CPAP machines treat various conditions that affect your breathing while asleep. Some people might notice weight gain after using them. A smaller number might experience weight loss.

Disorders like sleep apnea can affect how you breathe during sleep, causing disruptions in your airflow that lead to low quality sleep, daytime fatigue, and cardiovascular complications.

Continuous positive airway pressure (CPAP) machines deliver a gentle, pressurized airflow through a mask to keep your airways open while sleeping. Many people notice immediate symptom improvement with this therapy.

As beneficial as CPAP is for sleep-breathing disorders, it may unexpectedly affect your weight. CPAP weight loss is less common than weight gain, but both are possible.

The link between CPAP and weight loss began as a theory. Experts believed that because CPAP machines improve oxygen flow and reduce daytime sleepiness, people using them would have the opportunity to be more active during the day.

When you feel more energized, you might be inclined to do more or start a regular fitness routine.

Increased activity is only one part of the CPAP and weight loss equation. Experts believed CPAP machine use could cause weight loss through improved appetite control.

In 2019, research suggested poor sleep contributes to hunger and cravings. In other words, the lower your quality of sleep, the more likely you might be to indulge in more food more often.

The theory seemed sound. Better sleep could equal increased activity and better appetite control, two critical aspects of losing weight.

The research proving those assumptions is less than clear, however. Several small studies have looked at the outcomes of CPAP use in weight loss and found conflicting results or have used very small participant groups.

In 2013, the first large-scale prospective, randomized, double-blind sham-controlled clinical trial revealed weight gain from CPAP is more likely than weight loss.

The 2013 study is often cited as a landmark in the debate about CPAP machines and weight changes. It found you were more likely to gain weight if you used a CPAP machine and that weight gain increased when CPAP use increased.

Since that time, other large-scale research has produced similar results. A meta-analysis of more than 3,000 people in 2015 confirmed a link between CPAP and increased body mass index and weight gain.

How could CPAP machines contribute to weight gain?

According to a 2016 systemic review, CPAP use doesn’t necessarily result in increased activity. Even if you feel less tired during the day, that doesn’t always mean you do more. You may feel an increase in alertness at work, for example, but your routine may stay the same.

The review also indicated CPAP use may decrease your resting and sleeping metabolic rate. Because it takes your body out of a state of active stress at night, CPAP may inadvertently decrease your resting/sleeping energy expenditure.

The controversy between CPAP weight loss and CPAP weight gain continues.

In 2019, for example, a small study of 119 people found more than half of participants experienced weight loss very shortly after starting CPAP and only 6% experienced weight gain.

On the other hand, a 2021 meta-analysis on sleep apnea found CPAP treatment resulted in significant weight gain. Like the 2013 clinical trial, it found longer CPAP usage was linked to a higher weight increase.

Overall, the majority of large-scale, high quality research indicates CPAP use is more likely to cause weight gain, but that doesn’t mean you can’t lose weight during CPAP treatment.

If you feel more alert and energized after CPAP therapy, it can be a great opportunity to increase your activity levels. When paired with a structured diet plan, CPAP may contribute to weight loss.

It’s unlikely, however, to make the weight just melt off.

Obstructive sleep apnea, a sleep disorder commonly treated with CPAP, has a complex relationship with your weight.

Carrying excess weight can make sleep apnea worse by adding pressure to your airways, and sleep apnea can increase the chances you’ll gain weight from hormone fluctuations, decreased activity levels, and increased hunger.

It’s natural to be wary of adding CPAP to the mix when you’re already concerned about weight gain.

Putting on weight isn’t a reason to avoid CPAP therapy or to quit using it. Obstructive sleep apnea is associated with major health impacts and can negatively affect your overall cardiac function.

CPAP use in sleep apnea is linked to better long-term outcomes and lowered risk for stroke and cardiovascular events.

Your doctor can help work through any concerns you have about CPAP and weight gain. They can create a weight management program for you based on your specific health needs and overall weight goals.

CPAP is primarily associated with weight gain in research, but some evidence shows it can also contribute to weight loss for some people.

If you’re concerned about weight gain from sleep apnea or the use of CPAP, your doctor can help you find a weight management program that works for you.