You may well be aware of just how often nutritional advice seems to blow in the wind. For example, this week a study claimed to find a link between eating oily fish and an increased risk of diabetes. [1] Not surprisingly, this has led to some recommending caution with regard to our consumption of oily fish, with a spokesperson for the British Dietetic Association recommending that we consume no more than one portion a week. But does it really make sense for us limit our intake of a food, which, traditionally, has a very healthy reputation?
The research in question, published in the journal Diabetes Care, looked at the relationship between pesticide residues known as "persistent organic pesticides" (POPs) and diabetes risk. POPs include chemicals known as organochlorines and polychlorinated biphenyls (PCBs). Because pesticides tend to lodge in fat, POP residues can be found plentifully in oily varieties of fish (e.g. salmon, trout).
The Diabetes Care study found that higher blood levels of POP were associated with an increased risk of insulin resistance—itself believed to be a warning sign of Type 2 diabetes. The link between POPs and insulin resistance was highest for those with bigger waist sizes (increased waist circumference is itself associated with an increased risk of insulin resistance and Type 2 diabetes). Previous research has found that exposure to pesticide residues was associated with an increased risk of Type 2 diabetes. The suggestion here is that pesticide residues somehow act to promote insulin resistance and Type 2 diabetes.
The authors of the Diabetes Care study published this week have pointed out that their research does not prove that pesticide residues actually cause insulin resistance. They have also called for further research into how these chemicals might promote biochemical disruption in the body. This all sounds like good sensible stuff to me.
The precautionary principle dictates, I think, that the less of these chemicals we are exposed to, the better.
But does that mean we should eschew oily fish? After all, this foodstuff is rich in omega-3 fats that have been linked with a reduced risk of cardiovascular disease and seem to have benefits for the brain.
In recently published research in the Journal of the American Medical Association the pros and cons of fish eating were weighed up. The authors of this study concluded that even when contamination is taken into account, eating fish seems to do more good than harm [2]. In the ideal world all our food would be free from extraneous chemical contaminants. However, the totality of the evidence supports the idea that eating a piece of somewhat contaminated oily fish is better for us than not eating it at all.
References:
1. Lee D-H, et al. Association Between Serum Concentrations of Persistent Organic Pollutants and Insulin Resistance Among Nondiabetic Adults. Diabetes Care 30:622-628, 2007
2. Mozaffarian D, et al. Fish intake, contaminants, and human health. Journal of the American Medical Association. 2006; 296:1885-1899
Dr John Briffa is a London-based doctor, author, and health writer with an interest in nutrition and natural medicine.
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