Are you one of the many health conscious people who reach for tinned tuna to boost your protein intake? Then you could be seriously damaging your health.

Harmful Pesticides in the food chain

Most people have heard of DDT, the most infamous of a group of chemicals called organochlorines – or OCs, and probably know that despite being banned years ago it is still found in the body fat of most animals. Widely used as a pesticide, DDT and the other OCs are classed as POPs, or persistent organic pollutants. As the name suggests, this means that they stick around in our environment for an awfully long time polluting both our food supply and eventually us.

OC's banned in 1980's but still with us!

They were introduced into Australia in the 50s and 60s with the peak use occurring in 1974. By this stage people were starting to realise that toxic chemicals which accumulated in higher-level animals (namely us), and took decades to break down in soil and plants, were probably not the most sensible things to be using. Their use was phased out in most countries by the 80s but the damage was already done. Aquatic mammals in the Arctic tested positive to OCs despite their never having been used there, and 25 years after they were banned for agricultural use in Australia, our food is still found to contain them. These chemicals are here and they are staying for good.

Evidence linking OC’s with Insulin Resistance

The evidence linking OCs with the development of some cancers gets plenty of press but more recent research suggesting a role in the development of diabetes and weight gain seems to have flown under the radar. Exactly how they do it is still a bit of a mystery but it seems that these tenacious little chemicals make your body insulin resistant, the condition that normally precedes the development of diabetes by 10 to 20 years. Researchers have found that the higher the level of OCs a non-diabetic person has in their blood, the greater degree of insulin resistance that is present. This association is stronger as waist circumference increases. There was no association with obesity and insulin resistance if there were also no detectable OCs. This means that if you have high OCs in your blood, whether you’re overweight or not, there is a pretty good chance that you’ve also got insulin resistance.

Insulin resistance prevents weight loss

Other research found that the people with the highest amount of OCs in their body suffered the most “famine effect” when they lost weight. This means that the most toxic people experienced the greatest slowing of metabolism and reduction in satiety (I’m full now, stop eating) hormones. This could go a long way towards explaining why you find it so hard to keep weight off once you lose it; it’s not us, it’s the OCs. The OCs are fat soluble which means that they are stored in your fat cells, and released only if the fat is transported out of the cell, for instance, when you lose weight. It’s the perfect yo yo diet storm. You cut out the junk food and go for a run, thus burning up some body fat. OCs come flooding out into your system, slowing down your metabolism and making you hungry. You lose weight, you put it back on. “I think that it’s too early to state categorically that OCs are the cause of insulin resistance, diabetes and an inability to lose weight, but there is compelling evidence that they are certainly guilty accomplices”.

What’s wrong with Tuna?

So why the accusation against tuna? OCs are subject to something called bio-accumulation, which means that they make their way up the food chain, accumulating in amount as they go. They are potentially found in any animal product but are particularly fond of hanging around in fish, meat and dairy, so these provide the main dietary source for us. When you eat Australian produced meat and dairy you still risk being exposed to a small amount of OCs as they are now ubiquitous in our food chain, but when you eat fish from outside Australia, you are putting yourself at serious risk.

Oceans contaminated with DDT

The amount of DDT that has been found in tuna from the East and South China Seas and the Bay of Bengal indicates that India, China and other developing Asian countries are still using it. Check out your next tin of tuna to see where it comes from and chances are that it will say Thailand. Next look at a map of Thailand, and you’ll see that your tuna once swam in the Bay of Bengal, which means that you are probably getting a lot more than a cheap source of protein. It’s never too late to change your eating habits, so why not cut out tuna and help ease not only your own toxic burden but also that of your children.