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In the quest to lose weight fast many people drastically restrict calories. Not a good idea. Several studies indicate that reducing calories can negatively affect testosterone levels. Kiddy et al (1) examined the effect of a very-low-calorie diet (330 kcal/day) on testosterone levels in overweight women. After 2 weeks there was a -40% decrease in free testosterone levels. Strauss et al (2) measured testosterone levels in wrestlers during the competitive season and two months after the season. Large reductions in body fat induced by caloric restriction and exercise during the season resulted in the largest decreases in testosterone. The wrestlers with an extremely low body fat demonstrated abnormally low testosterone levels that returned to normal after the season. Other studies have also shown decreases in testosterone levels in wrestlers during consuming low energy (3). Guezennec et al (1994) measured testosterone in soldiers consuming low (1800 kcal/day), moderate (3200 kcal/day), or high (4200 kcal/day) calorie diets with similar ratios of carbohydrate, protein, and fat. The diets were consumed during 5 days of prolonged exercise and sleep deprivation (4 hrs/day). After 5 days, testosterone had decreased by -50% on the low calorie diet and only about -20% on the moderate and high calorie diets. These findings indicate that exhaustive exercise can decrease testosterone levels and that inadequate energy can augment the decrease in testosterone. Collectively the studies that have examined the effects of energy intake on testosterone indicate that large reductions in calories and body weight can reduce testosterone levels. This is especially true if a large reduction in calories is combined with prolonged and exhaustive physical activity. If weight loss is a goal, a much better approach would be to reduce calories slightly (about 300-500 kcal/day) and incorporate heavy resistance training into your exercise program. This should eliminate the decrease in testosterone that typically occurs when calories are reduced.

1. Kiddy, D.S. D. Hamilton-Failey, M. Seppala, R. Koistinen, V.H. James, M.J. Reed, and S. Franks. Diet-induced changes in sex hormone binding globulin and free testosterone in women with normal or polycystic ovaries: correlation with serum insulin and insulin-like growth factor-I. Clin Endocrinol (Oxf). 31:757-63, 1989.
2. Strauss, R.H., R.R. Lanese, and W.B. Malarkey. Weight loss in amateur wrestlers and its effect on serum testosterone levels. JAMA. 20;254:3337-8, 1985.
3. Roemmich, J.N. and W.E. Sinning. Weight loss and wrestling training: effects on nutrition, growth, maturation, body composition, and strength. J. Appl. Physiol. 82:1751-9, 1977.