Nutrition is no longer just the science of avoiding deficiencies, but rather is now focused on determining the levels of dietary nutrients that will optimise physiological and health outcomes. Nowhere is this change in the study of nutrition more evident than in the study of dietary fatty acids.

In a few short years we have progressed from the simple mantra "saturates are bad, polyunsaturates are good" to a far more sophisticated understanding of the way that individual fatty acids in our foods can manifest physiological change. We now know that not all saturated fatty acids cause a rise in plasma cholesterol levels — some are more atherogenic than others, which explains why some food fats cause a larger rise in plasma cholesterol levels than others. So, foods rich in saturates should still be avoided, but dietary advice can now be more targeted.

Equally important is that we have also come to realise that not all polyunsaturated fatty acids (PUFAs) are equal. Nutritionists now differentiate between omega-6 and omega-3 PUFAs, not only because their chemical structures differ, but also because they elicit different effects. Omega-6 PUFAs, for so long a common constituent of a huge variety of spreads, cooking oils and foods, have proven their worth in numerous studies on cholesterol lowering. However, some key studies conducted over the past 10 years have shown the potency of foods containing omega-3 PUFAs. The improved survival of people who had already experienced a cardiac event when they consumed diets rich in omega-3 PUFAs was remarkable. Whether the omega fatty acids were vegetable in origin1 or were marine oils,2 all-cause mortality rates were reduced by 30%–70% and induced comparable large reductions in non-fatal sequelae. These results were equivalent to effects seen in statin trials. In addition, the protective effect of the Mediterranean dietary pattern in the Lyon study1 was maintained up to four years after the first infarction, confirming the previous intermediate analyses and demonstrating the sustainability of this type of diet. Major traditional risk factors, such as high total blood cholesterol level and raised blood pressure, continued to be independent and joint predictors of recurrence, indicating that the diet did not alter, at least qualitatively, the usual relationships between major risk factors and recurrence, but provided additional protection. Given the low risk and low cost of this type of intervention, it seems vital that the usefulness of dietary intervention in secondary prevention be fully realised.

There have also been breakthroughs in the use of omega-3 PUFAs in preterm infant nutrition. Because of our limited ability to convert vegetable omega-3 PUFAs to the long-chain PUFA found in marine foods (such as docosahexaenoic acid [DHA]), several clinical trials have tested the effectiveness on short- and long-term development of supplementing formulas with DHA. The results have been consistently positive, highlighting the fact that fats are essential to the normal growth and development of children. Here, the mechanism may seem to be self-evident, as DHA is a major component of brain and retina, and the preterm infant is denied the natural flow of DHA from the mother, which is greatest in late pregnancy. However, the actual role of DHA in these tissues is still being unravelled. Importantly, change has occurred in the market place, and all preterm infant formulas sold in Australia are now supplemented with DHA.

There are a number of clinical areas where omega-3 PUFAs in the diet have shown promising results. Benefits have been well documented in down-regulating inflammatory responses in cells and animals, and these results are being translated into an effective treatment for some inflammatory conditions such as rheumatoid arthritis. Some inconsistencies between trial results may be due to the time between disease onset and treatment. Certainly, this disease has a lower incidence in fish-eating cultures, and a higher consumption of omega-3 PUFAs in the national diet may help prevent disease onset.

There are a number of challenges for the future. The mechanism of action of many dietary fatty acids is still not fully clear, and their interaction with existing drug therapies needs to be defined. There is no doubt that many effects of fatty acids are mediated by regulation of gene expression.

The real challenge for this decade is to quantify the effectiveness of primary prevention programs based on increased omega-3 intakes. After all, this is the area where the most public health benefit is to be gained, keeping people out of hospitals and ensuring the maximum number of healthy years to us all.

The following recommendations are provided to guide medical and allied health professionals working with people at all stages of the lifecycle.