Cutting calories may delay the ageing process and reduce the risk of disease, a long-term study of monkeys suggests.

通过对猴子的一项长期研究显示，削减热量可能延缓老化过程，降低疾病风险。

At 27 both these monkeys are elderly, but it\'s the one on the left who has eaten more over his lifetime and looks the worse for wear

The benefits of calorie restriction¹ are well documented in animals, but now the results have been replicated²（折叠，复制） in a close relative of man over a lengthy³（冗长的，漫长的） period.

Over 20 years, monkeys whose diets were not restricted were nearly three times more likely to have died than those whose calories were counted.

Writing in Science, the US researchers hailed the "major effect" of the diet.

It involved reducing calorie intake⁴ by 30% while maintaining nutrition and appeared to impact upon many forms of age-related disease seen in monkeys, including cancer, diabetes⁵（糖尿病）, cardiovascular（心脏血管的） disease and brain atrophy⁶（萎缩）.

Whether the same effects would be seen in humans is unclear, although anecdotal（轶事证据） evidence so far suggests people on a long-term calorie-restricted diet have better cardiovascular health.

The precise mechanism⁷（机制，原理） is yet to be established: theories involve changes in the body's metabolism⁸（新陈代谢） or a reduction in the production of "free radical⁹" chemicals which can cause damage.

Seventy-six rhesus（猕猴） monkeys were involved in the trial, which began in 1989 and was expanded in 1994.

Half had their diets restricted, half were given free rein¹⁰（完全的自由行动） at feeding time.

The rate of cancers and cardiovascular disease in dieting animals was less than half of those permitted to eat freely.

While diabetes and problems with glucose¹¹（葡萄糖） regulation were common in monkeys who ate what they wanted, there were no cases in the calorie controlled group.

In addition, while most brains shrink with age, the restricted diet appeared to maintain the volume of the brain at least in some regions.

In particular, the areas associated with movement and memory seemed to be better preserved.

"Both motor speed and mental speed slow down with ageing," said Sterling¹² Johnson, a neuroscientist（神经系统科学家） at the University of Wisconsin-Madison School of Medicine.

"Those are the areas which we found to be better preserved. We can't yet make the claim that a difference in diet is associated with functional¹³ change because those studies are still ongoing¹⁴.

"What we know so far is that there are regional differences in brain mass that appear to be related to diet."

Earlier this year, German researchers published findings from their study of elderly people which suggested that calorie reduction appeared to improve memory over a period of just three months.

Various studies on the positive effects of calorie restriction on the life spans of various organisms - from yeast¹⁵（酵母） to dogs - have been published over the last 70 years

But dieticians（营养学家） sounded a note of warning.

"Monkeys may be a close relation but there are significant differences which means not everything we see in them can be translated to humans," said Catherine Collins, spokeswoman for the British Dietetic Association.

"And there should be some serious reservations about cutting calories so dramatically, particularly for anyone under the age of 30. Any such diet would need to be very balanced to avoid malnutrition¹⁶（营养不良）, and it would be a long-term commitment.

"People would have to weigh up whether they are prepared to compromise their enjoyment¹⁷ of food for the uncertain promise of a longer life, and a life which could be dogged by all sorts of problems - including osteoporosis（骨质疏松症）."