Sir Keir told the BBC the jabs would be “very helpful” to people who want and need to lose weight.
“[The drug is] very important for our NHS, because, yes we need more money for the NHS, but we’ve also got to think differently”.
Streeting suggested the medicines could be “life changing” for individuals.
In an opinion piece for the Telegraph, external, the health secretary wrote: “Widening waistbands are also placing significant burden on our health service.”
“The long-term benefits of these drugs could be monumental in our approach to tackling obesity.”
The NHS’s latest Health Survey for England shows in 2022, 29% of adults in England were obese and 64% were deemed to be overweight.
Illnesses relating to obesity cost the NHS £11bn a year, Streeting said.
Obesity has also been linked to the development of type 2 diabetes, with the NHS spending around £10bn a year – 9% of its budget – to care for people with diabetes.
His words came as the government announced a five-year trial in Greater Manchester of the weight loss drug Mounjaro.
Mounjaro’s maker, Lilly – the world’s largest pharmaceutical company – is investing £279m as part of the trial, which will look at whether using the drug will reduce worklessness and NHS use.
NHS officials have suggested the roll-out of the drug across England will need to be staggered due to anticipated high levels of demand.
Nearly 250,000 people are expected to receive the Mounjaro jab over the next three years, officials said.
The health secretary added the weight-loss injections could benefit the economy too, reducing the number of sick days caused by obesity.
“Illness caused by obesity causes people to take an extra four sick days a year on average, while many others are forced out of work altogether,” he said.
However, individuals will still need to remain responsible for taking “healthy living more seriously”, as the “NHS can’t be expected to always pick up the tab for unhealthy lifestyles”, he said.
“As a country, we’re eating more, eating less healthily and exercising less. The costs to the individual are clear – a less healthy and shorter life.”
Obesity policy specialist Dr Dolly van Tulleken said the idea was unrealistic as the eligible population for this plan was “in the millions” with specialist weight management services only able to treat 49,000 per year.
She said the policy idea of incentivising unemployed people who are obese, was not new, and had previously gone down “very badly”.
Speaking to the Today programme, she said the plans look at people based on “their potential economic value” rather than their needs.
Some weight loss medicines are already prescribed by the NHS. The medication which supresses appetite is sold under the brand names Wegovy – used to treat obesity – and Ozempic, for diabetes.
It comes in the form of an injection and mimics the hormone GLP-1, making people feel fuller and less hungry.
Experts have warned in the past that the drug is not a quick fix or a replacement for eating well and exercising, and should only be offered under medical supervision.
Former health minister Lord Bethell said the NHS would have to make “concrete steps to pivot to prevention so that we’re not simply medicalising the national obesity problem.”
Amanda Pritchard, the chief executive of the NHS, said the drugs would be a “game-changer” for public health and could reduce the risk of diabetes, heart attacks and strokes.
David A Ricks, the chairman and chief executive of Lilly, said: “We welcome this opportunity to partner with the UK Government on tackling and preventing disease, and accelerating innovation to advance care delivery models.”