This review considers evidence for a protective effect of PUFA on chronic disease. Estimates of PUFA intakes in prospective cohort studies are usually based on FFQ or biomarkers of intake. Cohort studies suggest that both linoleic and linolenic acid intake are associated with a lower risk of CHD. The intake of fish, the major source of long-chain n-3 PUFA is associated with a lower risk of both stroke and CHD, particularly sudden cardiac death. No relationship with common sites of cancer (breast and colon) and PUFA has been found. However, some recent studies suggest an association of high intakes of n-3 PUFA with risk of prostate cancer. An updated Cochrane review of dietary fat modification (replacing SFA with PUFA) randomised controlled trials to prevent CHD found a 14 % lower incidence and a non-significant 7 % lower mortality from CHD. The effects of an increased intake of n-3 PUFA on CHD incidence mortality have been tested in patients with pre-existing CHD in randomised controlled trials. Meta-analysis of these trials showed no overall benefit on total mortality or CVD incidence but a trend for lower risk of cardiac death was 0·91 (95 % CI 0·85, 0·98). At present, there is little evidence from other trials demonstrating the clear benefits or harm from increased intakes of PUFA. In conclusion, present evidence intakes benefit from partial replacement of SFA with a balanced mixture of n-6 and n-3 PUFA which may contribute to CVD prevention.

Osteoporosis is a major public health problem, and as life expectancy and the world's population continue to increase will become even more important. Thus, there is an urgent need to develop and implement nutritional approaches and policies for the prevention and treatment of osteoporosis. Patients with some chronic inflammatory diseases appear to be more likely to develop osteopenia, and in some cases earlier in life, which is of particular concern as the incidence of inflammatory diseases in the Western world is increasing. While the cause of bone loss in patients with inflammatory disease is multifactorial, nutrition may have a role. Many of these patients may have one or more nutritional deficiencies, which can lead to altered rates of bone metabolism. On the other hand, some nutritional factors may attenuate the inflammatory process itself, and thus may indirectly benefit bone metabolism and bone health in patients with inflammatory disease. The present review will consider these issues, particularly in the context of inflammatory bowel disease, coeliac diease and atherosclerosis.

A considerable literature has been published on the health benefits of fish, oil-rich fish and fish oils and their constituent long-chain (LC) n-3 PUFA. Evidence from epidemiological studies highlights the cardioprotective attributes of diets rich in fish, especially oil-rich fish. Data from intervention trials are consistent in suggesting that LC n-3 PUFA lower the risk of CVD, probably by the multiple mechanisms of lowering serum triacylglycerols, improving the LDL:HDL ratio, anti-arrhythmic effects on heart muscle, improved plaque stability, anti-thrombotic effects and reduced endothelial activation. Research indicates LC n-3 PUFA provision has an impact during development, and there is preliminary evidence that docosahexaenoic acid supplementation during pregnancy could optimise brain and retina development in the infant. LC n-3 PUFA are also postulated to ameliorate behavioural and mental health disturbances such as depression, schizophrenia, dementia and attention deficit hyperactivity disorder. However, despite some positive evidence in each of these areas, use of LC n-3 PUFA in these conditions remains at the experimental stage. In the case of immune function, there is little doubt that LC n-3 PUFA have a positive effect. Although intervention trials in rheumatoid arthritis show strong evidence of benefit, evidence for efficacy in other inflammatory conditions, including Crohn's disease, ulcerative colitis, psoriasis, lupus, multiple sclerosis, cystic fibrosis and asthma, is inconsistent or inadequate. More promising evidence in some conditions may come from studies which attempt to modify the fetal environment using LC n-3 PUFA supplementation during pregnancy.