Key Findings
This review discusses evidence regarding how dietary fats may play a role in disease. Diets low in n-6 polyunsaturated fatty acid (PUFA) allow better endogenous conversion of alpha-linolenic acid to n-3 long-chain (LC) PUFA and permit better accumulation of n-3 LCPUFA into tissues. While increasing the n-3 fatty acid status of individuals can be brought about by consuming fish or fish oils, this strategy is unsustainable globally. These data suggest that both the total PUFA content and the balance of LA to ALA consumed are critical determinants of LCPUFA status, and it therefore stands to reason that we need to pay close attention to the complete FA profile of the diet, in particular, the balance of n-6 and n-3 fats, when evaluating its potential health benefits. Ensuring an adequate n-3 FA status in individuals is increasingly seen as important for optimizing long-term health outcomes. High dietary intakes of n-6 FAs through vegetable oils and spreads in many developed countries have made an intake of preformed n-3 LCPUFA conditionally essential to large numbers of people if they are to improve their n-3 LCPUFA status.
Abstract
Over the past two decades, there has been a marked shift in the fatty acid composition of the diets of industrialized nations towards increased intake of the n-6 fatty acid linoleic acid (LA, 18:2n-6), largely as a result of the replacement of saturated fats with plant-based polyunsaturated fatty acid (PUFA). While health agencies internationally continue to advocate for high n-6 PUFA intake combined with increased intakes of preformed n-3 long-chain PUFAs (LCPUFA) docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3) to reduce the incidence of cardiovascular disease (CVD), there are questions as to whether this is the best approach. LA competes with alpha-linolenic acid (18:3n-3) for endogenous conversion to the LC derivatives EPA and DHA, and LA also inhibits incorporation of DHA and EPA into tissues. Thus, high-LA levels in the diet generally result in low n-3 LCPUFA status. Pregnancy and infancy are developmental periods during which the fatty acid supply is particularly critical. The importance of an adequate supply of n-3 LCPUFA for ensuring optimal development of infant brain and visual systems is well established, and there is now evidence that the supply of n-3 LCPUFA also influences a range of growth, metabolic and immune outcomes in childhood. This review will re-evaluate the health benefits of modern Western diets and pose the question of whether the introduction of similar diets to nations with emerging economies is the most prudent public health strategy for improving health in these populations.
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