17 Surprising Reasons Why You’re Gaining Weight

If your jeans fit just a couple of months ago, and you haven’t done anything differently, you’re probably wondering, “why am I gaining weight?”

You’re not alone. Many people who eat healthy foods, stay loyal to their workout routine, and drink plenty of water may all experience sudden weight gain. It may seem like there’s no good reason, but experts tell us there are some common reasons why you’re suddenly gaining weight fast.

While your exercise and diet efforts are still important for you to achieve your weight loss goals, there are a number of factors that can cause you to gain weight that often go unnoticed.

We uncovered some of the top reasons why you’re gaining weight and asked experts how to overcome each, so you can get back to your ideal weight.

1. You don’t weigh yourself.

Of all the little white lies, the expression “what you don’t know can’t hurt you” is one of the worst, regarding weight loss. However, when we’re talking about weight gain, ignorance could be the very reason behind your ever-tightening waistband. “When you avoid the scale because you don’t want to know the number, that’s when you get into trouble,” says Christine M. Palumbo, MBA, RDN, FAND, an award-winning Chicago-area registered dietitian and nutrition expert. Rather than hinder your progress, stepping on the scale actually helps you lose weight. According to a study published in the journal Obesity, frequent self-weighing is associated with greater weight loss, less weight regain, and better weight gain prevention.

2. You stay up late and don’t get good sleep.

You eat right and exercise but, sadly, nearly all of your efforts are negated if you’re staying up all night binge-watching Netflix. A study in the Current Opinion in Clinical Nutrition and Metabolic Care journal states that shorter amounts of sleep are associated with higher BMI levels and larger waistlines. The primary reason? “Lack of sleep can lead to increased levels of the hunger hormone ghrelin, and decreased levels of leptin, the satiety hormone,” says Alissa Rumsey, MS, RD, CDN, CSCS, a Nutrition Therapist and Certified Intuitive Eating Counselor. “Research also shows that when we’re sleep-deprived, our brains respond more strongly to junk food and have less of an ability to practice portion control.”

3. Your job is stressful.

We don’t mean to suggest that you blame others, but your demanding boss may be why you’re gaining weight for no reason. “Our body releases the hormone cortisol when our body is under stress. This causes triglycerides to be relocated to visceral fat cells, increasing storage of belly fat,” explains Rumsey. “Elevated cortisol levels also cause an increase in blood glucose, while suppressing the effects of insulin, leading to constant feelings of hunger and can lead to overeating. To make matters worse, all of that unused blood glucose is eventually stored as body fat.”

4. You aren’t eating enough protein.

Are you suffering from a protein deficiency? Consuming enough protein is important for two reasons: Since it digests more slowly than refined carbohydrates, it’s satiating and staves off overeating. It also helps maintain lean muscle mass. “If you aren’t consuming enough protein to keep your muscles and cells healthy, the body ends up breaking down muscle to access the nutrients it needs—and this spells trouble. Less muscle mass means a slower metabolism, which over time, can cause weight gain,” explains Rumsey.

5. You never indulge.

“Why am I gaining weight if I’m sticking to my diet religiously?” you may ask. And we have the answer: you’re taking it a little too seriously. You don’t have to restrict yourself completely when you’re trying to lose weight—live a little! It’ll actually help you to reverse recent weight gain. Having a cheat day (or even cheat days) while dieting may actually help aid weight loss, according to an International Journal of Obesity study. Australian researchers found that when participants alternated between adhering to a strict diet for two weeks and following it with two cheat weeks lost more weight during the study than those who stuck to a strict diet the entire time. Bonus: The “cheater” group also gained back less weight after the study finished.

6. You’re working out too much.

If you’re working out but gaining weight, the problem may lie in the amount of time you’re spending exercising. There’s no denying that working out is an important weight loss factor, but oddly enough, thinking about your upcoming sweat sessions too often can make it more difficult to lose weight. An Obesity Reviews meta-analysis indicates that people tend to overestimate how many calories they burn when they work out—and will end up eating more on days they work out. A separate study supported this finding, showing that people tend to increase their food intake after exercise and end up eating more calories than they burn.

7. You suffered from an injury.

“Musculoskeletal conditions that cause pain can lead to a decrease in physical activity, which can cause weight gain over time—especially if you are eating the same amount that you were eating when you were more active,” says Rumsey.

8. You’re overeating healthy foods.

Portion size is just as important as eating healthy. The reason: Many nutritious foods—like avocados, oatmeal, quinoa, dark chocolate, nuts, and nut butters—can lead to weight gain when eaten in excess because they’re calorically dense.

9. You’re simply getting older.

With each passing birthday after the big 3-0, we start to lose muscle mass. As a result, Biggest Loser dietitian Cheryl Forberg, RD, tells us our metabolism naturally slows. That has got to be the worst birthday present of all time! “When our metabolism slows down, we will gain weight, especially if we continue to eat the same amount of food as we did when we were younger.”

10. You’re dehydrated.

A University of Birmingham study found that drinking two cups of water before each meal could significantly accelerate weight loss. So it should come as no surprise that not drinking enough H2O can have the opposite effect on your waistline. “Not only does water give us energy and help maintain body temperature, but it also helps us feel more full,” says Forberg. “Not drinking enough water can cause us to eat excess calories that could lead to weight gain. Plus, when you’re dehydrated, the body will conserve water for vital body functions, which can result in water retention and a higher number on the scale.”

11. You’re relying too much on exercise without changing your diet.

From building muscle mass to improving cardiovascular health, there are tons of obvious reasons to hit the gym. That said, exercise alone is unlikely to undo your ice cream, booze, and burger habit, says Rumsey. Plus, the type of exercise you do may also be making it hard to keep the pounds off. “Steady-state cardio, such as running at the same pace for three or four miles, can increase appetite,” warns Rumsey. “Many people who do these types of workouts end up eating more than they would have if they hadn’t worked out.”

12. You aren’t paying attention to your sodium intake.

A high-sodium diet can make you retain water and boat. And when you retain water in your gut, it can make it seem like you’ve experienced a sudden weight gain in your stomach—when it’s just water weight. As Palumbo says, “sodium-related weight gain is easy come, easy go.”

13. You kept all the junk food in your house.

“Whether it’s ice cream, cookies, chips or other items, just knowing that your trigger foods are in the kitchen or your office desk can derail your healthy eating program,” says Palumbo. “This is especially true between 3 p.m. and bedtime when cravings tend the be the most difficult to ignore.”

14. Your thyroid is to blame.

The thyroid, a gland in the neck that sits above the Adam’s apple, regulates a wide range of bodily functions including metabolism. But sometimes, for a variety of reasons, your thyroid may become under-active and result in a condition called hypothyroidism. One of the many symptoms of the condition? You guessed it, weight gain. The worst part is that the condition often develops slowly, so many people don’t notice the symptoms of the disease until they’re full-blown, says The National Institute of Diabetes and Digestive and Kidney Diseases. It gets worse: If a thyroid issue is to blame for your weight gain, it doesn’t matter how diligently your dieting and working out; it will be near impossible to shed the pounds.

15. You’re depressed.

“As many as 25 percent of people taking certain antidepressants report gaining ten pounds or more [after starting the medication],” says Rumsey.

“Some medications may cause food cravings, especially for carbohydrates, and some find that their medication increases their appetite. The drugs may affect metabolism negatively as well.” And since depression is often accompanied by a disinterest in food, another pool of thought is that once antidepressants become effective, people regain their appetites and overeat.

16. You’re taking medication.

From beta-blockers to birth control pills, and everything in between, there’s a long, long list of medications that can cause your waistline to bulge. And if you think your Rx is to blame for your ever-expanding waistline, you’re not alone. “Weight issues are often a primary reason for non-compliance with treatment,” Palumbo tells us. “Some drugs stimulate the appetite or slow the body’s metabolism. Others cause fluid retention or enough drowsiness to reduce physical activity, which can trigger weight gain.”

17. You eat too healthy.

“When my clients feel like they aren’t able to enjoy something indulgent from time to time, it often leaves them with hard-to-ignore cravings,” says registered dietitian Leah Kaufman, MS, RD, CDE.