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The scientific report guiding the US dietary guidelines: is it scientific?

BMJ 2015; 351 doi: (Published 23 October 2015) Cite this as: BMJ 2015;351:h5686

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Re: The scientific report guiding the US dietary guidelines: is it scientific?

It is debateable whether Hooper et al 2012 showed an effect of saturated fat, as reduction in non-fatal CVD events was only seen in studies in which polyunsaturated fat was increased. Changes in the intake of saturated fat were not independently associated with any outcome.

The designs always left open the possibility that diets unchanged in saturated fat, and in which polyunsaturated fat replaced carbohydrate, might be superior.

"This updated review suggested that reducing saturated fat by reducing and/or modifying dietary fat reduced the risk of cardiovascular events by 14% (RR 0.86, 95% CI 0.77 to 0.96, 24 comparisons, 65,508 participants of whom 7% had a cardiovascular event, I(2) 50%). Subgrouping suggested that this reduction in cardiovascular events was seen in studies of fat modification (not reduction - which related directly to the degree of effect on serum total and LDL cholesterol and triglycerides), of at least two years duration and in studies of men (not of women)."

Thus even at face value Hooper et al 2012 should not have influenced recommendations for women. However, very few studies in Hooper et al were pure tests of a change in fats. Most involved diets that were substantially different in quality between groups; including carbohydrate quality, for example low SFA. high PUFA arms being told to avoid baked desserts and pizza and to eat nuts and fish and wholegrains instead.

It could be argued that confounding from improved food quality, increased micronutrition (including vitamin E, of which plant oils are a good source) might have influenced the outcomes of these trials, explaining why the results were not consistent.

Competing interests: No competing interests

27 September 2016
George Henderson
research associate
Human Potential Centre, Auckland University of Technology
17 Antares Place