Salmon are what they eat

Salmon is rich in essential fatty acids, in particular the Omega-3 family of fatty acids. The description ’essential’ means that the body cannot synthesise or can only synthesise limited amounts of the substance in question.

The long-chain fatty acids in the Omega-3 family include the parent alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid. Oil-rich fish and supplements such as fish oil and cod liver oil are the richest and most readily available dietary sources of Omega-3.

The Omega-3 family of fatty acids has long been known to have positive health effects. Among other things, it is known to decrease triglyceride levels in the blood.

Farmed salmon have traditionally been fed, at least in part, on fish meal made from fast-growing, short-lived, oily, foraging fish species that are not generally used for human consumption. However, there is currently a short-fall in this fishery. In addition, pollutants such as dioxins become more concentrated as one moves up the food chain. Top predators such as salmon may end up with unhealthy levels. Feeding farmed salmon with fish meal may encourage this process.

These factors together with the fact that catching fish to feed fish is not especially environmentally friendly has led to efforts to find a land-based replacement for the fish meal component of the farmed salmon diet. The land-based feed uses vegetable oil instead of fish oil in the meal.

Healthy, vegetarian salmon

The proverb “you are what you eat” is well known and holds true for salmon as well as for us,” explains Berge. Fish that have had vegetarian feed will have lower levels of the valuable Omega-3 fatty acids EPA and DHA. While some plant oils have been shown to have positive health effects due to their Omega-3 contents, fish oils have been shown to be more effective.

Researchers at the Department of Medicine at UiB recently undertook a study to determine the health affects of vegetarian vs. fish-fed salmon. Participants in the study consumed 750g of salmon weekly, divided into five meals, for two eight-week periods. There were two groups of participants. One group ate vegetarian-fed salmon for the first eight-week period and fish-fed salmon in the second and the other group did the reverse.

Tests were taken before, during and after the study periods. The results showed that eating salmon had a positive lowering effect on the participants’ triglyceride levels and that there was no significant difference in this effect relating to the kind of salmon eaten. Thus vegetarian-fed salmon are just as healthy to eat as fish-fed salmon.

-These results may imply that small levels of ingested EPA and DHA are sufficient to have a positive effect on factors relating to heart and cardiovascular disease. Or it may well be that there is another factor in the fish that is bioactive in this area,” explains Prof Rolf Berge. He added that researchers believe that ingestion of healthy fish protein has positive effects on the lipid values in the blood and that protein metabolism can interfere with fat metabolism.

The results of the salmon diet have been published and researchers are now building on this work with new studies. Doctoral student Oddrun Gudbrandsen from the Department of Medicine, for example, is studying the relationship between fatty acids and fish protein. She explains that the work is not finished yet. She will defend her doctorate later this spring.

Studies in animal models have shown that fish protein alone can have a positive effect on lipid levels in the blood of rats. Clinical studies have also been undertaken in people comparing diets involving fish protein, salmon and fish oil. The results are now being analysed.