Why Does Depression Sometimes Cause You to Lose Weight?

More than 16 percent of adults will experience depression in their lifetime, according to the American Psychiatric Association. Depression affects many aspects of everyday life — including appetite, sleep, motivation and energy levels — and in some cases, it can lead to losing weight.

That weight loss can occur even if it feels like you're frequently eating. Here's what you need to know about how depression can affect your weight.

Major depressive disorder is diagnosed based on certain criteria, according to Alexandra Fuss, PhD, a clinical health psychologist specializing in gastrointestinal psychology at Yale New Haven Hospital.

Signs and symptoms of depression include the following, per the National Institute of Mental Health (NIMH):

• Feeling sad, hopeless, irritable, frustrated or generally low
• Losing interest in activities, or not feeling pleasure when doing them
• Fatigue or reduced energy
• Difficulty sleeping
• Changes in appetite or weight loss or gain that wasn't intended
• An inability to think clearly and make decisions
  
• Physical symptoms including headaches, cramps or GI problems
• Thoughts of death or suicide

Duration matters here: There's a difference between a sad day and unrelenting sadness. With depression, people have some of the symptoms "most of the day, nearly every day, for at least two weeks," according to the NIMH.

"You have to meet at least five of these symptoms, but it doesn't have to be all of them. The main piece is that the symptoms are impacting aspects of daily living," Fuss says.

Unintended and unexplained weight loss can occur during periods of depression and anxiety, according to the Cleveland Clinic. But exactly how does depression cause weight loss? Consider these two factors:

When you're depressed, your appetite may change, and you may find yourself less hungry than usual.

"When someone is experiencing depression, some people have less activity in the brain area that give hunger cues," Fuss says. That could lead to skipping meals or snacks, or generally eating less at mealtime. This reduction in calories can lead to weight loss.

"Fatigue and loss of energy can impact eating patterns," Fuss says.

That is, depression-related weight loss can happen as several symptoms manifest at once. For instance, if you're experiencing a lack of motivation and energy, plus fatigue, it might stop you from prepping a meal (or even ordering take out) or eating a snack.

So, while you're experiencing depression, you're still eating — but you may be eating less than usual (perhaps without even realizing it), which could lead to weight loss.

Another common symptom of depression is a change in sleep patterns.

"If you have a lack of energy and feeling down, cozying up with a blanket and taking more naps will make it harder to sleep at night," Fuss says.

Difficulty sleeping at night is one possible change due to depression. But another symptom is sleeping more than usual, which may potentially lead to weight loss. One randomized clinical trial looked at 80 adults with overweight who typically slept under 6.5 hours a night. Participants who increased their sleep by 1.2 hours ate about 270 calories less each day than the control group, per results published in February 2022 in ‌JAMA Internal Medicine‌.

Sleeping too much means less time to eat and consume daily nutrients.

"Some of these things can really cause a domino effect," Fuss says.

To support healthy habits while dealing with depression, Fuss suggests eating a well-rounded diet that includes fruit, vegetables and protein, getting adequate sleep and engaging in social activities keep you connected with friends.

If you take medications to treat depression, there's a chance it could affect your weight.

Most commonly, medications used to treat depression are associated with gaining weight, per the Mayo Clinic. Selective serotonin reuptake inhibitors (SSRIs) are the most popular medication prescribed for depression. They work by increasing levels of serotonin in the brain.

In a September 2019 study in ‌Obesity Reviews,‌ researchers found that antidepressant and antipsychotic medication can cause weight gain. Some of the medications used to treat depression such as Tofranil, Nardil, Paxil and Pexeva are associated with weight gain, per the Mayo Clinic.

But some medications (including some over-the-counter depression meds) can potentially lead to weight loss.

For instance, the SSRI Fluoxetine (Prozac) may cause a decrease in weight in adults with overweight or obesity, per an October 2019 review in the ‌Cochrane Database of Systematic Reviews‌. Another study found that bupropion (which you may know better by the brand name Wellbutrin) is associated with long-term weight loss for people who don't smoke, per results published in April 2016 in the ‌Journal of Clinical Medicine‌.

Bottom line: "Everybody responds to antidepressants differently," Fuss says.