Metabolic Effects Of Chronic Dieting - Brief Article - Statistical Data Included

Nutrition Research Newsletter, August, 2000 by J. Gingras, V. Harber, C. Field

A chronic dieter is an individual who consistently restricts energy intake to maintain an average weight at or below the average for their height. Chronic dieters generally have an obsession with body shape and weight, restrict their food choices for more than two years, and continually diet to achieve weight loss without success or with success but then with weight regain. Besides the psychological consequences of chronic dieting, there are many physiologic effects as well. These physiologic effects vary and may affect metabolism in the long term. It has been suggested that long-term energy restriction may lead to a decreased resting energy expenditure (REE). This may be a conservatory mechanism, allowing the body to conserve energy when in a fasting state. Dieting, including chronic dieting, is an extremely common behavior among women in North America.

A study was performed in Canada to determine whether metabolic and physiologic differences exist between two groups of chronic dieters: one with normal REEs and one with low REEs. A nonrandomized convenience sample including women aged 21-49 years was employed. All subjects confirmed that they were chronic dieters through standardized questions regarding dieting. Comparisons were made using a cross-sectional, observational study design. REE was measured using a metabolic chart. Body composition, aerobic fitness, physical activity, glucose and insulin responses, leptin and thyroid hormone states, dietary intake, and dietary restraint were measured and assessed.

The group of women with normal REEs was found to have greater lean body mass and a higher insulin response to a test meal, as well as higher thyroxine and reverse triiodothyronine concentrations and lower dietary restraint. The two groups did not significantly differ in regard to aerobic fitness, physical activity, total fat mass, bone mass, or dietary intake. Both groups were found to be less physically fit then the average Canadian woman. Leptin was found to be decreased significantly from baseline to two hours following an oral-glucose-tolerance test in both groups.

The researchers concluded that the differences in insulin response were associated with higher ratios of abdominal to gluteal body fat in the normal REE group. From this research, it appears that a normal REE does not always predict positive metabolic health among chronic dieters. This study confirms that these two types of chronic dieters have unique and different physiologic and behavioral characteristics.

J. Gingras, V. Harber, C. Field, et al. Metabolic assessment of female chronic dieters with either normal or low resting energy expenditures, Am J Clin Nutr 71:1413-1420 (June 2000) [Correspondence: L. J. McCargar, 4-10 Agriculture/Forestry Centre, Dept. of Agricultural, Food, and Nutritional Science, University of Alberta, Edmonton, AB T6G2 P5, Canada. E-mail: Imccargar@afns.ualberta.ca.]