Now, new evidence is emerging to show that fish and shellfish contain many other ingredients which prevent and cure life threatening diseases and other conditions.
"We have reached a turning point in our understanding of just what benefits to human health come from eating fish, and particularly shellfish," says Clive Askew, consultant to the UK’s Fishmongers’ Company.
Dr Askew was speaking after the recent Fishmongers’ Company conference on seafood and health, held in London, UK At that landmark conference, international experts presented, for the first time outside academic circles, results of medical trials which confound common perceptions that the cholesterol contained in shellfish is harmful, and describe the role of seafood in combating obesity.
Conference delegates also heard how the trace elements iodine and selenium and the vitamin D present in seafood are essential for good health.
Bruce Griffin, reader in Medical Sciences at Surrey University, told how, contrary to popular perception, there is no link between the dietary cholesterol in shellfish and the blood cholesterol in humans, so eating shellfish poses no risk of cardio-vascular disease. "There has been no convincing evidence over 30 years that this is the case. Saturated fats are the main dietary cause of the disease", he said.
Dr Griffin has carried out the first trial to substantiate the fact that the dietary cholesterol in shellfish – in this case coldwater prawns – does not increase the blood cholesterol level, or affect any of the other biomarkers of coronary heart disease.
In fact shellfish, along with oil-rich fish, represent a major dietary source of eicosapentaenoic (EPA) and docosahexaenoic (DHA) long chain omega-3 polyunsaturated fatty acids, and so act against ‘all manifestations of coronary heart disease’.
Lean [white, non-oily] fish has a low energy density combined with high protein levels, but is more satisfying than other high protein foods, according to Anna Karin Lindroos from the Elsie Widdowson Laboratory in Cambridge in the UK. Trials showed that it stopped people feeling hungry sooner than protein foods such as beef and chicken, she said. Of the main protein foods, fish has the highest volume but contains the lowest number of calories.
Dr Lindroos pointed out that obesity, caused by ‘eating more calories than you need’, is a major health problem in Western countries. And it is becoming worse. The USA tops the obesity league table, but in the UK 23% of the population is too fat, she said.
Fish and shellfish are exceptional sources of iodine and selenium, according to Barbara Demeneix, director of the Muséum National d’Histoire Naturelle in Paris. In fact, shellfish are probably the richest source of both trace elements, she said, and recommended eating mussels, oysters, lobster and prawns.
Iodine and selenium are needed to make thyroid hormones, and selenium has many other beneficial effects, even acting against cancer. (Professor Margaret Rayman, of the University of Surrey, told delegates that selenium works against mercury toxicity, ‘therefore pregnant women don’t need to restrict fish consumption’.)
Thyroid hormone is essential for brain development in the foetus and deficiency during pregnancy can lead to children being born with below average intelligence. Lack of iodine and selenium will have severe and irreversible repercussions on brain development throughout childhood, and will affect brain performance in adults, even leading to depression in old age.
Vitamin D is traditionally associated with calcium balance and bone health, according to Sarah Keogh, consultant dietician at the Albany Clinic in Dublin. However, deficiency is also linked to hypertension, Type 1 diabetes, multiple sclerosis, psoriasis, inflammatory bowel disease and prostate cancer, she said. "Increasing vitamin D levels is an area of growing importance in the human diet."
Exposure to ultra violet radiation from the sun is the main source of the vitamin, but people in northern countries cannot obtain enough during the winter and therefore must rely on what they eat. "Oil-rich fish is the best dietary source of vitamin D, but people also need supplements," Ms Keogh told delegates.
The benefits to health from ingesting the essential omega-3 long-chain polyunsaturated fatty acids present in seafood, was not neglected at the conference. Fish muscle is extremely rich in DHA, which is essential for the brain, according to Michael Crawford of the London Institute of Brain Chemistry and Human Nutrition. Professor Crawford said trials have shown that DHA given to pregnant women has resulted in better brain development in their children, whereas lack of DHA in the diet has led to a rise in mental ill health in all age groups.
"Why wait for disease to develop and then spend millions preventing it?" questioned Bill Lands from the USA, and stated that coronary heart disease, one of the biggest killers in Western countries, could be prevented if diets contained sufficient omega-3 fatty acids.
"Food [composition] has a direct connection to death," Professor Lands said. If the diet contained more omega-6 fatty acids – found in seed oils and therefore in many processed foods – than omega-3 fatty acids, then it posed a higher risk of causing a heart attack than a diet with more omega-3 than omega-6 fatty acids.
Professor Philip Calder from the School of Medicine, Southampton University, stated that there was now a "huge amount of data" showing that high fish consumption could lead to a major reduction in human mortality due to cardio-vascular disease.
Atherosclerosis, or the build up of fatty deposits on the inside of blood vessel walls, was slowed down or limited, then reversed, in just a few months by the ingestion of omega-3 fatty acids.
"Omega-3s have a bigger effect than statins [in preventing heart attacks]," he said, and added that there was a reduction in overall mortality as well as coronary mortality if the diet contained more omega-3 fatty acids.
Tom Gilhooly believes that omega-3 fatty acids will cure many serious illnesses: cardiac disease, depression, arthritis – "they have none of the side effects of anti-inflammatory drugs such as Ibuprofen" – eczema, and ADHD (behavioural disorders).
Dr Gilhooly, who set up The Essential Health Clinic in Glasgow, has been in general practice for 20 years. He prescribes omega-3 fatty acids in fish oil capsule form because this is easier for patients to take, although it is better to eat seafood because of the trace elements and extremely powerful antioxidants it contains.
The only downside to the avalanche of positive news presented at the conference was the fact that there are not enough fish in the world’s oceans to provide the recommended level of EPA and DHA (essential long-chain omega-3 fatty acids) in the diet.
"About 219 million tonnes of fish need to be eaten globally to reach this level, whereas FAO reports annual catches of 94-104 million tonnes, of which a third is fed to animals," said Professor Crawford. ‘We’ve got to think seriously about the 'agriculturisation' of the oceans; we’ve got to stop this hunting and gathering nonsense."
