Omega-3 Fatty Acids Superfood or Cancer Risk

Omega-3 Fatty Acids Superfood or Cancer Risk

Omega-3 fatty acids made the headlines last week as a study apparently found increased rates of prostate cancer among men whose diets are rich in these fats. There's been enormous controversy about the interpretation of these findings, though. How are we supposed to make sense of these findings, and what – if any – implications do they have for our diet?

A beginner's guide to omega-3 fatty acids

When we talk about “fat” in our diet, we're actually using a very general term. We're lumping together three different groups of fatty acids – saturated, monounsaturated and polyunsaturated. Without going too far into the realm of biochemistry, fatty acids are basically chains of carbon atoms with varying numbers of hydrogen atoms attached to them. The number of hydrogen atoms is what determines the type of fatty acids.

  • Saturated fats are largely derived from animal sources – meat, dairy and eggs, but are also present in some plant-based food such as coconut oil and palm kernel oil. These fats are solid at room temperature. They have traditionally been seen as “bad” fats because it's been thought that they directly raise levels of “bad” (LDL) cholesterol, with attendant risks for cardiovascular disease. This thinking is being questioned now and remains a source of controversy.
  • Monounsaturated fats are liquid at room temperature but solidify at cooler temperatures. They have a reputation of being vegetable-derived fats (olives and olive oil, nuts and avocados are all high in monounsaturated fats) but it's worth remembering that meat, eggs and butter are also good sources. Monounsaturated fats are generally characterised as “good” fats and the ones that we should consume as part of a healthy diet.
  • Polyunsaturated fats have the least number of hydrogen atoms of all. Like monounsaturated fats, they're liquid at room temperature and enjoy a reputation of being healthy fats. They come in all sorts of different varieties depending on how exactly the carbon and hydrogen atoms are joined together. The two types of polyunsaturated fatty acids that we hear about most often in a dietary context are omega-3 fatty acids and omega-6 fatty acids. These two types of fatty acids are used by the body as building blocks to create compounds (called prostaglandins and eicosanoids) that have opposite effects on the body:
    • The main omega-6 fatty acids are linoleic acid (found in sunflower, safflower, sesame, corn, walnut and soya oil) and arachidonic acid (sources of which include meat, fish and shellfish). Eicosanoids derived from omega-6 fats encourage inflammation (an important healing response), blood vessel constriction and blood clotting in the body.
    • The main omega-3 fatty acids are alpha-linolenic acid (derived from plant sources such as flaxseed) and docosahexaenoic acid (which is found in oily fish and meat from grass-fed animals). Eicosanoids derived from omega-3 fatty acids have anti-inflammatory, blood-vessel-relaxing and blood-thinning effects.

As with so much in life, the important thing about polyunsaturated fatty acids and health is balance. We need a balance of omega-3 and omega-6 acids to function well, but our modern diet generally tends towards a glut of omega-6 fats (think of refined vegetable oils such as those found in margarine, fast food and processed food). Higher omega-6 to omega-3 ratios in the diet have been associated with increased risks of inflammatory conditions, autoimmune disease, heart disease, stroke and type 2 diabetes. Omega-3 fatty acids, on the other hand, have been hailed as a health hero because their anti-inflammatory properties protect against those very same illnesses.

The research study

In this context, it came as a bit of a shock to read that researchers at the Fred Hutchinson Cancer Research Center in Seattle had found a link between increased blood levels of omega-3 fatty acids and increased incidence of prostate cancer. Furthermore, higher levels of omega-6 fatty acids were actually associated with a lowered risk. Did we need to revise our thinking about polyunsaturated fats entirely?!

The media storm caused by the publication of this study was amazing. There was detailed, intelligent criticism of the study (of which more in a moment). There was also a certain level of hysteria and hype.

Critiques of the research put forward by doctors and scientists fell into two broad camps: Concerns about methodological and design issues, and evidence from other sources. The former included the old chestnut of association not being the same thing as causation – just because two variables occur together, that doesn't mean that one is causing the other. Then there were various design issues, many related to the fact that the data were collected in the context of an entirely different study that was not designed to assess the relationship between omega-3 fats and prostate cancer at all:

  • There was no differentiation made between men whose were diets rich in naturally occurring omega-3 and those who were taking supplements (it's possible, for example, that some men started taking supplements after being diagnosed with prostate cancer, which would turn the supposed causality on its head).
  • Omega-3 blood levels were measured using a single blood plasma sample, which may not be a representative measure of overall omega-3 consumption.
  • Finally, and perhaps most importantly, other variables that influence cancer risks, such as general diet, exercise levels, smoking and alcohol consumption, had not been included in enough depth.

These issues were significant enough in themselves for many experts to entirely discredit the findings of the study. It's also relevant to consider other sources of evidence for the health benefits of omega-3 fatty acids, though. The most striking of these is the Japanese population – a very large sample of men with some of the highest levels of omega-3 fat consumption in the world, thanks to the predominance of fish in the Japanese diet, and one of the lowest rates of prostate cancer.

So now what?

The general consensus amongst doctors and scientist remains that omega-3 fatty acids are a Good Thing and should be included in our diets in liberal amounts for their health benefits. But there is a slight caveat: It's probably better to eat plenty of oily fish than to take high-dosage omega-3 supplements. It's not that supplements are bad for you, but it's much easier to reach potentially toxic levels with fish oil capsules than with tins of sardines. Once again, it's not rocket science: Eat a diet rich in natural, unprocessed foods, and you'll reap the health benefits.



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