Let’s say you want to lose some weight. Which of these foods would you choose: A skim-milk latte, or the same drink with whole milk? A low-cal breakfast bar or steak and eggs? A salad tossed in light dressing or the same salad doused with butter milk ranch?

If you’re like most Americans, you either aren’t sure how to answer, or you’re very sure—but very wrong. And it’s not your fault. It’s the fault, experts say, of decades of flawed or misleading nutrition advice—advice that was never based on solid science.

The US Department of Agriculture, along with the agency that is now called Health and Human Services, first released a set of national dietary guidelines back in 1980. That 20-page booklet trained its focus primarily on three health villains: fat, saturated fat, and cholesterol.

Recently, research has come out strongly in support of dietary fat and cholesterol as benign, rather than harmful, additions to person’s diet. Saturated fat seems poised for a similar pardon.

“The science that these guidelines were based on was wrong,” Robert Lustig, a neuro-endocrinologist at the University of California, San Francisco, told Tonic. In particular, the idea that cutting fat from a person’s diet would offer some health benefit was never backed by hard evidence, Lustig said.

Just this week, some of Lustig’s colleagues at UCSF released an incendiary report revealing that in the 1960s, sugar industry lobbyists funded research that linked heart disease to fat and cholesterol while downplaying evidence that sugar was the real killer.

Nina Teicholz, a science journalist and author of the The Big Fat Surprise, said a lot of the early anti-fat push came from the American Heart Association (AHA), which based its anti-fat stance on the fact that fat is roughly twice as calorie-dense as protein and carbohydrates.

“This advice to avoid fat allowed the food industry to go hog-wild promoting low-fat, carb-heavy foods as ‘light’ or ‘healthy,’ and that’s been a disaster for public health,” Lustig said.

“They had no clinical data to show that a low-fat diet alone would help with obesity or heart disease,” Teicholz told Tonic. But because fat was high in calories, they adopted this anti-fat position, and the government followed their lead. Surely the 1960s research rigged by the Sugar Association, which was published in the prestigious New England Journal of Medicine, added to our collective fat fears.

By the 1990s, when Teicholz says the epidemiological data started piling up to show that a low-fat, high-carb diet did not help with weight loss or heart disease—calories be damned—much of the damage was already done. The US public was deep in what nutrition experts sometimes call the “Snackwell phenomenon”—a devotion to low-fat and low-calorie processed snack foods, which people pounded by the bagful because they believed them to be healthy.

“This advice allowed the food industry to go hog-wild promoting low-fat, carb-heavy packaged foods as ‘light’ or ‘healthy,’ and that’s been a disaster for public health,” Lustig said.

The stats back him up. Since the US government first published a set of national nutrition guidelines in 1980, rates of obesity and related diseases like diabetes have more than doubled. “Childhood diabetes was basically unheard of, and now it’s an epidemic,” Lustig said.

Overseas, national health authorities followed America’s lead on fat. The results have been similarly grim. Earlier this year, a UK nonprofit called the National ObesityForum (NOF) published a blistering condemnation of its government’s diet and nutrition policies.

In its report, the NOF argues that advice to cut back on fat and cholesterol is “the root cause” of Britain’s skyrocketing rates of obesity and diabetes. Speaking shortly after the report’s publication, Aseem Malhotra, a British cardiologist who consulted on the NOF report, said, “The change in dietary advice to promote low-fat foods is perhaps the biggest mistake in modern medical history.

Along with ripping its government’s “failed policies,” the NOF report called for a”complete overhaul of dietary advice and public health messaging.”

In a recent editorial appearing in the British Journal of Sports Medicine, researcher Zoe Harcombe from the University of the West of Scotland explains that obesity rates among British men and women rose from 2.7 percent in 1972 to 23 percent and 26 percent, respectively, by 1999.

“There are only three macronutrients,” Harcombe told Tonic, “protein, fat, and carbohydrates.” Nearly everything you eat or drink contains one or more of these. And if you followed the government’s advice to eat less fat, it’s inevitable that your carb consumption would shoot up, she said. That’s just what happened at a population level during the 1980s and 90s.

A whole generation of health professionals accepted—and passed on to their patients—the government’s guidance to avoid fat and cholesterol. Many still do.

To give credit where credit is due: The latest iteration of the US government’s dietary guidelines no longer makes a point of capping total fat and cholesterol intakes. But this omission is more a furtive walking back of bad advice than a public acknowledgment of error, Teicholz said. Worse: “When you look at the actual nutritional modeling that the government uses to inform its feeding programs, such as the National School Lunch program, they are all still low in fat,” she said.

Another example of the government’s persistent crusade against fat: The 2015 Dietary Guidelines for Americans still push low-fat dairy over full fat—a recommendation the latest research doesn’t support.

“Studies have not shown benefits of low-fat dairy over full-fat for weight loss, especially if the fat calories are replaced with sugar,” Walter Willett, chair of nutrition at Harvard School of Public Health, told Tonic. “If anything, the evidence goes the other way.”

Willett is quick to point out that he doesn’t consider whole milk and full-fat cheese “health foods.” Nuts, for example, are a healthier source of fat, he said. But if you’re going to sip some milk or eat some yogurt, the evidence suggests your waistline may be better off with the full-fat stuff—probably because it’s more filling and so curbs excessive eating.

Teicholz said it’s hard to overstate the effect of national health authorities’ pro-carb, anti-fat stance. A whole generation of health professionals accepted—and passed on to their patients—the government’s guidance to avoid fat and cholesterol. Many still do.

“Both professional and institutional credibility are at stake,” she said when asked why more doctors and policymakers aren’t making noise about the harms caused by the government’s dietary guidance. She also mentioned food industry interests, the potential for “massive class-action lawsuits,” and the shame of copping to nearly a half-century of bad diet advice as deterrents for USDA and other health authorities when it comes to admitting they were wrong.

In the United Kingdom, the disconnect between nutrition science and government dietary policy has opened rifts within the public health community. Since its report’s publication, the National Obesity Forum has lost four of its senior members, and the fallout has sparked a national debate among doctors, nutrition scientists, and policy makers over what sorts of food truly belong in a healthy diet.

“Our previous reports had garnered little interest, so we had no way of knowing this one would go interplanetary,” David Haslam, chair of the National Obesity Forum and a professor of obesity sciences at Robert Gordon University, told Tonic.

Repeating the advice put forward in his organization’s report, Haslam said he firmly believes public health would be greatly improved if we all just ate fewer refined carbohydrates—stuff like baked goods, chips, breakfast cereals, and other packaged goods—and instead ate more “natural foods” regardless of their macronutrient content.

This last point—that we should all pay less attention to a food’s nutrient makeup—is an important one. Harvard’s Willett said focusing only on a food’s specific macro and micronutrient content is confusing, and not a good way to evaluate an item’s health impacts.

So what’s a confused dieter to do?

Jenny Knight, 30, is a speech therapist and mother of two in Norman, Oklahoma. “I’ve struggled with my weight since I was eight years old,” Knight told VICE. At 5-foot-9 and close to 250 pounds, she’s obese by any definition.

Like many heavy Americans, Knight has experimented with a hundred different diets that, when you boil them down, all advocate for cutting fat or calories in order to lose weight. Sooner or later, all of them failed her. “Even when they were working, it was all about willpower,” she said. “I’d be so hungry I’d be shaking, and eventually I wouldn’t be able to keep that up anymore, and I’d gain all the weight back.”

But since February, Knight has been on a fat-centric diet championed by David Ludwig, a professor of nutrition at Harvard.

Speaking to Tonic, Ludwig said that cutting fat from your diet in favor of processed carbs can trigger a cascade of unhealthy metabolic shifts that fuel diseases like diabetes and cause your body’s fat cells to lock in—rather than dump—their energy. All this results in “out-of-control” hunger, he said. Cutting more calories from your diet just adds fuel to that fire.

His plan, which he lays out in his book Always Hungry?, champions a shift away from carb-heavy processed food in favor of a diet heavy in fats from nuts, full-fat dairy, natural oils, and other whole foods.

So far, Knight has lost 32 pounds on Ludwig’s plan. But it’s not just the lost weight that has her feeling optimistic. “This is the only dietI’ve ever tried that feels effortless—just no willpower required,” she said. “It honestly feels decadent to eat things like dark chocolate or peanut butter or coconut milk, and I’m not hungry like I used to be.”

Ludwig’s diet may or may not be the answer to all our weight-loss prayers. But one thing is clear: Dietary fat was never the boogeyman health authorities made it out to be.

“I think most of us would be 90 percent of the way to a really healthy diet if we just cut out processed foods,” UCSF’s Lustig said. “We wouldn’t need diet guidelines if we ate real food.”