How was the study carried out?
They tracked 116,000 women for two decades - from 1991 until 2011 - until they were all post-menopausal.
Those whose calorific intake included at least 9 per cent vegetable protein - such as tofu, soy, nuts, brown pasta, brown rice and whole grains - had a 59 per cent lower risk of an early menopause than those for whom vegetable protein made up less than 4 per cent of their diet.
The researchers, whose work is published in the American Journal of Epidemiology, said women who are vegetarian are the most likely to eat this much vegetable protein.
But the millions of people in Britain adopting a so-called 'flexitarian' diet - becoming vegetarian a few days a week - are also likely to benefit.
Part-time vegetarians
Figures published by consumer analyst Mintel last year revealed 35 per cent of people in Britain are now eating meat-free meals several times a week - a 'part-time' vegetarianism which involves finding alternative sources of protein, such as nuts, grains and tofu.
The menopause, which occurs on average at the age of 51, happens when the body stops naturally producing oestrogen and other sex hormones, ending a woman's reproductive life.
The scientists suspect vegetable protein- which is in a different form to meat protein - protects the ovaries and reduces depletion of the follicles, which are key to the reproductive process.
They think that if they can work out exactly how this happens, they may eventually be able to help prevent early menopause.
Better understanding needed
The authors wrote: "A better understanding of how dietary vegetable protein intake is associated with ovarian aging may identify ways for women to modify their risk of early onset menopause and associated health conditions."
The researchers said very few women in the study actually met the 9 per cent dietary requirement that reduced their risk by 59 per cent.
But 20 per cent of women got 6.5 per cent of their calories from vegetable protein - enough to reduce their risk of early menopause by 16 per cent.
They wrote: "For a woman with a 2000 calorie diet, this is equivalent to 32.5 grams of vegetable protein per day, or three to four servings of protein-rich foods such as enriched pasta or breakfast cereal, tofu and nuts."
Previous research
A previous study, published in the JAMA medical journal last year found that women who experienced early-onset menopause were 50 per cent more likely to suffer coronary heart disease, 11 per cent more likely to die as a result of a heart attack, and 12 per cent more likely to die early from any cause.
But the benefits of a 'flexitarian' or vegetarian diet extend beyond women and early menopause.
Research published by the University of Navarra in Spain in May revealed eating one or two meat-free meals a week halves the risk of becoming obese.
That research, which involved tracking 16,000 people over a decade, found that those who ate just 25 per cent less meat every week was linked to a reduction in the risk of obesity by 43 per cent.