Understanding the New Science of Cholesterol

Photo: Shutterstock

Even those of us with only the fuzziest understanding of nutritional science have managed to grasp this basic fact: cholesterol bad. More specifically, we’ve been told for decades to avoid eating foods, like eggs, that are high in cholesterol, because they’re terrible for our heart health — but that advice could soon be changing.

Every five years, officials from the USDA and the U.S. Department of Health and Human Services meet to review and revise national dietary guidelines; before they do so, an advisory panel made up of some of the nation’s top nutrition scientists recommend changes to the officials — recommendations which are sometimes ignored, and sometimes enacted. This year, that panel is expected to recommend softening long-standing restrictions on the consumption of high-cholesterol foods. 

The recommendations are expected later this month, and while we don’t yet know exactly what they’ll say, notes from a December meeting give us a hint: the advisory panel stated that “cholesterol is not considered a nutrient of concern for overconsumption.” So … that means what, exactly, in practical terms? Science of Us recently contacted nutrition experts to understand more about the new science of cholesterol. Here’s what they had to say.

First — what was the old, now-outdated way of thinking about cholesterol, again?
According to Walter Willett, a nutrition scientist at Harvard School of Public Health, since the 1960s, public-health experts have advised people to keep their cholesterol consumption very low — about 300 milligrams a day, and no more than two eggs per week. The thinking was that eating a lot of cholesterol-laden foods would increase the cholesterol in your bloodstream, clogging up your arteries and leading to heart disease. 

Two eggs a week is not a lot of eggs! But researchers are backing off from this line of thinking?
Right. More recent research shows that consuming cholesterol does not actually seem to have much, if any, impact on the amount of cholesterol found in the blood. According to Willett, the link between dietary cholesterol and cholesterol in the bloodstream has always been weak, “and, actually, there’s never been a single study that showed higher egg consumption is related to higher risk of heart disease,” he said. The latest research suggests that if you even can drive up your cholesterol levels by consuming lots of foods that are high in cholesterol, the effect is likely very modest. “If we double our cholesterol intake, we don’t double our blood cholesterol level — we may increase it 5 percent,” Willett said.

This is part of a broader shift away from the idea of a tight connection between diet and cholesterol levels in the bloodstream. Your genes, as it turns out, are a much bigger factor in determining whether you’ll have lots of cholesterol in your bloodstream.”Basically, our bodies make a lot of cholesterol,” Willett said. “So, really, we are our own most important source of cholesterol.” Cholesterol is a key building block of many essential hormones, including sex hormones, and dietary cholesterol doesn’t appear to affect those functions, either.

So what caused this shift in thinking?
There does appear to be a small number of people who are sensitive to dietary cholesterol, in that consuming it greatly increases the amount found in their bloodstream. “So this has been debated for more than 40 years now,” said David Klurfeld, a nutrition scientist at the USDA. To complicate matters, Klurfeld said, there’s not a good way of testing which people will respond to dietary cholesterol this way. But, Klurfeld said, “the reason this has been such a source of controversy among scientists is that the dietary guidelines are supposed to be for the whole country,” not a small number of individuals. 

But the way scientists study the effect of cholesterol in the diet has also changed, Klurfeld said. “Part of the problem is we don’t study humans nearly as much as we study experimental animals,” he said. For many years, the rabbit was the standard test subject for studies on cholesterol consumption. Cholesterol is only found in animal products, and rabbits are herbivores, “so they don’t handle cholesterol at all,” he said. In other words, you can’t directly extrapolate results from rabbit studies to (mostly) omnivorous humans. Long-term, well-controlled studies in humans helped to change experts’ understanding of dietary cholesterol, and these findings are expected to be reflected in the advisory panel’s recommendations.

What are the new standards?
Again, we don’t know yet. The advisory panel is expected to complete its report early this year, likely by the end of the month. These are recommendations that the USDA and Health and Human Services (HHS) will consider when revising the dietary guidelines later this year — they don’t have to follow the panel’s suggestions. 

What’s some practical advice to take away here? (In other words, is it cool if I eat eggs every day now?)
It’s probably just fine to eat a couple of eggs a day instead of a couple of eggs a week, as was previously recommended, the experts said. “It looks like eggs are more or less neutral when it comes to heart disease risk,” said Willett. Sure, there are better things you could be eating for breakfast — he suggested some combination of whole grains, berries, nuts, and yogurt — but an omelette a day is very unlikely to harm you, even if our outdated nutritional guidelines say otherwise.