Aaron Carroll:
   Cholesterol! For decades it's been demonized as the reason why so many people have heart disease. We've been watching it and avoiding it like the plague. Why? Does that do any good? The answer may surprise and depress you. This is Healthcare Triage. 

   Healthcare Triage Intro

   OK, let's start with heart disease, which is still pretty much the biggest killer in the industrial world. Most of the problems come from atherosclerosis, where the blood vessel walls thicken and fatty plaques form. Later, clots can develop, or fragments of plaques can break off and clog up other vessels. If those blockages occur in vessels that feed the heart, you have a heart attack. If those vessels feed the bran, you have a stroke. Neither is good.
    And look, you need cholesterol; it's not poison. Your liver makes about 1000 milligrams of it a day, 'cause you need it to make certain vitamins and hormones, it's necessary to make cell walls, and it helps digest and move fat around your body. It gets around in two forms. Low density lipoprotein, or LDL cholesterol, is the bad kind. It's the one that's been implicated in causing atherosclerosis. But there's also high density lipoprotein, and that's the good cholesterol.
    Now, there are many things that have been linked to heart disease, and serum cholesterol is just one of them. Plus, the right metric about cholesterol to focus on is debatable. Is it the total amount, the LDL level only, the ratio of LDL to HDL, something else? All hotly contested. But what wasn't contested, at least, not terribly publicly, was that we should avoid cholesterol in our food, and that is where the dietary recommendations come in.
    For a long, long time, we've been told that we should limit our intake of cholesterol to no more than 300 milligrams a day. That's not a lot; just one egg  has about 220 milligrams of cholesterol in it, so, you know, a two-egg omelette would be a bad idea. Forget a three-egg omelette. And that's if you ate nothing else with cholesterol in it all day.
     Cholesterol warnings have been in effect since the 1960s. Since 1994, laws required food in the United States to report cholesterol values on nutrition labels so people could make more informed choices. And we cut out eggs. We cut out meat. We cut out shrimp. Some of us even cut out milk, which was a good idea for other reasons. And that sucked. Today, the average male in the United States consumes about 340 milligrams of cholesterol a day, and experts complain that's not good enough. Plus, I ate egg white omelettes. Have you tried them? Tasteless! Was it necessary? To the research!
      Turns out that there have been good studies on whether dietary cholesterol affects the level of cholesterol in your blood. For instance, a 2004 study took people in randomized them to one of two groups. One was given the equivalent of more than three eggs a day for 30 days, and the other got a placebo. Then they switched the groups. They measured their serum cholesterol after each intervention period. What they found and what's been found in many other studies is that about 70 percent of people are what we call hypo-responders to dietary cholesterol. This means that after consuming three eggs a day for 30 days, they'd see no real increase in their plasma-cholesterol ratios. Their cholesterol levels have almost no relationship to what they eat.
      There have been many randomized controlled trials in this area. In 2013 researchers published a systematic review of all recent studies just from 2003 or after. 12 of them met criteria and 7 controlled for background diet. Most of the studies that controlled for background diet found that altering cholesterol consumption had no effect on the concentration of blood LDL cholesterol. A few studies could only detect differences in small subgroups of people with certain genes or a predisposition to problems. In other words, in most studies ALL people didn't respond to changes in their intake of cholesterol. In just a few, a minority of patients responded to changes in their dietary cholesterol.
     Have recommendations changed with the publication of any of these studies? No? I still get lectures from people telling me that this or that has too much cholesterol in it. But all that may be about to change. In December, a dietary guideline subcommittee met to discuss possible changes to the next set of dietary guidelines for the United States to be released this year. After their meeting, they published a report. You can go look at it. It said, and I quote, "Cholesterol is not considered a nutrient of concern for overconsumption." I'm sure that will come as a surprise for the vast majority of Americans and people worldwide, who, for decades, have been watching their cholesterol intake religiously. It's very possible that the US government might finally change their dietary guidelines this year to reflect this fact, though we don't yet know for sure.
    Now that doesn't mean that bad levels of cholesterol in your blood aren't dangerous. It also doesn't mean that all the people on drugs to help reduce their level of cholesterol don't need them. It's now thought that it's the consumption of saturated and trans fats perhaps which make more of a difference, and that's what we should focus on. 
    But we haven't been totally fact-based in our fat recommendations either, and that's the subject of next week's Healthcare Triage. 

Healthcare Triage Outro