Why wise flyers take their own food

On friday morning I was booked on Air Canada flight 869 from Heathrow to Toronto. But, when I should have been at check-in, I was at the check-out, at Tesco - on doctor's orders.

On friday morning I was booked on Air Canada flight 869 from Heathrow to Toronto. But, when I should have been at check-in, I was at the check-out, at Tesco - on doctor's orders.

My shopping list had been prescribed by Dr Steve Ray, senior lecturer in clinical physiology at Oxford Brookes University. He outlined ingredients for the ideal picnic to help me through the eight-hour flight. What's more, it began on the way to the airport.

Who needs airline meals? Not our bodies. "The rule for in-flight eating should be 'little and often'," Dr Ray says. "Exactly what you don't want is what the airlines provide: a big meal that you have to hurry through before the tray is taken away." He explained: "You need to build up potassium before you go, which is most easily done by eating fruit such as bananas or grapefruit." I tucked into one of each as soon as I was out of the supermarket.

The body's metabolism is best prepared to digest food early in the day. It slows at altitude. Eating steak on an evening flight is digestively disastrous. A piece of beef takes six hours to digest; at altitude, its journey through 10ft of intestine could take longer than the 3,500-mile flight to Toronto.

The only way, then, to be sure of your in-flight food is to take your own. At Tesco, I spent less than £10 on what I hoped would be enough fuel for the eight-hour flight. Dr Ray recommended fish, white meat and pasta, easily digested and quickly absorbed. My salmon was smoked, my turkey low-fat.

Liberal use of fat and oils in in-flight catering is unwise. "All the fat content goes through the lymphatic system, which delivers it through the neck," says Dr Ray. "In a hypobaric [low-pressure] environment, that can cause headaches." Another advantage of self-catering is that you can eat whenever you wish. As the captain announced a 40-minute air traffic control delay, my fellow-passengers' stomachs began to rumble. I tucked into more bananas. As we began to taxi for take-off, my neighbour looked on enviously as I munched a mid-morning snack of salmon, tomatoes and brown bread.

You have to be careful, though, warned Professor Michael Kipps, a food management expert at Surrey University, where applications have just closed for the world's first professorship in airline catering. Carry-on food may harbour dangerous bacteria. "A seemingly harmless ham sandwich, taken on board a long-haul flight, prepared by someone with a trace of the staphylococcus bacterium on their hands, could result in a nasty upset stomach by the end of the journey," he explained.

The airlines could do without mass catering, too. This winter, fares across the Atlantic are running at less than £200 return. Serving passengers two meals in each direction costs at least 10 per cent of the fare paid, with free drinks draining more from the airline's earnings. Ah, the drinks. "Fluids, fluids and yet more fluids," is Dr Ray's rule for long-haul flying. He doesn't mean wine. Fluids are essential to aid digestion, and the only way to compensate is to drink plenty. So the most effective component of my picnic was three litres of mineral water. I started quaffing on the Heathrow Express, which is also when I attacked the grapes. "Fruit puts energy into the liver," said Dr Ray.

By the time the Boeing reached the end of the runway - where a "small technical problem" arose - we had been on board for 90 minutes, with only a tiny cup of orange juice being served.

Three hours after boarding, we had yet to take off. Then the captain announced that the plane was being taken out of service. The passengers trooped off - all but me in an advanced state of hunger - and went to queue for a refreshment voucher, then for a café table. Meanwhile all food on the grounded aircraft was destroyed.

* Additional research by Lisa Aldwinckle