From Laura Dolson,
Your Guide to Low Carb Diets.
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Return to Page One - Introduction to the Diet Study

Why was the weight loss so small, and why did people regain weight? There are probably several reasons for this - let's peek inside the study and look for clues.

1) Random Assignment-->Possible Diet Mismatches

Random assignment to groups is essential in a study of this kind, but it will probably affect the outcome as well. Inevitably, when assigned randomly to a diet group, some percentage of them aren't going to be happy with the group they landed in. Also, the evidence is accumulating that different people do well on different diets, so there will be some amount of mismatch when a person has no choice in the matter. Are there mismatches in this study? We don't know for sure of course, but there is a hint in the data of a possible mismatch. In this 2005 study, the people who were insulin resistant tended to lose more weight on a low carb diet, while the insulin sensitive people lost more weight on a low fat diet. This makes intuitive sense - as almost all carbohydrate breaks down into sugars, we could guess that people who have more trouble processing sugars would respond positively to eating less carbohydrate. In the current study, it turns out that by chance, the Atkins and Zone diets (both of which restrict carbohydrate at least to some extent) got the least number of dieters with metabolic syndrome. In addition, the Atkins diet group was the only group to have very few prediabetics (measured by a fasting glucose of over 100). So, more prediabetics and those with metabolic syndrome were in the higher-carb (read: high sugar) groups. It is conceivable that the results for all groups may have been improved with different group assignments, but no analysis of prediabetics or those with metabolic syndrome was done.

2) Diet Drift

Obviously, no diet will work if people don't follow it. How well did the dieters follow the diets assigned to them? Taking them one at a time:

The Atkins Diet group was eating an average of 61 grams of carbohydrate at 2 months. This is consistent with the Ongoing Weight Loss (OWL) Phase of the diet. By 6 months, the average was 113 grams, and at 12 months had blossomed to 138 grams. This "carb creep" can't help but produce weight regain in at least some of the dieters. (More about the Atkins Diet)

The Ornish Diet is supposed to be 10% fat (and very high in carbs - menu analysis shows it to be about 75% carbohydrate). Even at 2 months, essentially none of the participants achieved this, even though (as with all the groups) they had attended eight weekly class about the diet. The average fat percentage in the Ornish group was 20% at two months, and increased to 30% by the end of the study.

The LEARN Diet (basically a Food Pyramid diet with extra education - LEARN stands for Lifestyle, Exercise, Attitudes, Relationships, and Nutrition) produced a calorie reduction more than a change in fat, carbs, etc. Calories were lowest at 2 months and increased after that, but after 12 months the group members reported eating about 250 fewer calories per day than at the beginning.

The Zone Diet group increased its protein consumption and decreased carbohydrate slightly. They never achieved the 30 percent protein recommended, only getting as far as 23.7 percent at 2 months. By 12 months, the group reported eating about 400 calories less than at the beginning.

It certainly isn't surprising that this "diet drift" occurred. Permanent change in eating habits is difficult, especially if it makes people feel hungry, deprived, obsessed with food, or physically worse in some way, as some diets do in some people.

3. Most bodies resist maintenance of weight loss

This is just a very unpleasant fact. Even when people attempt to stick to a diet regime, at least some`weight regain is very likely to happen over time. Finding the right diet match, and regular exercise (perhaps up to 60-90 minutes per day for some) can help prevent regain, but bodies are different, and some people may need to be satisfied at their own "lowest sustainable weight", even if it is higher than the charts say is "normal".

Reference: Gardner, Christopher, Alexandre Kiazand, Sofiya Alhassan, et al. "Comparison of the Atkins, Zone, Ornish, and LEARN Diets for Change in Weight and Related Risk Factors Among Overweight Premenopausal Women." Journal of the American Medical Association. 297/9 (2007)