ORIGINAL ARTICLE Inclusion of fish or fish oil in weight-loss diets for young adults: effects on blood lipids I Gunnarsdottir 1,2 , H Tomasson 3 , M Kiely 4 , JA Martine ´z 5 , NM Bandarra 6 , MG Morais 7 and I Thorsdottir 1,2 1 Unit for Nutrition Research, Landspitali-University Hospital, Reykjavik, Iceland; 2 Department of Food Science and Human Nutrition, University of Iceland, Reykjavik, Iceland; 3 Faculty of Economics and Business Administration, University of Iceland, Reykjavik, Iceland; 4 Department of Food and Nutritional Sciences, University College Cork, Cork, Ireland; 5 Department of Physiology and Nutrition, University of Navarra, Navarra, Spain; 6 The National Research Institute on Agriculture and Fisheries Research, Lisbon, Portugal and 7 Department of Biochemistry, Faculty of Medical Sciences of Lisbon, Lisbon, Portugal Objective: To assess the effects of fish (lean or oily) and fish oil consumption on blood lipid concentration during weight loss. Design: Randomized, controlled 8-week trial of energy-restricted diet varying in fish and fish oil content. Subjects, 324 men and women, aged 20–40 years, body mass index 27.5–32.5 kg m 2 , from Iceland, Spain and Ireland, were randomized to one of four groups: (1) control (sunflower oil capsules, no seafood), (2) cod diet (3  150 g week 1 ), (3) salmon diet (3  150 g week 1 ), (4) fish oil (DHA/EPA capsules, no seafood). The macronutrient composition of the diets was similar between the groups and the capsule groups were single-blinded. Measurements: Total cholesterol (TC), high-density lipoprotein (HDL) and low-density lipoprotein cholesterol, triacylglycerol (TG) and anthropometrics were measured at baseline and end point. Results: The difference in logTG lowering between the control group and the cod diet, salmon diet and fish oil from baseline to end point was 0.036 (95% CI 0.079 to 0.006), 0.060 (0.101 to 0.018) and 0.037 (0.079 to 0.006), respectively. Reduction in TC was about 0.2 mmol l 1 greater in the fish groups (cod and salmon) than in the control group, but only of borderline significance when adjusting for weight loss. HDL tended to decrease less in the diet groups consuming a significant amount of n-3 fatty acids (salmon and fish oil). Conclusion: Weight-loss diet including oily fish resulted in greater TG reduction than did a diet without fish or fish oil. Controlled trials using whole fish as a test meal are encouraged to be able to elucidate the role of different constituents of fish for human health. International Journal of Obesity advance online publication, 20 May 2008; doi:10.1038/ijo.2008.64 Keywords: overweight; fish proteins; n-3 fatty acids; weight loss; lipids; human Introduction It is well known that excessive body weight increases the risk of developing a number of serious diet-related chronic illnesses, including cardiovascular diseases. In this context, countries with high fish intake have been shown to have lower rates of coronary heart disease, compared with other countries. 1–3 Studies testing the effects of fish as food in combination with weight loss are scarce. 4,5 Long-chain n-3 poly-unsatu- rated fatty acids (LC n-3 PUFAs), given as supplements, have in recent trials been shown to have beneficial effects on cardiovascular disease risk factors as an additional therapy to calorie restriction in overweight and obese individuals. 6–8 The triacylglycerol (TG) lowering effects of n-3 fatty acids are well documented, 9 and the beneficial effects of fish intake seen on blood lipids in previous trials have primarily been attributed to the presence of n-3 fatty acids. The role of other seafood constituents, such as fish proteins, has been studied in animals. 10–12 Hypocholesterolemic effects of fish proteins have been reported in animals together with lower hepatic TG concentration. 13 Very few human trials have addressed Received 14 August 2007; revised 4 March 2008; accepted 5 April 2008 Correspondence: Dr I Gunnarsdottir, Unit for Nutrition Research, Landspitali University Hospital, Eiriksgata 29, Reykjavik 101, Iceland. E-mail: ingigun@landspitali.is International Journal of Obesity (2008) 1–8 & 2008 Nature Publishing Group All rights reserved 0307-0565/08 $30.00 www.nature.com/ijo