LONDON — Preventing obesity and smoking can save lives, but it doesn't save money, researchers reported Monday.

It costs more to care for healthy people who live years longer, according to a Dutch study that counters the common perception that preventing obesity would save governments millions of dollars.

"It was a small surprise," said Pieter van Baal, an economist at the Netherlands' National Institute for Public Health and the Environment, who led the study. "But it also makes sense. If you live longer, then you cost the health system more."

In a paper published online Monday in the Public Library of Science Medicine journal, Dutch researchers found that the health costs of thin and healthy people in adulthood are more expensive than those of either fat people or smokers.

Van Baal and colleagues created a model to simulate lifetime health costs for three groups of 1,000 people: the "healthy-living" group (thin and non-smoking), obese people, and smokers. The model relied on "cost of illness" data and disease prevalence in the Netherlands in 2003.

The researchers found that from age 20 to 56, obese people racked up the most expensive health costs. But because both the smokers and the obese people died sooner than the healthy group, it cost less to treat them in the long run.

On average, healthy people lived 84 years. Smokers lived about 77 years, and obese people lived about 80 years. Smokers and obese people tended to have more heart disease than the healthy people.

Cancer incidence, except for lung cancer, was the same in all three groups. Obese people had the most diabetes, and healthy people had the most strokes. Ultimately, the thin and healthy group cost the most, about US$417,000, from age 20 on.

The cost of care for obese people was US$371,000, and for smokers, about US$326,000.

The results counter the common perception that preventing obesity will save health systems worldwide millions of dollars.

"This throws a bucket of cold water onto the idea that obesity is going to cost trillions of dollars," said Patrick Basham, a professor of health politics at Johns Hopkins University who was unconnected to the study. He said that government projections about obesity costs are frequently based on guesswork, political agendas, and changing science.

"If we're going to worry about the future of obesity, we should stop worrying about its financial impact," he said.

Obesity experts said that fighting the epidemic is about more than just saving money.

"The benefits of obesity prevention may not be seen immediately in terms of cost savings in tomorrow's budget, but there are long-term gains," said Neville Rigby, spokesman for the International Association for the Study of Obesity. "These are often immeasurable when it comes to people living longer and healthier lives."

Van Baal described the paper as "a book-keeping exercise," and said that governments should recognize that successful smoking and obesity prevention programs mean that people will have a higher chance of dying of something more expensive later in life.

"Lung cancer is a cheap disease to treat because people don't survive very long," van Baal said. "But if they are old enough to get Alzheimer's one day, they may survive longer and cost more."

The study, paid for by the Dutch Ministry of Health, Welfare and Sports, did not take into account other potential costs of obesity and smoking, such as lost economic productivity or social costs.

"We are not recommending that governments stop trying to prevent obesity," van Baal said. "But they should do it for the right reasons."