For decades, the accepted dietary wisdom has been to eat a low-fat diet, minimizing the intake of saturated fat in particular. This has been the official advice from the United States since 1977 and was echoed by the United Kingdom in 1983, but a new study published today questions the scientific validity of both sets of fat-restricting advice.
"Government dietary fat recommendations were untested in any trial prior to being introduced."
An international team of health scientists has completed a systematic study of the evidence available back in the 1970s and '80s and concluded that a relationship of causation between fat consumption and coronary heart disease was never established. The researchers found just six studies that fit the criteria to be considered proper randomized controlled trials, all limited to male subjects and most addressing the proportion of fat in the diet only indirectly.
"Government dietary fat recommendations were untested in any trial prior to being introduced," writes Zoe Harcombe of the University of the West of Scotland, lead author of the study. Despite this, "to date, no analysis of the evidence base for these recommendations has been undertaken," which is what prompted Harcombe and her team to conduct their investigation.
From among the data on various diet types that was available, there were no differences in the number of deaths from all causes, and no statistically significant changes in death from cardiovascular disease. Eating less fat was not shown to improve a person's heart health, even where changes in diet led to a reduction in blood cholesterol levels. "It seems incomprehensible that dietary advice was introduced for 220 million Americans and 56 million UK citizens, given the contrary results from a small number of unhealthy men," comments Harcombe.
Eating less fat was not shown to improve a person's heart health
At the time of issuing the original 1977 Dietary Goals for the United States, better known as the McGovern report, the Senate Committee's lead nutritionist, Dr. Hegsted of Harvard University, admitted that the evidence base was for the advice was somewhat lacking. "There will undoubtedly be many people who will say we have not … demonstrated that the dietary modifications we recommend will yield the dividend expected," remarked Hegsted. But his counterargument was that there was more to gain from switching to the recommended diet than there was to lose. Beyond reducing fat intake, the Dietary Goals also urged a reduction in the consumption of salt and sugar, whose deleterious health effects have been far better established.
Though they haven't materially changed since their introduction, the low-fat dietary guidelines have been undermined by subsequent research that has indicated that low-carbohydrate diets are more effective at promoting better health than low-fat ones. The longstanding advice to increase the consumption of carbohydrates as a way to offset the reduction in fat may now be proving Dr. Hegsted's assertion wrong: there could well be downsides to embracing the McGovern report's full recommendations.
The conclusion of the Harcombe study is stark and unequivocal: "The present review concludes that dietary advice not merely needs review; it should not have been introduced." It's remarkable that it's taken this long for a detailed analysis of the McGovern Committee's evidence to have been conducted, given that it was questioned right from the beginning. Without the necessary scientific rigour at the time or later evidence to support the original guidelines, the McGovern Committee's efforts now appear well intentioned but ultimately misguided.