Time for Fish-Oil Supplements?

Summarized by Robert W. Griffith, MD
July 18, 2007

Summary

A study in obese individuals shows that supplementation with fish oil improves several cardiovascular risk factors (blood triglyceride levels, HDL-C levels, and arterial function). Together with moderate exercise, fish oil supplementation reduced body fat mass.

Introduction

Whether you call it the metabolic syndrome or cardiometabolic risk, the cardinal initial sign is overweight or obesity. The next signs are diabetes, high blood pressure and lipid profile changes (decreased high-density lipoprotein cholesterol [HDL-C] and increased low-density lipoprotein cholesterol [LDL-C] and triglycerides). Unless these signs are reversed by appropriate lifestyle changes, atherosclerotic vessels will lead to coronary and cerebral artery disease, with the increased risk of heart attack or stroke. So this makes overweight a worthwhile target for preventive action.

Unfortunately, some people exercise and apparently eat right, yet the pounds won't drop off. The intake of fish-oil, which contains plenty of omega-3 fatty acid, is associated with the rate of mortality from coronary heart disease. So researchers in Australia examined the benefits of adding omega-3 fatty acid supplements to an exercise regime, and have reported their findings in the American Journal of Clinical Nutrition. Here's a summary of what they found.

What was done

The subjects for this study were between 25 and 65, overweight or obese (i.e. body mass index or BMI above 25), and had one or more of the following cardiovascular risk factors: raised blood pressure (over 140/90 mm Hg), raised triglyceride level (above 140 mg/dL) or raised total cholesterol (above 212 mg/dL). Those exercising more than once a week or having a good intake of omega-3 fatty acid were excluded, along those who had diabetes, liver disease, cardiovascular disease, or were on a weight-reduction diet.

Seventy-five such volunteers were allocated randomly to one of four treatment regimes: supplemental fish oil (6 grams of tuna fish oil daily), fish oil-plus-exercise, 6 grams of placebo oil (sunflower oil) daily, and sunflower oil-plus-exercise. Exercise consisted of running or walking for 45 minutes at a heart rate corresponding to 75% of their age-predicted maximum heart rate, 3 times a week.

Blood lipids, blood pressure, arterial function were assessed at baseline and after 6 and 12 weeks; good arterial function was based on good endothelial function, which was measured by flow-mediated dilatation (FMD) of the brachial (arm) artery assessed by high-resolution ultrasound.¹ A similar technique was used to measure small artery compliance.

Body composition, assessed by dual-energy X-ray absorptiometry (DXA) at baseline and 12 weeks, demonstrated changes in fat and lean mass. Red blood cell fatty acid concentrations were determined at baseline and after 6 and 12 weeks; they provided information on absorption of the omega-3 supplementation.

What was found

The average age of the participants was 50. There were 65 subjects who completed the study; 24 of them (37%) were men. The average baseline BMI was 34 (i.e. obese), and the average body fat at baseline comprised 42% of the body mass.

Both the groups treated with fish oil supplements had increased red blood cell omega-3 fatty acids concentrations; the change, which was attributed totally to increased docosahexaenoic acid (DHA), was from about 10.4% to 13.7%.

Fish oil supplements significantly increased HDL-C and lowered triglycerides in the two groups where they were given. A beneficial effect of exercise on HDL-C was minimal. There were no other effects on lipid levels in any group.

There was a significant beneficial effect of fish oil on flow-mediated dilatation of the brachial artery at 6 and 12 weeks after baseline; the increases were between 6% and 10%, depending on the group and time. Sunflower oil produced no such increases. Small artery compliance was significantly increased (by 26%) in those subjects who did the exercise regime.

While the calorie intake of participants didn't change over the study period, there was a significant reduction in fat mass in the fish oil-plus-exercise group.

What the findings mean

This study shows that supplementation with DHA-rich fish oil improves several cardiovascular risk factors (blood triglyceride levels, HDL-C levels, and one arterial function test - FMD). The exercise regime, which was of moderate intensity, had no effect on these risk factors, whether with or without fish oil; however, it did improve small artery compliance and reduced fat mass.

We have posted several articles on this site about the benefits of omega-3 fatty acids supplementation (see related links below). There's no doubt that there are plenty of reasons for people to increase their omega-3 intake in an effort to bring their diet closer to that eaten by our ancestors, at least from the omega-3:omega-6 ratio viewpoint. In the USA and in other countries where omega-3 fatty acid consumption is low, recommendations should encourage people to eat more fatty fish; the potential risk of fish toxins is smaller than the risk of too low omega-3 levels. Alternatively, one can take an appropriate supplement. In either case, keep exercising.

Source

• Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors. AM. Hill, JD. Buckley, KJ. Murphy, PRC. Howe, Am J Clin Nutr, 2007, vol. 85, pp. 1267--1274

Footnotes
1. The endothelium consists of the cells that line the inner surface of all blood vessels, including arteries and veins. Endothelial dysfunction is a key early event in the development of atherosclerosis.

Related Links
The Latest View on Omega-3 Fatty Acids
Omega-3s Are Superior to Defibrillators in Saving Lives
Omega-3 Intake and the Brain

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