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Tuesday, 14 October 2014
It is time to revisit current dietary recommendations for saturated fat
Current guidelines on dietary fat and saturated fat (SFA)
The first American food guide was defined in 1916. It included 5 “food groups” ((i) meat, milk, other; (ii) cereals, other; (iii) vegetable, fruits; (iv) fatty foods; (v) sugars) and suggested that dietary fats should constitute about 30% of daily calories (Hunt 1916). These recommendations were of course based on rather primitive scientific evidence, as nutrition research in those days had not yet bloomed to its current status.
The 1950s and the 1960s have produced the first of several determinant moments in nutrition research. The Seven Countries Study has provided the first evidence suggesting that dietary SFA intake increases the risk of coronary death (Keys 1957). It revealed that areas such as Crete and other Mediterranean countries with dietary SFA intake corresponding to less than 7% of calories had a very low rate of coronary death (Aravanis et al. 1970). Although criticized for not having used all data available to them at the time of analysis (Yerushalmy and Hilleboe 1957), the pioneering studies by Keys et al. had an immense impact on identifying SFA as the villain in subsequent research efforts.
In 1977, the US Senate Select Committee on Health and Human Needs published 2 editions of a report entitled Dietary Goals for the United States (US Senate Committee 1977b, 1977a). It was argued that the research and health professional communities were relatively unanimous in identifying intake of fat and SFA as 2 of the most important nutritional risk factors for chronic diseases, including cardiovascular disease (CVD). The US Senate Select Committee proposed specific dietary goals, including “… reducing overall fat consumption from 40% of calories to about 30%, and reducing saturated fat consumption from 16% of calories to about 10%.” The uncertainties surrounding the proposed targets for total fat and SFA are obvious, as emphasized by the wording of the recommendations.
The USDA in 1977 did not agree with the US Senate Committee’s position and argued that there was no absolute scientific proof of the danger and risk posed by dietary fat and SFA (Gifford 2002). USDA through the Dietary Guidelines for American Committee (DGAC) released their first dietary guidelines for Americans in 1980, with revisions every 5 years thereafter. Before 1985, recommendations regarding total dietary fat and SFA were written as “Avoid too much”, with no specific targets (Gifford 2002). But the legacy of the senatorial report was so strong that even DGAC in its 1990 revision of their dietary recommendations “gave in” and identified for the first time the ≤30% of energy target for total fat and ≤10% of energy for SFA. In 2005, DGAC changed their recommendations for total fat to 20%–35% for SFA to less than 7%.
In their 2010 revision of its dietary guidelines, DGAC proposed for the first time that the various SFAs should be considered differently according to their impact on blood lipids. Their recommendation is that stearic acid (C18:0) should not be categorized as a cholesterol-raising fatty acid, unlike lauric (C12:0), myristic (C14:0), and palmitic (C16:0) acids and industrially produced trans-fatty acids. DGAC also indicated in its 2010 report that setting the recommended percent of energy from these cholesterol-raising fats to less than 5% to 7% will help maintain blood cholesterol at desirable concentrations (USDA and US Department of Health and Human Services 2010). Modelling of current food patterns indicated that if all solid fats were removed and isocalorically replaced with oils, total SFA would be decreased to 7.0%–7.5% of calories and the cholesterol-raising fatty acids would be decreased to 5.0%–5.5% of calories. This was the rationale for proposing the “7% or less” cut-off point for SFA intake. Of course, this is a highly theoretical scenario since SFA cannot be fully substituted by PUFAs because these nutrients come as part of very different foods, with each having different nutrient profiles.
The recent 2010 DGAC report has been severely criticized for having included an incomplete body of relevant science, for inaccurately representing, interpreting, or summarizing the literature, and for drawing conclusions and (or) making recommendations that do not reflect the limitations or controversies in the science (Hite et al. 2010; Hoenselaar 2012). Thus, it appears that even the interpretation of the current body of knowledge on SFA and CVD risk poses a challenge within the scientific community. The next section provides a brief overview of some of the available evidence linking dietary SFA to CVD.