"let me assert my firm belief that the only thing we have to fear is fear itself"
~ Franklin D. Roosevelt
Is eating saturated fat bad for your heart? That's the conventional wisdom, but I shall describe what led to this belief and show that the available evidence does not support it. Then I shall explain how the nocebo effect might override this evidence-based conclusion.
It's difficult to make a determination of the effect of a nutrient on one of the little rodents kept prisoner in a laboratory. First you must obtain a series of identical subjects by inbreeding or cloning. Then you must compare two individuals (or, better, two groups of individuals) who differ only in whether or not they have received the nutrient in question. You must know where to look for differences and how to measure them (blood tests, growth rates, etc.). And you can be confident of your final result only with respect to these particular subjects and their particular living conditions, which, in the case of the little prisoners, usually include an unstimulating environment and a lack of exercise.
The problem is even more difficult for investigators who want to make such a determination on people. People have relatively long life spans, on the order of magnitude of the investigators'. Groups of identical subjects are hard to come by and their living conditions are not readily subject to control. And because different groups of free-living people (occupants of different countries, followers of different diets, members of different ethnic groups) differ in so many characteristics, one must be very cautious in imputing an observed difference in an outcome to an observed difference in behavior. Thus, it comes as no surprise that different investigators have come to different conclusions about the effect on people of eating saturated fat, the nutrient which is the subject of this essay.
But aren't such questions of only academic interest? After all, some time ago Dr. John Yudkin, a British physician, pointed out that our appetites should lead us to suitable diets. Our remote ancestors chose their diets on the basis of palatability (I use the term to include not only taste and smell, but also other attributes such as appearance). Their diets were good enough to enable them to survive and procreate and they passed on to us the tastes which led them to choose suitable diets. You can't have ancestors whose tastes led them to diets which resulted in early and childless death. And tastes can be shown to be hereditary. For instance, thiourea, a substance found in plants of the cabbage family is considered by some people (including me) to be extremely bitter but is tasteless to others. The trait of experiencing it as bitter is passed along in accordance with the Mendelian rules of inheritance.
Wild animals thrive by choosing their dietary constituents according to their palatability and availability, but it doesn't work as well for us because of a number of ways in which we have separated the palatability which signals the nutrient content of foods from the nutrients whose presence they normally signify. An extreme example is Kool-Aid which has some of the palatability of fruit, but none of its important nutrients. Artificial flavors and colors defeat the evolved system for choosing a proper diet. Other factors include religious and social taboos, storing or shipping food long distances during which nutrients are lost, preserving foods by heating, canning or freezing them, and politeness — have you ever ignored what your inherited sense of palatability was telling you and eaten something that failed to appeal to your senses so as not to hurt the feelings of the person who offered it to you?
Our appetite for foods containing saturated fat, (e.g., fatty meats, butter, coconut oil) suggests that these may be essential components of our diet, yet the conventional wisdom now seems to be that eating saturated fat is a risk factor for heart disease. How did this belief come about?
There is a clear-cut villain here. Ancel Keys, a researcher from Minnesota started the boule de suif rolling by demonstrating that a plot of fat intake versus coronary mortality, using data from six countries, showed a smooth correlation between the two. Others soon pointed out that if data from all twenty-two countries for which such data were then available were plotted, the result was a formless random array, that the data from countries which Keys had left out suggested that level of physical activity was the most accurate predictor of cardiac risk and that sugar was the dietary constituent most closely correlated with heart disease. This didn't stop Keys from going on to present a massive collection of data from seven carefully chosen countries which bolstered his claim of a correlation of saturated-fat intake with heart disease. No matter, that as Dr. Malcolm Kendrick has shown, the data would have shown an inverse correlation if the countries chosen had been Finland, France, Germany, Israel, Netherlands, Sweden and Switzerland rather than Finland, Greece, Italy, Japan, Netherlands, Yugoslavia and the U.S.A. I note also that the lack of value of such country comparisons is illustrated by the fact that if all these countries are compared to see if there is a correlation between primary language spoken and the incidence of heart disease, the correlation between speaking English or Finnish and developing heart disease is quite impressive.
But Keys' hypothesis became the conventional wisdom and was quickly adopted and promulgated by many groups in the field of public health. These included governmental bodies which provide advice on diet and the American Heart Association (which had been much slower to warn against the dangers of smoking tobacco, despite the fact that 60% of the excess deaths from smoking are from heart disease — only 13% are from lung cancer.) And, of course, manufacturers of oleomargarine and other substitutes for natural foods were delighted to devote their massive advertising budgets to the cause.
Keys' studies didn't prove a relationship between intake of saturated fat and heart disease, but aren't there other, more convincing, studies which indicate such a causal relationship? Kendrick has recently surveyed the available evidence, and the following paragraphs show what he found.
- A review in the British Medical Journal in 2001 concluded that "Despite decades of effort and many thousands of people randomised, there is still only limited and inconclusive evidence of the effects of modification of total, saturated, monounsaturated, or polyunsaturated fats on cardiovascular morbidity and mortality."
- A Swedish paper published in the Journal of Internal Medicine in 2005 reported on a study covering 30,000 people over six years. The conclusion was that "Saturated fat showed no relationship with cardiovascular disease in men. In women, cardiovascular mortality showed a downward trend with increased saturated fat intake."
- A study involving 48,835 women and lasting more than 8 years was reported in the Journal of the American Medical Association in 2006. Reducing consumption of saturated fat had no effect on coronary heart disease, stroke, total mortality or cancer.
- A report published in The Lancet in 2004 gave the results of an international search (262 centers in 52 countries) for risk factors for heart disease. Nine risk factors were identified. Consumption of saturated fat was not among them.
- This last conclusion was hardly surprising. A study reported in the Journal of the American Medical Association in 1982 had shown that a series of changes which included decreasing the saturated fat consumption of 361,662 men by 28% produced no beneficial effect on incidence of coronary heart disease or total mortality
These studies fail to show any detrimental effect on the heart (or anything else) of eating saturated fat. If anything, they suggest that there might be a beneficial effect in women. But let me explain how eating saturated fat can be detrimental to your health — it might even result in a heart attack.
You're probably familiar with the placebo effect: If you really believe that some medicine or treatment can cure a disease condition, it might do so just because of your belief. For instance, as much as 50% to 75% of the therapeutic effects of antidepressant medications have been attributed to the placebo effect. The effect is real and can be demonstrated by studies on the brain as well as by observation of the patient.
And you may be aware of the converse as well, but not of its name: the nocebo effect. This effect explains the real dangers of belief in the powers of witch doctors and of the evil eye. Here's how researcher R. A. Hahn defined it in Preventive Medicine in 1997: "The nocebo hypothesis proposes that expectations of sickness and the affective states associated with such expectations cause sickness in the expectant. The nocebo phenomenon is a little-recognized facet of culture that may be responsible for a substantial variety of pathology throughout the world." This was recognized by reporter Brian Reid, who wrote, in an article on the nocebo effect, in The Washington Post for April 30, 2002: "Ten years ago, researchers stumbled onto a striking finding: Women who believed that they were prone to heart disease were nearly four times as likely to die as women with similar risk factors who didn’t hold such fatalistic views." He was referring to data amassed during the massive collection of data on the causes of heart disease in Framingham Massachusetts.
The nocebo effect is not often referred to as such in the medical literature, but continues to be illustrated therein, A study made at the University of Southern California which was reported on last year, found that men who exhibited symptoms of anxiety (worried about saturated fat in their diet?) were up to 76% more likely to have heart attacks than the less anxious. Worrying about purported risk factors for heart disease may be the way the risk factors endanger some people.
So, eating saturated fat is not harmful for most people. It may even be good for you. But, if you have fallen for the conclusions drawn from the bad science initiated by Ancel Keys and promulgated by the American Heart Association, government agencies and many other advisors on nutrition, it is a fat nocebo and could kill you.
May 23, 2009