Third of weight loss from injections is actually muscle and bone - not fat

Almost a third of pounds shed from blockbuster weight loss jabs is actually muscle and bone density, a study has shown. Experts warn it is vital that people change their lives and do exercise while losing weight on the jabs to sustain it in the long term. Appetite-suppressing injections have become a global sensation with 2.5 million Brits on them and millions more expected to be prescribed them in the coming years. Research unveiled at the European Congress on Obesity in Istanbul reviewed 21 studies which used high tech scanners to assess where weight was being lost from on the body. It showed that of the weight lost after taking jabs, 31.5% of it was “fat free mass” such as muscle and bone density. This compared to 14.3% for diet and exercise alone. Co-author Professor Signe Torekov, of the University of Copenhagen, said: “These findings underscore the importance of incorporating strategies aimed at preserving fat-free mass.” Experts have warned that if people stop taking the injections because the side effects become too much, or they can no longer afford what is an expensive treatment, they often pile the fat back on but muscle mass does not return. This leaves people much weaker and with less muscle with which to burn calories so losing weight in future is much harder. Loss of bone density leaves people at greater risk of osteoporosis and frailty as they age. Experts said those taking jabs should also do strength training or risk losing bone and muscle mass. Data from earlier trials of semaglutide, known as Ozempic or Wegovy, shows a heightened risk of certain fractures linked to frailty. Women over the age of 75 were eight times more likely to be hospitalised with hip fractures and ten times more likely to be hospitalised with pelvic fractures when on weight-loss jabs. Professor Donna Ryan, of Pennington Biomedical Research Center in the US who has led trials of weight-loss jabs, said: “We really need to be promoting exercise. You need to be physically active. When you're losing a lot of weight, the way to protect your muscles and bones is to do resistance training.” Weight loss jabs mimic the hormone GLP-1 to make users feel full sooner but can come with side effects such as nausea, constipation and diarrhoea. Scientists say body composition is crucial to assessing long term effectiveness of weight loss jabs. They analysed this on 1,334 study participants using dual-energy X-ray absorptiometry, computed tomography (CT) and magnetic resonance imaging (MRI). The review compared changes in fat-free mass which is mainly muscle and bone as well as organs. All participants lost at least 10% of body weight as a result of either weight loss surgery such as gastric bands, weight loss jabs or from diet and exercise alone. Those losing weight from diet and exercise lost on average only 1.8kg of fat-free mass, compared to 4.8kg from GLP-1 drugs and 9.1kg from surgery. As a percentage of weight loss, muscle and bone mass made up 14.3% for diet and exercise, 31.5% for weight loss drugs and 32.9% for surgery. Bone density loss is a concern because four out of five weight loss jabs prescribed privately are for women who are at greater risk of osteoporosis and fractures. Phil Day, superintendent pharmacist at Pharmacy2U, said drugs should not be seen as a “hack to not do exercise”. He said: "Patients moving their body, through strength or cardio, will not only retain muscle mass, but enjoy better overall health, while also building good habits to keep the weight off longer term." The study was unable to establish how much of the fat-free mass lost was muscle, bones or even organs. But separate research is ongoing to examine the impact of jabs on grip strength, which is an indicator of frailty and osteoporosis.