Fish Oil May Reduce Hunger and Appetite
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 (Link).
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 (Link).
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 (Link).
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.
Fish Oil May Increase Metabolism
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% (Link).
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 (Link).
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% (Link).
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 (Link).
Fish Oil May Boost the Effects of Exercise
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 (Link).
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 (Link).
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 (Link).
However, other studies have found that fish oil does not appear to affect the type of fuel the body uses during exercise. Thus, more studies are needed before strong conclusions can be made (Link 1, Link 2).
Fish Oil May Help You Lose Fat and Inches
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 (Link).
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 (Link).
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 (Link).
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 (Link).
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.
Written by Alina Petre, MS, RD, Healthline