Effects of diet and exercise on insulin, sex hormone‐binding globulin, and prostate‐specific antigen

Abstract

A diet high in fat has been linked to prostate cancer, possibly through an influence on hormones. Sex hormone-binding globulin (SHBG) binds androgens and is regulated in part by insulin. Diet and exercise can modify insulin levels, potentially affecting SHBG and the biologically available levels of androgens. To determine the effects of a low-fat (< 10% of calories), high-fiber diet plus daily exercise on insulin, SHBG, prostate-specific antigen (PSA), and serum lipids, we measured the levels of these factors in the serum of 27 obese men undergoing a three-week diet-and-exercise program. Insulin decreased from 222 +/- 30 to 126 +/- 21 pmol/l (p < 0.01), and SHBG increased from 18 +/- 2 to 25 +/- 3 nmol/l (p < 0.01). Body mass index decreased from 35 +/- 1.9 to 33.4 +/- 1.8 kg/m2 (p < 0.01). PSA levels were normal and did not change significantly, although in a small subset of men (n = 3) with slightly elevated PSA levels (> 2.5 ng/ml) all showed a decrease. The three-week diet-and-exercise intervention decreased insulin and lipid levels while increasing SHBG. The increase in SHBG would result in more testosterone being bound and, therefore, less of the androgen available to act on the prostate. The decrease in insulin might also decrease mitogenic activity in the prostate. The diet-and-exercise regimen did not have a significant impact on normal PSA levels. Although modest, these changes may be protective against the development of prostate cancer.

Effect of diet and exercise intervention on the growth of prostate epithelial cells

“…13,20 The importance of daily exercise should be emphasized as exercise has an insulin-like effect to increase glucose transport and reduce serum insulin. In the present study just 2 weeks of diet and exercise intervention improved insulin resistance, lowered fasting insulin by 30% and reduced the growth of cultured prostate epithelial cells by 13% over 4 days of growth.…”

“…22 Reducing insulin by diet and exercise increases SHBG and lowers free testosterone even while total testosterone remains unchanged. 12,20 In addition to suppressing SHBG Lifestyle and prostate growth RJ Barnard et al production by the liver, insulin also increases production of insulin-like growth factor-I (IGF-I) while suppressing the production of IGF-binding protein-1 (IGFBP-1) to increase free IGF-I. 23 IGF-I is a peptide growth factor and is known to play a pivotal role in regulating cell growth, differentiation and apoptosis.…”

Heterocyclic amines and genotype of N-acetyltransferases as risk factors for prostate cancer

“…There are reports that show patients who have PCa are at increased risk of bladder cancer. 28,29 Recent studies have reported that high fat diets could alter steroid hormone profile 30,31 and overcooked red meats contain high amounts of heterocyclic amines, 22,23 both of which are suggested to increase advanced prostate cancer risk. 32 Contradictory to an earlier result, 5 it was recently concluded that dietary fat rather than red meat was associated with PCa.…”

Glycemic index in chronic disease: a review

“…Diets rich in fat, refined sugars and excess calories, all factors that favour the development of hyperinsulinemia, increase risk of prostate cancer Franceschi, 1994). Conversely, a lowfat=high-fiber diet plus daily exercise has been shown to decrease insulin and increase SHBG levels in obese men (Tymchuk et al, 1998).…”