The equation should be simple: eat less + exercise more = lose weight. Yet, researchers generally find that weight loss diets only cause people to lose about half the weight that would be predicted by this simple model.
Researchers have known for more than 50 years that the amount of weight loss seen with reduced-calorie diets tends to be much less than would be predicted. Even worse, weight loss seems to start off at a rapid clip, then weight plateaus or even drifts back upward by the end of the first six months.
An article published in the American Journal of Clinical Nutrition attempted to figure out why this phenomenon occurs. They looked at three potential explanations:
- that people eating low calorie diets absorb food more efficiently, getting more nutrition from less food;
- that people eating low calorie diets slow their metabolism down to match their dietary intake; or
- that people demonstrate reduced ability to follow low calorie diets for long periods of time.
The reviewers were able to present compelling evidence that food absorption and changes in metabolism were not enough to explain the difference between expected and measured weight loss in clinical research. Because of this, they concluded that people tend to drift away from low calorie dietary strategies, compromising their effectiveness.
This is no big surprise to doctors or nutritionists. We just discussed in a recent blog another in a series of research trials where weight loss was compromised by poor compliance with dietary recommendations.
A more interesting question is why people do a poor job of following diets over time. This is a much harder question to answer, but I would like to suggest a few possibilities:
- Counting calories is hard. Diets that have successfully controlled diabetes, blood pressure, and cholesterol have focused more on patterns of food intake (kinds of foods eaten and general quantity) than absolute amounts.
- Diets based on numeric goals don’t necessarily eliminate the worst food choices. I find the most effective weight loss strategies are the ones that eliminate most of the extra calories from nutrient-starved processed foods, especially refined sugars and fatty, salty snacks.
- Low calorie diets often leave people hungry. Hungry people snack, and this compromises their diet. Foods high in fiber tend to prolong the feeling of fullness (or satiety) after meals. High dietary fiber is almost always a key focus of my weight loss diet instructions.
- Weight loss diets need to be flexible. As a doctor, I find weight loss diets to be a process of trial and error, and sometimes compromises are needed in some areas to make the overall diet one that my patient is willing to follow. A diet one person finds acceptable may not work for another person. Researchers use uniform strategies in their studies and I believe this is why they almost always see poor compliance impair results.
Whole foods is the bottom line. I believe no weight loss diet will ultimately be successful unless it prioritizes whole foods. Not only do whole foods help control weight, but virtually every epidemiological study shows that whole foods diets reduce the risk of most diseases.
- Heymsfield SB, Harp JB, Reitman ML, et al. Why do obese patients not lose more weight when treated with low-calorie diets? A mechanistic perspective. Am J Clin Nutr. 2007;85:346-54
- Gardner CD, Kiazand A, Alhassan S,, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A TO Z Weight Loss Study: a randomized trial. JAMA. 2007;297(9):969-77.
- Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction: a randomized trial. JAMA. 2005;293(1):43-53