The global figures for obesity are little short of startling: the World Health Organisation reports that there are more than 1.9 billion overweight adults — 39 per cent of the adult population.
Of these, 650 million — or 13 per cent of the adult population — are obese, meaning their body mass index (BMI) is at least 30.
“When we look at obesity, it’s a growing public health problem,” said Dr Richard Holt, professor in diabetes and endocrinology at the University of Southampton in the UK.
“The number of people now overweight or obese is getting larger and larger. Being overweight is associated with significant medical problems as well as social problems, such as stigma.”
But could the new drug tirzepatide be the answer?
What is tirzepatide and how did it perform in clinical trials?
Produced by the American drug producer Eli Lilly, tirzepatide decreases appetite by mimicking the effect of hormones released in the body after a person eats.
On Thursday, Eli Lilly released the results of clinical trials involving 2,539 patients, some of whom were given 5 milligram, 10mg or 15mg treatment regimes of the drug.
For the lowest dose, average weight loss was 15 per cent of body weight; in the 10mg group, it was 19.5 per cent; and in the 15mg group, 20.9 per cent. Among patients given a placebo, average weight loss was 3.1 per cent of body weight.
In a statement announcing the results, Dr Jeff Emmick, Eli Lilly’s vice president of product development, said the drug was the first to achieve an average weight loss of more than 20 per cent in a late-stage trial.
Almost two thirds of those on the highest dose lost at least 20 per cent of their body weight.
How does this compare to lifestyle changes?
Dr Holt said that diet and lifestyle management — trying to reduce a person’s calorie intake and increase their energy expenditure — is often the first line of treatment for significantly overweight people.
“There are very, very many diets advertised for the management of obesity. It’s probably fair to say none of them are particularly effective if you look across the whole of the population,” he said.
“We might expect weight loss of up to 5 per cent with lifestyle management on a population basis. It’s not to say lifestyle is not useful; some people respond very well to lifestyle.
“We would expect two out of 10 to lose a significant amount of weight with lifestyle. That leaves eight out of 10 who haven’t lost a significant amount.”
With lifestyle changes, people might find it straightforward to lose weight, Mr Holt said, but harder to maintain that weight loss over time.
How does tirzepatide compare to other drugs or surgery?
After lifestyle and dietary changes, the next level of treatment is drug therapy, of which there are “very few licensed for the management of obesity”, Mr Holt said.
Obesity drugs have often been launched only to be withdrawn because of “significant side effects”.
Aside from tirzepatide, another key drug is semaglutide, which acts in a similar way. Clinical trial results released a year ago showed it cut body weight by about 15 per cent and produced only modest side effects. One third of patients lost more than 20 per cent of their body weight.
At the time, it was described as “a game-changer” by one researcher who co-wrote a paper outlining the results, achieving weight reductions “no other drug has come close to”.
Semaglutide is being used by clinicians to help people lose weight, but the latest results suggest tirzepatide could be even more effective. With both drugs, side effects appear to be modest.
Regardless, Dr Holt said he didn't think the drug should be used for everyone.
“Lifestyle interventions are where we should start. With people with more serious [obesity] or who have tried lifestyle changes and these have been unsuccessful, drug therapies are a successful option,” he said.
“This would be a useful treatment to include in the treatment armamentarium.”
The latest drugs offer a “major, major step forward in the amount of weight loss”.
Beyond drugs, the next treatment is obesity or bariatric surgery, which include having a gastric band placed around the stomach so that the patient feels full after eating a smaller amount.
Dr Holt said the results achieved by tirzepatide were “the sort of level you might expect to see with people with bariatric surgery”.
Prevention is better than cure
While drug treatments are improving, preventing obesity from developing in the first place is often seen as more effective than trying to achieve weight loss after a person has become obese.
“Reduction is really difficult because the brain is structured in a way that changing your behaviour takes a long time to settle in your brain,” said Dr Antje Hebestreit, a nutritional epidemiologist at the Leibniz Institute for Prevention Research and Epidemiology.
“Once you already have these behaviours leading to obesity, to really get rid of them takes a long time … This is why prevention is the favourite [approach].”
Dr Hebestreit said that some ways to prevent obesity in adults, such as using mobile phone apps that monitor a person’s diet, physical activity and sleep patterns, may reduce the risk of obesity by 40 to 75 per cent if users adhere to the recommendations.
Interventions are best started early on, she added, especially during childhood.
Parents have a big influence on whether their children become obese, she said, with the mother’s BMI and education level linked to the risk of obesity in her children.