Totality of evidence again fails to support dietary guidelines for fat: Researchers

20-Dec-2017 - Last updated on 20-Dec-2017 at 15:43 GMT

National dietary guidelines in the US and the UK to restrict fat intakes, and saturated fat in particular, are not supported by scientific evidence, and should be re-examined, says a new meta-analysis and systematic review that again questions if saturated fats have been unfairly cast as a dietary bête-noire.

Dietary guidelines around fat intakes have been in the spotlight for several years, with the public conversation around the macronutrients changing from “fat is bad/ low-fat is good” to a more nuanced (but perhaps still simplistic) discussion of “good fats” like the long chain omega-3s and “bad fats” like trans fats.

Three previous meta-analyses* examining the evidence from randomized controlled trials (RCTs) and prospective cohort studies failed to support the dietary recommendations made by US and British committees in 1977 and 1983, respectively. A new meta-analysis, which examined data from 89,801 participants of epidemiological studies, also found no supporting evidence for the recommendations in order to reduce the risk of developing coronary heart disease (CHD).

“This is the final one of four systematic reviews examining the RCT and epidemiological evidence at the time dietary fat guidelines were introduced and RCT and epidemiological evidence currently available. Not one review has found evidence to support public health dietary fat guidelines,” wrote researchers from the University of the West of Scotland and the University of South Wales in the British Journal of Sports Medicine.

“Public health advice on dietary fat has prevailed since 1977/1983 in the absence of supporting evidence. Dietary advice in both nations need re-examination.”

Consistent results

Commenting on the new paper, Greg Miller, PhD, chief science officer at the National Dairy Council, told us: “This systematic review and meta-analysis is consistent with previous meta-analyses on saturated fat that have been published in the last few years indicating that saturated fat is not negatively associated with cardiovascular disease.

“In this instance, the study honed in on coronary heart disease and found no association with mortality. The body of emerging research suggests there could be more flexibility of nutrient-rich foods that contain saturated fat as part of healthy eating patterns,” added Dr Miller.

Study details

Public health dietary advice in both the US and UK recommends that overall fat consumption should be reduced to 30% of total energy intake, while saturated fat consumption should be no more than 10% of total energy intake.

The three previous meta-analyses have looked data from RCTs available to the dietary guideline committees, currently available data from RCTs, and data from epidemiological studies available to the dietary guideline committees. The new meta-analysis closes the loop by examining all epidemiological studies to date, including those published since the dietary guidelines were formulated.

The UK-based scientists found seven studies (with almost 90,000 participants) met their inclusion criteria. The data revealed that there were no statistically significant associations between total or saturated fat consumption and coronary heart disease (CHD) deaths.

“This study finds that epidemiological evidence currently available does not support the extant dietary fat guidelines,” wrote the researchers.

“These dietary fat guidelines have prevailed until 2016 and thus the validity of their evidence base remains important to examine. UK dietary fat guidelines are unchanged. The Dietary Guidelines for Americans, issued in January 2016, were conspicuously silent on the subject of total fat, but reiterated that saturated fat should be restricted to no more than 10% of calorie intake,” wrote the researchers.

Time mag Eat Butter — Several other meta-analyses have come to similar conclusions, including a 2010 paper in the American Journal of Clinical Nutrition (Vol. 91, No. 3, pp. 535-546) by scientists from the Children’s Hospital Oakland Research Institute and Harvard School of Public Health. These earlier meta-analyses led to some high profile coverage in the media, including this (in)famous Time magazine cover (June 11, 2014).

“The conclusion of the four systematic reviews and three meta-analyses is that there was no evidence to support the dietary fat guidelines being introduced and there is no evidence currently available to support them. Public health authorities need to urgently review dietary advice.”

“Protein is present in all foods, except pure fats and sucrose, and thus tends to form [about] 15% of total calorie intake. Restricting total fat intake to 30% concomitantly sets a carbohydrate intake of 55%. Diabetes and obesity have increased dramatically since guidelines to restrict fat intake. This association needs examination,” they added.

Not carte blanche to eat lots of bacon and butter

Some nutrition and dietetics experts have previously noted that it is too simplistic to say we got it all wrong about dietary fat, and that such reports shouldn’t give consumers carte blanche to eat lots of fatty meat and cream.

“The bottom line is that dietary patterns are probably more important than single nutrients,” Dr Tom Sanders, Professor of Nutrition & Dietetics at Kings College London, told FoodNavigator-USA in 2014.

Source: British Journal of Sports Medicine
December 2017, Volume 51, Number 24, Pages 1743-1749, doi: 10.1136/bjsports-2016-096550
“Evidence from prospective cohort studies does not support current dietary fat guidelines: a systematic review and meta-analysis”
Authors: Z. Harcombe et al.

* Previous meta-analysis:
Harcombe et al., Open Heart, 2015;2:e000196. doi:10.1136/openhrt-2014-000196

Harcombe et al., Open Heart, 2016;3:e000409. doi:10.1136/openhrt-2016-000409

Harcombe et al., British Journal of Sports Nutrition, doi:10.1136/bjsports-2016-096409