A study published in the International Journal Of Obesity split 324 subjects into four diet groups: control, lean fish, fatty fish, and fish oil.

All four of the groups had the same macronutrient (protein, fats, carbs) and calorie breakdown.  On a side note, this was a pretty crummy diet, and all four groups lost weight.  Just goes to show that following ANY plan is better than following none.

The control group took sunflower seed oil capsules, and didn’t get any seafood.

The second group got cod (150g) three times a week.

The third group got salmon (150g) three times a week.

The fourth group took fish oil capsules, and didn’t get any seafood.

The average weight loss over the study was 14 pounds, and everyone who had ANY of the marine products: lean fish, fatty fish, or fish oil, lost an additional 2.2 pounds over 4 weeks.

Conclusion: If you’re following a diet, adding fish or fish oil will help you lose more weight

Here’s the citation:

Int J Obes (Lond). 2007 Oct;31(10):1560-6. Epub 2007 May 15.
Randomized trial of weight-loss-diets for young adults varying in fish and fish oil content.
Thorsdottir I, Tomasson H, Gunnarsdottir I, Gisladottir E, Kiely M, Parra MD, Bandarra NM, Schaafsma G, Martinéz JA. Unit for Nutrition Research, Department of Food Science and Human Nutrition, Landspitali University Hospital, University of Iceland, Eiriksgata-29, 101 Reykjavik, Iceland.

And this is a link to the abstract: Weight Loss For Young Adults Varying In Fish Content