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During the first few months of this year, we’ve seen at least three strong signs suggesting that health authorities have misled the public for several decades about dietary fats. This finding is of particular interest because later this year the 2015 Dietary Guidelines for Americans will be published.
Ever since the beginning of the 1960s, “eat less fat, in particular, less saturated fat and cholesterol” has been repeatedly emphasized by medical professionals and other experts.
Food manufacturers have played along by emphasizing low-fat food varieties of all possible kinds, whether it’s dairy products or something else. Butter consumption has decreased, and cooking oils have become very popular, all according to public health advice with the aim to eliminate cholesterol and saturated fat from our dishes.
What started all this was observational data showing an association between blood cholesterol and the risk of cardiovascular disease. Many health experts assumed that by reducing cholesterol and saturated fat in our diet the epidemic of heart disease might be stopped because these interventions would lower blood cholesterol. However, this was an untested hypothesis.
Nobody knew what would happen after the first US dietary recommendations were launched in 1980 because the implications of such an advice had never been tested in a scientific study.
Today, these guidelines may be regarded as a research protocol for the biggest dietary intervention trial so far performed. The trial was designed without a control group; everybody had the same advice. There was no informed consent and the trial wasn’t performed according to defined ethical principles for medical research involving human subjects (1).
However, to be fair, the death rated from coronary heart disease has dropped dramatically in most western countries for the past 30 years. Of course, this achievement is due both to modification of risk factors and improved treatment. Data from the US and many other countries suggest that lowering of cholesterol in the population may have contributed to this benefit (2).
On the other hand, since the introduction of the dietary guidelines, rates of obesity and diabetes have risen dramatically.
In fact, questions have repeatedly been asked about the Dietary Guidelines for Americans. It has been pointed out that the guidelines were implemented despite lack of supportive evidence and in the face of contradictory evidence (3).
Recently, the Dietary Guidelines Advisory Committee published its Scientific Report (4) preparing for the upcoming 2015 edition of the Dietary Guidelines for Americans. The U.S. Department of Health and Human Services (HHS) and the U.S. Department of Agriculture (USDA) jointly publish the Dietary Guidelines every five years.
The Scientific Report reflects important changes regarding dietary fats compared with previous guidelines. At the same time, two recent scientific publications suggest that our basic assumptions on dietary fats may have been wrong from the beginning.
Recommendations to reduce dietary cholesterol were initiated by the American Heart Association (AHA) in the 1960s and have been a mainstay of the USDA and other public health guidelines for many years. All this time, excess dietary cholesterol has been regarded as a public health concern.
According to the Recent Scientific Report from the Dietary Guidelines Advisory Committee (4), ”Cholesterol is not considered a nutrient of concern for overconsumption.” It is assumed that this change of direction will make it to the final guidelines that will be published later this year.
Although blood levels of cholesterol are still considered an important risk factor for cardiovascular disease, the abrupt change of direction reflects scientific data suggesting that cholesterol consumed in food appears to play a minor role in determining the blood levels of this substance.
So apparently, the guidelines have been wrong for decades. There is no reason anymore to believe that eating eggs or other food rich in cholesterol will cause heart disease.
It will be interesting to see how the AHA will approach this recent change of heart.
Saturated Fat and Heart Disease
From the beginning, dietary guidelines have underscored the importance of limiting the amount of saturated fat in our diet. This advice was based on observational data showing an association between the intake of saturated fats and death rate from heart disease.
It is well known that although observational studies may show an association between two variables, they can very rarely prove a causative relationship. Although dietary guideline committees have always been aware of this fact, they have been determined to stick with their initial approach regarding saturated fat, most likely because of their immense respect for blood levels of LDL cholesterol (5).
For decades, LDL cholesterol has been regarded as an important target when it comes to reducing the risk of heart disease. It’s often assumed the almost every measure able to lower LDL cholesterol will be beneficial.
There is some evidence linking the consumption of some types of saturated fat with raised LDL cholesterol. Accordingly, these fats will increase risk. But, using surrogate markers like LDL cholesterol to determine risk may be misleading (6).
Only randomized clinical trials can prove that the intake of saturated fats will increase the risk of heart disease. Interestingly, results from such trials were available the time of the publication of the first dietary guidelines
Last month, British investigators published a systematic review and meta-analysis of results from randomized clinical trials that were available when the first US and UK dietary guidelines were published in the late 1970s and early 1980s (7).
The authors found six dietary trials, including a total of 2.467 male participants. The intervention differed somewhat between studies but all aimed at reducing total fat and/or saturated fat consumption in the intervention group.
There were no differences in all-cause mortality and non-significant differences in mortality from heart disease, resulting from the dietary interventions. The reductions in mean serum cholesterol levels were significantly higher in the intervention groups.
So despite lowering cholesterol, interventions aimed at reducing saturated fat intake did not lower mortality nor decrease death rate from heart disease.
The authors arrived at three pretty sobering conclusions:
Government dietary fat recommendations were untested in any trial prior to being introduced
Dietary recommendations were introduced for 220 million US and 56 million UK citizens by 1983, in the absence of supporting evidence from randomized clinical trials
The present review concludes that dietary advice not merely needs review; it should not have been introduced
Macronutrient Consumption Data
In 1977 the U.S. Senate Selection Committee on Nutrition and Human Needs issued Dietary Goals for the United States, which recommends that fat consumption be reduced to 30% of energy intake, and that carbohydrate consumption be increased to account for 55-60% of energy intake (8).
The focus on the relative contribution of different macronutrients was maintained by the first Dietary Guidelines for Americans that were launched by the USDA in 1980 and have remained largely unchanged since then.
There were two reasons experts believed reducing fats and increasing carbohydrates would be beneficial. Firstly, this would lower blood cholesterol and thereby the risk of heart disease. Secondly, because one gram of fat contains more calories than one gram of carbohydrates, the intervention would reduce the risk of obesity.
A recently published U.S. paper addresses the long-term dietary consumption of the U.S. population from 1965-2011 based on NHANES (National Health and Nutrition Examination Survey) data focusing on Americans aged 18-64 (9).
The main goal of the study was to address whether Americans have been following dietary guidelines with regards to the macronutrient composition of the diet.
In 1965, fat consumption comprised 44.7% of calories of adult Americans’ diets, compared with 39% for carbohydrate. By 1999, fat consumption reached a through of 32.4% while carbohydrate consumption hit its peak at 52.1%. Protein consumption remained relatively constant throughout the period.
In 1971, saturated fat comprised 13.5% of total calories. By 2011, Americans were eating 10.7% of their calories as saturated fat (a 20.5% reduction since 1971).
Per capita cholesterol consumption decreased down below 300 mg/day, from over 400 mg/day in 1971.
The study also confirms a clear shift towards more obesity during the study period.
The authors underscore that there is a strong correlation between the increase in carbohydrate share of total intake and obesity.
They also address the question whether the increased prevalence of obesity can be explained by an increase in overall calorie intake by conducting their tests over two subsamples of participants who consumed similar calories over time. They conclude “the increase in calorie consumption since 1971 is not likely to offer any significant explanation for the increase in BMI (body mass index) over the last four decades.”
The main findings of the study were
- Americans have been adhering to federal dietary guidelines for the past 40 years
- Fat consumption by U.S. adults has decreased from 45% to 34% between 1965 and 2011
- Carbohydrate consumption has increased from 39% to 51% over this same period
- There is a high correlation between the change in diet and the rise of obesity
- The percentage of overweight adults has increased from 42% to 66% since 1971
The Bottom Line
Recently we have seen important evidence suggesting that the fear of dietary fats, in particular, the fear of saturated fats and cholesterol is not based on reliable scientific data.
This evidence adds further to the belief that we have been misinformed for decades by public authorities about dietary fat intake.
Although authors of dietary guidelines seem to have admitted that there is no reason to avoid dietary cholesterol, I’m still afraid they haven’t got it right. For example, the advice to avoid saturated fats was never based on evidence from randomized clinical trials.
It is hard to accept that public health recommendations are not based on solid scientific evidence.
A part of the problem is that the guideline process is too complicated, and recommendations are often hard to change.
The dietary fat history is a tragic example of how easy it is to mess things up for years when you get it wrong from the beginning.
Guideline writers should acknowledge the lack of evidence for most recommendations and write shorter guidelines. They should stick to hard evidence. Who needs hundreds of pages of expert consensus? The public deserves to be guided by real science.
Finally, despite the forthcoming 2015 Dietary Guidelines for Americans, this could be the year of the fat.