Effects on glucose tolerance, insulin secretion, insulin-like growth factor 1 and its binding protein, IGFBP-1, in a randomized controlled diet and exercise study in healthy, middle-aged men

Abstract

Objectives: To study the effects of advice on diet, exercise and their combination on oral glucose tolerance (OGTT), insulin secretion, insulin-like growth factor-1 (IGF-1) and its binding protein, IGFBP-1.

Design: A 6-month, randomized, controlled intervention study.

Setting: Primary health care centres in Sollentuna, Stockholm and the Department of Medicine, Karolinska Hospital, Stockholm, Sweden.

Subjects: One hundred and fifty-seven normoglycaemic healthy men, mean age 46 years, range 35-60 years, with slightly to moderately raised cardiovascular risk factors.

Interventions: Advice on diet (D, n = 40), exercise (E, n = 39) a combination of both (DE, n = 39) and a control group (C, n = 39).

Main outcome measures: An OGTT, insulin secretion, IGF-1 and its binding protein, IGFBP-1.

Results: The number of pathological OGTTs in the intervention groups decreased from 42/118 to 33/118 whilst the number in the control group did not change. Fasting insulin levels decreased in groups E and DE from 8.8-7.4 mU L-1 (P < 0.01) and from 8.3-6.7 mU L-1 (P < 0.01), respectively. Accordingly, the insulin area under the curve decreased from 5278 to 4828 (P < 0.05) in group E, and from 5482 to 4809 (P < 0.01) in group DE. IGF-1 only increased in group D. The most prominent changes were noted for IGFBP-1, which increased in all three intervention groups and to the highest degree in group DE (from 33.7-42.6 micrograms L-1, P < 0.001).

Conclusions: A combination of increased exercise and improved diet, as well as increased exercise alone, favourably affect glucose and insulin homeostasis in middle-aged men with moderately elevated cardiovascular risk factors. The most marked changes were noted for IGFBP-1, possibly suggesting a decreased insulin secretion and an enhanced insulin sensitivity.