In the 1980s, the federal government encouraged Americans to eat fewer foods containing high-calorie saturated fats, like butter and dairy. Magazines featured low-fat recipes. Fat-free snack foods hit grocery stores.
But it didn't go as planned. Instead of losing weight and improving their health, people had higher rates of obesity and type 2 diabetes.
"That's because to make a low-fat cookie taste good, you add more sugar," explains Mayo Clinic dietitian Tara M. Schmidt, M.Ed., RDN, LD.
The fat-free craze is just one example of a diet trend that has changed over time. Here's more on that and 4 more weight-loss rules to reconsider.
Outdated rule No. 1: Eating fat makes you fat
Since fat has 9 calories per gram while carbohydrates and protein each have 4, cutting fat was once seen as a quick way to reduce overall calorie intake.
But weight loss isn't just about counting fat grams. Fat helps you feel full and satisfied with your meal, so you're less likely to eat more.
"If you don't feel satisfied after eating 2 scoops of low-fat ice cream, you might eat the whole pint," Schmidt explains. "But would you have stopped after 2 scoops of the full-fat version? If so, you might have been better off getting the full fat."
Instead of reducing overall fat, try to get more healthy unsaturated fats, like the ones in olive oil, avocados and nuts, Schmidt says. Cut back on saturated fats in meat, cheese and ice cream. Avoid trans fats that are used in fried foods, ultraprocessed baked goods and sticks of margarine.
Outdated rule No. 2: Carbohydrates are the enemy
People often use "carbs" to mean starchy carbohydrates like pasta, bread and potatoes. But carbohydrates are also a macronutrient in fruit, vegetables, whole grains and beans. Carbohydrates give people energy and help protect against disease.
"It's really important to look at the foods that are providing empty calories or excess calories, if you're looking at weight management," Schmidt says. "Many of those foods do contain carbohydrates, like pretzels, chips, crackers, cookies and granola bars."
Instead of writing off all carbohydrates, replace sugary snacks with fruits, vegetables and grains that offer a variety of vitamins and minerals.
Outdated rule No. 3: It's best to eat 5 small meals a day
For some people, eating small meals more frequently helps them get the calories they need. For others, eating 5 meals a day would increase their total calorie intake.
"I don't think we'll ever have a perfect recommendation because it really would need to be individualized to that person," Schmidt says.
Whether a person eats 5 meals that are about 300 calories each or 3 meals that are 500 calories each, they're still getting about 1,500 calories. But if people eat their main meals and snack in between, they may be eating more than they intended to.
"We do know that, generally speaking, the more often someone eats, the more calories they tend to consume in a 24-hour period," Schmidt says.
If you're noticing unexpected weight gain, it might be worth tracking how much and how often you're eating. Snacks can help you get to your next meal, but make sure to drink water and include foods with protein or fiber to help fill you up.
Outdated rule No. 4: The serving size is how much you're supposed to eat
The serving size listed on the Nutrition Facts label is a standard size. The amount you eat is your portion size. You might have more or less than the serving size, depending on your body size, how hungry you are and what else you're eating.
"I think it's important to assess your hunger level to decide if a serving is going to satisfy you or not," Schmidt says.
If you eat more than the serving size, though, remember that you're also getting more calories than the label indicates.
Outdated rule No. 5: Healthy foods taste bad
You might think that eating healthy means eating a raw celery-only diet. But plenty of foods can make up a healthy diet. They also can be cooked and seasoned.
Healthy eating can take time. With some basic cooking skills, you can learn to experiment and see what you like. If you don't like the taste of quinoa, for example, try brown rice. If you don't like steamed broccoli, try roasting it.
But be patient, especially if you're used to eating mainly packaged or restaurant meals. They're designed to be delicious, so they're often high in sugar, salt and fat.
"Those foods taste good to us," Schmidt says. "If you're going to start limiting these foods, it's going to take time for your taste buds to adjust."