Butter or margarine? Olive oil or canola oil? Low fat diets or high fat diets? You would think that after literally thousands of studies we would have some straight forward answers about the effect of fat on our health. But such is not the case. There is pretty solid evidence that saturated fats raise blood cholesterol. There is also solid evidence that high levels of blood cholesterol are a risk factor for heart disease. But then there is the conundrum. Studies have not been able to show that saturated fats raise the risk of heart disease. How is that to be explained?
There are several ways that the relationship between fat intake and health can be studied. Animals, rodents mostly, can be fed diets containing different fats and their health can be monitored. This is close to useless. The natural diet of these animals is very different from that of humans, as is their physiology. Also the manipulated dietary changes are much greater than that seen in human diets. Of greater significance are observational studies in which people are asked to fill out food frequency questionnaires from which the fat components of the diet are calculated. But people are notoriously unreliable in remembering what they have eaten and in judging amounts. Somewhat better are studies that actually measure blood levels of fatty acids which are a reflection of diet, but these do not determine the source of the fats. For example, saturated fats from meat may not have the same effect on health as those from dairy because both meat and dairy contains numerous other compounds that can have an impact. Then there is the issue that not all saturated fats are created equal and their effect may depend on the number of carbon atoms in the molecule. So-called medium chain fats, as found in coconut fat, may have a different impact than the longer chain saturated fats in chocolate, which may yet be different from those found in meat or dairy. Add to this the fact that diets also contain a variety of monounsaturated and polyunsaturated fats, which again can have a different effect on health than saturated fats, and we have an increasingly complex picture. Of course, fats are not eaten in isolation, they are part of a diet. If someone cuts down on fatty foods, they have to be replaced with something. Unfortunately, the replacement often turns out to be loaded with refined carbohydrates, particularly sugar, which pose a cardiovascular risk themselves. So in such a case, cutting back on saturated fats would not lead to a reduction in cardiovascular risk.
Where does this leave us? While studies examining saturated fats in isolation have not been able to link them to heart disease, there is plenty of evidence that replacing saturated fats with polyunsaturated ones leads to lower cholesterol levels and a reduction in the risk of cardiovascular disease. So if saturated fats are to be replaced, they should be replaced by unsaturated fats rather than by carbohydrates. As they are in the Mediterranean diet, which is heart healthy despite being high in fat. But the fat comes mostly from nuts, seeds and olive oil, not meat or butter.