Fish oil is one of the most common supplements on the market.
Researchers have also suggested that fish oil omega-3s may help people lose weight more easily. However, studies are not unanimous, and opinions on this potential benefit remain split.
This article reviews the current evidence on whether omega-3s from fish oil can help you lose weight.
Omega-3 fatty acids are a family of fats that’s essential for human health.
There are several types of omega-3 fats, but the most important ones can be categorized into two main groups:
- Essential omega-3 fatty acids: Alpha-linolenic acid (ALA) is the only essential omega-3 fatty acid. It is found in a wide range of plant foods. Walnuts, hemp seeds, chia seeds, flaxseeds and their oils are the richest sources.
- Long-chain omega-3 fatty acids: The two most known are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). They are mainly found in fish oil and fatty fish, but also in seafood, algae and algae oil.
ALA is considered essential because your body can’t produce it. This means you must get this type of fat from your diet.
On the other hand, EPA and DHA aren’t technically considered essential, because the human body can use ALA to produce them.
However, this conversion is not very efficient in humans. Your body turns only about 2–10% of the ALA you consume into EPA and DHA (5).
For this reason, many health professionals advise taking around 200–300 mg of EPA and DHA per day. You can do this by eating about two portions of fatty fish per week, or you can take a supplement.
There are many fish oil omega-3 supplements on the market, usually available as oil drops or capsules.
Summary: Fish oil is rich in the omega-3s EPA and DHA, which are involved in many important body functions. Other sources of these two omega-3s include fatty fish, seafood and algae.
Fish oil omega-3s may help people lose weight in several ways, the first of which involves reducing hunger and appetite.
This effect may be particularly useful for those who are following weight loss diets, which sometimes lead to increased feelings of hunger.
In one study, healthy people on a weight loss diet consumed either fewer than 0.3 grams or more than 1.3 grams of fish oil omega-3s per day. The high-fish-oil group reported feeling significantly fuller up to two hours after a meal (12).
However, these effects are not universal.
For instance, in another small study, healthy adults not following a weight loss diet were given either 5 grams of fish oil or a placebo each day.
The fish oil group reported feeling around 20% less full after a standard breakfast and experienced a 28% stronger desire to eat (13).
Interestingly, one study observed that fish oil omega-3s increased the levels of a fullness hormone in obese people, but decreased levels of the same hormone in non-obese people (17).
Thus, it is possible that effects vary depending on your health status and diet. However, more studies are needed before strong conclusions can be made.
Summary: Fish oil may be most effective at reducing hunger and appetite in healthy people following a weight loss diet. However, more studies are needed.
Another way fish oil omega-3s may help you lose weight is by increasing your metabolism.
Your metabolism can be measured by your metabolic rate, which determines the number of calories you burn each day.
The higher your metabolic rate, the more calories you burn and the easier it is to lose weight and keep it off.
One small study reported that when healthy young adults took 6 grams of fish oil per day for 12 weeks, their metabolic rates increased by around 3.8% (18).
In another study, when healthy older women took 3 grams of fish oil per day for 12 weeks, their metabolic rates increased by around 14%, which is the equivalent of burning an extra 187 calories per day (19).
More recently, a study found that when healthy adults took 3 grams of fish oil per day for 12 weeks, their metabolic rate increased by an average of 5.3% (20).
Most of the studies reporting increases in metabolic rates also observed an increase in muscle mass. Muscle burns more calories than fat, thus an increase in muscle mass may explain the higher metabolic rates observed in these studies.
That said, not all studies have observed this effect. Thus, more studies are needed to understand the exact effects of fish oil on metabolic rates (21).
Summary: Fish oil may increase the speed of your metabolism. A quicker metabolism can help you burn more calories each day and potentially lose more weight.
The metabolic effects of fish oil may not be limited to simply increasing how many calories you burn each day.
Research suggests that consuming fish oil may also amplify the number of calories and amount of fat you burn during exercise.
Researchers believe this happens because fish oil may help you switch from using carbohydrates to fat as a source of fuel during exercise (22).
One study reports that women given 3 grams of fish oil per day for 12 weeks burned 10% more calories and 19–27% more fat when they exercised (19).
This finding may explain why some studies have found that taking fish oil supplements in combination with exercise was more effective at reducing body fat than exercise alone (23).
Summary: Fish oil may help increase the number of calories and amount of fat burned during exercise, both of which may help you lose weight. However, more studies are needed.
Even if fish oil omega-3s don’t help some people lose weight, they may still help them build muscle and lose body fat.
Sometimes your weight on the scale can be misleading. It may remain the same even if you’re gaining muscle and losing fat.
That’s why people who want to lose weight are often encouraged to use a tape measure or track their body fat percentages to assess their progress, rather than rely only on the scale.
Using body weight to track loss of body fat may also explain why some studies have failed to find any effect of fish oil omega-3s on weight loss. However, studies that use more precise measurements of fat loss often tell another story.
For instance, a study of 44 people reported that those given 4 grams of fish oil per day failed to lose more weight than those given a placebo.
However, the fish oil group lost 1.1 more pounds (0.5 kg) of body fat and built 1.1 more pounds (0.5 kg) of muscle than those not given fish oil (24).
In another study, six healthy adults replaced 6 grams of fat in their diets with 6 grams of fish oil each day for three weeks. They lost no more weight following the fish oil-rich diet, but they did lose more body fat (18).
Similarly, another small study observed that people who took 3 grams of fish oil per day lost 1.3 more pounds (0.6 kg) of fat than those given a placebo. However, participants’ total body weights remained unchanged (26).
Accordingly, a review of 21 studies concluded that fish oil doesn’t reduce body weight more effectively than a placebo. However, the review showed that fish oil does reduce waist circumference and waist-to-hip ratio more effectively (27).
Thus, fish oil may not help you lose weight per se, but it may make it easier for you to lose inches and help you go down in clothing sizes.
Summary: Fish oil may help you lose more fat or inches without actually reducing your weight on the scale.
According to the US Food and Drug Administration (FDA), intake of fish oil omega-3s is considered safe if the daily dose does not exceed 3,000 mg per day (29).
However, the European Food Safety Authority (EFSA), the European equivalent of the FDA, considers daily intakes of up to 5,000 mg from supplements to be safe (30).
It’s good to keep in mind that omega-3s have blood-thinning effects that may cause excessive bleeding in some people.
If you’re taking blood-thinning medication, talk to a healthcare professional before adding fish oil supplements to your diet.
In addition, be careful with the type of fish oil supplements you take. Some may contain vitamin A, which can be toxic when taken in high amounts, especially in pregnant women and young children. Cod liver oil is one example.
And finally, make sure you pay attention to the content of your fish oil supplements.
Unfortunately, certain types actually don’t contain much fish oil, EPA or DHA. To avoid these “fake” products, pick a supplement that has been tested by a third party
To get the most benefits from your omega-3 supplements, choose one that is made up of at least 50% EPA and DHA. For instance, it should have at least 500 mg of combined EPA and DHA per 1,000 mg of fish oil.
Summary: Fish oil is generally safe to consume. To maximize the benefits of your supplements, take 300–3,000 mg per day. If you take blood thinners, check with a healthcare professional before adding fish oil supplements to your diet.
The omega-3 fatty acids in fish oil have various potential health benefits, one of which is aiding weight loss.
More importantly, fish oil omega-3s may help you lose inches and shed body fat.
However, studies have found these effects appear to be modest, and they may not apply to everyone.
Overall, fish oil omega-3s are likely to have the most beneficial effects when combined with lifestyle factors like proper nutrition and regular physical activity.
An evidence-based nutrition article from our experts at Authority Nutrition.