The Myth about Fish Oil and Fat Loss

There's a lot of talk about the potential beneficial effect of fish
oil and omega-3s on fat loss and muscle growth.

It's true that the effect of omega-3s on fat loss has been shown repeatedly in animal studies. One study, for example, looked at fat mass in rats after feeding them a diet of either fish oil or lard.

Although calories were kept constant, rats consuming fish oil had 50-80% less fat mass compared with rats consuming lard.

Which is all very exciting... if you're a rat! But does it work as well in humans?

Research published in the American Journal of Clinical Nutrition shows that daily doses of oil containing omega-3 fatty acids, combined with moderate exercise like walking for 45 minutes, can result in significant weight loss.

But taking the oil without exercise, or exercising without taking the oil, does not result in any weight loss, according to researchers from the University of South Australia.

"When we divided up a number of people in our research program, we found that those taking fish oil combined with exercise lost significantly more fat mass than any other group in the study," says study co-author, Professor Peter Howe.

The researchers examined the effects of effects of fish oil and exercise, alone and together, on fat mass, lean mass, and cardiovascular health in 75 overweight adults (age range 25-65).

They were divided into four groups — a group taking fish oil and exercise, another taking just fish oil, a third group taking sunflower oil without exercise and a fourth being asked to combine sunflower oil and exercise.

The group using fish oil took 6 grams of fish oil per day. The supplement provided 260 milligrams of DHA and 60 milligrams of EPA in each 1-gram capsule, for a total of 1.9 grams of long-chain omega-3 fatty acids per day.

Body composition was assessed at the start and end of the study with the use of dual energy X-ray absorptiometry (DXA), a fairly sophisticated method to measure body fat.

The clear winners in the study were those in the group who were given fish oil and who walked or ran for 45 minutes three times a week.

Exercising subjects who used fish oil lost around 1.5 kilograms (3.3 pounds) of fat. The group that took the sunflower oil (which does not contain omega-3 fatty acids) but who exercised lost a very small amount of weight. The two groups that did no exercise (including those on fish oil) also lost no weight. You can see the results more clearly in the figure below.

Subjects taking part in the study were instructed to maintain their normal diet during the study. They completed a 3-day weighed food record on two weekdays and 1 weekend day before attending the clinic at each of three time points. Daily calorie intake in each of the four groups is shown in the table below.

FO, fish oil; FOX, fish oil and exercise; SO, sunflower oil; SOX, sunflower oil and exercise

This brings us to the main problem with the study, that of self-reported food intake, which is a notoriously inaccurate way to measure calorie intake.

In other words, this was not a study where the diet was tightly controlled by the researchers. And it shows in the results. Subjects using sunflower oil without exercise, for example, actually gained weight, despite the fact their daily calorie intake supposedly dropped from 2520 calories in week 0 to 2229 calories in week 12.

So how does fish oil work?

One theory put forward by the researchers is that fish oil increases the elasticity of blood vessel walls and improves the flow of blood to muscles during exercise. This increased blood flow, in theory at least, could accelerate fat loss via an increase in the delivery of lipolytic stimuli to fat cells.

Although it's an interesting idea, I'm not sure that an increase in blood flow would be sufficient to account for all of the extra weight loss seen in the group using fish oil.

The effect of fish oil may also be due to some kind of impact on appetite control and calorie intake. There is research to show a link between fish oil and leptin sensitivity, so the idea that fish oil can speed up weight loss via improved appetite control and a subsequent reduction in calorie intake is a plausible one.

Other studies I've seen show that the long-chain omega-3s (DHA and EPA) appear to function as fuel partitioners by directing fatty acids away from synthesis and towards oxidation.

If you want to increase your intake of omega-3s, eat more deep-colored cold-water fish such as salmon, trout, mackerel and sardines. On days when you don't eat any cold-water fish (or if you don't eat fish at all), use a fish oil supplement.

However, despite the fact it has a number of important health benefits, the idea that fish oil is some kind of magic bullet for weight loss is a myth. You can't just pop a few fish oil capsules and expect the fat to melt away without making changes to your diet and exercise program first.

And while there's plenty of research demonstrating the effect of fish oil on fat loss in rats and mice, research showing a direct effect on body fat in humans is limited in both size and quality.

In fact, other than this recent study, I could find only a handful of published trials to show that long-chain omega-3s accelerate fat loss in humans. And even then, the effect is a relatively small one.

To my knowledge, no such studies exist for alpha-linolenic acid (the short chain omega-3 fatty acid found in walnuts and flaxseed). If anyone knows of any that have been done, I'd love to hear about them.

About the Author

Christian Finn holds a master's degree in exercise science, is a certified personal trainer and has been featured on BBC TV and radio, as well as in Men's Health, Men's Fitness, Muscle & Fitness, Fit Pro, Zest and other popular fitness magazines.

If you want better, faster results from the time you spend in the gym, click here now for instant access to his step-by-step muscle-building and fat-burning workout routines.

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References
Hill, A.M., Buckley, J.D., Murphy, K.J., & Howe, P.R. (2007). Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors. American Journal of Clinical Nutrition, 85, 1267-1274