Each teaspoon of cod liver oil contains 5 grams of fat and 45 calories, so it probably doesn't sound like something that would help you lose weight. Surprisingly, some preliminary evidence shows that cod, cod liver oil and other types of fish oil may be beneficial for this purpose. However, the potential weight loss appears to be very small, so you're likely to get better results by cutting calories and exercising more. Check with your doctor before taking this or any other supplement to confirm this is safe for you.
Cod and Weight Loss
You may be able to get weight-loss benefits from simply eating more cod. A study published in "Nutrition, Metabolism and Cardiovascular Diseases" in December 2009 found that people who ate cod five times per week for eight weeks lost almost 4 pounds more than people who didn't eat seafood, but followed a diet with the same amount of fat, protein and carbohydrates.
Cod Liver Oil and Weight Loss
Studies using cod liver oil for weight loss have included mainly animal studies, and the results have yielded conflicting results. A review article published in "Nutrients" in 2010 notes that more studies using people are necessary, but that some small studies have shown inverse relationships between omega-3 fats and obesity, especially when the omega-3 fats are consumed as part of a reduced-calorie diet. The review highlighted one study that used cod liver oil and found that, although it didn't cause a statistically significant difference in weight loss in rats, it did cause them to build up more omega-3 fats in their tissues, which could cause the rats to accumulate less body fat in the future.
Fish Oil and Weight Loss
Fish oil in general has been linked to small increases in weight loss. A study published in the "International Journal of Obesity" in 2007 found that men who ate fish three times per week or took a fish oil supplement for eight weeks experienced about 2 pounds greater weight loss than those who didn't eat seafood or take a fish oil supplement. A review article published in "Obesity Reviews" in November 2009 noted that fish oil may cause you to use more energy, reduce your appetite and cause other changes that minimize the deposits of fat, but that further research using people is necessary to verify these effects. However, because fish oil supplements can come from several sources -- not necessarily cod liver -- the results might not mirror the effects of taking cod liver oil.
Safety and Considerations
Fish oils, including cod liver oil, can cause side effects, including belching, an upset stomach, an unpleasant taste in your mouth, a mild rash or back or chest pain. These oils may also interact with certain medications, including birth control pills, diuretics, beta-blockers and blood thinners. Cod liver oil can cause vitamin A toxicity in relatively small amounts, as just 2 teaspoons provides 10,000 international units, which is the tolerable upper intake level for vitamin A for adults.