Potential Underlying Causes of Weight Gain

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Most people who aren't overweight think that the root cause of overweight and obesity is deceptively simple. If you take in more calories than you use, you'll gain weight. And if you eat less, you lose weight. But in reality, there are several underlying weight gain causes that can contribute to your weight beyond just calories consumed and calories burned.

Normal Weight Gain in Daily Life

Some weight gain is a normal part of life, particularly for women. Weight gain occurs with pregnancy, and many breastfeeding mothers maintain a certain amount of weight while nursing. In addition, most women experience a periodic weight gain each month before and during menstruation.

The food you eat can also cause weight gain that has nothing to do with fat gain. A meal that is high in sodium or high in carbohydrates may lead to fluid retention and a temporary increase in weight.

Much of this weight gain is referred to as water weight and you can gain or lose water weight quickly. Typically, you can expect a weight fluctuation of one to five pounds throughout the day (because of water weight or other factors). These daily weight fluctuations are typical. So many people get used to rising and falling numbers on the scale. In addition, there is some research showing that weight often rises over the weekend and decreases during the workweek.

But rapid weight gain that can't be attributed to these normal causes may be a sign of dangerous fluid retention, and anyone experiencing it should notify their doctor.

Weight Gain Due to Aging

Aging also contributes to natural weight gain in many adults. While it's unclear whether or not aging actually causes weight gain, it is clear that most of us gain at least a small amount of weight as we get older—starting at about age 30.

As we age, our body composition changes, we often lose muscle mass, metabolism slows, and our lifestyles change. Our hormones also change as we get older. Each of these factors can contribute to weight gain unless we reduce the amount of food we eat and get enough exercise to maintain our weight.

Other Possible Causes of Weight Gain 

You may also gain weight because of other reasons that are not a part of everyone's daily life. These are some underlying weight gain causes to consider if you start to add pounds or inches.

  • Significant alcohol use. Booze calories add up quickly. And when we drink we often indulge in empty calories that can contribute to weight gain.
  • The use of certain drugs such as corticosteroids, cyproheptadine, lithium, tranquilizers, phenothiazines, some antidepressants, and medicines that increase fluid retention and cause edema. If you've started a new prescription and notice weight gain, talk to your doctor or pharmacist to make sure that the weight change is normal.
  • Emotional factors, such as guilt and anxiety can contribute to changes in your weight. Some people lose weight during a divorce, job change or other difficult transitions but other people gain weight during times of stress
  • Quitting smoking often leads to weight gain in some people. Why? It may be that smoking was the way that you managed anxiety or nerves. Without cigarettes, some people turn to food.

Medical Causes of Weight Gain

If you notice that you're putting on weight and there is no apparent lifestyle cause, it is possible that something more serious is at play. Weight gain can be a symptom or the result of certain medical conditions. These can include:

  • Certain endocrine diseases, such as Cushing syndrome and hypothyroidism
  • Heart disorders
  • Lung disorders
  • Polycystic ovary syndrome (PCOS)
  • Depression

It's important to talk to your doctor today if you have unexplained weight gain and any of the following symptoms:

  • Constipation
  • Hair loss
  • Sensitivity to cold
  • Swollen feet and shortness of breath
  • Uncontrollable hunger accompanied by palpitations, tremor, and sweating
  • Vision changes

A Word from Verywell

If you suspect that there is a medical issue that is causing your weight gain (or weight loss), don't be afraid to speak to your health care provider. The good news is that in most cases, weight gain can be managed with consistent lifestyle and dietary changes and an increase in physical activity. Your physician can help you determine whether or not these underlying causes may be leading to weight gain in your own personal situation. He or she may also be able to refer you to experts, including a registered dietitian, physical therapist, or behavioral health expert, for additional help. 

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  2. Wilkinson DJ, Piasecki M, Atherton PJ. The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans. Ageing Res Rev. 2018;47:123-132. doi:10.1016/j.arr.2018.07.005