Potential Causes Of Sudden Weight Gain According To Weight Management Experts

If the number on the scale shocks you, does it mean you’ve got a health problem? Here are some potential causes for unexplained weight gain.

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Sudden weight gain. Three words few people want to hear. And yet, there you are. You’ve stepped on the scale, and seemingly out of nowhere, your weight has skyrocketed. If you haven’t eaten a Thanksgiving-sized meal or recently found out you’re pregnant, a sudden weight gain can send you into a tailspin, wondering exactly what the heck is going on with your body. Are you getting sick? Is your thyroid acting up? Is it cancer? Or are you absolutely fine and just need to refocus on your fitness? That depends on how much weight you’ve gained and how fast, says Susan Besser, MD, a primary care physician with Overlea Personal Physicians and a physician certified in treatment of obesity through the American Board of Obesity Medicine. Most of us gain a few pounds every now and then, whether it’s because we’ve been spending a lot more time sitting or we’ve been under the weather. Weight gain isn’t typically a problem unless it’s sudden, Besser says, but even then, a pound or two is considered well within the range of normal. It’s when you’ve gained at least 10 pounds in as little as a week that Besser says she starts to get concerned. She’s quick to point out that it’s not just the weight gain itself but other symptoms that tend to coincide with sudden weight gain, such as obvious swelling of the legs, sudden shortness of breath, or chest pain. “These things all suggest a systemic illness,” Besser explains. “Alternatively, many chronic health problems don’t cause sudden weight gain but slow, steady unexplained gain.” If you’ve had sudden weight gain like the type Besser has described, here’s what the experts say could be going on (and what to do about it).

Causes of Sudden Weight Gain


If you’ve had a change in medicine recently, and your weight has increased suddenly, a call to your pharmacist might be in order. There are a range of drugs that can cause varying degrees of weight gain, says Julie Cantrell, MD, lead physician at OhioHealth Medical Weight Management. Some may cause sudden weight gain, while some may cause the body to pack on weight more slowly, albeit still significantly. One of the worst offenders is prednisone, a steroid used to fight inflammation in patients with everything from asthma to lupus to psoriasis. Known for giving patients a “moon face” because of swelling, prednisone and similar steroids cause both fluid retention and an increased appetite, Cantrell says. Together, these symptoms can cause the numbers on the scale to climb, and for folks who have a chronic disease that requires extended steroid usage, weight management can be a significant challenge. Antidepressants make the list too, in large part because they affect many of the different hunger hormones, Cantrell says. In particular, Paxil is known for its effect on hunger and resulting weight gain. Other drugs that can cause a fluctuation in weight include anticonvulsants, beta blockers, diabetes medications, antipsychotics, and heart medications, although Cantrell notes that typically gains are slow rather than sudden.

Heart and/or Kidney Disease

The medications used to treat heart disease aren’t the only trigger of weight gain. Heart disease itself, along with kidney disease, can also cause a spike when you step on the scale. That’s because congestive heart failure and renal failure both result in “significant water retention,” Besser says. If you don’t have a medication to blame, and you’ve noted sudden weight gain, the risk of heart or kidney disease is a reason to call your doctor ASAP. “Increased weight due to heart or kidney disease could be life threatening,” Besser warns, not because of the weight itself but because of the underlying disease.


When patients show up in Cantrell’s office complaining of weight gain, they often hope it’s a malfunctioning thyroid, she says, “because then we can fix it!” Some 12 percent of Americans will develop a thyroid disorder during their lifetime, according to the American Thyroid Association, but up to 60 percent of Americans with a malfunctioning thyroid never know it. For those who have hypothyroidism, meaning the thyroid gland is not producing enough hormones, weight gain can be a problem, along with fatigue, depression, and forgetfulness. “The thyroid is like the body’s gas pedal, determining how many calories we burn at rest,” explains Jacob Teitelbaum, MD, author of the Beat Sugar Addiction NOW! series. “For most of us, that plays a much larger effect than exercise on weight.” Treatment of hypothyroidism with synthetic hormones will typically help reverse weight gain.

Cushing’s Disease

Although it’s considered a rare condition, Cushing’s disease, or Cushing’s syndrome, can sometimes be the culprit of sudden weight gain. Most common in adults aged anywhere from 20 to 50, Cushing’s is an illness that results in excessive levels of cortisol, an adrenal stress hormone. “This triggers insulin resistance and marked fat deposition,” Teitelbaum explains. That means fat won’t be spread evenly across the body; instead it’s often deposited in spots on the upper body such as around the neck, while legs and arms may remain thin. Treatment for Cushing’s disease is dependent on the cause, as some cases of the condition are familial (meaning it was passed down through your genes), while others can actually be caused by medications such as the steroids described earlier.


It may be a major fear for most of us when we note body changes, but this is one that can typically be written off when it comes to a sudden weight gain, says Avram Abramowitz, MD, a board-certified oncologist and hematologist with Queens Medical Associates. Typically, cancer will cause weight loss rather than weight gain. “The way cancer works is that tumors produce their own chemistry, which interferes with the body’s ability to use the nutrition intake. Whether people eat a lot or a little, well or poorly, is almost irrelevant when cancer takes over the body,” Abramowitz notes. “Their ability to use nutrients is subsumed by the behavior of the cancer.” The only time cancer may cause weight gain, he adds, is at the end stage. Called ascites, this weight gain is actually a filling of the body with fluid, but other symptoms are apparent long before this point.

Pregnancy Complications

Most women gain steady weight while pregnant, and according to Nancy P. Rahnama, MD, a bariatric physician, as long as the weight gain isn’t sudden, it’s normal. “General progression of weight gain will vary, but an average of four pounds a month is considered normal as long as the mother stays within the appropriate range,” Rahnama says. It’s when you see sudden weight gain that you should have a talk with your doctor or midwife.   “Any more weight gain may be suggestive of gestational diabetes, which can be detrimental to the baby and the mother,” Rahnama says. Preeclampsia, HELLP syndrome, and other hypertensive disorders that are singular to pregnancy can also cause sudden weight gain in much the same way that kidney and heart disease can cause a weight spike in a non-pregnant woman. According to the Preeclampsia Foundation, “Damaged blood vessels allow more water to leak into and stay in your body’s tissue and not to pass through the kidneys to be excreted.”

Mental Health Issues

Although typically people suffering from depression or a binge eating disorder see slow weight gain rather than sudden weight gain, as lack of energy and increased appetite cause the body to build fat, stepping on the scale and seeing a big jump can be a sign of a mental health issue. Sometimes, Cantrell says, the weight gain was gradual but seems sudden because “we put our heads in the sand.”

When to Call the Doctor

Whatever may be to blame for sudden weight gain, doctors advise against self-diagnosing in favor of a call to your physician. “Inappropriate weight gain without an obvious cause that is consecutive should be evaluated,” Rahnama stresses. “When this weight gain is associated with other symptoms, such as fatigue, depression, hair loss, change in skin texture, or a lack of menstruation, the evaluation should be done sooner than later.”

Jeanne Sager
Jeanne Sager is a writer and photographer from upstate New York. She has strung words together for The New York Times, The Washington Post, The Atlantic, and more.