It will make unpleasant reading for dieters who have been hoping that light exercise was the key to weight loss.

For it seems the most successful slimmers chalk up a marathon a week, according to research.

A study found that those who exercised for 60 to 90 minutes a day - walking the equivalent of a marathon each week - tended to shed at least two stones and kept the weight off for six years.

The data contradicts the popular theory that gentle exercise is enough to stay slim.

The American Association for Advancement¹ of Science's conference on Sunday also heard fresh calls from a British expert for a more urgent global response to the obesity² crisis.

Professor Philip James, chairman of the International Obesity Task Force, believes the obesity epidemic³ is now too serious to be treated as a "lifestyle choice" issue.

"Just as the threat of climate change has begun to be taken seriously when it may be almost too late, the threat of an obesity-related health disaster around the world needs urgent action because, like climate change, its effects are exceptionally difficult to reverse," he said.

The professor wants governments and industry to work together to tackle the causes of obesity - just as they have done to cut carbon emissions⁴.

And he warned the crisis would not be resolved simply by telling people to exercise and eat less.

Calling on world leaders to agree a pact⁵ on fighting obesity, Professor James said major changes were needed in food production, advertising⁶ and town planning.

Healthy food should be made cheaper, the advertising of junk food to children clearly regulated and towns built not around roads and cars but around walking and public transport.

"We can no longer afford to wait," he said.

"If we fail to act until we have the perfect solution, it will be too late."

In Britain, a quarter of women and a fifth of men are classed as obese⁷, at a cost to the NHS of £1billion a year.

一直希望通过少量运动即可减肥的人士看到这篇文章后一定会不开心。

因为研究表明，最成功的瘦身人士每周坚持走一次“马拉松”。

一项研究发现，每天锻炼60分钟至90分钟的人（相当于每周走一次马拉松）至少可以减掉两英石（相当于28磅）的体重，而且六年不会反弹。

这一数据否认了“少量运动即可保持身材”的普遍说法。

在美国科学促进协会上周日举行的研讨会上，一名英国专家呼吁世界各地对肥胖危机做出更为积极的回应。

国际肥胖特别机构主席菲利普•詹姆斯教授提出，目前肥胖流行问题十分严重，已不能将其视为一个“生活方式选择”的问题。

“就像气候变化问题现在开始得到重视，但为时已晚；所以世界各地由肥胖引起的健康威胁急需解决，因为肥胖与气候变化一样，产生的后果极难挽回。”

詹姆斯教授希望政府与行业部门通力合作，根治肥胖问题——就像治理气候变化过程中控制二氧化碳的排放一样。

他提出警告，单靠让人们运动、节食是无法解决肥胖问题的。

詹姆斯教授呼吁世界各国领导人签署抵制肥胖协议，他说，食品生产、广告和城镇规划等领域都需要“大动作”。

要降低健康食品的价格、明确禁止针对儿童的垃圾食品广告、城区不应以马路和车为主，而应多设人行道和公交设施。

他说：“我们再也等不起了。”

“如果我们等找到最完美的解决方案再行动，那就太晚了。”

英国有四分之一的女性和五分之一的男性存在肥胖问题，全国卫生服务系统每年要为此支付10亿英镑。
 

Vocabulary: 

chalk up:达到；取得（如: chalk up a record 取得一个新记录）