July 19, 2016

expert reaction to study investigating omega 3 intake and survival after colorectal cancer diagnosis

The effect of omega-3 fatty acid intake on survival after colorectal cancer (CRC) is examined in a paper published in the journal Gut in which the authors report that high intake of omega-3 polyunsaturated fatty acids from fish after CRC diagnosis is associated with lower risk of mortality due to CRC.

Dr Elizabeth Lund, Independent Consultant in Nutrition and Gastrointestinal Health, and former Research Leader at The Institute of Food Research, said:

“This is a very interesting study building on the already established concepts that fish consumption seems to be protective in relation to bowel cancer development. Now we have provisional evidence that it may be protective in relation to disease prevention. It is generally assumed that the protective effects of fish consumption are due to intake of omega-3 fatty acids and there are a number of potential mechanisms by which these may work. Having both observational data such as reported here and plausible mechanisms of action make the idea more convincing than just looking at life style in cohorts of people association with disease risk. Although it is generally believed fish is protective due to its fatty acid composition this is not certain and it is probably best that people consume fish rather than take supplements.

“This study was based entirely on US populations, who in general eat relatively little fish, therefore it would be interesting to see a similar analysis of European populations to see if the pattern is seen this side of the Atlantic. The top category of intake in the study was people eating greater than 0.3g of fish oil per day which is equivalent to about one small portion of oily fish a week. Current UK guidelines are to eat at least one portion of oily fish a week so for now British people should all be trying to follow this advice.”

Dr Alister McNeish, Lecturer in Pharmacology (and researcher into cardiovascular effects of n-3 PUFA), University of Reading, said:

“The paper provides interesting and robust evidence that high omega-3 (n-3; fish oils) intake is associated with improved colorectal cancer survival in those who have been diagnosed with the condition. It is worth noting that those who had a high intake of n-3 also had reduced risk factors and other behaviours that may be beneficial for colorectal cancer survival (e.g. more likely to be physically active, not smoke, and consume more vitamin D and fibre) so this could potentially affect the conclusions. It is also important to note that this study does not demonstrate causality and definitely does not provide a mechanistic insight into how an effect on colorectal cancer might occur.

“Omega-3 “Fish oils” are generally considered to improve blood flow so the idea that  fish oils reduce tumour  blood flow seems paradoxical; this is likely due to reduced vascularity (blood vessel formation  aka angiogenesis) of the tumour rather than reduced blood flow per se. Therefore people consuming omega-3 for cardiovascular benefits should not be concerned by this report.”

Prof. Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:

“This is an observational study and it is not possible to attribute the lower risk of bowel cancer specifically to omega-3 fatty acids because vitamin D may also have protective effects against colorectal cancer. People who eat fish may eat less of other foods linked to risk such as red and processed meat. Intervention trials with advice to eat more oily fish in patients with early bowel cancer failed to show benefit. This study provides no support of taking omega-3 supplements but does support to the notion that eating oily fish once/twice a week is good for health especially if it replaces red and processed meat.”

‘Marine ω-3 polyunsaturated fatty acid intake and survival after colorectal cancer diagnosis’ by Song et al. published in Gut on Tuesday 19th July. 

Declared interests

Dr Elizabeth Lund: No conflicts of interest to declare.

Dr Alister McNeish: I currently have no conflicts of interest but research into the beneficial effects of fish oils on vascular health in my laboratory is currently funded by the British Heart Foundation

Prof. Tom Sanders: “Prof Tom Sanders is a Scientific Governor of the charity British Nutrition Foundation, member of the scientific advisory committee of the Natural Hydration Council (which promotes the drinking of water), and honorary Nutritional Director of the charity HEART UK. Prof. Tom Sanders is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks. In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof. Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006. Tom also used to work for Ajinomoto on aspartame about 8 years ago.  Tom was a member of the FAO/WHO Joint Expert Committee that recommended that trans fatty acids be removed from the human food chain. Tom has previously acted as a member of the Global Dairy Platform Scientific Advisory Panel and Tom is a member of the Programme Advisory Committee of the Malaysian Palm Oil Board. In the past Tom has acted as a consultant to Archer Daniel Midland Company and received honoraria for meetings sponsored by Unilever PLC. Tom’s research on fats was funded by Public Health England/Food Standards Agency.”