However, Prof Whitty said that GLP-1 medication to tackle obesity also carries major health risks unless efforts are made to conserve muscle mass.
The guidelines – the first ever by chief medical officers to address the risk of such medications – come as chemists embark on one of the biggest drug launches in history.
On Monday, sales opened for Britain’s first GLP-1 weight-loss pill, which works in a similar way to jabs such as Wegovy and Mounjaro.
Prof Whitty said: “It is really important that you maintain strength and also balance, but particularly strength, as you go through age.
“Once you get to about 50, your muscle mass is decreasing, and if you actually manage to get a good muscle mass, and then keep it through late middle age, you’ll be in much better shape in terms of ending up with frailty in old age than if you allow the muscle mass to essentially wither away.”
People taking GLP-1 drugs are at particular risk because muscle is lost alongside fat, and if weight is regained, it is more likely to return as fat.
“That’s another reason why physical activity, as you lose weight, as you maintain a lower weight, or indeed if you increase weight, maintaining strength and muscle is really important,” Prof Whitty said.