Earlier this week, the BMJ published an article claiming advice that saturated fat intake should be minimised to reduce heart disease is flawed. While this may sound tempting, it’s just not the case.
The author of the BMJ article notes that despite four decades of dietary advice against saturated fats, obesity, which he equates with cardiovascular risk, has been increasing.
In fact, the rates of cardiovascular disease have fallen in countries where efforts have been made to reduce saturated fat intake, but have risen in developing countries where consumption has increased.
Dietary guidelines are based on careful interpretation of sound scientific evidence, that has withstood scrutiny and shouldn’t be so easily discarded. And there are other reasons why obesity and diabetes rates keep going up.
You are what you eat
What we eat is important: most major diseases result from interactions between our genes and the environment, and the food we eat is a leading component of that environment.
A healthy diet involves variety because that ensures enough nutrient diversity and dilution of detrimental components.
And foods with abundant nutrients are preferred over those merely rich in energy (think tuna sandwich versus an iced donut because the former can meet requirements without causing weight gain).
During the last half century, scientific evidence has identified a dietary pattern that increases the risk of heart attack (coronary heart disease). This diet includes a high intake of trans and saturated fats.
Saturated fat is composed of straight chains known as fatty acids. If hydrogen atoms are removed from the chain, it becomes unsaturated. If an unsaturated fat remains straight, it is called “trans”, which are fats found in commercial frying compounds.
Straight chain saturated fats, such copha, and trans fats make foods hard at room temperature (think lard). They also increase blood cholesterol and adversely affect your arteries.
Populations that eat less trans and saturated fats have lower rates of heart attack and other vascular problems, such as stroke. This cause and effect is now beyond reasonable doubt; science shows that high levels of cholesterol cause arterial damage and this, in turn, causes coronary heart disease.
The relationship is not so obvious for individuals within a broader population (most of whom consume relatively similar diets) because genetics have a powerful effect on heart health, obscuring the effects of smaller differences in diet.
These findings have been misinterpreted by the author of the BMJ article and others to indicate saturated fat intake is unimportant.
Replacing fat sensibly
Recent media reports of the demise of low saturated fat intake as a central component of a healthy eating pattern fail to recognise the reason for lower rates of coronary heart disease in trials among people eating Mediterranean-style diets.
These diets are low in saturated fat but high in mono- and polyunsaturated fats, which are found in olive oil and vegetable seed oils.
Mono- and polyunsaturated fats are different to trans and saturated fats because the removal of hydrogen atoms from the fatty acid chains of these foods introduces one or more kinks, which makes the fats more liquid.
The BMJ article’s author prefers to blame carbohydrates for causing heart disease, but he mainly provides information about the link between carbohydrate and obesity.
The kind and amount of carbohydrate consumed may influence coronary heart disease risk factors, such as weight and blood fats.
Fat and carbohydrate are the two main sources of energy in our diet; consuming a low-fat diet without attention to replacing the fat with healthy alternatives can also affect blood lipids (a broad term for materials that do not dissolve in water) adversely and increase the risk of coronary heart disease.
A diet like this may not be harmful for lean, active people, but for those among us who are sedentary and overweight, an increased intake of sugar and refined carbohydrate may stimulate appetite and insulin release. This is counterproductive because it promotes obesity and diabetes, both of which increase the risk of coronary heart disease.
Just as unsaturated fats such as the fat in avocados offer a favourable replacement for trans and saturated fat, complex carbohydrate foods are preferable replacements to sugar or highly refined carbohydrates.
This is the basis of most guidelines to healthy eating and for the avoidance of coronary heart disease.
While there are many factors involved, it’s noteworthy that deaths from coronary heart disease have fallen steeply in the past 50 years in many Western countries. A constant feature of dietary guidelines throughout this period has been saturated-fat restriction.
Other dietary options
Several other patterns of diet are compatible with low risk of coronary heart disease and other chronic illnesses, but few today would regard them as acceptable.
Palaeolithic “hunter-gatherer” diets and early agricultural and agrarian diets, for instance, are not associated with coronary heart disease.
Nor is the “Eskimo” diet, which was studied because it seemed paradoxical that a diet with one of the highest fat contents in the world could be free of adverse effects on coronary heart disease. The diet’s benefit was subsequently attributed to its high content of certain polyunsaturated fatty acids and relatively low content of saturated fat.
Widespread reduction in the intake of saturated fats would require the food industry to make considerable adaptations. Some companies have made an effort to do so; but others appear to regard dietary guidelines recommending low saturated fat intake as a threat.
It’s curious that there seems to be a sudden campaign to exonerate saturated fat.
Skyrocketing rates of coronary heart disease in developing countries and the epidemic of obesity and type 2 diabetes globally has prompted consideration of taxation measures to influence patterns of food consumption.
The BMJ published another article on the same day showing that a 20% tax on palm oil, which is rich in saturated fat, would prevent a quarter to half a million heart attack deaths in the next ten years.
Nevertheless, a junk food tax would probably not provide a nutritional panacea. We need to keep reinforcing the message that saturated and trans fats should be minimised, along with nutrient-poor, energy dense foods such as sugar, refined carbohydrate and alcohol.