GLP-1 Weight-Loss Drugs and Malnutrition: What You Need to Know

Introduction

Medications like Ozempic, Wegovy, Saxenda and Mounjaro — known as GLP-1 receptor agonists — have changed the way obesity and diabetes are treated. They are powerful tools, but like all treatments, they come with risks.

Recent studies, including a BMJ editorial, have highlighted that malnutrition may be an underestimated side effect of GLP-1 use. At the same time, regulators such as the MHRA have reported serious gastrointestinal problems and even deaths linked to these drugs.

Whether you’re a patient considering treatment, or a legal professional following the rising number of claims, the question is the same: what are the risks, and how should they be managed?

GLP-1 use for weight management is booming but at what cost?

How GLP-1s Work

GLP-1 medications work by:

• Slowing stomach emptying, which helps you feel full quicker.

• Increasing insulin release and reducing glucagon, which lowers blood sugar.

• Acting on the brain to reduce appetite.

The result is often rapid weight loss. In some trials, patients lost over 10kg within 6 months. But this effect can come at a cost — very low calorie intake, sometimes as little as 800 kcal a day. Without proper support, that can tip people into malnutrition.

GLP-1 drug Malnutrition

Malnutrition isn’t just about being underweight. It can mean:

• Not getting enough energy (undernutrition).

• Lacking key nutrients (iron, B12, vitamin D).

• Having too much of certain nutrients (for example, iron overload).

• Even obesity with poor diet quality (overnutrition).

We’ve seen this before with bariatric (weight-loss) surgery. Despite decades of experience and clear NICE guidelines, studies still show high rates of deficiencies:

• Iron deficiency in ~20% of patients.

• Vitamin D deficiency in up to 70%.

And that’s with structured follow-up care. With GLP-1 drugs now widely used, the risk of malnutrition without proper monitoring is obvious.

Why Monitoring Matters

Safe use of GLP-1s requires:

• Baseline nutritional screening before starting treatment.

• Regular monitoring of weight, diet, and blood tests.

• Clear dietary guidance from a qualified professional.

• Follow-up support to catch problems early.

  
  

Without these steps, people may slip into deficiencies that affect energy, mood, immunity, and long-term health.

The Legal Angle

In the U.S., thousands of lawsuits have already been filed against manufacturers of GLP-1 drugs, with analysts estimating potential liabilities in the billions of dollars. These cases often involve serious side effects like gastroparesis (stomach paralysis).

Here in the U.K., litigation is still emerging. But the same themes apply:

• Were patients warned about foreseeable risks?

• Was nutritional status checked before treatment?

• Was there proper follow-up and monitoring?

These are the types of questions that matter in both clinical care and legal cases.

Conclusion

GLP-1 drugs are an important advance in treating obesity and diabetes. But they aren’t risk-free. Malnutrition is a foreseeable complication if the right checks and support aren’t in place.

For patients, that means asking about nutritional screening and ongoing care before starting treatment. For solicitors, it means recognising where gaps in care from poor consent to inadequate monitoring — could form the basis of claims.

I specialise in helping patients use these medications safely and providing expert nutrition reports in cases where these issues are contested, ensuring courts get the clarity they need.