Like an old wives’ tale, the notion of fish oil and the benefits it allegedly has on weight loss are certainly known, but those benefits haven’t been truly understood … until now.

According to a study published in the American Journal of Clinical Nutrition, fish oil will not help accelerate weight loss if you have already started dieting and exercising before incorporating the omega-3 rich nutrient into your diet.

This fact only affects humans, says Dr. Laura F. DeFina of the Cooper Institute in Texas: “There is evidence from animal studies that omega-3 fatty acids promote weight loss but studies in people have mixed results,” she said.

A study in which obese adults enrolled in a diet and exercise program and took either omega-3 or a placebo found that the people in the omega-3 group lost 5.2 kilos on average while the placebo group lost almost 5.8 kilos.

DeFina cited fish oil’s various other health benefits for why it has an inconsistent effect on human weight loss. Those other benefits include improved insulin sensitivity and reduced cholesterol and blood pressure.