It appears that 1.5-2g of fish oil per day for at least 4 weeks may help weight stabilisation and improve quality of life in some people with advanced cancer1,2. However, there are a few considerations and you should always discuss with your health care team before starting any supplements, so the real answer is, “It all depends”. Read on for the background, evidence and potential concerns with people living with cancer taking fish oil.
Oily fish such as salmon, mackerel, sardines and to a lesser degree tuna are good sources of omega 3 polyunsaturated fatty acids which are important for general health as well as demonstrated benefits for heart, eye and brain health. It is known that eating fish 2-3 times a week is great for heart health and eating “real” fish as opposed to fish oil supplementation is probably the best way of obtaining these heart-health benefits3. Omega 3’s from seaweed and algal sources appear to be as effective and more environmentally sustainable sources.
For the past few decades researchers have been investigating the anti-inflammatory and potential anti-tumour impact of higher levels of omega 3 fatty acid from supplements in people with cancer (as the amounts are higher than can be obtained naturally through the diet by just eating fish). Early lab and animal studies appeared very promising2. Even the first human trials which were Open label, meaning that the person knew they were consuming fish oil supplementation showed improvements in weight and quality of life2. However, the larger doubled blinded randomised placebo-controlled trials (Gold standard) showed conflicting results. One might automatically conclude that fish oil supplements are of no benefit in people with cancer. However, because fish oil has become so widely available when they analysed the blood samples of people in the trials it was found that some in the fish oil group where not taking the amount recommended and some in the control group had been consuming fish oil supplements without notifying the researchers. When analysed by the amount of fish oil in the blood (plasma EPA) then the beneficial weight stabilisation and quality of life results were seen2. So while the evidence is limited and of course we would like to see stronger evidence before providing a general recommending to patients I’m not sure if we ever will. This is because of the wide availability of fish oil and the ethics requirements of performing studies (i.e. I think future studies will be focusing on different levels of fish oil rather than fish oil vs. placebo).
So while weak, the evidence does suggest that 1.5-2g fish oil per day for at least 4 weeks may help cancer patients who are experiencing metabolic changes, unintentional weight loss, loss of appetite, and loss of muscle resulting in poorer quality of life1,2 (called Cachexia which is common in those with pancreatic and lung cancer-future blog topic) halt the weight loss and improve quality of life.
To help manage unintentional weight loss I like to recommend the multimodal approach as illustrated below. This demonstrates the importance of anticancer treatment e.g. chemo or radiotherapy or medication. Good nutrition and counselling by an Accredited Practising Dietitian (APD) or Registered Dietitian Nutritionist (RDN) remains the cornerstone of management of unintentional weight loss in people living with cancer4. Exercise, both the inclusion of weight bearing and cardiovascular is important in maintaining muscle and quality of life1. Ant-inflammatories, like fish oil can help round out the treatment. In my experience all of this requires a great support system (e.g. healthcare team, family, friends, carers) with particular focus on mental health to help manage any anxiety and/or depression.
Potential side effects and concerns
High amounts of fish oil can thin the blood so discuss with your health care team if you are on Warfarin or other anticoagulant therapy. Generally, fish oil is regarded as safe and the main discomfort is “fishy” burps or aftertaste.
There has been an animal study which suggested that fish oil decreases the effectiveness of chemotherapy5 despite other studies showing that it may increase the effectiveness of certain anti-cancer medications6. Preliminary human data suggests that those on fish oil didn’t have any improvement or negative effects in terms of chemotherapy but as this is as yet unpublished its watch this space.
What about mercury?
Use a fish oil that has been tested for mercury and pesticides and states this on the label. When eating fish, stick to the ones mentioned above and limit intake of large fish like shark (flake), swordfish and deep-sea perch (orange roughy).
If you have cancer and losing weight you might want to add fish (or algal) oil to your plan. Always discuss with your healthcare team, especially if you are on blood thinners and/or having cancer treatment. While fish oil is not a magic bullet, there is more evidence to support its benefits for improved quality of life than a lot of other things people with cancer are taking e.g. herbs and other supplements. So as long as the person is aware of the potential benefits and discomforts, discuss it with their doctor then I personally think it can be a useful tool to have in the overall toolbox of managing unintentional weight loss in people with cancer. It’s also good to see that algal sources are providing a more environmentally friendly source of omega 3 fatty acids.
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1. Arends J et al. ESPEN guidelines on nutrition in cancer patients. Clin Nutr, 2017; 36(1), 11-48. doi:10.1016/j.clnu.2016.07.015
2. Bauer J et al. Cancer Cachexia Guidelines. Nutrition & Dietetics. 2006; 63 (Suppl. 2): S5–32 https://onlinelibrary.wiley.com/doi/full/10.1111/j.1747-0080.2006.00099.x
3. Fish and seafood, Heart Foundation. https://www.heartfoundation.org.au/healthy-eating/food-and-nutrition/protein-foods/meat-poultry-and-seafood (accessed 4/8/2019).
4. Isenring E et al., Current Opinion in Supportive and Palliative Care. 7(4):390–395, 2013.
5. Daenen, L. et al. Increased Plasma Levels of Chemoresistance-Induced Fatty Acid 16:4(n-3) After Consumption of Fish and Fish Oil. Retrieved from: http://jamanetwork.com/journals/jamaoncology/article-abstract/2212208 2015
6. Murphy R et al. .Supplementation with fish oil increases chemotherapy effectiveness (2011) Cancer, 117 p.3774 https://www.onlinelibrary.wiley.com/doi/full/10.1002/cncr.25933