The concentrations of serum total and free testosterone were studied in 30 healthy, middle-aged men during a dietary intervention program. When men were transferred from their customary diet to an experimental diet, which contained less fat with a higher polyunsaturated/saturated ratio (P/S-ratio) and more fibre, there was a significant decrease in serum total testosterone concentrations ( +/- vs +/- nmol/l SEM, P less than ). Furthermore, serum free, unbound testosterone fell from +/- to +/- nmol/l SEM (P less than ). The hormonal changes were reversible. This observation suggests that testosterone activity in plasma can at least partly be modified by changing the composition of the diet.
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The possible effect of dietary fat content and the ratio of polyunsaturated to saturated fatty acids (P/S-ratio) on serum sex hormones was studied in 30 healthy male volunteers. The customary diet of the subjects, which supplied 40% of energy as fat (mainly from animal sources, P/S-ratio ) was replaced for a 6 weeks period by a practically isocaloric experimental diet containing significantly less fat (25% of energy) with a higher P/S-ratio () and other environmental factors were stabilized. Serum testosterone and 4-androstenedione decreased from +/- nmol/l to +/- nmol/l, (SEM, P less than ) and from +/- nmol/l to +/- nmol/l (SEM, P less than ), respectively. These changes were paralleled by a reduction in serum free (non-protein bound) testosterone (P less than ) suggesting a possible change in biological activity. During the low fat period a significant negative correlation between serum prolactin and androgens was observed. All the changes in androgen levels were reversible. With the exception of a small but non-significant decrease in serum estradiol-17 beta, the other hormone parameters were practically unaffected by the dietary manipulation. Our results indicate that in men a decrease in dietary fat content and an increase in the degree of unsaturation of fatty acids reduces the serum concentrations of androstenedione, testosterone and free testosterone. The mechanism and importance of this phenomenon is discussed in the light of epidemiological and experimental data.