Fatty fish consumption and CVD

Is it just snake oil?

What is the evidence for fish or fish oil capsule consumption in the prevention of Coronary Heart Disease (CHD), Cardiovascular Disease (CVD) and all-cause mortality?

This meta analysis of observational studies Fish Consumption and the Risk of Chronic Disease: An Umbrella Review of Meta-Analyses of Prospective Cohort Studies found only moderate quality evidence for a 12% reduction in CVD, but worryingly found a 35% increase in liver cancer for each 100 gm per day of fish. It also found a positive association between fried fish and increased risk of heart failure.

The second DART trial also showed negative results. Lack of benefit of dietary advice to men with angina: results of a controlled trial followed over 3000 men and showed that ‘Men advised to eat oily fish, and particularly those supplied with fish oil capsules, had a higher risk of cardiac death.’ Perhaps these men, who all had the warning signs of angina, mistakenly thought they were protected by fish oil and didn’t make their lifestyles more healthy.

A study of Associations of Fish Consumption With Risk of Cardiovascular Disease and Mortality Among Individuals With or Without Vascular Disease From 58 Countries found 175 gms of fish per week, 2 servings, was associated with an increase in LDL cholesterol and was not associated with a reduction in CVD nor all-cause mortality.

When looking at studies that replace saturated fat with ‘polyunsaturated fats’ ie fish, we should bear in mind that a fillet of cooked mackerel has 7.1 gms of saturated fat and a fillet of herring have 6 gms (ie comparable with ham or lamb). A 6 oz fillet of farmed salmon has 4.1 gms of saturated fat (comparable with a chicken leg).

In this meta analysis of observational studies higher levels of EPA/DHA were associated with a 15%, 11% and 13% relative reduction in death from CVD, cancer and all cause mortality compared to groups with lower levels. Blood n-3 fatty acid levels and total and cause-specific mortality from 17 prospective studies. EPA and DHA can be converted by the body from ALA, which is found in chia and flax seeds. This occurs with increased efficiency if EPA/DHA are not obtained directly from the flesh of animals. EPA and DHA are indeed found in fish, but the fish get them from eating algae. Algae present a much less polluted source of EPA/DHA supplementation particularly for pregnant and breast feeding women, who need to avoid heavy metal consumption, and for young children or older adults if the quality of their diet is poor.

Eating fish does increase the levels of EPA and DHA but only by around 10% compared to not eating fish and may not necessarily have any influence on outcomes at all. Dietary intake and status of n-3 polyunsaturated fatty acids in a population of fish-eating and non-fish-eating meat-eaters, vegetarians, and vegans and the product-precursor ratio [corrected] of α-linolenic acid to long-chain n-3 polyunsaturated fatty acids: results from the EPIC-Norfolk cohort

Improvements in the diet and the substitution of fish for even more unhealthy animal products may explain reduction of risk of a second heart attack in people who have already had one. However, substituting plant protein is even healthier. The Nurses Health study and the Health Professionals Follow up study following over 100,000 people for over 20 years showed that replacing just 3% of fish protein with plant protein reduced the risk of dying by 6%. Association of Animal and Plant Protein Intake With All-Cause and Cause-Specific Mortality ‘Higher animal protein intake was positively, whereas plant protein was inversely, associated with mortality, especially among individuals with at least one lifestyle risk factors. Substitution of plant protein for animal protein… was associated with lower mortality, suggesting the importance of protein source.’

My biochemistry text book tells me that both omega 6s (such as linoleic acid for skin barrier function and found in beans and corn) and omega 3s such as ALA are essential in the diet. The omega 3s are converted into EPA and DHA. EPA inhibits neuro-inflammation and produces less inflammatory prostaglandins. Prostaglandins are involved in the stress response. DHA is thought to be important for retinal rods and brain function also inhibits prostaglandins and stimulates anti-inflammatory mediators such as resolvins and protectins.

Omega 6s are converted into arachidonic acid which stimulates other inflammation controllers such as leukotrienes and is then converted into more potent, inflammatory and damaging prostaglandins. The omega 3s and the omega 6s compete for enzymes. This is where the dogma of trying to limit the omega 6 to 3 ratio of 4 to 1 maximum comes from. Fortunately a stress stimulus in both animal and human bodies is required for the production of any prostaglandins.

People on diets containing animal products, the most popular in the US being chicken and eggs, but also fish, are unfortunately consuming preformed arachidonic acid which will be produced in the animal by the stress of slaughter and capture in fishing nets The advice should therefore be to avoid or limit all animal products. The Mediterranean and Asian diets higher in vegetables, tofu, beans, nuts and seeds and lower in junk food and animal products may be health giving despite the presence of fish and not because of it.

Fried fish and supplementation with fish oil capsules causes an increase risk of CVD. There is not enough evidence to recommend increased oily fish consumption for CVD prevention and it may increase liver cancer risk. Most of the world’s oceans are overfished or exhausted and imbalances in the ecosystem has led to a loss of plankton, which produce half of the world’s oxygen. All oceans, and therefore all fish and shellfish, are heavily contaminated with mercury, PCBs and other toxins. Over half of the plastic waste filling the oceans is discarded fishing equipment and fish farming is an animal welfare, human health and ecological nightmare.

The recommendation to consume fish or to take fish-oil supplements is not supported by the evidence and is irresponsible and destructive.

🐒