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Lisa Te Morenga, Rachael McLean, Murray Skeaff, Jim Mann
The validity of advice to reduce total and saturated fat in order to reduce obesity and coronary heart disease (CHD) has been questioned from time to time.1,2 International guidelines3-6 recommend intakes of saturated fatty acids (SFAs) of below 10% of total energy, and polyunsaturated fatty acids (PUFAs) sourced mainly from plant oils, nuts, seeds and fish of 5-11% of total energy.
Implementation of this advice would involve a modest to substantial reduction in saturated fat intake in most Western countries and some increase in polyunsaturated fat. More recently it has been suggested that a wider range of intakes of total fat than had previously been suggested, is acceptable: up to 40% of total energy in the Nordic recommendations.7 Recommended amounts of monounsaturated fatty acids (MUFAs) are derived by differences (% energy from total fat - [combined % total energy from SAFA + PUFA]), implying a similarly wide range of acceptable intakes.
Such evidence-based recommendations are derived from a consideration of the totality of evidence relating to a wide range of health issues, most importantly cardiovascular disease, and obesity and its wide ranging consequences. It is timely to review the suitability of advice relating to fats in the light of recent publications, and the increasing rates of obesity in New Zealand.
A recent systematic review and meta-analysis examining the association between dietary fatty acids and coronary heart disease (CHD) by Chowdhury et al concluded that "current evidence does not clearly support guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats, and that nutritional guidelines may need reappraisal to reflect the current evidence".8
Fierce criticisms regarding a number of errors and omissions in the paper resulted in its undergoing revisions a day after publication. However the conclusions of the corrected version, now republished, remain unhelpful and a leading group of nutritional epidemiologists from Harvard have continued to call for the article to be retracted for misrepresenting the evidence on dietary fats.9 Here we consider the limitations of this new review and whether its conclusions are valid.
Chowdhury et al suggest that their review offers substantially new insights into the effects of dietary fats on CHD. They reported finding no significant association...