New data reveals unexpected heart health changes linked to GLP-1 weight loss drugs

A new study tracking people on GLP-1 weight loss jabs has picked up on changes happening inside the body that go far beyond the number on the scales, some of which are catching experts off guard.

GLP-1 drugs have dominated the weight loss conversation over the last couple of years, with most of the attention focused on how much weight users lose.

But wearable tech company WHOOP has set out to look at what else was going on, tracking heart rate, sleep and recovery data rather than relying on before-and-after photos.

The performance science team analysed data from 132 WHOOP members collected between November 7, 2023, and April 16, 2024, comparing 66 members using a GLP-1 medication against 66 matched controls who weren't.

The study ran for 12 weeks and used causal inference methods to separate the drug's effects from normal day-to-day variation.

GLP-1 drugs are more popular than ever for weight loss (Getty Stock Image)

The findings were peer-reviewed and published in the American Journal of Physiology, Heart and Circulatory Physiology, and are considered among the first pieces of real-world evidence on how GLP-1 therapy interacts with physical activity, rather than lab conditions or a clinical drug trial.

What weight loss did the WHOOP study find on GLP-1 drugs?

The headline finding was significant weight loss. Ninety per cent of GLP-1 users in the study lost at least five per cent of their body weight within 12 weeks, and the average member lost 10 per cent of their body weight over the same period, figures WHOOP says exceed the weight loss typically reported in pharmaceutical trials of the same medications.

But weight loss wasn't the only change picked up by the wearables.

Across the 12 weeks, GLP-1 users saw an average three beats-per-minute increase in resting heart rate, alongside a six millisecond decrease in heart rate variability.

It's important to incorporate exercise while using weight loss jabs (Getty Stock Image)

A rising resting heart rate paired with falling heart rate variability is generally read as added strain on the cardiovascular system, even while the medication does its job on the scale.

WHOOP's own assessment of the finding is that these are notable changes in heart health markers worth monitoring closely if starting a GLP-1 medication, not just tracking weight loss alone.

Can exercise offset the heart rate changes from GLP-1 medication?

There was a more encouraging discovery buried in the same data.

On average, GLP-1 users added 30 minutes of physical activity a week, and those who exercised more saw smaller increases in resting heart rate than those who didn't.

Those who exercised more saw smaller increases in resting heart rate than those who didn't (Getty Stock Image)

WHOOP describes this as the first real-world evidence suggesting that staying active can help counteract some of the cardiovascular side effects of GLP-1 therapy, rather than being a general health tip.

Keeping up strength training appears to matter too. According to WHOOP's guidance, GLP-1 therapies can lead to a reduction in lean muscle mass without an active strength-training routine, which is why the company recommends resistance work and lean-mass tracking alongside any GLP-1 prescription, rather than cardio alone.

WHOOP now logs GLP-1 use as one of more than 300 behaviours tracked in its Journal feature, allowing members on the medication to see how their weight, resting heart rate, heart rate variability and activity levels move together week to week, rather than relying on how they feel.

The findings come as GLP-1 medications continue to grow in popularity worldwide, with millions of people now using the drugs for weight loss and other health conditions.

UNILAD has approached Norvo Nordisk, Eli LILY, and WHOOP for comment.