Physiological Adaptations to the Metabolic Syndrome Following Exercise Training and Omega-3 Fatty Acid Supplementation

Abstract

Despite reduced levels of coronary heart disease (CHD), mortality statistics remain a worldwide concern. Interacting risk factors appear to underlie CHD development, of which insulin resistance may be a central theme. This may be particularly relevant to higher mortality levels evident in British South Asians. The objective of this research was to investigate the effects of two interventions (exercise and omega-3 (n-3) fish oils) on insulin sensitivity, cholesterol, obesity, hypertension and inactivity. The study also investigated whether benefits were sustained, and whether differences existed between South Asians and Europeans. Ninety two volunteers participated following pre-screening classification of the highest risk tertile from a normal population (age 35-49 years). Subjects were randomised within six groups, based on a double blind (for oil), controlled cohort 3x2 factorial design. These being: control, placebo (Gl); control, drug (G2); exercise, placebo (G3 & 5); exercise, drug (G4 & 6). Groups 3 and 4 were tested 24h post-intervention, whereas groups 5 and 6 were assessed five days post to evaluate sustainability.Drug allocation was 3g day -1 n-3 fatty acids, whereas placebo constituted olive oil capsules. Exercise was prescribed at 70% V02 max for 30-40 min, 3-4 times per week, for 12 weeks. Blood analysis occurred using specific assays for cholesterol components. Insulin sensitivity was assessed from the minimal model based on a frequently sampled intravenous glucose tolerance test. Other measurements were assessed during a cardiorespiratory fitness test using a modified Bruce protocol.Insulin sensitivity was not significantly altered between groups, although within-group increases were found in groups 3 and 4 (37.5% and 28.1% respectively, P<0.05). Omega-3 fish oils resulted in reduced triglyceride values from 1.65 ± 1.06 to 1.34 ± 0.83mM (P<0.05) within-group only. Combined interventions were beneficial for increased HDLC, and elevated levels of HDL2-C by 57.8% were sustained.  Bodyfat index was significantly reduced between groups, especially group 3 (16.4%, P<0.01). Exercise training decreased resting diastolic blood pressure from 82.5± 9.8mmHg to 75.3± 7.6mmHg (P=0.02), and maximal oxygen consumption and minute ventilation were increased by up to 15.5% and 19.5% respectively. In all cases, no differences were identified between Asians and Europeans, and higher mortality statistics remained unexplained in terms of central adaptations to the metabolic syndrome. It was concluded that potential beneficial effects of exercise on insulin sensitivity were short term, reflecting a cumulative effect. Improved efficiency in insulin kinetics may be secondary to increased blood flow and muscular contractions associated with aerobic exercise. This has implications in that low intensity, frequent bouts of exercise may be more beneficial.

Date of Award	Nov 1997
Original language	English