Cholesterol and saturated fat: not a black-and-white story

For years the story was simple. Saturated fat was bad. Cholesterol was dangerous. Butter was swapped for margarine, whole milk for skimmed versions, and eggs disappeared from many people's daily menu. The thinking behind this came from the so-called diet-heart hypothesis: saturated fat raises LDL cholesterol, and higher LDL was thought to lead directly to more cardiovascular disease.

But science doesn't stand still. Over the past fifteen years, this theory has been extensively re-examined. Some conclusions turn out to be less solid than once thought; other insights have actually been confirmed. The real story is more nuanced than "good" or "bad".

What do recent meta-analyses say?

Large systematic reviews and meta-analyses of randomised intervention studies (the strongest form of nutrition research) show that reducing saturated fat on its own does not have very clear effects on total mortality. For cardiovascular mortality, small risk reductions are sometimes found when saturated fat is specifically replaced by polyunsaturated fats, although those effects are sometimes modest. Heart health is the multifactorial problem par excellence.

An important detail: what takes the place of saturated fat? When people eat less saturated fat but replace it with refined carbohydrates such as white flour and sugar, cardiovascular risk does not improve. In some studies, markers such as triglycerides even get worse.

Recent reviews therefore emphasise that the overall dietary pattern matters more than any single nutrient. The evidence that saturated fat on its own is the cause of cardiovascular disease is weaker than was assumed decades ago. At the same time, it is not the case that any amount is automatically neutral. Context is everything.

The evolutionary perspective

If we zoom out to human evolution, we see that saturated fat is no newcomer to our diet. Hunter-gatherers ate animal fat, organ meats and bone marrow. In tropical regions, coconut and palm fruits were important sources of fat. Industrial seed oils and ultra-processed products did not exist.

Many populations living traditionally showed low levels of obesity, type 2 diabetes and heart disease. Still, we must be careful with simple conclusions. Their lifestyle differed fundamentally from ours: more exercise, less chronic stress, no fast food and hardly any refined sugars. It is likely that the absence of diseases of affluence was the result of the overall picture, not of a single nutrient.

What is well established is the harmfulness of industrial trans fats. Large international studies have convincingly shown that trans fats increase the risk of cardiovascular disease. That insight has led to legal restrictions worldwide. The sharp rise in heart disease in the twentieth century coincided with an increase in trans fats, ultra-processed food and sugar consumption. That link is more robustly documented than the link between natural saturated fats and heart disease.

What about cholesterol from food?

Dietary cholesterol also has an eventful history. Eggs were a topic of debate for years. We now know that the body makes cholesterol itself and usually adjusts that production to the intake from food. In most people, extra cholesterol in the diet leads to only a limited rise in blood cholesterol.

In 2015, the US Dietary Guidelines dropped the fixed upper limit for cholesterol intake, because there was insufficient evidence that dietary cholesterol directly leads to more cardiovascular disease in the general population. That does not mean blood cholesterol is unimportant. Elevated LDL cholesterol remains an important risk factor for atherosclerosis. The difference lies in the nuance: in most people, dietary cholesterol does not translate one-to-one into dangerously high LDL levels.

Large cohort studies show that moderate egg consumption in healthy people is usually not associated with an increased risk of heart disease. In people with diabetes or existing cardiovascular disease the results are less clear-cut, suggesting that individual sensitivity plays a role.

Quality over quantity

Modern nutrition science is increasingly shifting from individual nutrients to dietary patterns. Diets rich in vegetables, fruit, legumes, nuts, fish and minimally processed products are consistently associated with a lower risk of cardiovascular disease. Within such a pattern, a moderate intake of saturated fat appears less problematic than in a diet full of fast food, sugary drinks and ultra-processed snacks.

Increasing attention is also being paid to insulin resistance, chronic low-grade inflammation and the composition of lipoproteins. Excessive intake of fast carbohydrates and highly processed food demonstrably contributes to unfavourable metabolic changes, including raised triglycerides and a drop in HDL.

This does not mean that saturated fat is healthy without limit, but it does mean that demonising a single nutrient does not do justice to the complexity of the human body.

Traditional fat sources in perspective

As mentioned, what is well established is that replacing industrial trans fats with natural fats brings health benefits at population level. Natural, unprocessed fat sources always fit better within a healthy diet than highly processed alternatives.

Bone marrow, traditionally widely used (straight from bone broth or in capsules), consists largely of fats, complemented by smaller amounts of protein, micronutrients and structural compounds. The fat fraction reflects a natural combination of saturated and unsaturated fatty acids, such as palmitic acid and stearic acid, which serve as a source of energy and as building blocks for cell membranes and signalling molecules. Bone marrow also provides fat-soluble vitamins and trace elements involved in basic processes such as enzyme activity, oxidation-reduction reactions and the regulation of cellular metabolism. It also contains amino acids and collagen-related components such as glycine, which play a role in protein structure, nitrogen balance and various biochemical pathways in the body.

The net effect of regularly eating bone marrow will therefore depend on a person's overall diet, lifestyle and individual health situation. Within a diet that focuses on unprocessed, whole foods, it can be an excellent source of fat.

The big picture

The debate about saturated fat and cholesterol is no longer black and white. The evidence that saturated fat on its own is the main cause of cardiovascular disease is less convincing than was once assumed. At the same time, elevated LDL cholesterol in the blood remains an important risk factor, and replacing saturated fat with unsaturated fats is beneficial in many cases.

The key message from recent research is clear: look at the big picture. Avoid trans fats and highly processed products. Limit refined sugars. Choose real, unprocessed food. In that context, saturated fat need not automatically be seen as the enemy, but fits perfectly well within a balanced and well-considered diet.