Atherosclerosis is the most common underlying cause of cardiovascular disease (CVD. It is caused by a complex interplay between lipoproteins, white blood cells, the immune system and the normal elements of the arterial wall.
Atherosclerosis can affect all arteries in the body but seems to have a strong affinity for the coronary arteries. The resulting thickening of the arterial wall and the building of plaques may lead to blockages and blood clotting causing damage to the heart muscle. The result is coronary heart disease, the most common cause of death in most countries around the world.
Lipids and lipoproteins appear to play a role in the development of atherosclerosis. Lipoproteins are the particles that transport cholesterol and triglycerides in the blood stream. It is possible to measure a number of different lipoproteins in blood as well as they amount of fat carried by specific lipoproteins.
According to the experts, blood levels of cholesterol transported in low-density lipoprotein cholesterol (LDL cholesterol) are strongly associated with the risk of developing coronary heart disease while cholesterol transported by high-density lipoprotein cholesterol (HDL cholesterol) is associated with low risk.
In other words, LDL cholesterol is atherogenic while HDL cholesterol is not.
Consequently, food that raises LDL cholesterol may be considered atherogenic and should be avoided while food that lowers LDL cholesterol should be preferred. This is the foundation of the diet-heart hypothesis, the cornerstone of public health advice on diet and health.
Apolipoprotein B (apoB) is another example. High blood levels of apoB are associated with increased risk of heart disease. On the other hand, apoA1 is associated with low risk. Studies suggest that the apoB:apoA1 ratio is more effective at predicting heart attack risk, than either the apoB or apoA1 alone. So, a high apoB:apoA1 ratio is atherogenic while a low ratio is not.
Health authorities in most countries recommend restricting saturated fats because of their adverse effects on blood lipids. Instead, monounsaturated and polyunsaturated fats are recommended.
Thus, because of its high content of saturated fat, the intake of regular fat cheese should be restricted, and replacement of high-fat dairy products with low-fat alternatives is recommended.
Red meat is also regarded as a major contributor to saturated fat intake. Therefore, limited intake is recommended by most health authorities.
On the other hand, fiber and complex carbohydrates are recommended because they tend not to lower LDL cholesterol and are therefore not considered atherogenic.
But, can we rely on these public health recommendations? Should we avoid food because of the simple fact that it contains saturated fat? Is it possible that specific saturated fatty acids may affect blood lipids differently? Furthermore, could the effects of saturated fats on blood lipids depend on other nutrients in the food matrix?
Recently these issues were addressed in an interesting scientific paper by Danish investigators at the Department of Nutrition, Exercise and Sports at The University of Copenhagen. The results were published online in the American Journal of Clinical Nutrition and can be assessed here.
Which is Most Atherogenic, High-Fat Cheese, High-Fat Meat or Carbs?
The Danish investigators compared the effects of three different diets on blood lipids and lipoproteins. Two of these diets had a high content of saturated fat in the food matrix of either cheese or meat. All three diets contained the same amount of calories.
The CHEESE diet contained high amounts of dairy fat while the MEAT diet had a high content of high-fat processed and unprocessed meat containing similar amounts of saturated fat.
The third diet had a high-carbohydrate content. The energy from cheese fat and protein in the CHEESE diet was replaced by carbohydrates and lean meat creating a low-fat, high-carbohydrate diet (CARB).
The main carbohydrate-rich foods used to replace cheese in the CARB diet were fruit, white bread, pasta and rice, marmalade, and cake, sweetened biscuits, and chocolate.
In the CHEESE and MEAT diets, 35% of energy came from fat, and 50% from carbohydrate, whereas in the CARB diet 25% of energy came from fat and 60% from carbohydrates. The protein content was the same (15%) in all three diets. In the CHEESE and MEAT diets, 15% of energy was from saturated fat.
Fourteen overweight postmenopausal women were randomized to three full-diet periods of two weeks duration separated by washout periods of no less than two weeks. A cross-over design was used, Hence, the participants tested all three diets but the sequence of the diets was randomized.
The CHEESE diet caused a 5% higher HDL cholesterol, and 8% higher apoA1 concentration, and a 5% lower apoB:apoA1 ratio than the CARB diet.
The MEAT diet caused an 8% higher HDL cholesterol, and a 4% higher apoA1 concentration than the CARB diet.
There were no differences between the CHEESE and MEAT diets in HDL cholesterol and apoA1 concentrations.
There were no significant differences between diets in total cholesterol, LDL cholesterol, triglycerides, and apoB concentrations.
Furthermore, there were no differences in fasting glucose, insulin concentration or insulin resistance (HOMA-IR) between the three diets.
The authors of the paper conclude that cheese consumption of 2-3 times the average intake in Danish adults did not have detrimental effects on blood lipids and lipoprotein concentration.
They write, “Danish dietary guidelines recommend reducing the intake of saturated fat to reduce CVD risk. However, our trial and others studies suggested that the choice of nutrients or foods as a replacement for saturated fatty acids is highly important with respect to CVD risk. Recent meta-analyses on dietary fatty acids and risk of coronary outcomes did not suggest monounsaturated or polyunsaturated fatty acids to be preferable replacements for saturated fatty acids (1,2).”
Furthermore, the authors conclude that the fact that total cholesterol and LDL cholesterol were similar with the CHEESE, MEAT, and CARB diets may be explained by the relatively high content of monounsaturated fats in the CHEESE and MEAT diets. Studies suggest that monounsaturated fats may reduce LDL cholesterol and raise HDL cholesterol significantly.
And, the paper’s final words:
Diets with cheese and meat as primary sources of saturated fatty acids cause higher HDL cholesterol and apoA1 concentrations and therefore, appear to be less atherogenic than a low-fat, high-carbohydrate diet.
The Bottom Line
The Danish paper suggests that based on lipid and lipoprotein measurements in overweight postmenopausal women, a low-fat, high-carbohydrate diet is more atherogenic than a high-fat diet rich in cheese or meat.
It is highly likely that other macro or micronutrients in food will affect the effect of specific fatty acids on blood lipid and lipoproteins. Hence, the general recommendation to restrict saturated fat intake appears pretty senseless.
But, can atherogenicity be based solely on simple lipid measurements?
Well, so far we have believed so, and it certainly is one of the reasons health authorities came to the conclusion that saturated fats are bad and carbs, and mono and polyunsaturated fats are good.
But, let us remember that there is scientific data suggesting that the effects of diet on cardiovascular health are mediated through many other biologic pathways, including oxidative stress, low-grade inflammation, insulin sensitivity, endothelial dysfunction and blood clotting mechanisms.
Would the results of the study be different if the participants were younger or not overweight?
Possibly. We don’t know the answer. But the question illustrates the fact that dietary recommendations have to be tailored to the individual. A normal-weight person may respond differently to a certain diet than someone with overweight and insulin resistance.
The Danish paper adds further evidence to the belief that the widespread recommendation to restrict the intake of saturated fat is misleading, if not absurd, and should be omitted.