No free lunches when it comes to popular weight-loss drugs

Upwards of 40 per cent of the weight lost by people using weight-loss drugs is muscle, according to a group of health researchers who are sounding the alarm about the unintended negative health consequences of trendy over-the-counter weight loss medications.

Carla Prado, a nutrition researcher in the Faculty of Agricultural, Life & Environmental Sciences, along with colleagues at McMaster University and the Pennington Biomedical Research Center in Louisiana have published a commentary in the November issue of The Lancet that suggests these medications, celebrated for their effectiveness in treating obesity, have raised concerns regarding the potential for substantial muscle loss, as much as 25 to 39 per cent of total weight lost over a period of 36 to 72 weeks.

Prado explains this rate of muscle decline is significantly higher than what is typically observed with calorie-reduced diets or normal aging and could lead to a host of long-term health issues — including decreased immunity, increased risk of infections and poor wound healing — brought on by muscle loss.

“Muscle does much more than just help us move or lift things, it is a powerful organ that keeps us healthy in a number of ways,” she says.

For example, muscle stores important building blocks — amino acids — that the body uses when we’re sick, stressed or injured to repair itself and stay strong. It also plays a huge role in managing blood sugar, which helps prevent diabetes.

As well, Prado notes muscle also releases special molecules, called myokines, that signal other parts of the body to help fight infections and support our immune system.

“When we lose muscle, it can weaken our immune system, and even reduce our overall health and independence,” she says. “That’s why preserving muscle is so important, especially during weight loss treatments—it’s not just about staying strong, but about keeping our whole body resilient and healthy.”

In the commentary, the authors suggest that muscle loss due to weight reduction —or from weight cycling if people stop taking these medications—may also exacerbate conditions like sarcopenic obesity — characterized by a combination of high body fat and low skeletal muscle mass — which contributes to poorer health outcomes, including cardiovascular disease and higher mortality rates.

Though the short-term effects of muscle loss on physical strength and function remain unclear, the commentary calls for future research to explore how reductions in muscle mass might improve muscle mass and composition. The authors stress the need for a multimodal approach to weight loss treatment, combining these drugs with exercise and nutritional interventions to preserve muscle mass. 

To keep muscle strong while losing weight, Prado says it is essential to focus on two main things: nutrition and exercise. Proper nutrition means getting enough high-quality protein and essential vitamins and minerals and other “muscle-building” nutrients. Sometimes, this can include protein supplements to make sure the body has what it needs.

“Exercise is just as important — specifically resistance training, like lifting weights or using resistance bands. This type of exercise helps keep muscle from breaking down during weight loss and maintains strength.”

She adds, for anyone using weight loss medications, it’s best to follow a balanced program that includes both enough protein and resistance training.

“This can help people lose fat while minimizing muscle loss, which helps them get the full health benefits of treatment and stay strong.”