Fish is a good choice for the protein portion of a balanced diet and can offer positive health benefits. White fish such as cod, plaice and haddock are low in fat and therefore a good protein source when following a low fat diet. Oily fish such as salmon, trout, sardines, mackerel and pilchards (tinned, fresh or frozen) are higher in fat than white fish and contain a special type of polyunsaturated fat known as ‘omega 3’ fat. White fish contain some omega 3 but at much lower levels than oily fish. This type of fat has been shown to help protect against cardiovascular disease. It also helps to lower a type of fat in your blood known as triglycerides.
How much should I eat?
People with diabetes are at increased risk of cardiovascular disease and are therefore encouraged to try to eat oily fish at least twice a week (a portion is about 140g cooked). This is higher than what is recommended for the rest of the population - they are encouraged to eat at least 2 portions of fish a week, including one of which should be oily. Even though oily fish is higher in fat and calories it is still a good choice even if you are trying to lose weight as it reduces the risk of cardiovascular disease.
Women who aren’t going to get pregnant in the future, men and boys can eat up to four portions of oily fish a week. Girls and women likely to become pregnant in the future should stick to a maximum of two portions of oily fish a week as should women who are pregnant or breastfeeding.
Pregnant women should avoid marlin, swordfish and shark due to the risk of exposure to methyl mercury which at high levels can be harmful to the development of the baby. Children should avoid marlin, swordfish and shark as these levels of mercury in these fish can affect the development of children’s growing nervous systems. Adults should limit their intake to one portion a week.
Oily fish is generally rich in vitamin D too, which is important to maintain calcium balance in the body. Most of us make our own vitamin D when our skin is exposed to sunlight, but eating foods that contain vitamin D is essential for people who are housebound or rarely expose their skin to sunlight.
Foods fortified with omega 3 fatty acids contain relatively small amounts and will only make a small contribution towards helping people meet their nutritional requirement.
Fish Oil Supplements
Diabetes UK can only make general recommendations for all people with diabetes and because everyone’s needs are so different we cannot give individualised advice.
Diabetes UK does not generally recommend that people with diabetes take any kind of supplements as there is not enough evidence available to support their use in diabetes care. Pharmacological doses of fish oil supplements (eg greater than 3g daily) also have the potential to worsen blood cholesterol levels especially the LDL cholesterol (the bad type of cholesterol).
There is clinical evidence both for and against the use of fish oil supplements. People with diabetes should consult their doctor if they already take fish oils supplements or are thinking about taking them. People who are taking high doses of fish oil supplements (greater than 3g per day) should ask their doctor to monitor the effect on their cholesterol and triglyceride levels. As with starting any new treatment (including fish oil supplements) people with diabetes should monitor their diabetes control more carefully to check the effect of the treatment they are taking. Fish oil supplements can adversely interact with medications including warfarin, aspirin and clopidogrel and should only be taken after discussion with your doctor.
NICE provides specific advice for people who have had an MI and recommends for people who have had an MI in the last 3 months should aim to consume 7g of omega 3 fatty acids per week from two to four portions of oily fish and provides detailed advice on this (1). People who have had an MI in the last 3 months should speak to their healthcare team for individual advice.
References
- Secondary prevention in primary and secondary care following a myocardial infarction. Clinical Guideline. No. 48. National Institute for Clinical Excellence, 2007. www.nice.org.uk
- Nutritional Subcommittee of the Diabetes Care Advisory Committee of Diabetes UK. The implementation of nutritional advice for people with diabetes. Diabetic Medicine; 2003, 20: 786-807.
- Scottish Intercollegiate Guideline Network ( SIGN) (February 2007 p11) National clinical guideline- risk estimation and the prevention of cardiovascular disease
- Thomas B, Bishop J. (2007 pp 596 – 600) Manual of Dietetic Practice 4th edition. Oxford, UK: Blackwell publishing
- Scientific Advisory Committee on Nutrition (SACN) Committee on toxicity (COT). Advice on Fish consumption: benefits and risks. London. The stationery office, 2004
Erratum - Fish Oils and Glycaemic Control
The nutritional recommendations for people with diabetes (reference number 2 above) state that:
“The use of pharmacological doses of fish oils, eg >3g daily, to treat hypertriglyceridaemia is not recommended because of potential deleterious effects on LDL cholesterol and glycaemic control”.
A technical review published in Diabetes Care stated that glucose metabolism was not found to be adversely affected with the use of omega 3 fatty acids [1]. A Cochrane systematic review also concluded that supplementation with fish oils has no effect on glycaemic control in people with Type 2 diabetes [2]. In light of these two pieces of evidence the text “and glycaemic control” should be deleted from the nutritional recommendations.
[1] Friedberg CE, Janssen MJEM, Heine RJ, Grobbee DE. Fish oil and glycaemic control in diabetes: a meta analysis. Diabetes Care 1998; 21: 494 – 500.
[2] Farmer A, Montori V, Dinneen S, Clar C. Fish oil in people with Type 2 diabetes mellitus. The Cochrane Database of Systematic Reviews; 2003 Vol 3.
February 2009