“Every last shred of evidence”: Why low-fat dietary guidelines should never have been introduced

By Kurt Wood
22nd June 2015
In Depth
 
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1.

When the US government introduced “Dietary Goals for the United States”, they did not have unanimous support. The guidelines, which urged the public to cut saturated fat from their diet, were challenged by a number of scientists in a Congressional hearing. The findings were not based on sufficient evidence, they argued.

They were ignored. Dr. Robert Olson recounts an exchange he had with Senator George McGovern, in which he said: “I plead 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.”

And so, backed by a questionable base of evidence, the guidelines were implemented, triggering one of the most complex and controversial scientific debates of the last three or four decades.

George McGovern low-fat

Senator George McGovern had a big influence on the introduction of low-fat dietary guidelines. He also argued that “senators don’t have the luxury that the research scientist does of waiting until every last shred of evidence is in.” image source: usnews.nbcnews.com

2.

We are only now seeing a significant challenge to the low-fat guidelines. In June of last year, Time published Bryan Walsh’s “Ending the War on Fat.” Walsh quotes Philip Handler, who was president of the National Academy of Sciences in 1980. He called the fat guidelines a “vast nutritional experiment.” According to Walsh, “the experiment was a failure. We cut the fat, but by almost every measure, Americans are sicker than ever.”[1]

“Senators don’t have the luxury that the research scientist does of waiting until every last shred of evidence is in.”

On June 1, 2015, Open Heart, The BMJ‘s cardiology journal, published “Evidence from randomised controlled trials did not support the introduction of dietary fat guidelines in 1977 and 1983: a systematic review and meta-analysis,” the first study to comprehensively critique the body of evidence supporting the low-fat guidelines.

The study, led by Zoe Harcombe, argues that “dietary recommendations were introduced for 220 million US and 56 million UK citizens by 1983, in the absence of supporting evidence from [randomised controlled trials].”

The study presents a number of findings, including:

The original RCTs [randomised controlled trials] did not find any relationship between dietary fat intake and deaths from CHD [coronary heart disease] or all-causes, despite significant reductions in cholesterol levels […] this undermines the role of serum cholesterol levels as an intermediary to the development of CHD and contravenes the theory that reducing dietary fat generally and saturated fat particularly potentiates a reduction in CHD.[2]

In other words, it’s generally believed that having lower cholesterol levels means having a lower risk of heart disease, and the best way to lower cholesterol levels is to reduce one’s intake of fat. But the study punctured this belief: there is no real established link between cholesterol levels and risk of heart disease. Therefore, reducing fat intake isn’t going to reduce the risk of heart disease.

Uffe Ravnskov, a Danish researcher notorious for challenging the conventional wisdom surrounding heart disease, makes a similar point:

Today a reduction of the intake of saturated fat is one of the cornerstones in dietary prevention of obesity, diabetes and cardiovascular disease. However, several recent trials have documented that the main argument for this advice, its alleged influence on blood cholesterol, is questionable. More disturbing is that a large number of epidemiological, clinical, pathological and experimental studies have falsified the idea that a high intake is harmful to human health and that a reduction may be beneficial; indeed, several observations point to the opposite.[3]

Harcombe et al also identify flaws in the research, flaws that compromise the integrity of their findings. For example, many of the original studies focused on men who had suffered a myocardial infarction. But they failed to take into account that:

men who have suffered a myocardial infarction (MI) subsequently make multiple lifestyle changes (weight loss, smoking cessation, increase in physical activity, for example), which makes them a poor group for testing the lipid hypothesis.

Ms Catherine Collins, Principal Dietitian at St. George’s Hospital NHS Trust, also described the failings of the original research:

Studies had small numbers (most with a history of heart disease) were highly varied in dietary and lifestyle approach, and reviewed outcomes over a short time scale – around five years on average. All these factors would influence the outcome – whatever dietary changes were made.

In short, the body of evidence that led to the introductions of anti-fat dietary guidelines was incomplete. The researchers – Harcombe et al – summarised the huge gaps:

At the time dietary advice was introduced, 2467 men had been observed in RCTs. 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.

Whoever decided to implement the anti-fat guidelines seems to have done so by ignoring all evidence to the contrary. A few supportive studies seem to have been given a greater importance, even though, as Ravnskov notes,  “A few supportive studies cannot outweigh more than one hundred studies that have falsified the hypothesis.” And, having wrongfully supported the anti-fat guidelines, fresh evidence to the contrary has also been ignored. The guidelines remain unchanged. Ravnskov argues that what is “most disturbing is that the numerous contradictory epidemiological, pathological and clinical observations […] have been ignored by all guideline authors.”

So the guidelines were pushed through on the back of a thin suggestion that saturated fat was the biggest cause of heart disease, without any of the rigorous, comprehensive examination that should come with it. The decision to promote anti-fat guidelines seems to stem from a selective attitude to evidence. Because, as Ravnskov notes, “any idea can be verified if one looks for confirmation only.” It wasn’t just flawed; it was woefully inadequate. Or, as the researchers put it: “dietary advice not merely needs review; it should not have been introduced.”

Zoe Harcombe low-fat

Zoe Harcombe is the lead author of a new study that debunks the low-fat myths. Image source: walesonline.co.uk.

3.

People with diabetes have been tarred with the low-fat brush as much as anybody. Historically, all the official advice, from the NHS to Diabetes UK, has urged people with diabetes to avoid fat. This despite the fact that anecdotal evidence has for some time suggested that people with diabetes find a low-carb, high-fat diet more conducive to good blood glucose control.

The NHS recommends “reducing the amount of fat” in the diets of people with type 2 diabetes, and including “starchy carbohydrates, such as pasta,” while Diabetes UK suggest that people with diabetes “choose low-fat alternatives wherever possible,” while having “some starchy food” every day.

Slowly but surely, the advice is changing. Last year, Dr. David Unwin published “Low carbohydrate diet to achieve weight loss and improve HbA1c in type 2 diabetes and pre-diabetes: experience from one general practice.” The study, published in Practical Diabetes, indicated that a low-carb diet could enhance weight loss and improve HbA1c levels in people with type 2 diabetes, in contrast to the official guidelines of the NHS and Diabetes UK.[4]

Other studies report similar findings. Halton et al’s “Low-carbohydrate-diet score and the risk of coronary heart disease” concluded that “diets lower in carbohydrate and higher in protein and fat are not associated with increased risk of coronary heart disease in women. When vegetable sources of fat and protein are chosen, these diets may moderately reduce the risk of coronary heart disease.”[5]

The two pieces of advice are more or less mutually exclusive. If we cut down on carbs, we have to make up for it by eating more fat. If we cut down on fat, we have to compensate by eating more carbs. Broadly speaking, there can only be one winner. The original low-fat guidelines recognised this, telling people to “increase carbohydrate consumption to account for 55 to 60 per cent of the energy (caloric) intake [and] reduce overall fat consumption from approximately 40 to 30 per cent energy intake.” But according to Richard Feinman, the Editor of Nutrition and Metabolism, “fat consumption, if anything, went down during the obesity epidemic – almost all of the increase in calories was in carbohydrates.”[6]

Low-fat yoghurt

Shops are full of low-fat alternatives to yoghurt, butter and the like. But are they the answer to heart disease and obesity?

4.

So why were the guidelines introduced, if they were so obviously flawed from the start?

It’s not the sinister conspiracy we might have hoped. In fact, the motives for introducing the guidelines appear to have been completely noble and well-meaning. On the publication of the guidelines, Senator George McGovern said:

My hope is that this report will perform a function similar to that of the Surgeon General’s Report on Smoking. Since that report, we haven’t eliminated the hazards of smoking, nor have people stopped smoking because of it. but the cigarette industry has modified its products to reduce risk factors, and many people who would other be smoking have stopped because of it. The same progress can and must be made in matters of nutritional health.[7]

If anything, the sincere desire to improve health may have been at fault for the implementation of such shoddily-evidenced guidelines.

“Fat consumption, if anything, went down during the obesity epidemic – almost all of the increase in calories was in carbohydrates.”

Matters were exacerbated by another commendable motive: the desire to propose guidelines that ordinary people could stick to. Dr. D.M. Hegsted, Professor of Nutrition at the Harvard School of Public Health in Boston, Massachusetts, said when the guidelines were published:

It is increasingly obvious that if new knowledge is to result in new behaviours then people must be able to act, without undue obstacles, in accordance with the information they learn. The problem of education for health as it has been practiced is that it has been in isolation, not to say oblivion, of the real pressures, expectations, and norms of society which mould and constrain individual behaviour. There must be some coordination between what people are taught to do and what they can do.

This is a noble approach for the most part. Certainly, modern dietary guidelines would be more effective if they took into account the practical realities of people lives. And yet, at the same time, the approach can be simplistic. This is a complex issue, and ignoring its complexity in order to make more convenient guidelines isn’t going to help anyone.

Ironically, the guidelines were introduced because “there needs to be less confusion about what to eat and how our diet affects us,” yet ended up triggering one of the biggest scientific debates of the century.

Butter and low-fat

The low-fat dietary guidelines are finally being challenged, with a number of experts suggesting that it’s carbohydrates, and not fat, that does the damage.

5.

When it comes to dietary guidelines, there is no simple answer. Studies will always conflict, and findings will always be questionable to some degree. Harcombe’s study isn’t perfect; according to Christine Williams, Professor of Human Nutrition at the University of Reading, it takes

a classical pharmaceutical approach to the evidence, with the assumption that RCTs also provide the gold standard for diet, representing the pinnacle of the evidence hierarchy against which other types of study are inevitably weaker. Most dietary guidelines have been developed using an approach which takes the degree of consistency of a number of lines of evidence as the gold standard for risk assessment. This approach uses RCTs where such data is available.[8]

Ironically, the guidelines were introduced because “there needs to be less confusion about what to eat and how our diet affects us,” yet ended up triggering one of the biggest scientific debates of the century.

And it isn’t productive to insist people adhere to any one strict diet; different things will work for different people. But it is necessary to call out deeply-flawed guidelines. A number of studies have suggested a “protective effect of saturated fat from dairy products.” We may be increasing our risk of heart disease by avoiding saturated fats.

Maybe so, maybe not. Decades of scientific dispute haven’t put the fat versus carbs debate to bed; it’s very unlikely to happen in this article. But whatever you believe, the debate shows how important it is that we insist on a thorough scientific basis for dietary guidelines. We need to ask questions of the researchers. Otherwise we’re stuck with low-fat recommendations that could, just maybe, be killing us.

What do you think?

References