May 23, 2007 — In overweight patients, fish oil supplements and regular aerobic exercise reduced body fat and improved cardiovascular and metabolic health, according to the results of a study published in the May issue of the American Journal of Clinical Nutrition.

"Regular exercise and consuming long-chain n-3 fatty acids (FAs) from fish or fish oil can independently improve cardiovascular and metabolic health, but combining these lifestyle modifications may be more effective than either treatment alone," write Alison M. Hill, from the University of South Australia in Adelaide, and colleagues. "Although several studies have investigated the potential for regular aerobic exercise to independently improve body composition and CVD [cardiovascular disease] and metabolic risk factors, few properly controlled studies have investigated the effect of n-3 FA supplementation on these risk factors, particularly body composition."

In this study, 75 overweight volunteers (body mass index [BMI], > 25 kg/m2) with high blood pressure, cholesterol level, or triacylglycerol level were randomized to 1 of the following interventions: fish oil (6 g of tuna fish oil per day), fish oil and exercise, sunflower oil (control; 6 g of sunflower oil per day), or sunflower oil and exercise. The exercise intervention consisted of walking 3 days per week for 45 minutes at 75% of age-predicted maximal heart rate. Plasma lipids, blood pressure, and arterial function were evaluated at 0, 6, and 12 weeks, and body composition was evaluated by dual-energy x-ray absorptiometry at 0 and 12 weeks only.

Compared with the sunflower oil groups, the groups receiving fish oil supplementation had lower triacylglycerol levels, increased high-density lipoprotein (HDL) cholesterol levels, and improved endothelium-dependent arterial vasodilation (P < .05). Compared with the groups not receiving the exercise intervention, those in the exercise groups had better arterial compliance (P < .05). Both fish oil and exercise were independently associated with reduced body fat (P < .05).

"FO [fish oil] supplements and regular exercise both reduce body fat and improve cardiovascular and metabolic health," the authors write. "Increasing intake of n-3 FAs could be a useful adjunct to exercise programs aimed at improving body composition and decreasing cardiovascular disease risk."

The compliance rate was greater than 85%, suggesting that the intervention was well tolerated, probably because of the modest level of physical activity required and because subjects did not need to change their background diet.

"Thus compliance may be sustainable in the longer term," the authors conclude. "Future research should evaluate the efficacy of this combined intervention over a longer duration and investigate the mechanism underlying the improvements in body composition."

A University of Adelaide postgraduate award supported this study. Fish oil and placebo capsules were donated by Nu-Mega Ingredients Pty Ltd. The authors have disclosed no relevant financial relationships.

Am J Clin Nutr. 2007;85:1267-1274.

Clinical Context

The risk for mortality from coronary artery disease decreases with the intake of n-3 fatty acids from fish or fish oil, according to a study by Mozaffarian and Rimm in the October 18, 2006, issue of JAMA. Warburton and colleagues noted in the March 14, 2006, issue of CMAJ that cardiovascular disease risk factors are reduced by exercise. But the effects of combined n-3 fatty acid intake and exercise are not clear. In the June 1990 issue of the Journal of Sports Medicine and Physical Fitness, Brilla and Landerholm reported that a combination of fish and fish oil did not affect body fat in lean men.

This placebo-controlled study compares the individual and combined effects of n-3 fatty acid supplementation and exercise on body composition and cardiovascular risk factors in overweight adults.

Study Highlights

• 75 adults aged 25 to 65 years with BMI greater than 25 kg/m2 and at least 1 cardiovascular risk factor (mild hypertension between 140/90 and 160/100 mm Hg, plasma triacylglycerol levels > 1.6 mmol/L, or total cholesterol level > 5.5 mmol/L) were enrolled.
• Exclusion criteria were exercise more than once per week, ingestion of fish oil capsules or fatty fish meal more than once per week, diabetes, liver disease, cardiovascular disease, medication for blood pressure or hyperlipidemia, pregnancy or lactation, and weight-loss diet.
• After balancing 4 groups based on sex, BMI, and triacylglycerol levels, each group was randomized to a treatment regimen for 12 weeks:
  • 18 subjects in fish oil group received 6 g of tuna fish oil daily.
  • 19 subjects in fish-oil-and-exercise group received fish oil plus exercise (running or walking 3 times per week for 45 minutes at heart rate of 75% of age-predicted maximum).
  • 18 subjects in sunflower oil group received 6 g of sunflower oil (placebo) daily.
  • 20 subjects in sunflower-oil-and-exercise group received sunflower oil plus exercise.
• Baseline characteristics were similar for all groups.
• Outcome measures of height, weight, arterial compliance, endothelial function, lipid analysis, and erythrocyte fatty acids were measured at baseline and at 6 and 12 weeks.
• Body composition using dual-energy x-ray absorptiometry was measured at baseline and 12 weeks.
• 24 men and 41 women (67%) completed the study.
• Data for 10 subjects were not used: 6 withdrew, and 4 did not comply with exercise requirements.
• Long-chain n-3 fatty acids in erythrocytes increased in fish oil group (from 10.7% - 13.7%) and in fish-oil-and-exercise group (from 10.4% - 13.5%) because of increase in docosahexaenoic acid.
• Triacylglycerol levels decreased in fish oil group vs sunflower oil group (14% reduction vs 5% increase; P < .05).
• HDL cholesterol level increased in fish oil group vs sunflower oil group (10% increase vs 3% increase).
• Results of long chain n-3 fatty acids in erythrocytes from baseline to 12 weeks correlated with changes in HDL cholesterol levels, but not triacylglycerol levels.
• Lipid levels were not improved by exercise.
• Small arterial compliance increased by 26% (SD, 8%) in exercise groups vs 1% (SD, 4%) in nonexercise groups.
• Large artery compliance did not differ among groups.
• Energy intake was similar for all groups.
• Body weight or composition did not have significant oil × exercise × time interactions.
• Body weight had significant exercise × time interaction
• Fat mass was reduced by both fish oil and exercise (significant oil × time and exercise × time interactions).
• Lean mass was not affected by exercise or oil.

Pearls for Practice

• In overweight adults, both fish oil supplementation and exercise independently reduce body fat mass.
• In overweight adults, fish oil supplementation reduces triacylglycerol levels, increases HDL cholesterol levels, and improves endothelium-dependent arterial vasodilation; exercise improves small arterial compliance.