By Georgina Kenyon

David Tarr from Hillingdon, Middlesex is six-foot two-inches tall and a strapping, slim and healthy 37-year old, by all accounts.

A fitness instructor, he says the secret of his good health is down to eating nothing but jam sandwiches between the ages of three and six.

He is not alone. Many children become fixated with eating a particular food but grow up to be seemingly healthy and often tall adults.

Could this mean health experts are unnecessarily concerned in advising us to eat a wide variety of foods each day?

If you love something as much as I did jam sandwiches it can't be all bad for you

David Tarr

The World Health Organization in Geneva, for instance, recommends eating five portions of fruit and vegetables a day.

But could there be something especially nutritious in a jam sandwich?

Not according to Professor Andrew Prentice of the Public Health Nutrition Unit, London School of Hygiene and Tropical Medicine, who has studied obesity.

Hidden health dangers

He says a person who exclusively eats jam sandwiches as a child has a larger risk of becoming obese and developing heart disease and cancer, because of the relatively high calorie count and lack of vegetables and fruit in the diet.

"The child may seem healthy but the reality may be very different.

"You cannot assess someone's health on the inside by just looking at a person. A child can look healthy but their internal workings can show something very different.

"A person's height is not an absolute measure of health either. In fact very tall people have a slightly greater tendency to develop cancer than shorter people due to growth hormones."

It is very hard to say today that a wide various diet is not important

Professor Andrew Prentice

Studies in America of autopsies of children who had died in car accidents before the age of 20 showed many were already suffering from a build up of fatty deposits in their arteries, a classic indication of heart disease in later life.

Research has shown that fruit and vegetables contain antioxidants which prolong the life of cells.

Professor Prentice says: "Oxidant stress is inevitable by just living and breathing in oxygen. But diet can resist the premature ageing and stress on cells, leading to illness such as cancer."

But he said it was never too late to slow down the effects of a bad diet.

"It is universally believed in the medical community that preventing disease is a balancing act between nutrition and genes. It is very hard to say today that a wide various diet is not important."

Sport support

Eating too many jam sandwiches also attracts a beating from many nutritionists, as the wheat in the bread is often said to be cause of allergies, leading in turn to irritability, skin eruptions and respiratory problems, especially in children, even when eaten in moderation.

But those working with athletes are more open to the benefits of the jam sandwich.

A spokesperson from the Australian Institute of Sport in Canberra says: "We actually recommend our athletes to eat from a selection of carbohydrate rich foods before, after, and in some cases, during exercise.

"A jam sandwich is exactly one such food we recommend."

Mr Tarr shrugs off any negative speculation about his diet.

"I used to just adore jam sandwiches as a child. You couldn't get me to eat anything else and my parents did try. If you love something as much as I did jam sandwiches, I say it can't be all bad for you."