The six most common reasons men gain weight

If you have recently lost or lost a few pounds, do not panic: small fluctuations in weight are common and rarely worry. But if you've already taken 5 or more pounds in a few weeks or even days, it's time to become aware of it. "For a guy, five pounds, it's a bit – scathing – something is happening here," says Lawrence Cheskin, MD, director of the Johns Hopkins Weight Management Center.

Cheskin explains that five-pound weight fluctuations are more common among women, but not as much among men. Especially if your weight is stable for months or years, a sudden weight gain is remarkable, he adds. What could be the cause? Here are the six most common explanations.

You eat too much salt

Sodium intake causes your body to retain water, says Cheskin. Water has weight and volume. So, if you eat a lot of salty food for several days in a row, you can quickly gain weight, he says.

Restaurant food – and especially fast food – tends to be loaded with sodium. If you've had a long weekend away from home and filled your days with take-out and restaurant meals, this could be the reason for your sudden influx of books.

You are taking a new medicine

"Many medications can lead to weight gain," says W. Scott Butsch, MD, director of obesity medicine at the Bariatric and Metabolic Institute of Cleveland Clinic. In fact, medications can cause up to 15% of cases of obesity, he says.

Drugs against depression (including SSRIs) and drugs for heart disease (beta-blockers) are two of the main culprits, says Butsch. But prescription sleeping pills, pain killers and even some antihistamines blocking allergies can cause "weight gain," he says.

Add steroids and drugs or testosterone stimulating supplements to this list, says Cheskin. These drugs work on your hormones, which could certainly lead to weight gain. This includes over-the-counter or Internet supplements, he adds.

You eat (or drink) more

This one may seem obvious. But if you have consumed more calories than before, this change could increase your weight by 5 to 10 pounds over a period of a month or more, says Cheskin.

"Alcohol is also a consideration," he adds. "It contains calories just like food." Especially if you make a change that will add regular calories to your weekly intake, you can gain weight, he says.

It is important to recognize that these changes can be subtle. Perhaps you have started attending a weekly happy hour. Or maybe you bought new dishes and your portions went up without you knowing it. "If you only eat 500 extra calories a week, it can build up over time," he says.

You are moving less

Even small changes in your physical activity habits can lead to weight gain, says Cheskin. "Maybe you were walking a lot for work, and now you're driving," he suggests.

If you had the habit of lifting weights and you stopped, this could also explain your weight gain, even if you have replaced this strength training with another form of exercise. Cheskin says that muscle mass (and the strength training that builds it) tend to keep your metabolism high, which helps you burn calories.

Give up on your usual gym routine – or change it to lose muscle – and slowing down your metabolism may cause you to gain weight, he says.

You recently lost weight

It would be really good if the lost weight was lost. But the opposite is true.

"Our weight and body fat are tightly regulated, and [our system] will act to maintain balance, "says Butsch. In other words, the pounds you manage to lose are likely to come back – even if you maintain your weight loss routines, he adds.

So, if you have recently lost weight, it is very likely that you will take back some of it, no matter how much you eat or do exercise.

You have an endocrine disorder

According to a National Institute of Health, about one in five adults has an underactive thyroid, also called hypothyroidism. Although this condition is much more common in women, Cheskin says that many men suffer from hypothyroidism, which can lead to sudden and significant weight gain.

Although less typical, some other hormonal disorders, including Cushing's disease, can also lead to weight gain, says Butsch. If you have any of these endocrine disorders, weight gain will probably not be your only symptom, he adds. Fatigue, weakness, headaches, thought problems, depression and irritability are all signs of these hormonal disorders, according to the Mayo Clinic.