Previous work has shown that vegetarians tend to have lower blood pressure and lower cholesterol, cutting their risk of heart attacks. They are also less likely to be obese.

Alternatively, a diet which is rich in fruit, vegetables and wholegrains may somehow boost brain power.

Dr Gale said: 'Although our results suggest that children who are more intelligent may be more likely to become vegetarian as adolescents or young adults, it does not rule out the possibility that such a diet might have some beneficial effect on subsequent cognitive performance.

'Might the nature of the vegetarians' diet have enhanced their apparently superior brain power? Was this the mechanism that helped them achieve the disproportionate nature of degrees?'

High-profile vegetarians include singers Paul McCartney and Morrissey and actress Jenny Seagrove.

Past exponents of a meat-free lifestyle include George Bernard Shaw and Benjamin Franklin.

Promoting the cause, Shaw said, 'A mind of the calibre of mine cannot drive its nutriment from cows', while Franklin stated that a vegetarian diet resulted in 'greater clearness of head and quicker comprehension'.

Liz O'Neill, of the Vegetarian Society, said: 'We¡¯ve always known that vegetarianism is an intelligent, compassionate choice benefiting animals, people and the environment. Now, we¡¯ve got the scientific evidence to prove it.

'Maybe that explains why many meat-reducers are keen to call themselves vegetarians when even they must know that vegetarians don¡¯t eat chicken, turkey or fish!'

1

2