You don’t need us to tell you that losing weight — and keeping it off — is hard. About 80 percent of people who lose weight gain it all back, and sometimes more, within a year, experts say. But understanding why weight loss is so difficult can help you stop beating yourself up over every little setback, and increase your chances of success. Forget the gimmicks, and come to terms with these difficult weight-loss lessons.

Hard Truth No. 1: Your Body Works Against You

It’s not your imagination. When you try to lose weight, you’re not only fighting your cravings, but also your own body. When you lose body fat, you decrease the hormone leptin, which signals your brain that you’re full, and you increase the hormone gherlin, which stimulates hunger, Australian researchers found. The bad news is that this hormone imbalance continues long after dieters succeed at weight loss, making it even harder for them to keep the pounds off. But if you try to cut too many calories for weight loss, your body will go into hibernation mode so that you don’t starve, and your metabolism will slow, Sarah Dolven, MD, an endocrinologist in Charleston, S.C. explains.

It’s also important to realize that once you reach your weight-loss goal and start eating a little more again, the pounds can come back pretty quickly, so it’s smart to increase your calories gradually.

Hard Truth No. 2: There Are No Quick Fixes

Wishing you were 30 pounds lighter in time for your high school reunion next month will not make it so, and there are no magic pills or miracle cures that can make it happen. “When you’re trying to lose weight, it’s hard to be patient,” says Mark Pettus, MD, chief of medicine at St. Peter’s Hospital in Albany, N.Y., who also developed and teaches the Healthy Living program at the Western Massachusetts Kripalu Center for Yoga and Health in Stockbridge. But you have to be patient because quick starvation diets can wreak havoc on your metabolism, damaging your weight-loss efforts for the long term. As you start your diet, remember that slow and steady weight loss is the easiest to maintain, Pettus says, and aim for one to two pounds of fat loss each week.

Hard Truth No. 3: Exercise Can’t Conquer All

Yes, exercise helps you lose weight and keep it off — the National Weight Control Registry reports that people who maintain their weight loss exercise for at least 60 minutes most days — but it’s nearly impossible to lose weight from exercise alone, Pettus says. Just do the math: A 135-pound person biking 60 minutes at 12 miles an hour will burn 369 calories. You can put all that back on with just a post-workout protein bar. To lose a pound of fat, you have to burn 3,500 calories more than you consume, so you can see how hard it is to exercise your way through a poor diet. Instead, you have to watch what you eat and exercise, Pettus says. If there’s any “magic” to dieting, it’s in that combination.

Hard Truth No. 4: Diet Supplements Don’t Work

Those little pills that claim to supercharge your metabolism are tempting, but there’s little evidence that they work. After a review of thousands of dieters, researchers at Beth Israwl Deaconess Medical Center in Boston found that liquid diets, fad diets, and over-the-counter supplement were not linked to weight loss. So what worked? Portion control, regular exercise, and group support. As Dolven says, “nothing replaces a low-calorie diet and exercise for weight loss.”

Hard Truth No. 5: Fad Diets Don’t Work

Grapefruit. Maple syrup. Cabbage. Apple-cider vinegar. Juice. All these “miracle” diets are supposed to help you melt pounds and trigger fat burning. The hard fact: Not only is it hard to lose weight on fad diets, but also they can be so restrictive that they’re almost impossible to follow, and they can damage your metabolism. When it comes to weight loss, Dolven warns that if it seems to be too good to be true, it probably is. Not to belabor the point, she says, “but the key to weight loss is to be diligent about eating quality calories and staying physically active.”

Hard Truth No. 6: One Diet Doesn’t Fit All

Every body is unique, so the diet that works for your friend, your co-worker, your mother, or your sister might not work for you. When looking at how best to lose weight, consider your health and family history, your metabolism, your activity level, your age, your gender, and your likes and dislikes. When you’re dieting, it’s important to allow yourself some foods that you enjoy, Dolven says, or else you’ll feel deprived and be less likely to stick with an overall healthy eating plan. For weight-loss success, tailor your diet to your body and accept that one diet won’t work for everyone.

Hard Truth No. 7: Building Muscle Is Hard Work

Because a pound of muscle burns more calories at rest than a pound of fat, an increased muscle mass is the key to a revved metabolism — plus it helps you look more sleek and svelte. Unfortunately, many dieters skip strength training when in reality, it’s one of the most important components if your weight-loss plan. Schedule it into your routine two to three times a week, along with at least three 30-minute cardio sessions.

Hard Truth No. 8: He Can Eat More Than She Can

It doesn’t seem fair, but men can eat more than women and still lose weight. That’s because men tend to naturally burn more calories than woman, thanks to their larger size, muscle mass, and elevated levels of the hormone testosterone, which promotes muscle growth. Plus, the male body is genetically designed for more muscle and less fat than the female body because men do not have to store the energy required to bear children. Once you come to terms with this fact and start eating less than your male partner or friends, the scale will thank you.

Hard Truth No. 9: It’s Not a Diet, It’s a Lifestyle Change

If you want to lose weight and keep it off, you have to change your behavior not just until you reach your goal weight, but for the months and years to follow. That’s because as soon as you stop your “diet,” you’re likely to gain back the pounds you worked so hard to shed. To be successful at weight loss, you need to make lifestyle changes, healthy food choices at most every meal, and exercise almost every day for a minimum of 30 minutes a session (60 is even better). Getting to your healthy weight and staying there really has to be a way of life for the long haul, Dolven says.