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What evidence for the benefits of ‘5-a-day’, a Mediterranean diet and sodium restriction on health?


Guidelines for healthcare professionals encourage the provision of dietary advice to promote healthy eating, especially to patients at risk of chronic disease.1 Yet the evidence base for dietary interventions relies heavily on epidemiological studies, which are subject to the challenges associated with observational research. Such problems include difficulties of assessing and measuring outcomes, misclassification, confounding and establishing causation. This reliance on epidemiological evidence may reflect the difficulty and cost of carrying out large-scale long-term randomised controlled studies of diet.2 In addition, there is a dearth of organisations willing to fund such research.

Recent publications have questioned the ‘5-a-day’ advice for fruit and vegetable consumption and population-level attempts to lower salt consumption.3,4 Studies of lifestyle advice are widely reported in the media, which may lead to public confusion about dietary advice when conclusions differ. Some researchers have urged a move from assessing how single foods or nutrients affect risk factors, to a consideration of the overall diet pattern, as this may overcome the risk of confounding the effect of one food type by others in the diet.5 The Mediterranean diet pattern is one of the most studied, since its identification in the late 1970s. Here, we provide an update of evidence for three aspects of dietary recommendations that feature regularly in the media—fruit and vegetable intake, salt reduction and the Mediterranean diet.

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