LONDON (Reuters) - Decades of progress in the United States on cutting cholesterol, blood pressure and smoking are being stalled by rising obesity rates, and heart disease will kill around 400,000 Americans this year, experts said on Monday.

A study by British scientists found that around half of those deaths could be averted if people ate healthier food and quit smoking, and experts warned there was no room for complacency when it came to heart health risks.

Simon Capewell of the University of Liverpool said recent weight trends were alarming, with 1.5 billion adults worldwide expected to be overweight by 2015.

Although (heart disease) death rates have been falling in the United States for four decades, they are now leveling off in young men and women, he wrote in a study in the World Health Organization's weekly journal.

Recent declines in total blood cholesterol have been modest, blood pressure is now rising among women and obesity and diabetes are rising steeply in both sexes.

The researchers calculated the number of deaths based on lifestyle trends, taking the year 2000 as a base.

They found that almost 200,000 lives could be saved if certain heart risk factors were cut, even modestly, in particular, Capewell said, if people ate healthier food and stopped smoking.

Two-thirds of U.S. adults and nearly one in three children are overweight or obese -- a condition that increases their risk for diabetes, heart disease and other chronic illnesses.

U.S. health officials last week introduced first lady Michelle Obama as their latest weapon in a fresh campaign against the increasingly-costly weight burden.

But Shanthi Mendis, an expert on chronic disease prevention at the Geneva-based WHO, noted that the United States was not alone in facing an obesity epidemic, and said lifestyle choices now directly affected the health of many of the world's people.

Worldwide, nearly one billion adults are overweight and, if no action is taken, this figure will surpass 1.5 billion by 2015, she said in the study.

By avoiding tobacco, eating a healthy diet and engaging in regular physical activity, people can dramatically reduce their risk of developing heart disease, stroke or diabetes.

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