Do you gain weight if you take omega-3?: Separating Myth from Fact

October 10, 2025 •

4 min read

While fat contains 9 calories per gram, the idea that taking omega-3 supplements inevitably causes weight gain is a common misconception. In fact, the relationship between these healthy fats and your body weight is far more complex, with numerous studies suggesting that, in combination with a healthy lifestyle, they can actually support fat loss rather than cause weight gain.

Quick Summary

Omega-3 fatty acids rarely cause weight gain at typical intakes. These healthy fats can positively influence metabolism, fat-burning, and body composition when combined with a balanced diet and active lifestyle.

Key Points

Calorie Content is Minimal: Typical omega-3 supplements contain very few calories, making weight gain unlikely from the supplement itself.
Metabolism Booster: Studies suggest that omega-3s can increase metabolic rate and enhance fat burning, particularly with regular exercise.
Improved Body Composition: Omega-3 intake has been linked to reductions in body fat and waist circumference, even when overall body weight remains stable.
Quality Over Quantity: Low-quality, rancid, or contaminated supplements may cause adverse health effects, which can contribute to inflammatory conditions.
Balanced Ratio is Key: Maintaining a healthy balance of omega-6 to omega-3 fatty acids is important for overall weight management and can counter the pro-inflammatory effects of high omega-6 intake.
Overall Lifestyle is Paramount: The effect of omega-3 on weight is modest and works best when combined with a proper diet and regular physical activity.

Understanding Omega-3 and Your Weight

Omega-3 fatty acids are essential polyunsaturated fats that play a crucial role in various bodily functions, from brain health to reducing inflammation. The three main types are EPA (eicosapentaenoic acid), DHA (docosahexaenoic acid), found in marine sources like fish oil, and ALA (alpha-linolenic acid), found in plant-based sources. The primary concern regarding weight gain comes from the caloric content of these supplements, but it’s a concern that often overlooks the broader metabolic effects of omega-3s.

The Calorie Fallacy: Separating Fact from Exaggeration

Each gram of fat, including the fat in fish oil, does contain about 9 calories. However, a typical omega-3 capsule contains a very small number of calories. Considering the usual intake, the additional caloric contribution is minimal and highly unlikely to cause weight gain on its own. Weight gain is typically the result of a long-term calorie surplus from overall diet and lifestyle, not a few dozen calories from a supplement. A potential risk, though, lies in low-quality products. As pointed out by one source, a lower-concentration fish oil could require consuming more capsules to reach an effective amount of EPA and DHA, potentially leading to a higher, and less beneficial, caloric intake.

How Omega-3 Can Positively Influence Weight Management

Instead of causing weight gain, omega-3 fatty acids have been shown to influence several metabolic processes that support weight management, and potentially fat loss, when incorporated into a healthy routine.

Boosting Metabolism: Some studies suggest that omega-3s can increase your metabolic rate, meaning your body burns more calories throughout the day. This effect is particularly pronounced when combined with regular exercise.
Enhancing Exercise Benefits: Research indicates that taking fish oil may help your body switch from burning carbohydrates to burning fat during exercise, leading to more efficient fat loss.
Reducing Appetite and Increasing Satiety: Findings on omega-3 and appetite are mixed, but some studies suggest that taking fish oil can increase feelings of fullness, especially for those on a weight-loss diet.

The Importance of Body Composition Over Body Weight

One of the most revealing findings from omega-3 research is its effect on body composition. The number on the scale can be misleading because it doesn't differentiate between fat mass and muscle mass. Studies have found that individuals taking omega-3 supplements can experience a decrease in body fat and waist circumference, even if their total body weight remains unchanged. Since muscle weighs more than fat, you might be losing fat and gaining muscle simultaneously, which is a positive health outcome not always reflected on the scale.

The Damaging Role of a High Omega-6 to Omega-3 Ratio

A significant factor contributing to obesity in modern diets is the imbalanced ratio of omega-6 to omega-3 fatty acids. Western diets are typically high in omega-6 fatty acids from vegetable oils and processed foods and low in omega-3s. A high omega-6 to omega-3 ratio promotes inflammation and can increase the risk of obesity, whereas increasing omega-3 intake can help balance this ratio and promote metabolic homeostasis.

Comparison of High-Quality vs. Low-Quality Omega-3 Supplements


Feature	High-Quality Omega-3 Supplement	Low-Quality Omega-3 Supplement
Purity	Independently tested for contaminants (mercury, PCBs, dioxins).	No testing or questionable results; may contain toxins.
Potency (EPA/DHA)	Higher concentration per serving.	Lower concentration, potentially requiring more servings to reach an effective amount.
Freshness	Low oxidation value; no fishy aftertaste or burps.	High oxidation value, indicating rancidity; causes fishy burps.
Bioavailability	In natural triglyceride or reformed triglyceride form, for better absorption.	Often in ethyl ester form, which is less bioavailable.
Source	Small fish with short lifespans (anchovies, sardines) to minimize contaminant buildup.	Larger, predatory fish higher up the food chain, increasing risk of contaminants.

The Importance of Overall Context

While omega-3s offer numerous potential benefits, they are not a magic pill for weight loss. Their effects are modest and are best realized as part of a broader healthy lifestyle. This includes a balanced diet rich in whole foods, regular physical activity, and choosing high-quality supplements when necessary. The potential fat-reducing and metabolic-boosting properties are a welcome side effect, but the main benefits for heart, brain, and joint health remain the primary motivation for most people to incorporate omega-3s into their diet.

Conclusion

No, you will not gain weight if you take omega-3 supplements, provided you take a high-quality product within general recommendations. The calories are negligible, and the metabolic benefits may even assist in fat loss. Focusing on overall diet, exercise, and choosing a pure, potent supplement will maximize the significant health benefits of omega-3 fatty acids, without the risk of unwanted weight gain.

For more information on dietary supplements, you can visit the NIH Office of Dietary Supplements.

Frequently Asked Questions

At typical intakes, fish oil supplements are very low in calories and are not known to cause weight gain. The minor caloric intake is typically offset by the supplement's positive metabolic effects.

Research is mixed on the effect of omega-3s on appetite. Some studies suggest they can increase satiety in people on a calorie-restricted diet, while other findings vary depending on the individual's health status.

Low-quality or rancid fish oil can be less potent and may contain contaminants. While these are unlikely to cause significant weight gain, the resulting inflammation and reduced health benefits could indirectly affect weight management.

A typical omega-3 softgel contains a small number of calories. The caloric intake is minimal and does not pose a risk for weight gain at standard intakes.

Yes, omega-3s may assist with fat loss. Studies have shown they can increase fat burning during exercise and may help reduce overall body fat mass and waist circumference, even without significant weight change.

For general health, a typical daily amount is often recommended. For specific health concerns, consult a healthcare provider.

Yes. An excessive intake of omega-6 fatty acids relative to omega-3s, which is common in modern diets, can lead to chronic inflammation and is associated with increased obesity risk.