The diet-heart hypothesis: A diet high in saturated fat raises the blood cholesterol level and this then causes cardiovascular disease.
By the early to mid-1980s, the diet-heart hypothesis had become very widely accepted both by the scientific community and the general public. Dietary guidelines were developed, which became the basis for the food pyramid in the U.S. and the eatwell plate in the U.K. Both recommended the same percentages of foods to be consumed. The primary goal was to reduce fat/saturated fat consumption.
- Bread, rice, potatoes, pasta, and other starchy foods – 33%
- Fruit and vegetables – 33%
- Milk and dairy foods – 15%
- Meat, fish, eggs, beans, and other non-dairy sources of protein – 12%
- Foods and drinks high in fat and/or sugar – 8%
Some researchers strongly felt that the evidence did not support the diet-heart hypothesis. Dr. George Mann, a nutritional biologist and physician, was a long-term critic. He had studied populations, such as the Masai in Africa, who had a very high consumption of saturated fat, low cholesterol levels, and almost no deaths from heart disease.
He brought together researchers from around the world to discuss the diet-heart hypothesis. Following their meeting, they published a book called Coronary Heart Disease: The Dietary Sense and Nonsense (1).
Mann stated in the preface:
For 50 years an increasingly specious, pseudoscientific dogma has been growing in the Western World. This hypothesis originally proposed that coronary artery disease, the main cause of death here, is caused by the kind and amount of fat in our diets. That hypothesis was based upon fragile and selected data. The hypothesis has now been tested in dozens of clinical trials costing hundreds of millions of dollars. In adequate trials, that answer has been the same: dietary treatments are not effective.
In the U.K., nutritional researcher Professor John Yudkin was convinced from his work that if any dietary substance could be implicated in causing cardiovascular disease, sugar was a more plausible culprit. He wrote a book called Pure, White, and Deadly: How Sugar Is Killing Us and What We Can Do to Stop It. It was originally published in 1972, and in 2013 was republished and later reviewed in the British Medical Journal (BMJ) in 2013. There, Professor J.T. Winkler wrote:
Becoming a prophet in your own country can be difficult. So can becoming a medical classic in the BMJ. The travails of both are illuminated by John Yudkin and Pure, White and Deadly, his most famous and recently reissued book.
Despite its startling title, the work is a sober analysis of the health problems, especially heart disease, associated with sugar. Published in 1972, it seemed perfectly timed for rapid conversion from nutrition science into nutrition policy. Yudkin was then serving on the advisory panel on heart disease of the UK Department of Health’s Committee on the Medical Aspects of Food and Nutrition Policy (COMA).
But opponents, notably Ancel Keys, high priest of fat theorists, publicly ridiculed Pure, White and Deadly. Others ignored it. When COMA published its conclusions in 1974, Yudkin felt compelled to append a note of reservation, concluding that “the Report has exaggerated the possible role of dietary fat in causing IHD [ischaemic heart disease], and has minimized the possible role of dietary sucrose.” The 1984 version of COMA never mentioned Yudkin or the role of sugar at all (2).
There were many others who believed the diet-heart heart hypothesis was not scientifically valid, and more importantly, that it was not supported by the facts. This position was validated by recent researchers who looked back at the evidence that existed in 1977 to support the dietary guidelines first published in the U.S. in 1977 and the U.K. a few years later.
The paper was entitled “Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis.” Its authors wrote:
National dietary guidelines were introduced in 1977 and 1983, by the US and UK governments, respectively, with the ambition of reducing coronary heart disease (CHD) by reducing fat intake. To date, no analysis of the evidence base for these recommendations has been undertaken. The present study examines the evidence from randomised controlled trials (RCTs) available to the US and UK regulatory committees at their respective points of implementation.
Conclusions: Dietary recommendations were introduced for 220 million US and 56 million UK citizens by 1983, in the absence of supporting evidence from RCTs (3).
As the authors concluded in their discussion section:
From the literature available, it is clear that at the time dietary advice was introduced, 2467 men had been observed in RCTs (randomised controlled studies). No women had been studied; no primary prevention study had been undertaken; no RCT had tested the dietary fat recommendations; no RCT concluded that dietary guidelines should be introduced. 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.
An exchange between Dr Robert Olson of St Louis University and Senator George McGovern, chair of the Dietary Committee, was recorded in July 1977. Olson said “I pleaded in my report and will plead again orally here for more research on the problem before we make announcements to the American public.” McGovern replied “Senators don’t have the luxury that the research scientist does of waiting until every last shred of evidence is in.”
In medical research, a randomized controlled trial is considered the gold standard. Yet, when the nutritional guidelines were introduced, there was no RCT evidence to support them. Since that time, there has been no further evidence from any RCT in support of the guidelines (4).
Very large epidemiological (observational) studies have also failed to support the diet-heart hypothesis. The PURE study looked at over 150,000 people in countries around the world. The findings were reported at the European Society of Cardiology Congress in 2018:
135,335 individuals aged 35 to 70 years from 18 low-, middle- and high-income countries (across North America, Europe, South America, the Middle East, South Asia, China, South East Asia and Africa) suggest that high carbohydrate intake increases total mortality, while high fat intake is associated with a lower risk of total mortality and has no association with the risk of myocardial infarction or cardiovascular disease-related mortality.
Furthermore, a higher saturated fat intake appeared to be associated with a 21% lower risk of stroke. … explains Professor Salim Yusuf (McMaster University, Hamilton, Ontario, Canada), senior investigator for the PURE study. “The problem is that poorly designed studies performed 25–30 years ago were accepted and championed by various health organisations when, in fact, there are several recent studies using better methods, which show that a higher fat intake has a neutral effect,” he continues, citing the example of the Women’s Health Initiative trial conducted by the National Institutes of Health in 49,000 women that showed no benefit of a low-fat diet on heart disease, stroke or cardiovascular disease.
“We need greater investment in nutritional sciences to reach more reliable conclusions. We need to question established dogma and to look at the evidence more objectively” (5).
The next article in this series will review the biochemistry and physiology of fat metabolism in the human body.
Malcolm Kendrick is a family practitioner working near Manchester in England. He has a special interest in cardiovascular disease, what causes it, and what may prevent it. He has written three books: The Great Cholesterol Con, Doctoring Data, and A Statin Nation. He has authored several papers in this area and lectures on the subject around the world. He also has a blog, drmalcolmkendrick.org, which stimulates lively debate on a number of different areas of medicine, mainly heart disease.
He is a member of THINCS (The International Network of Cholesterol Sceptics), which is a network of doctors and scientists who believe that cholesterol is not the main underlying cause of heart disease. He remains a proud Scotsman, whisky drinker, and failed fitness fanatic who loves a good scientific debate — in the bar.
references
- Mann G, ed. Coronary Heart Disease: The Dietary Sense and Nonsense. Janus Publishing Company: London, England, 1993.
- Winkler, JT. Pure, White and Deadly. 346(2013). Available here.
- Harcombe, Z, et al. Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis. Openheart 2.1(2015). Available here.
- Harcombe, Z. Dietary fat guidelines have no evidence base: Where next for public health nutritional advice? Brit. J. of Sports Med. 51.10(2016). Available here.
- Dehghan M, et al. The PURE study: Understanding the relationship between nutrition and heart disease. Lancet 390(2017): 2050–2062. Available here.
The diet-heart hypothesis, part 2 — Dietary Fat and Cardiovascular Disease