Your metabolism is a collection of all the small chemical reactions taking place in your body that work to keep you alive. These reactions are fueled by burning up the calories that exist in all the food you eat. If you eat more calories than you need to power these reactions, the excess food energy will be stored as fat. Each person’s metabolism is different, just like every person is different. Throughout July we’ll be exploring the different ways metabolisms work, and how understanding your own metabolism can help you become healthier.
Dietary guidelines for heart health recommend low fat intake and portion control to keep calorie counts down. But how does the fat from that juicy cheeseburger or the calories in those crispy fries turn into the plaque that clogs arteries and leads to heart attacks?
Om Ganda, M.D., Director of the Lipid Clinic at Joslin Diabetes Center and Associate Professor of Medicine at Harvard Medical School, is an expert in heart health. In today’s blog he talks about the complicated road from a tasty meal to a clogged artery.
“There’s definitely a role of total calories that you consume and after that the most important factor is the type of fat rather than the total amount of fat,” he says. “There is some controversy of the role of saturated fat, but when all is said and done every guideline still recommends that we need to cut down the saturated fat.”
From Dietary Fat to a Clogged Artery
Take, for example, a typical homemade cheeseburger and fries meal. Though it may not feel like it, you’d be consuming nearly 1,000 calories, 50g of fat—22g of which are saturated fat, and 64g of carbs.
As you digest the food, the dietary fats get absorbed by particles called chylomicrons. Those chylomicrons travel to the liver. There, they get converted into smaller and smaller particles, eventually becoming LDL (short for low-density lipoprotein) particles. These particles house fatty cholesterols and circulate through the blood stream.
Carbohydrates can also become LDL cholesterol if you are eating more than your body can use for energy. Some of the excess carbs are stored as white fat. But some make their way into the liver and get converted into VLDL particles, which get broken down into LDL particles. This takes a little longer than the direct fat-to-LDL process, but the results are the same.
“So you are in trouble both if you have a high calorie meal with high carb, or a high calorie meal with high fat,” says Dr. Ganda. “The mechanism of getting there is different but eventually one can get a significant rise in the LDL cholesterol; but particularly with the high fat diet.”
Most people have receptors on the cells in their bodies that can trap LDL particles and force them back into the liver to be metabolized. But someone consistently eating an unhealthy, unbalanced diet can wind up with more LDL particles in circulation than the LDL receptors can handle. (One in 500 people are born with only 50 percent of their receptors, a condition called familial hypercholesterolemia. Even rarer, one in 1 million people are born without these receptors at all.)
Once the bloodstream is overwhelmed with LDL particles, they start making their way towards the blood vessels of the heart.
“The LDL cholesterol is carried in this LDL particle that is small enough to get into the arterial wall. But to get to the arterial wall, the wall itself has to be somewhat damaged,” says Dr. Ganda. This damage can occur in a few ways: history of smoking, high blood pressure, and uncontrolled diabetes.
“Diabetes itself causes long-term low-grade inflammation, particularly when the sugars are out of control. And once the artery becomes inflamed, it becomes somewhat leaky you could say, so that the LDL cholesterol can actually traverse through, penetrate the vessel wall and it ends up getting inside,” he says.
Once there, the LDL particles trigger a reaction from cells called macrophages. Macrophages are protector cells; they’ll consume anything they see as a threat, including the cholesterol-laden LDL particle.
“The macrophages engulf the cholesterol. It becomes like their food,” says Dr. Ganda. “They’re really trying to protect the body. But when there’s too much of this LDL coming through the macrophages eventually burst themselves after eating so much fat and that becomes the cholesterol plaque.”
Cholesterol plaques happen after years of mistreating the body, whether you are young or old. Some studies have even seen plaque in children who have elevated LDL levels or high blood pressure. Having this arterial blockage makes you more likely to have a heart attack.
“In time this cholesterol plaque gets bigger and bigger. Inflammatory cells inside the plaque try to reduce the damage, but they actually make the plaque likely to burst itself. And that’s when you get a heart attack,” Dr. Ganda explains. The plaque doesn’t even need to be blocking the whole artery for a heart attack to occur.
Keep Your Heart Safe
So what’s the best way to protect yourself from a heart attack if you have diabetes? Keeping blood sugar under control is key, to protect the vessels of your heart. But most important: lower your LDL cholesterol.
“There is no question that there is much persuasive evidence now from many studies that have been done around the globe that keeping your LDL cholesterol down is extremely important,” he says. Eating a diet low in saturated fat will decrease circulating LDL levels, allowing the body to start chipping away at the cholesterol clog in the arteries.
“Controlling portion size and reducing the total calories is the most important point,” says Dr. Ganda. “We hear about all kinds of diets these days, but ultimately it all boils down to total calories. And in the case of cholesterol, how many calories come from saturated fat.” Saturated fat should only take up less than 10 percent of your daily total calorie intake.
Recently adopted guidelines say that high-risk individuals, such as those with diabetes (and particularly those over age 40), should lower their circulating LDL cholesterol anywhere between 30 and 50 percent. For people who have already had a heart attack or angina, that recommendation bumps up to more than 50 percent from baseline. That’s more of a reduction than you can achieve on diet alone, so medication needs to be introduced to the routine in most people with diabetes
Statins are a well-studied medication that have proven to be very successful in reducing LDL cholesterol. They’re not without their side-effects, but the benefits of their LDL-lowering power greatly outweigh their risks. And a new class of a cholesterol-lowering drug has recently been approved by the FDA. Long-term trials are still underway, but early results were so promising they have already been released onto the market for use when statins are not able to lower LDL enough.
“There’s no question that there’s a lot of people out there in our community who we can help by lowering cholesterol better than we have in the past,” says Dr. Ganda. “And this message really needs to continue to be propagated that not only is lowering cholesterol important, but we have to lower it enough in people who need it.”