Why after-dinner coffee and a nap are good for you
Reports by Roger Highfield, Aisling Irwin and Robert Uhlig
THE reason we like to drink a stimulating cup of espresso at the end of a feast has been discovered by scientists as part of a research programme that has underlined how a number of meal-time rituals have evolved for good reason.
Prof Ian Macdonald, of Nottingham University, told the science festival of the British Association in Cardiff that he had studied the demands that food places on the heart and blood system and shown why, over the ages, rituals such as the post prandial coffee and snooze have come to be so popular.
In a series of careful studies on healthy elderly people at the Queen's Medical Centre, Prof Macdonald has shown that both healthy meals with a high carbohydrate content - such as potato and pasta -as well as sugary convenience foods cause a drop in blood pressure. Insulin released by the meal causes blood vessels to relax. This is compensated to a degree by the body's autonomic nervous system except in the elderly, where it works less efficiently.
Failure to take this into account explains why, in homes for the elderly, dizzy spells, ''funny turns'' and faints are common after a main meal.
Careful design of the diet can help prevent a drop in blood pressure, for instance by having frequent snacks rather than big meals.
Grandfather had another answer - to nod off for an hour. Prof Macdonald said this was ''a good idea because if you tried to get him to get up and walk around you might have had trouble''. Another approach was to have a stiff cup of coffee, because of the stimulating effects of caffeine that helped constrict blood vessels and raise blood pressure.
Although the effect diminishes with repeated coffee consumption, Prof Macdonald believes it could explain why we like to drink coffee after meals, rather than before.
''If you are used to having a cup of strong coffee at the end of each meal, and you don't have it, then you could have a problem, in that you might get a bigger fall in blood pressure,'' he said.
Similar effects can be seen in middle-aged people suffering from angina, where attacks occur more rapidly if exercise is taken after a meal.
''What was not known is that the composition of the meal has an effect on that relationship between food and exercise-induced angina,'' said Prof Macdonald.'
A high-fat meal is one way to avoid angina attacks directly after a meal , because it has been shown not to trigger insulin release.
''Blood pressure fell after the high carbohydrate meal and the high fat plus insulin infusion but not after fat alone,'' he said. However, he said the chronic effects of a high-fat diet would worsen heart disease, outweighing any benefits.
