So You Think Dietary Fat Causes Heart Disease?

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If you believe in unicorns, myth and mythology, you can continue to believe that fat in the diet causes heart blockages and heart attacks. If, on the other hand, you believe in science and evidence, you might want to question those beliefs. Because the evidence is in, and most people are wrong.

Bad science

So what was the problem to begin with? Americans made huge changes to their diets, the food industry changed its grocery store offerings, and lots of patients received rather severe tongue lashings from their doctors. All for no good reason. How could so many people be so wrong for so long?

Well, the answer is bad science.

Correlation is not causation

Scientists, including doctors, conduct trials to see if a particular theory or hypothesis is correct. Now, there are trials, and there are trials.

We have epidemiological studies, where segments of the population are followed for a number of years, and their health outcomes are noted. Observations are then made to see if those outcomes are correlated with certain habits or risk factors.

So what is the problem?

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Correlation is not causation. If two things are correlated, one does not necessarily cause the other. A rooster’s cry and the rising of the sun are correlated, but the rooster does not cause the sun to rise.

A murky beginning

The whole saga appeared to start in the 1970s. The Seven Countries Study by Ancel Keys revealed a strong correlation between the average amount of saturated fat in the diet, the average blood cholesterol levels, and the 10 year death rates from coronary heart disease (blockages in the heart arteries). Again, the key word is correlation. No cause and effect was proved.

However, what followed was an avalanche of government advice, and change in the food industry offerings. There were other epidemiological studies, but there was a lack of well-designed trials to support this undertaking.

What is a good trial?

Well, the gold standard is the so-called randomized controlled trial, often shortened to RCT. The details of such trials are beyond the scope of this article, but RCTs are better suited to look for a cause and effect relationship.

What were we told?

For over fifty years, we have been sold a bill of goods which was defective. And all of this based on epidemiological studies, of doubtful quality.

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Governments, and scientists, and doctors, told us that saturated fat was bad for us, that fat was bad for us. That consuming too much fat would cause blockages in the heart, leading to heart attacks, and premature death.

We were advised to cut down on fat, so that no more than 30% of our daily calories came from dietary fat. We were also told to limit saturated fat intake to no more than 10% of daily calories.

So what happened next?

Well, our calories come from carbohydrates, protein, and fat. If you eat less fat, you will tend to eat more of the other stuff. And that is what people did when they were asked to cut down on fat. They loaded up on carbohydrates. Not protein. Carbohydrates. In fact, in the late 20th century, the US government advised the public to start eating more carbohydrates, including 6-11 servings of grain products daily.

What next?

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Americans have dutifully heeded their government’s warnings about fat. Fat used to provide 40% of daily calories in the past. This has dropped to 30% in the last 30 years. But people have become heavier. Obesity rates have tripled in the last few decades. You don’t need data to know this. Just go to any mall or sports stadium and look around. Alarmingly, the incidence of type 2 diabetes has gone up many-fold.

So what is the problem?

It is clearly not dietary fat.

A meta analysis of prospective studies evaluating the association between saturated fat consumption and cardiovascular disease was published in the American Journal of Clinical Nutrition in January 2010. It analyzed 21 studies, which followed nearly 350,000 people over 5-23 years. It revealed that there was no significant evidence for concluding that saturated fat in the diet is associated with an increased risk of coronary heart disease or stroke.

Fat out, sugar in

Sugar

Sugar

The law of unintended consequences can be seen at work in this entire saga. Governments want less fat in the diet, so industry is urged to offer more low-fat products. But fat makes food taste good. Taking fat out worsens the taste. Thus, industry has been replacing fat with sugar, with results that we are seeing all around us: fatter people, with more diabetes. Also, we are witnessing a plateau in cardiovascular disease, which had been showing a decline for decades. And we may well see an uptick in this disease if things continue the way they are.

So is a calorie a calorie?

Not necessarily.

Food has metabolic consequences. A low-fat diet can lead to biological adaptations, such as increased feelings of hunger, a lower metabolic rate, and other components of a starvation response which tend to oppose weight loss.

Sugary drinks and sweets, as well as simple carbohydrates and starches, tend to increase blood levels of insulin, which is related to many chronic diseases, including diabetes and obesity.

Low-carbohydrate diets and low-glycemic index diets (with foods containing complex carbohydrates) tend to lower the levels of insulin in the blood, thus helping people maintain the weight loss they have achieved. Such diets might be protective against chronic diseases such as diabetes.

More recent studies

The Women’s Health Initiative Dietary Modification Trial revealed that over a mean of 8.1 years, a low-total fat diet did not significantly reduce the risk of heart disease or stroke in postmenopausal women.

The PREDIMED trial was a study of the Mediterranean diet in high risk people who were free from known coronary disease at the beginning of the trial. This study showed a 30% lower risk of having a major cardiovascular event in the higher- fat dietary groups compared with the low- fat control. This risk reduction is similar to that shown in the statin (cholesterol lowering drugs) studies, but at no cost to the health system!

Higher death rates?

A study by DD Wang and associates, published in JAMA Internal Medicine in August 2016, noted that men and women following low-fat/high-carbohydrate diets had higher rates of premature death, not lower.

Lesson learned?

Hardly!

The US government, through its Dietary Guidelines for Americans, 2015-2020, still recommends cutting down on saturated fat. These guidelines also state that a healthy eating pattern includes fat-free or low-fat dairy.

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School lunch programs in the US provide only low-fat milk. No whole milk is provided at all, although they do allow chocolate skim milk with its added sugars. And this is in spite of the Dietary Guidelines calling for a restriction on added sugar.

And the general public, of course, keeps buying low-fat everything. In fact, at most grocery stores, it is hard to find full-fat dairy.

And this is in spite of a study published in the reputable journal Circulation early in 2016 which found that people consuming full-fat dairy had a 50% lower risk of diabetes, compared to those consuming the low-fat variety.

So what to do?

  • Don’t obsess about fat. The link between fat, especially saturated fat, and heart disease is tenuous at best.
  • Trans-fat is still bad for you. This is found in cakes, pies, cookies, biscuits, crackers, and many fried or processed foods.
  • Try to eat whole or minimally processed foods.
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  • Include lots of fruits and vegetables in your diet.
  • Cut down on sweets and sugary drinks, as well as simple carbohydrates.
  • Include whole grains in your diet.
  • Eating an ounce of nuts daily is good for you.
  • Low-fat dairy has no benefits over the full-fat variety, and may well be worse, according to recent data.

And finally

Focus more on the overall dietary pattern.

As Dr. Mozaffarian, a leading researcher, says, “If something has a food label, it’s probably not the best choice. We need to move away from the idea that we can manufacture an artificially healthy diet.”