Thursday, February 21, 2008

Conventional Wisdom: Yo-Yo Dieting Slows Your Metabolism

We've all heard that repeated cycles of dieting and weight regain can result in a permanent lowering of the metabolism and a "rebound effect," where dieters end up weighing more than ever. But is there a scientific basis for this claim?

Most people who try to lose weight encounter plateaus as a result of a metabolic slowdown. This phenomenon has been well characterized in scientific studies (1-4). Leibel et al. (4) conducted a particularly convincing study in which 18 obese and 23 never-obese subjects were admitted to the hospital so their food intake and activity could be strictly controlled. These subjects were then over- or under-fed until they had reached a 10% increase or decrease in their body weight. In both the obese and never-obese groups, a 10% increase in body weight resulted in a 16% increase in energy expenditure. Correspondingly, the 10% weight loss groups decreased their energy expenditure by 15%. The authors' interpretation of this study was that these changes in energy expenditure represent an attempt by the body to return to its "setpoint" weight.

So, changes in body weight do seem to result in changes in energy expenditure. But do repeated changes in body weight permanently affect your metabolism?

A number of researchers set out to answer this question using animal studies in the 1980s and 1990s. Ernsberger et al. (5) looked at rats with a specific genetic mutation making them prone to obesity and mimicked yo-yo dieting by putting half of the rats through a process of "weight cycling." The weight cycled rats were fed ad lib for 4-6 weeks, and then switched to a very low calorie diet (16.7% of baseline calories) for 12 days. This cycling of ad lib and restricted feeding was done three times. The researchers found that the cycled rats had a higher final body weight than controls which were fed ad lib throughout the study. They also found that the cycled rats lost slightly less weight each successive time they were put on the very low calorie diet. Similarly, Lim et al. (6) found that weight cycled rats had a lower resting metabolic rate than rats that were consistently food restricted (both groups were restricted to 70% of the food control rats ate), but that exercise on a treadmill eliminated that difference. These studies seemed to validate the hypothesis that yo-yo dieting had lasting effects on metabolism. However, Lu et al. (7) found that weight cycling of rats facilitated the development of insulin resistance, but didn't have any effect on body weight.

In humans, the story appears to be somewhat more consistent. While one paper (8) found that adolescent male wrestlers who engaged in yo-yo dieting had lower energy expenditure than those that didn't, subsequent studies of humans have repeatedly failed to see any permanent effects of yo-yo dieting on weight or metabolism in either obese or lean individuals (9-16).

So why the differing results in the human and animal studies? I can think of a few possible explanations. One possibility is that humans and rats may simply differ physiologically with respect to the effects of repeated weight cycling. Another possibility is that since the rat studies tended to involve a greater degree of restriction, there may be effects of weight cycling that don't kick in until the person or animal is in a severely hypocaloric state. This might also explain why the one human paper that did show an effect of yo-yo dieting was in adolescent male wrestlers...adolescent males have tremendous caloric needs so severe dieting may have more of an impact on this group. A third possibility is that rats exposed to involuntary food restriction with no knowledge of when their food access will return to normal may differ physiologically from people who voluntarily restrict their food intake, knowing that food is available to them if they need it.

The upshot is that while weight loss can decrease your metabolic rate, this change appears to be reversible with a return to "normal" weight.

1. Ravussin E, Burnand B, Schutz Y, Jéquier E. Energy expenditure before and during energy restriction in obese patients. The American Journal of Clinical Nutrition 41(4): 753-759, 1985.

2. Weigle DS, Sande KJ, Iverius PH, Monsen ER, Brunzell, JD. Weight loss leads to a marked decrease in nonresting energy expenditure in ambulatory human subjects.
Metabolism 37(10): 930-936, 1988.

3. Keesey RE, Hirvonen MD. Body weight set-points: determination and adjustment.
The Journal of Nutrition 127(9): 1875S-1883S, 1997.

4. Leibel RL, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight.
The New England Journal of Medicine 332(10): 621-628, 1995.

5
. Ernsberger P, Koletsky RJ, Baskin JS, Collins LA. Consquences of weight cycling in obese spontaneously hyperactive rats. American Journal of Physiology--Regulatory, Integrative and Comparative Physiology 270(4): R864-R872, 1996.

6. Lim K, Murakami E, Lee S, Shimomura Y, Suzuki M. Effects of intermittent food restriction and refeeding on energy efficiency and body fat deposition in sedentary and exercised rats.
Journal of Nutritional Science and vitaminology 42(5): 449-468, 1996.

7. Lu H, Buison A, Uhley V, Jen KL. Long-term weight cycling in female Wistar rats: effects on metabolism.
Obesity Research 3(6): 521-530, 1995.

8. Steen SN, Oppliger RA, Brownell KD. Metabolic effects of repeated weight loss and regain in adolescent wrestlers.
Journal of the American Medical Association 260(1): 47-50, 1988.

9. Jebb SA, Goldberg GR, Coward WA, Murgatroyd PR, Prentice AM. Effects of weight cycling caused by intermittent dieting on metabolic rate and body composition in obese women.
International Journal of Obesity 15(5): 367-374, 1991.

10. Nitzke SA, Voichick SJ, Olson D. Weight Cycling Practices and Long-term Health Conditions in a Sample of Former Wrestlers and Other Collegiate Athletes.
Journal of Ath

11. Wadden TA, Bartlett S, Letizia KA, Foster GD, Stunkard AJ, Conill A. Relationship of dieting history to resting metabolic rate, behavior, and subsequent weight loss. American Journal of Clinical Nutrition 56: 203S-208S, 1992.

12. McCargar L, Taunton J, Birmingham CL, Paré S, Simmons D. Metabolic and anthropometric changes in female weight cyclers and controls over a 1-year period.
Journal of the American Dietetic Association 93(9): 1025-1030, 1993.

13. Brownell KD, Rodin J. Medical, metabolic, and psychological effects of weight cycling.
Archives of Internal Medicine 154(12): 1325-1330, 1994.

14. Muls E, Kempen K, Vansant G, Saris W. Is weight cycling detrimental to health? A review of the literature in humans.
International Journal of Obesity and Related Metabolic Disorders 19(Suppl ): S46-S50, 1995.

15. Platte P, Wurmser H, Wade SE, Mercheril A, Pirke KM. Resting metabolic rate and diet-induced thermogenesis in restrained and unrestrained eaters.
International Journal of Eating Disorders 20(1): 33-41, 1996.

16. Li Z, Wong E, Maxwell M, Heber D. Weight cycling in a very low-calorie diet programme has no effect on weight loss velocity, blood pressure and serum lipid profile.
Diabetes, Obesity and Metabolism 9(3): 379-385, 2007.

No comments: