"Remember this: classics never make a comeback. They wait for that perfect moment to take the spotlight from overdone, tired trends." Tabatha Coffey
Cholesterol! For decades, it’s been demonised as the number one reason for causing coronary heart disease. Most of the evidence, however, was based on epidemiologic studies, rather than on randomised controlled trials that show causation instead of correlation and are more structured from a scientific point of view. Interestingly, large trials did exist along with observational studies, but they were ignored.
Do we need cholesterol in the first instance?
Yes, we do. Our liver generates about 1000 milligrams of cholesterol a day to make vitamins and hormones, to build cell walls and to help digest and transport fat around the body. The cholesterol molecules show up in two forms. Low-density lipoprotein, or LDL cholesterol, the bad one causing atherosclerosis and high-density lipoprotein, the protective one.
The right metrics about cholesterol to focused on are still disputable. In fact, we still don’t know how to measure it: is it the total amount of cholesterol, the LDL only, the ratio of LDL and HDL or perhaps something else? This area is still open to debate, but what isn’t open to debate is that cholesterol is all bad and we should avoid it in our foods.
For a long time, we have been taught to limit cholesterol intake to no more than 300 milligrams a day. That’s not a lot considering that just one egg has 220 milligrams. This recommendation started a crusade against dietary cholesterol causing people to cut eggs, meat, shrimps and even milk.
So, what research says and what can we learn from it? In 2015, a systematic review of randomised controlled trials was published summarising available evidence when the old cholesterol guidance was published. This meta-analysis with 2,467 men was looking at the relationship between dietary fat, cholesterol and mortality. Some participants had known heart problems already, and many were at high risk. It turned out that there was no significant difference between the groups in the rate of death from coronary heart disease and no difference in mortality from all causes.
The researchers concluded: “Dietary recommendations were introduced for 220 million US and 56 million UK citizens by 1983, in the absence of supporting evidence from RCTs.”
These old dietary recommendations are very important as they gave birth to the glorification of the low-fat diet that has become very popular in the next few decades. The evidence that the low-fat diet is beneficial for our health remains weak as all examined groups didn’t have a different clinical outcome which is ultimately what we are looking for in any well-designed research.
In 2004, another study randomised people to one of two groups. One group was given the equivalent of three eggs a day for 30 days, and the other got a placebo. Then they switched the groups. Researchers measured their serum cholesterol level after each intervention period. What they found was that more than 70% of people are so-called hypo-responders to dietary cholesterol meaning, that after eating three eggs a day for a month, they would see no increase in their plasma cholesterol ratios. In other words, their cholesterol levels have no relationship to what they eat.
In 2013, scientists published a systematic review of all studies from the past decade looking at how dietary cholesterol may influence blood cholesterol levels. Again, most of the studies found that reducing cholesterol consumption had no effect on the concentration of blood LDL cholesterol.
Significant differences were indeed detected, but only in small subgroups of people with a genetic predisposition or family history of hypercholesterolaemia.
A new dietary guideline is about to be published. A brief report states: “cholesterol is not considered a nutrient of concern for overconsumption.”
Take home message Research doesn’t say that high level of bad cholesterol is good for us, or that people who are taking statins to reduce their blood cholesterol should stop taking them. Research suggests that perhaps the source of high cholesterol in our blood is caused by the consumption of saturated and trans-fat foods rather than cholesterol alone.