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Fish Oils and Weight Loss

Kathleen Martin

October 8, 2009

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With rates of obesity rising at an alarming rate, it is becoming increasingly important to find products and treatments that can aid in weight loss. It is no doubt that the most significant factor contributing to weight gain and obesity is diet and nutritional intake. The increase in high-calorie, low-nutrient foods is causing sickness as a result of weight gain around the world, but especially the United States. Most people are using diet-foods and exercise programs to help control the weight gain, and one of the treatments gaining popularity in recent news is the use of omega-3 fatty acids in the form of fish oils. This report will examine studies of the correlation between omega-3s and weight loss. 

What are Fish Oils? What are the Benefits of Fish Oils?

“Fish Oils” refer to the Omega-3 fatty acids derived from the tissues of oily fish. The Omega-3 fatty acids contain EPA and DHA, which are said to have many benefits, such as increased learning ability, mental development, and visual acuity. They are also both considered to have beneficial effects on the prevention and management of chronic diseases, especially heart disease. In fact, it is recommended that individuals with coronary heart disease take 900 mg/day of fish oil supplements. “There has been a dramatic surge in interest recently, amongst the public and health professionals alike, of the health effects of omega-3 fatty acids derived from fish and fish oils-consisting of DHA and EPA.” ( Omega-3 fatty acids are not produced by fish, but are accumulated through their diets.

          While the most efficient source of omega-3 fish oils is through the consumption of oily fish, the use of supplements has become increasingly popular, especially in populations that cannot afford fish rich in Omega-3 or simply do not like the taste. While the majority of people eat fish or take omega-3 supplements for preventative benefits, new studies have shown that there may be a correlation between omega-3 fatty acids and weight loss. As one advertising website states: “Surprised that there are proven benefits for fish oil and weight loss? It’s true! Recent studies on fish oil show that people who get the most fish oil with DHA burn more fat, have less obesity, weight less and have less depression while dieting than those who get the least amount of fish oil”. (


Fish Oils and Weight Loss (what do fish oils do to fat? Good vs. bad fat)

          Many people aren’t aware that there are certain foods that can increase the number of fat calories that your body burns each day. Fish is one of these foods. “Although fat burning foods are important for anyone who wants to lose weight and keep it off for good, they’re vital if you’re one of those people who find it hard to lose weight. No matter how much exercise you do or how hard you diet, your genetics and metabolic make-up play a vital role in determining how fast and how much weight you lose.” ( This particular website, aimed at helping people lose weight and especially fat, explains different kinds of fat and presents examples of why fish oil is a “good” fat.

          There are two types of fat, polyunsaturated and monounsaturated fat. Polyunsaturated fats are considered “good” fats and monounsaturated are the “bad fats”. Omega-3 fish oil is a polyunsaturated “good” fat, which is said to reduce triglyceride levels, inflammations and growth of tumors. Polyunsaturated fats such as omega-3 oils are also known to help improve immunity and protect from heart disease.

In a recent study published in the International Journal of Obesity, researchers wanted to see if supplementing a diet with omega-3 fish oil increased the number of calories burned in a single day. Two groups were fed the same diet but one was given 6 grams of fat daily in the form of oils and the other was given 6 grams of fat daily in the form of omega-3 fish oil. After 3 weeks, the researchers measured the changes in fat oxidation, body fat percentage, and metabolic rates. The chart below contains the results:


With Fish Oil

Without Fish Oil

Measurement of Body Fat:

-2 lbs.

-0.7 lbs.

Daily Metabolic Rate:

1775 calories

1710 calories


As indicated in the result chart, the group that supplemented their diet with fish oil burned fat 26% faster than those without the fish oil supplementation.   Because both groups were given the exact same diet and the only difference was the fish oil supplementation, one can conclude that the fish oils played a role in the way the body processed and burned fat and calories. “One of the key reasons as to why omega-3 fish oil has such a powerful effect on fat metabolism is that the insulin levels were 50% lower when subjects used the fish oil. Insulin is a hormone that reduces the use of fat or fuel, while also promoting fat storage in the presence of excess calories.” Because fish oil reduced the insulin levels of the subjects who used fish oil, more fat was used as a source of energy, thus increasing the amount of fat lost.

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Research Studies

          The International Journal of Obesity did a study in 2007 on the effect of including seafood and fish oils as part of a diet in young overweight adults over a period of 8 weeks. This randomized controlled trial tested 324 overweight men and women by giving one group lean or fatty fish or fish oil as part of their diet and giving the other group no seafood or fish oil supplement whatsoever. After 4 weeks, most of the weight loss results were only significant in men. Because this study was completed in only 4 weeks, researchers concluded that the addition of seafood and fish-oil supplements may boost weight loss, but the evidence was not conclusive enough to find a clear answer.

          Another study of fish oil supplementation in The American Journal of Clinical Nutrition found that when omega-3 fatty acids are combined with regular aerobic exercise, cardiovascular and metabolic health, as well as body composition, improved more than when these two treatments were used independently. Because seafood-derived fatty acids have been shown to decrease the growth of adipose (fat) cells and regular aerobic exercise induces weight loss, both are independently useful in decreasing body fat. However, this study concluded that increasing the intake of fatty acids could be a useful addition to exercise programs aimed at improving body composition.


          While not one of the studies of websites presented in this paper concluded that fish oil supplementation alone would cause weight loss, all agreed that the implementation of fish and omega-3 fish oils in the diet is a good idea for body composition, heart health and prevention of chronic illness. “When it comes to weight loss, there is no simple quick fix. Most Doctors or nutritionists will suggest eating a balanced diet and exercising to lose weight. Because studies have shown that omega-3 increases metabolic rate and decreases body fat, it is suggested to incorporate omega-3 fish oils in the form of fish or supplements as a catalyst for weight loss”.



Alison M Hill, Jonathan D Buckley, Karen J Murphy, & Peter RC           Howe. (2007). Combining Fish-oil Supplements With Regular Aerobic        Exercise Improves Body Composition and Cardiovascular Disease Risk          Factors1,2,3. The American Journal of Clinical Nutrition, 85(5), 1267.

Thorsdittor, Tomasson, Gunnarsdittor, Gisladottir, Kiely, Parra, Schaafsma. (2007, October). Randomized Trial of Weight-Loss-Diets for Young Adults         Varying in Fish and Fish Oil Content. International Journal of Obesity, 31(10), 1560.




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