Selected Compounds-Sports

By:Robert Baird Baird




Further research examining the influence of diet on testosterone has been performed by Volek et al., who simultaneously studied the effects of nutrients on cortisol, a catabolic hormone. According to their research, results indicate that specific nutrients may have the potential to alter the regulation and metabolism of testosterone, whereas effects on cortisol remain unclear. Their evidence verifies that testosterone levels positively correlate with percentages of dietary fat and negatively correlate with percentages of energy that is protein. Likewise, it appears that the protein-to-carbohydrate ratio is negatively correlated with testosterone levels Regarding fat, a previous investigation has also observed a significant positive correlation between percent energy fat and testosterone in young athletic men, and preliminary evidence also suggests a positive relationship between monounsaturated and saturated fatty acids on resting testosterone concentrations In contrast, a negative correlation between the polyunsaturated-to-saturated fatty acid ratio and testosterone was reported.

A study by Raben et al also found similar results when studying the hormonal responses to a meat-rich diet versus a vegetarian diet. In a study of male endurance athletes, the investigators reported a significant decrease in testosterone concentrations and an attenuation of the exercise-induced increase in testosterone when the subjects switched to vegetarian diets. These results may be explained by the likelihood that vegetarians consume less fat, saturated fatty acids, and a higher polyunsaturated-to­saturated fatty acid ratio than meat-eaters, and therefore exhibit lower concentrations of testosterone Interestingly, both diets in this study derived equal amounts of energy from protein, carbohydrates, and fat, indicating that the supply of energy from the macronutrients was not responsible for the effect on testosterone. Thus, the composition (in this case, vegetarian versus animal sources) of the energy-providing macronutrients may also modify testosterone concentrations.

The findings of these studies are particularly important for athletes and exercise enthusiasts who are attempting to increase or maintain strength and muscle mass, especially during periods of intense training, which can elevate levels of cortisol. Overtraining may also be responsible for a decline in resting testosterone concentrations, further signifying the need for appropriate dietary habits. Accordingly, such debilitating effects of overtraining may be exacerbated by a diet low in fat, which many athletes (i.e., wrestlers, gymnasts) consume

Further studies have examined the ratio of carbohydrate to fat in the diet and its effect on nitrogen retention. Such an investigation was performed by McCargar et al who also studied this ratio's effects on substrate use and hormone response in healthy males. The researchers found that the high-fat diet (45% of total calories) increased nitrogen retention, especially when maintenance energy intakes were consumed. The authors also stated that their findings indicated a potentially increased fat oxidation in those subjects consuming a high-fat diet, and that the nitrogen-sparing effect of such a diet was likely substrate mediated (as opposed to being hormonally mediated). The results also indicated that the high­carbohydrate diet (60% of energy) induced elevated triglyceride levels, which may be a reflection of additional fat synthesis in the liver owing to the presence of excess glucose. The significance here is that once energy and glycogen needs are met, surplus carbohydrates may lead to hypertriglyceridemia.

Studies examining the impact of caloric intake on resting testosterone levels have discovered a depressive effect on such concentrations. For instance, one study showed that fasting for 5 days can lower testosterone levels by as much as 30_50%. It also appears that severe caloric restriction, even if induced by excessive exercise, lowers testosterone levels. Combine these revelations with the possibility that increased fat intake may enhance testosterone levels, and the importance of adequate fat, as in the overtrained state, becomes paramount.

Yost and colleagues investigated the effects of macronutrient composition on the activities of adipose tissue lipoprotein lipase (an enzyme that breaks down fat) and insulin sensitivity. The researchers studied the reaction of these compounds to both a high-carbohydrate (55% of total kcal) and high-fat (50%) diet. They concluded that after 16 days of the high-carbohydrate diet only the responsiveness of adipose tissue lipoprotein lipase was increased. There was no effect on insulin sensitivity, although other researchers have found that diets containing a higher percentage of energy from fat produce insulin resistance. Of course, if such findings are conclusive, the development of type 2 diabetes, hypertension, and cardiovascular disease are possible adverse consequences.