Myth #1: Eating cholesterol and saturated fat raises cholesterol levels in the blood.
Most of us grew up being told that foods like red meat, eggs and bacon raise our cholesterol levels. This idea is so deeply ingrained in our cultural psyche that few people even question it. But is it really true?
The diet-heart hypothesis—which holds that eating cholesterol and saturated fat raises cholesterol in our blood—originated with studies in both animals and humans more than half a century ago. However, more recent (and higher quality) evidence doesn’t support it.
Cholesterol and saturated fat: dietary enemies or innocent victims of bad science?
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On any given day, we have between 1,100 and 1,700 milligrams of cholesterol in our body. 25% of that comes from our diet, and 75% is produced inside of our bodies by the liver. Much of the cholesterol that’s found in food can’t be absorbed by our bodies, and most of the cholesterol in our gut was first synthesized in body cells and ended up in the gut via the liver and gall bladder. The body tightly regulates the amount of cholesterol in the blood by controlling internal production; when cholesterol intake in the diet goes down, the body makes more. When cholesterol intake in the diet goes up, the body makes less.
This explains why well-designed cholesterol feeding studies (where they feed volunteers 2-4 eggs a day and measure their cholesterol) show that dietary cholesterol has very little impact on blood cholesterol levels in about 75% of the population. The remaining 25% of the population are referred to as “hyper-responders”. In this group, dietary cholesterol does modestly increase both LDL (“bad cholesterol” and HDL (“good cholesterol”), but it does not affect the ratio of LDL to HDL or increase the risk of heart disease. (
2)
In other words, eating cholesterol isn’t going to give you a heart attack. You can ditch the egg-white omelettes and start eating yolks again. That’s a good thing, since all of the 13 essential nutrients eggs contain are found in the yolk. Egg yolks are an especially good source of choline, a B-vitamin that plays important roles in everything from neurotransmitter production to detoxification to maintenance of healthy cells. (
3) Studies show that up to 90% of Americans don’t get enough choline, which can lead to fatigue, insomnia, poor kidney function, memory problems and nerve-muscle imbalances. (
4)
What about saturated fat? It’s true that some studies show that saturated fat intake raises blood cholesterol levels. But these studies are almost always short-term, lasting only a few weeks. (
5) Longer-term studies have not shown an association between saturated fat intake and blood cholesterol levels. In fact, of all of the long-term studies examining this issue, only one of them showed a clear association between saturated fat intake and cholesterol levels, and even that association was weak. (
6)
Moreover, studies on low-carbohydrate diets (which tend to be high in saturated fat) suggest that they not only don’t raise blood cholesterol, they have several beneficial impacts on cardiovascular disease risk markers. For example, a meta-analysis of 17 low-carb diet trials covering 1,140 obese patients published in the journal Obesity Reviews found that low-carb diets neither increased nor decreased LDL cholesterol. However, they did find that low-carb diets were associated with significant decreases is body weight as well as improvements in several CV risk factors, including decreases in triglycerides, fasting glucose, blood pressure, body mass index, abdominal circumference, plasma insulin and c-reactive protein, as well as an increase in HDL cholesterol. (
7)
If you’re wondering whether saturated fat may contribute to heart disease in some way that isn’t related to cholesterol, a large meta-analysis of prospective studies involving close to 350,000 participants found no association between saturated fat and heart disease. (
8) A Japanese prospective study that followed 58,000 men for an average of 14 years found no association between saturated fat intake and heart disease, and an inverse association between saturated fat and stroke (i.e. those who ate more saturated fat had a lower risk of stroke). (
9)
That said, just as not everyone responds to dietary cholesterol in the same manner, there’s some variation in how individuals respond to dietary saturated fat. If we took ten people, fed them a diet high in saturated fat, and measured their cholesterol levels, we’d see a range of responses that averages out to no net increase or decrease. (If dietary saturated fat does increase your total or LDL cholesterol, the more important question is whether that’s a problem. I’ll address that in the next article in this series.)
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