“Eat less cholesterol:” It’s still a mainstay of typical health advice. And it’s based on logic that sounds reasonable: the more of a nutrient you eat, the more of it you’ll have in your body. That’s what happens with other nutrients - that’s the whole reason why we bother to eat nutritious foods in the first place. That’s why eating foods rich in Vitamin C cures Vitamin C deficiency (aka scurvy) - you get the Vitamin C from your food, and it raises the levels of Vitamin C in your body.
With cholesterol, most people want less rather than more, so the idea is that if you consume less of it from diet, you’ll have less of it in your blood. But completely leaving aside the question of whether or not high cholesterol is actually a problem, let’s focus on the second the idea that eating foods rich in cholesterol raises blood cholesterol, or that avoiding foods rich in cholesterol will lower blood cholesterol.
For most people*, that part just isn’t true. Your body has a very sophisticated mechanism for regulating its own cholesterol levels, and it’s always trying to preserve homeostasis: to keep cholesterol levels constant.
*There are some people called “cholesterol hyper-responders” who do have an elevated response to dietary cholesterol (although some research suggests that this might not be such a big deal). This is not a post about them. If this is you, dietary cholesterol restriction may very well be a legitimate strategy for lowering your cholesterol levels, and your doctor should be the one to discuss it with.
This review goes over the way that homeostasis is maintained through...
- Synthesis: how much cholesterol you make in-house. This is a much larger percentage of your total cholesterol than the cholesterol you get from food. Most of it happens in the liver, but almost every cell in your body can synthesize cholesterol.
- Absorption: how much cholesterol you absorb. Your homemade cholesterol is much more efficiently absorbed than dietary cholesterol.
- Excretion: how much cholesterol you send right back out the other end, rather than keeping it in your body.
In general, the more dietary cholesterol you give a person, the less they make themselves, and the less they absorb. Restrict dietary cholesterol, and they’ll make more themselves and absorb more of what they do get. The review described it as a “push-pull:” bodies compensate for changes in dietary cholesterol by making more or less, to keep overall cholesterol levels roughly the same.
It’s not that difficult for your body to make the balancing act happen, because the amount of cholesterol you get from your own body’s cholesterol synthesis is much, much larger than the amount you get from diet. The exact numbers will vary depending on how much dietary cholesterol you eat, but according to the review above, even people eating a typical American diet of Big Macs and cheesy fries get much more cholesterol from their own body’s cholesterol synthesis than they do from their diet.
Dietary cholesterol is also less efficiently absorbed than synthesized cholesterol, so 1mg of cholesterol from diet will ultimately affect your total cholesterol levels much less than 1mg of cholesterol that your body makes itself. Even your food is helping your body out with the DIY cholesterol factory. Various components of foods, like phospholipids in egg yolks and sterols and fiber in plants, that reduce the absorption of cholesterol from those foods….while provoking an increase in homemade cholesterol.
Ultimately, dietary cholesterol just isn’t that big of a player in total cholesterol levels.
This makes total sense, because cholesterol is too important to be left up to the assumption that we'll have cholesterol-rich foods to eat.
What if (back in the caveman days) there was a famine or a drought, and we had to live without animal foods for a while? Your body really needs ways to “defend” its cholesterol levels and make sure you always have enough.
Just from this, it should be pretty clear that the typical advice about cholesterol doesn’t make much sense at all. “Eat less cholesterol” - but the amount of cholesterol even in a “bad” diet pales in comparison to the amount of cholesterol your body produces on its own. “Eat less cholesterol” - but your body will just adjust by synthesizing more. “Eat less cholesterol” - but you’ll just get more efficient at absorbing it. Statin drugs, which really do force cholesterol levels down, do it by affecting the process of cholesterol synthesis, because that’s really the important part.
Maybe that’s why studies haven’t actually shown dietary cholesterol to have a significant effect on blood cholesterol. It’s small fry.
This Doesn’t Mean that Blood Cholesterol Isn’t Important
Whether blood cholesterol is important or not isn’t the issue at stake here. The point is that if you care about blood cholesterol, diet isn’t the place to look. The place to look is your body’s mechanisms for synthesizing and absorbing cholesterol, since those are much more powerful drivers of total cholesterol levels.
And it turns out there are some reasons why high cholesterol might represent an underlying problem - but the problem isn’t “too much dietary cholesterol.” The problem is “some health issue affecting cholesterol synthesis.” The review above stresses that everyone does this a little differently, and everyone’s body makes adjustments in slightly different degrees.
Factors that affect cholesterol synthesis include…
- Body weight (per pound of body weight, obese people make more cholesterol than normal-weight people). It’s possible that one reason for this is high leptin levels in obese people, and there are definitely ways to improve leptin sensitivity and get leptin levels under control.
- Meal times and circadian rhythms: delaying meals can alter synthesis rates. It might be worth your while to focus on eating regular meals, and eating breakfast shortly after waking up to fix any issues with circadian alignment.
- Genetic variation. Not much anyone can do about this one, unfortunately, except to know about it and not freak out.
- Metabolic health: there’s a lot of evidence connecting insulin resistance to increased cholesterol synthesis - and not just in people with diabetes. This study found that problems with insulin sensitivity were associated with steadily increasing cholesterol dysregulation (more synthesis/less absorption) all the way from garden-variety blood sugar problems up to full-on diabetes.
- Early-life feeding: breastmilk has a high concentration of cholesterol, much higher than cow’s milk (and soy milk formula has none at all). Babies who are breastfed have lower cholesterol levels later in life. It’s possible that breastfeeding sends an epigenetic signal to “relax about this cholesterol thing; there’s plenty coming in; no need to go into overdrive about making it.” This isn’t something anyone reading this can change, but it’s worth keeping in mind if you’re thinking about kids.
- Your gut flora. The gut is a critical site for cholesterol breakdown and absorption, and there's some evidence that gut-health problems might contribute to high cholesterol. For example, did you know that probiotics can actually lower cholesterol?
If you’re eating Paleo and concerned about high blood cholesterol, one good place to start could be getting these factors under control. Instead of fixating on cholesterol in foods, which doesn’t matter all that much, go for the abnormalities in cholesterol synthesis, and fix the homeostatic mechanism.
Summing it Up
Even if you start from the premise that blood cholesterol is something to worry about, putting dietary cholesterol under the microscope just doesn’t pan out: it’s not that important in the grand scheme of things. The real target should be the homeostatic mechanisms (synthesis and absorption) that easily adjust for changes to dietary cholesterol. DIY cholesterol synthesis has a much, much higher effect on total cholesterol levels than anything you eat.
Considering that cholesterol-rich foods are often very nutritious, it’s hard to see any benefit of cutting them out of your diet. From a Paleo perspective, if you’re concerned about cholesterol, hormonal and metabolic health is probably a better place to start than getting rid of extremely nutritious cholesterol-rich foods like liver and shrimp.