Healthy You
Cholesterol Confusions
How much does the cholesterol in your food really matter?
True or false:
1. Most people’s blood cholesterol levels rise a lot when they eat a lot of cholesterol.
2 Some foods contain “good” cholesterol, others “bad” cholesterol.
3. Beef contains more cholesterol than chicken.
4. Like the U.S., most countries have set an upper limit for daily cholesterol consumption.
Answers: All are false. To find out why, read on.
Most Americans are watching their cholesterol, as they should be. More are getting tested, and more are successfully treating their undesirable levels (via diet, weight loss and/or drugs) than ever before. But we aren’t necessarily clearer about what it all means. If you’re like most people, you’re tripped up by some fundamental questions, especially about the connection between the cholesterol you eat and that in your bloodstream.
Cholesterol is essential to life—a part of cell membranes, nerve fibers, hormones and other vital substances. A waxy substance classified as a lipid, it’s found in all animals, and thus in all animal products we eat. Though we measure the cholesterol in the blood, it’s actually in all our cells.
Many people think that all the cholesterol in their blood (and elsewhere in the body) comes from the cholesterol they eat, which is called dietary or preformed cholesterol. In fact, most of it is made by our livers. In addition, the average American consumes about 300 milligrams of cholesterol from food every day (the amount in an egg plus 5 ounces of meat). Excess cholesterol is excreted by the liver, but some is deposited in the walls of your arteries, where it is involved in the formation of plaque, thus contributing to atherosclerosis and possibly heart attack or stroke.
The body makes more than enough cholesterol to meet its needs—you don’t have to eat any to stay healthy. Strict vegetarians eat none and do fine without it.
Fellow travelers
Fat and cholesterol are independent substances. Fat cells contain cholesterol, but no more than other cells do. Thus fatty meat has about as much cholesterol as lean meat does. All meats—beef, pork and poultry, whether lean or fatty—average about 25 milligrams of cholesterol per ounce.
Some foods—eggs and most shellfish, for instance—are high in cholesterol but not saturated fat. In contrast, vegetable oils, avocados and nuts are rich in fats (usually healthy unsaturated fats) but have no cholesterol.
The type and amount of fat you eat affect your blood cholesterol levels—much more so than does the cholesterol you eat. In particular, saturated fat (found mostly in animal products) and trans fat (in many processed foods) raise blood levels of LDL (“bad”) cholesterol—though recent research suggests that some types of saturated fat, as in chocolate and coconut oil, do this less than others.
Is 300 the right number?
The American Heart Association (AHA) recommends that healthy people limit cholesterol consumption to 300 milligrams a day. For those with heart disease, diabetes, undesirable cholesterol levels or other coronary risk factors, the limit is 200 milligrams. The government’s Dietary Guidelines agree.
But some researchers believe that these guidelines are too strict and endorse a higher daily limit for cholesterol for healthy people—perhaps 500 milligrams a day.
Many other countries, including Canada, the U.K. and Australia, don’t set any recommended upper limits, citing a lack of evidence that dietary cholesterol has a major impact on blood cholesterol across the population. Moreover, though some large observational studies have found a significant link between dietary cholesterol and heart disease, others have not.
While dietary cholesterol raises blood cholesterol levels at least a little in most people, this effect depends on genetics, insulin levels, body weight and other dietary and metabolic factors. It’s estimated that only about 15 to 25 percent of people have a significant response to cholesterol in food. There is no test to identify such “hyper-responders.”
Searching for good cholesterol
Have you ever looked for “good” cholesterol on a food label? Don’t. All the cholesterol you eat is the same, and is chemically identical to that made by the liver.
What’s called “good” cholesterol is HDL (high-density lipoprotein), which is assembled in the liver and circulates in the blood. Lipoproteins are packages of proteins and lipids, which transport fats and cholesterol in the blood. HDL is “good” because it collects excess cholesterol from artery walls and elsewhere in the body and brings it back to the liver for reprocessing or excretion. In contrast, LDL (low-density lipoprotein) carries cholesterol to the cells—and leaves any unused residue of cholesterol in the arterial walls, which is why it’s called “bad.”
BOTTOM LINE: Most people don’t need to worry much about dietary cholesterol, since it will have a small effect on blood cholesterol, at most. It’s far more important to keep saturated and trans fats low and to replace them with foods rich in unsaturated fats and/or fiber, which are beneficial for blood cholesterol. But if you are obese or have diabetes, for instance, you should stick to the AHA guidelines.
The sunny side of eggs?
Eggs have a bad reputation because of their cholesterol (the yolk of a large egg has 185 milligrams), but they can still be part of your diet. According to the U.S. Dietary Guidelines, “evidence suggests that one egg per day does not result in increased blood cholesterol levels, nor does it increase the risk of cardiovascular disease in healthy people.” Indeed, several well-designed studies (some sponsored by the egg industry) have found no link between dietary cholesterol and heart disease—except in people with diabetes.
One factor may be that dietary cholesterol, at least when it comes from eggs, can raise HDL (“good”) as well as LDL (“bad”) cholesterol, so the ratio stays the same. And when it does boost LDL, it tends to be the larger LDL particles, which are less risky.
UC Berkeley Wellness Letter, September 20
No comments:
Post a Comment