Why Am I So Cold After Losing Weight on a GLP-1?

You used to be perfectly comfortable.

Now everyone else is sitting around in a T-shirt while you're considering whether bringing a blanket to the couch counts as a personality change.

If you've lost a significant amount of weight on a GLP-1 and suddenly feel colder than you remember, you're not necessarily imagining it.

But there's an important distinction:

Feeling colder after GLP-1-supported weight loss may be related to weight loss, reduced energy intake and changes in energy expenditure rather than a direct effect of the medication itself. Persistent or extreme cold intolerance can also have other causes and deserves a conversation with your healthcare professional.

So, why might losing weight leave you reaching for another sweater?

Why can you feel colder after losing weight?

Your body is constantly producing and losing heat.

Body size and composition are part of that equation, but the explanation isn't as simple as you lost your insulation.

When you lose weight, your body's energy requirements change. And during weight loss, energy expenditure can sometimes fall beyond what would be expected from changes in body size and composition alone.

Researchers call this adaptive thermogenesis.

It's essentially an energy-conservation response that has been observed during and after weight loss.

But it's also an area where the science deserves some nuance.

A systematic review examining 33 studies and 2,528 adults found evidence of adaptive thermogenesis in 27 of those studies. However, the researchers also found considerable variation between studies, and better-designed studies tended to report smaller or non-significant effects. Adaptive thermogenesis may also diminish after a period of weight stabilization.

In other words: your body's energy expenditure can change during weight loss.

Exactly how much varies.

Does eating less lower body temperature?

This is where things get particularly interesting for people using GLP-1s.

For some people, these medications can substantially reduce appetite and food intake.

And eating considerably less means less energy is coming in.

Researchers have studied what long-term calorie restriction does to body temperature in humans.

In one study, scientists measured the core temperature of 24 adults who had practiced calorie restriction for an average of six years, along with 24 sedentary adults eating a typical Western diet and 24 endurance athletes.

The endurance athletes were particularly useful because they were matched to the calorie-restricted participants for body fat.

The calorie-restricted group consumed an average of 1,769 calories per day, compared with 2,798 calories per day among the endurance athletes.

Despite similar leanness between those two groups, average 24-hour core temperature was lower in the calorie-restricted participants: 36.64°C compared with 36.86°C in the endurance athletes.

Their daytime and nighttime temperatures were also significantly lower.

The researchers concluded that long-term calorie restriction itself, rather than simply being lean, was likely contributing to the lower core temperature.

That's an intriguing finding.

It is not, however, evidence that someone taking a GLP-1 will experience the same temperature change.

The study wasn't conducted in people taking GLP-1 medications, and it measured long-term calorie restriction in a small group of healthy, weight-stable adults.

That's an important limitation.

Do GLP-1 medications directly make you cold?

This is where correlation can become confusing.

You start a GLP-1.

You lose weight.

You're eating less.

And somewhere along the way, you notice you're cold all the time.

It's understandable to conclude:

The medication is making me cold.

But several things changed at once.

Your body weight changed. Your body composition may have changed. Your food intake may have changed substantially. Your energy requirements changed. And your body's energy expenditure may have adapted during weight loss.

That gives us several plausible reasons someone might feel different after losing weight without needing to assume the medication itself directly altered their internal thermostat.

You lost weight. Apparently your thermostat had opinions about it.

This distinction matters because not every symptom that appears while you're taking a medication is necessarily caused directly by that medication.

What is adaptive thermogenesis?

The term sounds considerably more dramatic than the concept.

Your body uses energy simply to keep you alive: maintaining tissues, circulating blood, breathing, regulating temperature and carrying out thousands of other processes you thankfully don't have to remember to do.

When body weight decreases, some reduction in energy expenditure is expected because there's simply less body to maintain.

Adaptive thermogenesis describes an additional reduction in energy expenditure beyond what researchers would predict from changes in body weight and composition alone.

Scientists have observed it in many weight-loss studies, although estimates of its magnitude vary substantially and some higher-quality studies find little or no meaningful effect.

So adaptive thermogenesis is real enough to study seriously.

It is not a universal explanation for why every person who loses weight suddenly needs thicker socks.

When should you talk to your healthcare professional about feeling cold?

Feeling a little chillier than you used to is one thing.

Being persistently or extremely cold is another.

Cold intolerance can have causes unrelated to weight loss or GLP-1 treatment.

MedlinePlus lists potential causes including anemia, hypothyroidism, blood-vessel problems such as Raynaud phenomenon, chronic illness and other conditions. It recommends contacting a healthcare professional for long-term or extreme intolerance to cold.

So if you're constantly freezing, the change is pronounced, or something simply doesn't feel right, don't automatically file it under GLP-1 things.

And if feeling cold is happening alongside other new or concerning symptoms, tell your healthcare professional.

Sometimes the answer really is another sweater.

Sometimes it's worth checking.

The Takeaway

Feeling colder after losing weight on a GLP-1 isn't necessarily in your imagination. But that doesn't mean the medication itself is directly making you cold.

Research suggests that calorie restriction can influence body temperature and that energy expenditure can adapt during weight loss. Changes in body size, composition and food intake may all be part of the picture.

What we don't have is evidence that everyone using a GLP-1 should expect to feel cold or that feeling cold can automatically be attributed to the medication.

So yes, keep the sweater.

Just don't let the sweater replace a conversation with your healthcare professional if being cold becomes persistent, extreme or concerning.

Sources & Further Reading

Nunes CL, et al. Does adaptive thermogenesis occur after weight loss in adults? A systematic review. British Journal of Nutrition. 2022;127(3):451–469.
https://pubmed.ncbi.nlm.nih.gov/33762040/

Soare A, Cangemi R, Omodei D, Holloszy JO, Fontana L. Long-term calorie restriction, but not endurance exercise, lowers core body temperature in humans. Aging (Albany NY). 2011;3(4):374–379.
https://pubmed.ncbi.nlm.nih.gov/21483032/

MedlinePlus Medical Encyclopedia. Cold intolerance. U.S. National Library of Medicine.
https://medlineplus.gov/ency/article/003095.htm

This article is for educational purposes only and is not a substitute for individualized medical advice. Talk with your healthcare professional about persistent, extreme or concerning cold intolerance or other symptoms.