January 28, 2016

If you want to sleep at night, it doesn’t pay to think too hard about the human heart. It’s a muscle, nothing more, nothing less, but it’s a muscle like no other. It started beating roughly four weeks after you were conceived, and it will continue beating, a bit more than once every second, for your entire life. When it stops, you die. As simple as that.

It’s the centrality of that muscle–its place in the middle of our bodies and its primal role in keeping things running–that has imbued it with so much romance and meaning. There’s a reason we don’t decorate our Valentine’s Day cards with little kidneys. And yet treasure our hearts though we do, we’re not taking terribly good care of them.

An estimated 610,000 Americans will die of cardiovascular disease this year. It’s the No. 1 killer of both men and women and the cause of 1 in 4 deaths overall. That’s true in the U.S., and it’s increasingly true all around the world, even in a time when we know more than ever before about how to keep our hearts well.

The rates of cardiovascular death are down–way down, depending on when you start measuring. The risk of dying of heart disease dropped 67.5% from 1969 to 2013, thanks to better detection, lifesaving drugs and lifestyle interventions, like changes to what people eat and how much of it, how much they exercise and how little they smoke.

Some health experts have claimed that America is winning the war on heart disease, but 610,000 deaths are still 610,000 deaths. And even people who follow the rules and try to meet the right benchmarks can still find themselves in a world of cardiac hurt one day.

One reason: those heart-healthy benchmarks (and the advice they inform) can be, well, wrong–or at least based on outdated science. Is the familiar 120/80 still the target for healthy blood pressure? Is low-fat dairy still the right choice for your morning yogurt or latte? Even the simple dietary arithmetic of calories in and calories out for weight loss–does that thinking still hold?

The science has changed. That doesn’t mean it’s fickle; it means it’s getting better. It also means the advice issued by many well-meaning physicians may be different now from what it was when you first absorbed it. And in the case of cardiac disease, those changes can spell the difference between life and death.

Here are some of the most important ways the old thinking has been upended by new science–and what they can mean for you and the health of your heart.

CHOLESTEROL

Old thinking: Focus on lowering “bad” LDL cholesterol

New science: There are actually different kinds of LDL–and raising “good” HDL levels may be even more important

Ever since scientists learned in the 1970s that cholesterol could stick to cells, build up in arteries and contribute to heart disease, the logical thing to do was to send cholesterol-laden foods to the do-not-eat list.

But it was premature to damn cholesterol altogether. After all, even though experts believed it to be unhealthy, they had little information on how much of it in a diet would harm the heart. “When I was in medical school several decades ago, normal cholesterol was anything under 300 mg/dL,” says Dr. Steven Nissen, chair of cardiovascular medicine at Cleveland Clinic. “Then, for a while, under 240 was normal.” The target then dropped to under 100. Confusing things further, the latest 2015 Dietary Guidelines for Americans, issued by the federal government, doesn’t note a dietary upper limit at all.

The inability to pinpoint a healthy range for cholesterol–particularly cholesterol in the diet, where it is present in healthy foods like eggs, yolks and all, and protein-rich foods like shrimp–was only part of the problem. Scientists have since learned that there are bad and worse forms of LDL. One comes from fat in the diet and appears less harmful. Another tends to form when LDL attaches to certain fats that are produced when refined carbohydrates break down. Too much of the carb-fueled cholesterol can spell trouble for the heart–but Americans aren’t being told to reduce carbs enough.

Experts are getting more sophisticated about the different forms cholesterol takes. They also know that LDL has a better half: HDL. Studies show HDL can neutralize some of the harmful effects of LDL. Now nearly all heart experts agree that boosting HDL is beneficial to heart health. The most reliable ways to do that? Exercise, don’t smoke, and reduce body fat.

DIETARY FAT

Old thinking: All saturated fat is bad and should be seriously limited

New science: It’s complicated–but trans fats are the worst for your heart

It couldn’t have been easy being a hunter-gatherer, but the food choices were simple: more was better than less, now was better than later, and fat was a very good thing. Now we know better. There are several kinds of fats, not all are good, and the saturated kind–the kind in red meat and cheese and coconut oil–is the one that’s the worst.

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Except it isn’t. In recent years, evidence has continued to mount that saturated fats aren’t quite as bad for us as they once seemed to be. Full-fat dairy has a place in a healthy diet, science has shown, as do modest amounts of red meat. And in moderation, both appear to be better than the refined carbohydrates that filled the American diet when the low-fat message took hold.

Trans fats, on the other hand–which are present in an estimated 27% of processed foods, even the low-fat kind–raise LDL and lower HDL, making them particularly damaging to the heart. The risk is so real that the FDA has taken the rare step of banning them from the U.S. food supply, giving manufacturers three years to clear them from supermarket shelves. With trans fats, in other words, there’s no nuance. They’re just plain bad.

“It doesn’t matter what we compare trans fats to–saturated fats, good fats,” says Russell de Souza, an assistant professor and registered dietitian at Ontario’s McMaster University. “They’re harmful, and they’re worse for you than any other type of fat.”

Ironically, it was the scare over saturated fat, which took hold in the 1980s, that got food manufacturers trying to create a replacement, which they did by adding hydrogen to oils. (The term partially hydrogenated oil on a food label is the red flag for trans fats.) It’s not going to be easy to get trans fats out of the food supply, and even foods labeled zero trans fats can contain up to 0.5 grams per serving.

That means, for now, it pays to avoid products that are likely to contain them–including store-bought cakes and cookies, chips and even some processed breads and crackers. After that, say goodbye for good. Trans fats are one thing that are never likely to come around again.

BLOOD PRESSURE

Old thinking: The 120/80 ratio signals healthy blood pressure and a healthy heart

New science: Your blood pressure may need to drop even lower

For decades, doctors treated 120/80 as the holy grail of heart health, urging everyone to keep their blood pressure (BP) at that level to avoid heart attacks and strokes. In recent years, they have even incorporated more wiggle room around the 120/80 goal, loosening their advice and letting older people–whose blood pressure creeps up naturally with age–to hit 140/90.

But according to the latest science, that could be a bad idea. In the most recent and largest study on the subject, called SPRINT, scientists showed that to protect the heart, people may need to get their systolic pressure–the top number–to below 120.

In the study, people who took blood-pressure-lowering drugs to bring their BP to below 120 were less likely to die from any cause than those who dropped their pressure only to under 140. The results were so dramatic that the researchers stopped the trial early so those in the higher-blood-pressure group could start working with their doctors to bring their BP lower.

It was the first head-to-head comparison of how people at the different targets fared, and it challenged decades-old thinking that as they aged, people needed to have higher blood pressure to keep blood flowing to the brain. It’s increasingly clear that high blood pressure strains blood vessels–and that wear and tear can attract plaque-forming agents from the immune system that eventually block blood flow.

With the landmark SPRINT study, all the people were at higher risk of developing hypertension, and all used medications–up to six in some cases–to bring their numbers down. Major public-health groups are now discussing whether taking so many drugs is a realistic and safe strategy as they weigh new guidelines for blood-pressure control that are expected later in 2016.

In the meantime, some doctors say drugs aren’t the only way to manage blood pressure. Exercising and eating a low-salt diet, as well as controlling stress, can also maintain a healthy BP.

DAILY ASPIRIN

Old thinking: Take a baby aspirin a day to prevent a heart attack

New science: If you haven’t already had a heart attack, the pill is not advised

Simple and affordable, aspirin has long been the unglamorous workhorse of medicine, relieving pain and reducing fever for thousands of years. But in the 1990s, aspirin became a hot drug, with experts concluding its anti-inflammatory powers–and its ability to thin blood and prevent clots–might make it an effective daily therapy to prevent heart attacks and strokes in otherwise healthy people.

Before long, aspirin was recommended for people who’d had a heart attack or stroke, as well as for those who hadn’t, particularly if they were at risk for heart disease. An immediate aspirin was also recommended for people suffering symptoms of a heart attack.

More recently, however, the FDA, reacting to mounting evidence, changed its guidelines. Aspirin is still recommended by many doctors for acute symptoms, like severe chest pain, and for people who have already had a heart attack or stroke. But for those who haven’t, science isn’t on aspirin’s side.

That’s because it can cause bleeding in the stomach and brain. It’s not common. The risk is not as much as 1% or even 0.1%, according to Dr. Robert Temple, the FDA’s deputy director for clinical science–but it exists. “We think the use of aspirin has a detectable effect in raising the risk of stroke,” Temple says.

A 2014 study followed more than 14,000 people. None had had a heart attack, but all had some risk factors. Half took a daily aspirin, and half didn’t. In the course of two years, 58 of the aspirin takers died of a heart attack, compared with 57 in the other group. In statistical terms, that’s no difference at all. “We concluded that the evidence wasn’t there” that aspirin works as a primary preventive, says Temple. This may not do much to change the thinking of people who take an aspirin a day no matter what, on the theory that it couldn’t hurt. But the studies of related bleeding have shown aspirin can hurt.

The guidelines are by no means final. The American Heart Association still recommends that high-risk people take a daily low-dose aspirin. The FDA also stresses that people should talk to their doctor since no two patients–and no two hearts–are exactly the same.

WEIGHT LOSS

Old thinking: Burn more calories than you take in if you want to lose weight

New science: It’s not just how many but where they come from that matters

Here’s something that isn’t news: excess weight puts a burden on the heart, driving blood pressure up and weakening blood vessels in the process. Too much fat, meanwhile, can launch a cascade of biological changes, flooding the body with hormones that can increase the likelihood that a person will develop Type 2 diabetes, which is a major risk factor for heart trouble. But it’s also one of the few things within a person’s power to try to fix–if given the right information about how to go about doing it.

The decades-old mantra of watching your calories in order to shed pounds was based on the idea that people need to burn off more than they eat. But new science makes plain that that thinking was wrong. Dr. David Ludwig, a professor of pediatrics at Boston Children’s Hospital and Harvard Medical School and the author of the recent diet book Always Hungry, likes to put it this way: “Calorie balance is a useful concept if you’re a toaster oven. But the human body doesn’t respond to changes in calorie intake passively.”

What that means is that all calories are not created equal. Calories from a snack of nuts and apple slices come with an entirely different makeup from those in crackers and low-fat cheese–even if the crackers and cheese have fewer calories overall.

There is strong evidence that when refined carbohydrates (e.g., those crackers) enter the body, they raise insulin, and insulin serves as a hormone alarm of sorts–it prepares the body to hoard calories in case of famine. In that crisis-like mode, those calories are shuttled into storage in the fat cells. That explains why practically every dieter whose strategy is simply to eat fewer calories overall, regardless of where those calories come from, ends up feeling ravenous and cranky.

Ludwig is convinced that paying attention not to the number of calories but to the kind is the answer to shedding pounds. He recommends that in addition to eating lots of vegetables, eating fat has a place in the diet. When people eat this way, they tend to burn whatever calories they consume more efficiently. In a 2012 study by Ludwig, people ate three different diets for a month each. He found that just by eating lighter oils and fewer carbohydrates–a typical Mediterranean diet–people burned the same number of calories they would have if they’d exercised at a moderately vigorous level.

“Changing the quality of what you eat can lower your body set point, so instead of fighting to lose weight, you’re working with your body, which is an entirely new ball game,” says Ludwig.

CHOLESTEROL DRUGS

Old thinking: People with high cholesterol should likely be taking a statin

New science: Some people may need a different drug altogether–or none at all

When statins first appeared on pharmacy shelves in 1987, heart experts were so impressed with the drugs’ ability to lower cholesterol that they hailed them as wonder drugs that might finally push heart-disease rates down. But effective as they are, statins aren’t for everyone, and high cholesterol remains a leading cause of heart disease.

Statins are a safe and effective way to muscle down cholesterol for most of the millions of Americans who take them, but for others, statins aren’t tolerable. They can cause side effects, including severe muscle weakness, which can lead some people to stop taking their prescriptions.

Scientists are also learning that not everyone who qualifies for a statin needs one. A recent study found that 30% of people with high numbers may not actually have fatty cholesterol gumming up their arteries. That’s why some doctors want to incorporate a special scan that can help select out people who have plaques that could pose a problem from those who don’t.

Finally, for some people, the pills just aren’t enough. For them, there’s a new class of drugs, called PCSK9 inhibitors. Two such drugs were approved in 2015, and studies so far suggest they can lower LDL levels by as much as 60%. PCSK9 inhibitors are so far advised only for people who can’t take statins or who have extremely high cholesterol because of their genes–but doctors anticipate that more people will ask for them. “I have patients who say, ‘I’ve had a good response to a statin, so if I took this on top of it, I could cut my LDL in half. Doesn’t that mean good things?’ And the answer is yes,” says Dr. Elliott Antman, a professor of medicine at Brigham and Women’s Hospital and Harvard Medical School.

Most insurers won’t yet cover PCSK9 inhibitors unless patients have an intolerance to statins or another reason their cholesterol won’t come down. But with heart disease continuing to claim so many lives, you can bet that research will be starting soon.

This appears in the February 08, 2016 issue of TIME.

Write to Jeffrey Kluger at jeffrey.kluger@time.com.

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