chose their own level of adherence to the recommended diet. They were expected to exercise at least 60 minutes a week, and they had to complete food intake records for 3 consecutive days at intervals during the 1-year study period.

Exams done during the study included body weight, blood pressure, lipid profiles (total-, LDL-, and HDL-cholesterol, triglycerides), fasting blood sugar, and C-reactive protein (CRP).

What the study showed

There were 40 participants in each diet group - half of them were men, half women. Their ages ranged from 22 to 72, and their average body mass index (BMI) was 35 (ranging from 27 to 42).

A disappointingly small number of participants completed the 1-year study - 53% for Dr Atkins diet, 65% for Zone, 65% for Weight Watchers, and 50% for Ornish. In assessing the results of dieting, it was assumed that those who didn't complete the study had zero change from baseline.

For the completers, after 1 year there was an average loss of 2.1 kg (4.6 lb) for Atkins, 3.2 kg (7.1 lb) for Zone, 3.2 (6.6 lb) for Weight Watchers, and 3.3 kg (7.3 lb) for Ornish. About 10% of the participants lost more than 10% of their body weight. There was no significant difference between the four groups.

There were no significant effects on blood pressure or fasting blood sugar, but the ratio of low- to high-density lipoprotein was reduced (a beneficial change) with all four diets, by about 10%.

The amount of individual weight lost was, not surprisingly, linked to the degree of adherence to diet, but also to reduction in CRP blood levels and insulin levels. Here, too, there were no differences between the effects of the four diets.

What this means

This study shows that there is little difference between four different types of diet - low-carb, balanced carb-protein-fat, counting calories, and low-fat. All four had a high (over 50%) drop-out rate, and produced only moderate weight loss and cardiac risk reduction.

It's obvious that sticking with a diet will achieve a better result in both weight reduction and lessened cardiac risk factors. No single diet was better than another in these respects, or more effective than another. So, forget the latest fad diet. Instead of spending time and money trying to determine which diet is the right one, you should start one that you believe you can stick to - and then stick to it!

Source

• Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction. ML. Dansinger, JA. Gleason, JL. Griffith,  et al., JAMA, 2005, vol. 293, pp. 43--53

Related Links
In the Battle Against Weight, It's All About Maintenance
Moderate-Fat Diets for Weight Loss?
Putting Low-Carb Diets to the Test
Dr. Irene's Five Pitfalls of Dieting

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