9 Things You Should Never Do When Starting a Diet

By Christa Sgobba |

Avoid these common pitfalls and you’ll build—and maintain—the body you want.

diet mistakes

Maybe your doctor recommended losing some weight, or maybe your pants are suddenly tight. Whatever the reason, you've decided to make a change. Excellent choice.

“It’s never too late to start eating healthy,” says Christine Rosenbloom, Ph.D., R.D.N., author of Food and Fitness After 50. Revamping what goes on your plate not only helps you lose extra pounds, but it may also improve other important health markers, like cholesterol and blood sugar levels.

A diet sounds great in theory, but small mistakes can prevent you from seeing the results you want. And when the results don't come, the diet ends-and old habits reappear.

The good news: You can learn from other people's mistakes. Here are nine things you should never do when starting a diet.

Diet Mistake #1: You Set a Start Date

Whether it's next Monday or January 1, don't wait until any specific time to begin eating healthier. By scheduling your diet for the future, you risk getting into trouble before then.

"You go out to dinner on Friday and eat more than you want, and you just say, 'Oh, I might as well eat crummy the rest of the weekend. I've blown it so I'll just wait until Monday,'" Rosenbloom says.

This is a problem because it’s harder to lose weight than it is to keep it off in the first place, especially as you get older, Rosenbloom says.

Diet Mistake #2: You Throw Out All Treats

While you probably don't need three cartons of ice cream and five kinds of cookies in your cupboard, getting too strict with your pre-diet cleanout can backfire. "Not allowing for treats can make you feel deprived, which can cause you to go off the rails and overindulge when you finally get the food in front of you," Rosenbloom says.

A better strategy: Keep your favorite treat on hand, but portion out accurate serving sizes, she advises. That means a half-cup of ice cream, not an entire cereal bowl of it. Allowing yourself an occasional treat can help your healthy eating plan feel more sustainable.

Diet Mistake #3: You Load Up on Diet Foods

Foods marketed as diet-friendly, such as low-cal, protein-packed ice cream or low-fat cookies, can actually be gut bombs.

“If people see things like a low-sugar cookie or a low-fat cookie, they think they can eat more of it,” says Keri Gans, R.D.N., author of The Small Change Diet. In fact, people ate 28 percent more M&M’s when they were labeled as “low-fat” than when they were labeled regular, according to research from Cornell University.

Even if that cookie or scoop of ice cream has fewer calories than its regular counterpart, you negate any benefit by serving yourself more. And that can set you up for weight gain.

You’re better off enjoying a small portion of the real thing (see mistake #2).

Diet Mistake #4: You Exclude an Entire Food Group

Exclusionary diets-such as no dairy or no carbs-promise a quick fix, but they're rarely effective for lasting weight loss. "They're really hard to keep up and maintain," Rosenbloom says.

No matter the diet, they generally result in weight loss the same way-by reducing the number of calories you consume, she says. You may think you're losing weight faster on a low-carb diet, but that's just water weight.

"When you cut out carbs, you're reducing the glycogen stores in your muscles, which hold onto water. So you see this really quick weight loss," Rosenbloom explains. "But as soon as you start eating carbs again, you start storing that water, and the weight comes back."

Exclusionary diets can also take a toll on your health as you get older, Gans says. If you omit carbs, you're missing out on the heart-healthy benefits of whole grains, as well as the hit of fiber that can help keep constipation at bay. Eliminate dairy, and you may find yourself lacking bone-building calcium and vitamin D, which can put you at risk of fractures, she says.

The key takeaway: A truly sustainable diet won’t require you to eliminate any one food group.

If you are concerned you have a food allergy or find that a particular food is causing digestive distress, check in with your doctor. He or she will want to understand what’s causing any problems and make sure you’re not missing out on key nutrients.

Diet Mistake #5: You Take an All-or-Nothing Approach

Sustainable weight loss is a slow and steady process, so cleaning up your diet should be too.

"If you try to do too much at once, you most likely will get discouraged," Gans says. "And if you get discouraged, you aren't going to stay on it."

Instead, break up your day meal by meal, and tackle it in parts, she recommends. "Maybe you start with your breakfast and make it healthier, then you move on to lunch, then to dinner," Gans says. Baby steps can ease you into healthy eating so it eventually becomes a habit.

Another option: Think of your healthy eating plan as 80-20, meaning 80 percent healthy eating and 20 percent of the fun stuff. "That leaves room for that slice of pizza, those French fries, that piece of cake," Gans says. "You shouldn't have to feel like it's off-limits."

That said, you should plan for it in advance. For example, if you know you’re going to have a sugary slice of cake later, it might mean having a clean meal of lean protein and vegetables for dinner, and skipping the bread and other carbs, Gans suggests.

Diet Mistake #6: You Keep Your Plan a Secret

Keeping your eating intentions to yourself might end up working against you. After all, if your friends or family don't know you're watching what you eat, they could unknowingly be pushing you into temptation-say, encouraging you to take seconds at dinner or offering forkfuls of their decadent dessert.

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Enlist a healthy eating buddy. "I think that's a really critical thing," Rosenbloom says. "It can keep you accountable."

Just like having an exercise buddy waiting for you at the gym can motivate you to show up, having a dieting partner can help too. Plus, it provides some friendly competition, which can help keep you on target.

Diet Mistake #7: You Give Exercise Way Too Much Credit

No amount of exercise can make up for a poor diet. "People think that exercise by itself will help them lose weight," Rosenbloom says. "For weight loss, it's much more important to watch what you're taking in."

That said, exercise helps you stay on track with your weight goals. And as you get older, strength training is especially important, Rosenbloom says. That's because muscle mass naturally declines with age, and "muscle is a calorie-burning machine," she says.

Check out our beginners’s guide to strength training.

Diet Mistake #8: You Tie Success to the Number on the Scale

Instead of focusing only on your weight, let your health numbers guide you, Rosenbloom says. For instance, if your doctor tells you that your blood pressure or cholesterol is high, challenge yourself to follow a healthy eating plan to nudge those numbers down before your next appointment.

“If you start focusing on health goals, the weight follows,” Rosenbloom says.

Diet Mistake #9: You Tell Yourself That You’re “On” a Diet

When you say you’re on a diet, that implies it’s something you’ll go off of, something that will eventually have an end date, Gans says.

"Consider 'diet' as a style of eating, and that you're changing your style of eating to be healthier," she says. "That's a better approach. It's not something you start and then end-it's something you continue."

If you start changing your habits one step at a time, it'll start to become a way of life, not something you have to power through until it's over. "The goal is to never have to start again," Gans says, "because you never end it."

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