First, a confession: I’ve been writing about health, fitness, and nutrition since the early ’90s, and I’m pretty sure I’ve presented all the diet myths on this list as fact at least once.
If I missed one or two, my colleagues more than made up for it. Our passion for books and magazines is a big reason so many people continue to believe these diet myths long after they’re debunked. Even when we were the ones doing the debunking. We’ll start, appropriately, with the original sins of nutrition science.
Myth #1: Fat makes you fat
Those of you under 30 probably don’t remember the days when health-conscious people lived in fear of dietary fat. There were a lot of us in the ’80s and ’90s. If you worried about your weight, you cut fat. If you were an athlete who burned thousands of calories a day in the gym, you cut fat. A bodybuilder trying to get as lean as humanly possible? You cut fat.
We threw out egg yolks. Drank nonfat milk. And selected cuts of meat so devoid of fat it was like eating high-protein cardboard. You can read the whole sad story in How the Ideology of Low Fat Conquered America by medical historian Ann La Berge. If you do, you’ll see how my colleagues pushed ever-more-extreme notions of how little fat we should eat.
Turns out, fat isn’t the villain. “Extra calories can make you fat, regardless of source,” says Yoni Freedhoff. M.D., author of The Diet Fix. “If this were a simple magic-food issue—this food makes you fat, this food makes you thin—do you really think we’d be in this mess?” Don't fall for the worst of the diet myths. Eat your healthy fats.
Myth #2: No, carbs make you fat
Now we come to the idea that carbs, and only carbs, lead to excess body fat. If low-fat dieting was an ideology, low-carb diets are practically a religion. Even when studies like this one, which came out in 2015, show that cutting fat results in more body-fat loss than cutting the same number of carbohydrate calories, many refuse to believe the results.
Kevin Hall, Ph.D., author of that study, says it’s helpful to think of the body as a flex-fuel vehicle. But instead of having a gas tank, we’re made of the carbs, fat, and protein we need to survive. “The pieces of the vehicle are being constantly broken down and reformed,” says Hall. “We burn those fuels for energy. We can adjust over a short time to a variety of diet combinations.”
The ability to do so, he adds, is a product of millions of years of evolution. And as a result, allowing our human ancestors to thrive in every habitable environment. But instead of celebrating that flexibility, we have a tendency to look to the extremes. Which leads us to…
Myth #3: It takes a radical diet to lose a lot of weight
“My patients have lost weight in many different ways, none of which are especially radical,” says Spencer Nadolsky, D.O., an obesity specialist. “A diet doesn’t need to be radical for someone to lose a lot of weight. It just needs to be lower in calories.”
The trick, of course, is finding a way to cut calories that’s both tolerable and sustainable. “There are people who seem to respond extraordinarily well to certain kinds of diets. And other people who seem to respond poorly,” Hall says. “But I can’t tell who those people are in advance. I don’t know if it’s a function of both the diet and the person. Or if the person who was successful on Diet A would’ve been equally successful on Diet B.”
Myth #4: Fast weight loss leads to even faster weight regain
If the stars do align, and you lose weight fast on a new diet, there’s no reason to fear that your weight loss success dooms you to some kind of boomerang effect. Dr.Nadolsky says this is one of the diet myths his clients have disproved.
“This is a myth I see a lot,” Nadolsky says. “Studies actually show that those who lose weight faster tend to be more successful in the end. It’s a win right out of the gate. It helps psychologically, and there may be physiological benefits as well, including lower inflammation in the brain, which may help with cravings and hunger.”
Myth #5: You must eat breakfast
The breakfast myth, which I admit to perpetuating until recently, is based on solid observational research showing that people who eat breakfast tend to be leaner than those who don’t. It was easy enough to look at those correlations and conclude that eating early in the day makes you less hungry later.
A just-published study in Appetite takes that idea for a test drive and finds it isn’t true. When non-breakfast eaters tried eating breakfast every morning for four weeks, they ended up eating more total food, and didn’t compensate by moving more throughout the day. Another new study in Physiology & Behavior had habitual breakfast eaters try skipping breakfast, and found that they responded by both eating less and moving less.
Myth #6: Eating late at night makes you fat
Then there’s the parallel idea that late-night calories are more likely to be stored as body fat. Again, observational research suggests it does, especially when it’s confounded by sleep deprivation or shift work. But that doesn’t mean the hour of a meal, any meal, determines how much of the food is burned or stored.
“Generally, it doesn’t matter what time of the day you fill up your car, it only matters how much gas you put in it,” Freedhoff says. “Looking to the National Weight Control Registry”—an ongoing study of people who’ve lost at least 30 pounds and have kept it off for a year or more—“22 percent report not having breakfast. That’s 22 percent of a group of people who on average have lost 66 pounds, and kept them off for 5.5 years.”
Myth #7: Exercise is a great way to lose weight
People like me have both overstated and understated the case for exercise. First, we presented weight loss as simple math: Cut 3,500 calories from your meals, or burn 3,500 calories with exercise, or some combination, and you lose a pound of fat. As Hall showed in this 2011 paper in The Lancet, it doesn’t work that way.
“People keep using this outdated and patently false idea of translating 3,500 calories per pound of weight loss to make predictions,” Hall says. “Unfortunately, this idea assumes that nothing happens to metabolism as weight is lost, and that simply isn’t true.”
In fact, the human body makes lots of metabolic adjustments. With exercise, the adjustments might include an uptick in hunger, a reduction in overall physical activity, or fewer calories burned during exercise. That’s why, as Hall says, “exercise on its own isn’t a great weight-loss prescription.”
“If it were,” Freedhoff adds, “the gyms wouldn’t be full in January and empty in March.”
Myth #8: It’s impossible to lose weight with just exercise
But it’s also a mistake to say that exercise can’t or won’t help you lose weight. Exercise, like diet, affects different people in different ways. “If someone goes from a completely sedentary lifestyle to a very active lifestyle, they can lose a significant amount of weight,” Nadolsky says. “Especially if they keep it up, of course. I’ve had a few patients who’ve done this.”
With or without weight loss, everyone agrees that a regular workout routine and the improved fitness that results from it—along with the improved self-esteem and sense of well-being that comes from being more fit—can lead to lots of benefits that may not show up on the scale.
Same with tweaks to your diet, Hall notes. “If you change your diet from a lot of junk food to things that are more healthy for you over the long term, should you expect a huge change in weight? It might happen, but possibly not,” he says. “Does that mean you should stop eating those healthy foods? No! It probably means that weight regulates very carefully.”
Diet Myths Debunked: Everyone's Weight-Loss Journey is Different
That careful self-regulation, more than anything else, explains why we have so many nutrition and diet myths to begin with. We keep looking for loopholes. For ways to break free from that narrow range of body weights you can achieve and maintain without superhuman effort.
Some people indeed make that break. Their success may help perpetuate one of these diet myths, or it may launch a new one. But you can be sure of one thing: Eventually, it’ll be proven wrong and we all feel a little foolish for believing it.