Fish oil may or may not help you with weight management, or more specifically, fat management. Several factors come into play, some of which can enhance the positive effects of fish oil and others of which can undermine them.
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Health Research on Fish Oil

A huge amount of research has been dedicated to the effects of fish oil and fish oil supplements on human health. Most of these entail the impact of the two main omega-3 fatty acids in fish oil, EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Well-designed studies overwhelmingly show multiple benefits, all of which have been extensively reviewed in the scientific literature.

Poorly designed studies, however, are another story. One of the worst recent studies actually suggested that omega-3 fatty acids can cause prostate cancer. The stupidity of this suggestion, and the flawed study that led to it, became a media sensation. This topic deserves a post on its own, so I will defer my comments about it for a later time.

Other weak studies generally fail to account for variables that influence the effects of dietary fish oils. Conclusions from such studies are unpredictable. They may show positive results, negative results, or no effects at all. The purpose of this post is to explore those variables that undermine the benefits of fish oils regarding weight/fat management and what to do about them.

Fish Oil Weight Loss Research

Many studies have explored the effects of fish oil weight loss. However, comparatively few have contended with factors that can influence the results, either positively or negatively. If you search for studies on fish oil vs. weight loss on our national medical database, PubMed, you will find studies that show seemingly contradictory results.

Before you get overwhelmed with all the possibilities, and before you accept on face value the negative media about fish oils, I thought I’d show you what a well-designed study looks like and the lessons that you can take away from it for incorporating into your diet and lifestyle.

Let’s first take a look at the study that I am referring to, via the full citation data and complete published abstract here:

Hill AM, Buckley JD, Murphy KJ, Howe PR. Combining fish-oil supplements with regular aerobic exercise improves body composition and cardiovascular disease risk factors. Am J Clin Nutr. 2007 May;85(5):1267-74.

ABSTRACT

BACKGROUND: 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.
OBJECTIVE: We examined the individual and combined effects of n-3 FA supplements and regular exercise on body composition and cardiovascular health.
DESIGN: Overweight volunteers [body mass index (BMI; in kg/m(2)): >25] with high blood pressure, cholesterol, or triacylglycerols were randomly assigned to one of the following interventions: fish oil (FO), FO and exercise (FOX), sunflower oil (SO; control), or SO and exercise (SOX). Subjects consumed 6 g tuna FO/d (approximately 1.9 g n-3 FA) or 6 g SO/d. The exercise groups walked 3 d/wk for 45 min at 75% age-predicted maximal heart rate. Plasma lipids, blood pressure, and arterial function were assessed at 0, 6, and 12 wk. Body composition was assessed by dual-energy X-ray absorptiometry at 0 and 12 wk only.
RESULTS: FO supplementation lowered triacylglycerols, increased HDL cholesterol, and improved endothelium-dependent arterial vasodilation (P<0.05). Exercise improved arterial compliance (P<0.05). Both fish oil and exercise independently reduced body fat (P<0.05). CONCLUSIONS: FO supplements and regular exercise both reduce body fat and improve cardiovascular and metabolic health. Increasing intake of n-3 FAs could be a useful adjunct to exercise programs aimed at improving body composition and decreasing cardiovascular disease risk.

We can quibble until the cows come home about the experimental design. Indeed, that’s how scientists like me operate. Nevertheless, to keep this brief, what this study does that is helpful is address the compounding effects of exercise on fish oil intake and on the comparative effects of a vegetable oil that is high in omega-6 fatty acids (i.e., sunflower oil).

I will comment on other compounding and comparative effects below. For the moment, just take a look at the primary results of this study as summarized in the graph here, taken from the original published article. Note that I have added arrows to highlight what is most important, green for positive results and red for negative results.

As you can see from a brief inspection of this graph, the greatest benefits of fish oil intake accrue in combination with exercise. The two indicators here are a drop in fat mass and a rise in lean mass (green arrows). Fish oil intake without exercise had minimal, or even slightly negative effects on these outcomes.

Of particular interest here are the effects of an omega-6 fatty source, sunflower oil (red arrows). The combination of sunflower oil with exercise yielded comparatively insignificant positive outcomes. Note that the most negative outcomes came from consuming sunflower oil without exercise – i.e., both an increase in fat mass and a decrease in lean mass. Wow!

Take-Home Lessons

There are just three main take-home lessons from this study:

1) The first is that even moderate exercise will enhance the effects of fish oil weight loss. Indeed, the benefits of fish oil are insignificant in the absence of exercise.

2) The second is the amount of fish oil intake. This study did not do a dose-dependent study to find out what the optimal amount would be. Most studies fail in this regard. However, a daily intake of 1.9 grams of fish oil is at least a preliminary indicator of how much is necessary for simulating the results cited here. This is consistent with common recommendations that point to 2-3 grams as a good daily dose.

3) The results here add to a myriad of studies that harp on the negative impact of too much omega-6 fatty acid intake. Estimates are that dietary vegetable oils, which are all dominated by omega-6 fatty acids, are the basis for our average ratio of omege-6 to omega-3 fatty acids of 20:1 – i.e., twenty times the amount of omega-6 fatty acids as omega-3 fatty acids.

An overabundance of omega-6 fatty acids is highly inflammatory and severely damaging to human health in countless ways. We are adapted to a healthy ratio of omega-6 to omega-3 fatty acids of closer to 2:1. Achieving this ratio demands that we cut way down on vegetable oils and add a substantial quantity of fish oil (2-3 grams daily) to our diet.

Additional Compounding Factors

Although the study cited here compares intake of either fish oil or sunflower oil, the reality is that we combine them in our diet. Other research shows that the benefits of fish oil can be undermined completely when combined with overabundance of omega-6 fatty acids. The take-home lesson is still the same: consume plenty of fish oil and cut way down on vegetable oil and other sources of omega-6 fatty acids.

Let me point out one more compounding factor that many studies have also shown regarding the health benefits of fish oil, including weight/fat loss. Sugar. This should not be a surprise. Sugar undermines the beneficial effects of fish oil. Table sugar (sucrose) is bad enough. Fructose, which is so commonly added as high fructose corn syrup to a vast array of foods and beverages, is even worse.

If you are getting a good amount of high quality fish oil in your diet or as a supplement, and still not seeing the health benefits that you are expecting, then take a look at your sugar and omega-6 fatty acid intakes to see whether they might be undermining your efforts.

Of course, if you have read this post to here, you are likely a very health conscious person who has already minimized your sugar and vegetable oil intake. Now you just have more incentive to stay on that path.

In support of fish oil weight loss,

Dr. D