I Fish to Be Thin

Letter As more is understood about obesity, it is becoming clear that the disease is far more complex than a simple positive energy balance. Complex behavioural, social and environmental factors interact with poor quality nutrition to cause a perfect storm of metabolic dysfunction. However, without a poor quality diet, it is unlikely that the other factors could lead to obesity individually, as the low quality foods are the driver of the metabolic dysfunction that underlie weight gain. Increasingly, research is showing that forced calorie restriction and forced physical activity does not cause weight loss in humans. This is because such an approach does not address the underlying cause of the weight gain, which is poor quality nutrition containing high intakes of sugar. To these ends, the nutritional literature has identified a number of foods that can alter the quality of the diet and thus lead to weight loss without calorie restriction.

Fish and their oils are one group of foods that show promise as weight loss agents, and intervention studies have shown that supplementing the diet with fish oils and eating more fish may facilitate weight loss. For example, in one study1 researchers used an energy restrictive diet for 8 weeks to induce weight loss in a number of groups of subjects. One group served as the controls and were provided with a  dietary regimen that restricted calories by 30 %, while other groups followed a similar diet that contained either lean fish, fatty fish or fish oils. The fatty fish and fish oils provided eicosapentanoic acid (EPA, C20:5 (n-3)) and docosahexanoic acid (DHA, C22:6 (n-3)). The results showed that the weight loss and waist circumference in the lean fish, fatty fish and fish oil groups was greater than the control group. However this was true for men, but not women.  

This study is interesting because it highlights a number of important points about diet and weight loss. Firstly, it confirms findings from other studies to show that fish may be beneficial to weight loss. Fish oil is known to stimulate β-oxidation in humans and this in turn decreases adipose cell size. However, just why lean fish is also beneficial is not fully understood. It has been speculated that fish proteins may have physiological benefits, and this would explain the epidemiological evidence suggesting that fish eaters are more healthy. Another interesting finding of this study was the fact that calorie restriction itself was not likely the cause of weight loss in any group. In the control group many dietary changes were made before calorie restriction of 30 % was implemented, including the restriction of alcohol and changes to the macronutrient ratios which may have reduced sugar intake. Subjects were also asked to keep food diaries which may have altered behaviour. 

It is therefore not possible to say that forced calorie restriction was successful in causing weight loss. The fact that fish in the diet caused additional weight loss, with no further calorie restriction argues against this fact. If addition of a dietary component can cause weight loss greater than an equal calorie diet absent of that component, then logically, calorie restriction is not required to lose weight and the ‘eat-too-much, do-too-little’ theory of obesity is false. Also, if a single food can be substituted into a diet to cause weight loss with no calorie restriction, then logically a single food could also be substituted into a diet to cause weight gain with no change to the overall energy intake. In fact these scenarios are increasingly being seen as the main drivers of weight gain or loss, rather than the absolute energy intake.


1Thorsdottir, I., Tomasson, H., Gunnarsdottir, I., Gisladottir, E., Kiely, M., Parra, M. D., Bandarra, N. M., Schaafsma, G. and Martinez, J. A. 2007. Randomized trial of weight-loss-diets for young adults varying in fish and fish oil content. International Journal of Obesity. 31: 1560-1566

About Robert Barrington

Robert Barrington is a writer, nutritionist, lecturer and philosopher.
This entry was posted in Docosahexaenoic Acid, Eicosapentaenoic Acid, Essential Fatty Acids, Fish, Fish Oils, Protein, Weight Loss and tagged , , , . Bookmark the permalink.