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17 Surprising Reasons Why You're Gaining Weight

If your skinny jeans fit a couple of months ago—and you haven't done anything differently—what gives?
scale measuring tape

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. And while you're making these healthy changes, be sure to try out any of these 21 Best Healthy Cooking Hacks of All Time.


You don't weigh yourself.

stepping on scale

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.

The solution: Weigh yourself at least once a week—if not two or three—to monitor your progress. "I recommend weighing in on Monday, Wednesday, and Friday," says Palumbo. "If Monday is a bit higher than usual, all the better for getting back on track for the upcoming week. And Friday is good because if you're a bit on the high side then, well, it's all the more incentive to stay-the-course for the weekend and not go too crazy."


You stay up late and don't get good sleep.

Tired woman lying in bed can't sleep late at night with insomnia

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."

The solution: Rumsey assures us that after a week or two of adequate sleep—which she defines as seven to eight hours per evening—the surge of hunger and cravings should subside.


Your job is stressful.

frustrated and stressed businessman sitting at the office front a computer and holding head

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."

The solution: Discuss your workload with your manager. Alternatively, come into the office early when no one is around to bug you. You can also try some techniques to relax and de-stress like meditation and yoga.


You aren't eating enough protein.

The girl in the cafe, eats Caesar salad

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.

The solution: To keep your metabolism going strong, stock your kitchen with lean proteins such as chicken breast, turkey, and organic tofu. Depending on your gender and goals, this is how much protein you need per day for weight loss.


You never indulge.

Woman craving junk food while on a diet

"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.

The solution: To get back to a trimmer version of you, eat the real thing, but downsize your portion. If you love ice cream, for example, skip the fro-yo and have a small scoop of premium.


You're working out too much.

marathon. Tired female runner and man resting and breathing

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.

The solution: To prevent sudden weight gain, avoid excessive noshing after exercising. Pick up pre-portioned pre-workout snacks tailored to your fitness routine.


You suffered from an injury.

Man massaging painful knee, suffering from pain, 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.

The solution: People don't often want to exercise when their joints are hurting, but exercise can ease some arthritis symptoms. "Low impact activities like walking or riding a stationary bike are easier on joints, as is swimming and water aerobics," she says. "Working in some strength training exercises with light weights or therapeutic bands can help to improve joint stability and also help counteract weight gain."


You're overeating healthy foods.

Keto meal avocado egg boats with bacon

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.

The solution: Unless it's a fruit or a vegetable, don't make the assumption that the healthy food you're eating is low in calories. Next time you're whipping up a meal, remember these three portion control cues:

  1. A helping of nut butter or shredded cheese should be no larger than a ping-pong ball
  2. A true serving of rice and pasta is about the size of your fist
  3. Lean meats should be about the size of a deck of cards.

Sticking to the recommended serving size can help prevent sudden weight gain.


You're simply getting older.

Older woman in kitchen

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."

The solution: To keep your lean, youthful figure, Forberg says staying active is a must: "A combination of cardio and weight-bearing exercise will help preserve lean body mass and muscle tissue, keeping the metabolism elevated."


You're dehydrated.

with closed eyes drinking clean mineral water close up, young woman holding glass

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."

The solution: Sip water continuously throughout the day. And remember that water alone isn't the only way to stay hydrated, there are many water-rich foods you can eat along with other water-rich drinks like coffee, tea, and smoothies.


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

Woman reaching for junk sweet donut instead over fruits and vegetables

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."

The solution: Lay off the junk and switch up your workout. "More and more research is showing that high-intensity interval training type exercise is best to see improvements in muscle mass and cardiovascular function, without the associated increase in appetite," says Rumsey.


You aren't paying attention to your sodium intake.

salt food

A high-sodium diet can make you retain water and bloat. 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."

The solution: Up your water intake and cut back on the sodium. Cooking more at home with fresh herbs instead of salt should help your belly deflate in a day or so. Dining out? Scan nutrition info at home before you head out and pick a healthy restaurant dish with about 1,000 milligrams of sodium or less.


You kept all the junk food in your house.

Woman grabbing cookie from jar

"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."

The solution: One of the best ways to overcome a passing craving is to keep the foods you know you can't deny out of the house. Can't imagine kicking your favorite cookies out of the house for good? Individually portion off the foods you tend to overeat. If you know each Ziploc bag of chips is 150 calories, you'll be less likely to go back for a second serving.


Your thyroid is to blame.

doctor examines with her fingers, palpates her neck and lymph nodes

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.

The solution: Take a trip to the MD. "If you've suddenly put on weight for no apparent reason, I suggest you see a doctor so a medical professional can decide whether it is a thyroid issue or another cause," Forberg.


You're depressed.

Depressed woman

"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.

The solution: "Switching medications can often help since certain types are more apt to cause weight gain than others. However, if you change medications, it may not aid your depression as effectively. It can be a lot of trial and error," adds Rumsey. Consult your doctor before going on or off any medication.


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."

The solution: This is important, so listen up: "If you suspect your drug is causing weight gain, never stop taking it. Instead, make an appointment with your healthcare provider and ask if there might be an equally effective alternative that doesn't affect your weight. Everyone reacts to medications differently, so trying something else may help," says Palumbo.


You eat too healthy.

woman pouring water in kitchen sink over lettuce

"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.

The solution: "For this reason, I allow my patients to eat 100 discretionary calories each day. It allows them to satisfy their cravings without falling off track." Nine Peanut M&Ms, 12 gummy bears, and a single Reese's Peanut Butter Cup all come in right around 100 calories.