What Causes Unexplained Weight Gain?

Other conditions, like arthritis, can make exercise more difficult, while vitamin deficiencies — such as insufficient B12, which might lead someone to eat more and indiscriminately (including unhealthy foods) in response to hunger cues — can lead to weight gain, says Sukhpreet Singh, M.D., regional medical director for weight management and obesity medicine at Henry Ford Health in Detroit. (As with depression, nutritional deficiencies cut both ways: Some people gain pounds, while others lose weight.) 

Genetics, heredity, and weight gain: Predisposed but not predestined

Behavior, environment and genetics all play a role in whether a person becomes overweight or obese. As for the obesity epidemic in the U.S., which has only gotten worse in recent decades, “we’re pretty sure it’s due to the environment, because genes don’t change that quickly,” Apovian says. Much of the change is a result of decreased activity and access to all those calorie-dense foods, Kidambi adds.

This is where what’s called epigenetics comes into play. Put another way, our environment and the choices we make (as well as what our parents do when we’re younger) can modify the way our genes are expressed. For example, what a person eats can even alter the bacteria in their gut, and that, in turn, can lead to genetic changes that are linked to obesity.

That said, having a family history of obesity doesn’t mean you’re predestined to be overweight or obese. But you should probably be more vigilant about making lifestyle changes that help you lose pounds and maintain a healthy weight. 

Diet and weight gain: Understanding the why

Getty Images

You probably know that you should be getting the majority of your calories from nutrient-rich plant-based foods, such as dark leafy greens, nuts, beans and berries. But you may still have a proportion problem, with highly processed carbs tending to take over your plate.

In addition to capping total calories, re-proportioning your plate can help with losing pounds and maintaining a healthy weight. Half the food on your plate should be nonstarchy vegetables (think of salad as the entrée); one quarter should be lean protein, like skinless chicken or fish (or beans if you prefer a nonanimal protein); and one quarter carbs, like whole wheat pasta or brown rice.

The MyPlate guide from the U.S. Department of Agriculture can be helpful in determining “customized” portions. But maybe you already have a firm handle on all this, and your eating still doesn’t square with dietary advice. In that case, you need to dig into why you’re eating the way you are — or, for that matter, not getting enough exercise, Singh suggests.

Ask yourself, “Is it an internal barrier, or is it a time barrier? Is it financial? Is it physical limitations?” says Singh. Working an overnight shift, being tired or stressed, or facing other challenges can greatly influence eating. So think more deeply about what’s behind how — not just what — you eat to make more sustainable changes. 

Lifestyle and activity: A sedentary life can lead to weight gain

More than one-fourth, or 27.5 percent, of adults 50 and older are inactive, reporting they engaged in no physical activity outside of work in the past month, according to the Centers for Disease Control and Prevention. Compare that with the standing recommendation to get at least 150 minutes per week of moderate-intensity exercise, such as brisk walking, and it’s clear why this is a huge factor in America’s obesity epidemic. Singh again suggests his patients dig deeper to understand why they’re not able or willing to be active.

Making dietary adjustments can help here, too. For example, we need more protein as we get older, Apovian points out. And eating more lean protein can support strength training, which you should be doing at least two to three times per week, to build or preserve healthy muscle mass.

It takes more energy to build and maintain muscle than fat, which is why people with more muscle mass can have faster metabolisms and burn more calories. By contrast, when you lose muscle, your body needs fewer calories. Losing weight by following a diet that leads to a loss of muscle mass contributes to yo-yo dieting, Singh notes. You might easily regain the weight once you go off the plan, even if you eat the same number of calories.

Sleep and insomnia: Up at night, gaining weight during the day

Getty Images

You’re tired, and naturally you have little energy for activity, and you eat more caloric foods, which keep you awake.

The lack of sleep causes the hunger hormones to increase and the satiety hormones to decrease, Apovian notes. A poor night’s sleep causes the hormone cortisol to increase, which decreases metabolism and builds up fat stores, Singh adds.

It’s a cycle. Being overweight or obese can, in turn, increase one’s risk for health problems that rob you of more rest, like sleep apnea, in which a person’s breathing is interrupted many times each night. If you’re struggling to sleep, a comprehensive assessment, including a sleep study, might be warranted. Prescribed a sleeping pill? Make sure to ask your doctor whether it could increase your appetite. If the answer is yes, ask about alternative medications that don’t. 

Medications: Another possible cause of weight gain

Getty Images

Older adults tend to take more medications, and some can contribute to weight gain. This happens in a variety of ways, from increasing appetite to causing fatigue that makes it harder to be active.

The wide-ranging list of medications that may cause or contribute to weight gain includes:

• Insulin, used to treat diabetes
• Antidepressants
• Beta-blockers, such as those taken to control blood pressure
• Sleeping pills
• Steroids

The good news is that there are often other drugs that could be used to treat any given issue but don’t cause the same side effects. To explore your options, ask your doctor about “weight-neutral” medications for the condition you’re treating, Kidambi recommends.

As with ferreting out any unexplained cause that’s moving the needle on your scale, the key is to understand the big picture. That way you can start nudging the needle in the opposite direction and improve your overall health in the process.