Health myths uncovered

foodHere are the most common myths and a scientific explanation of why they are flawed...

Eating late at night makes you put on weight

It is a commonly held view that a late meal eaten before going to bed leaves calories unused and promotes weight gain. Research shows that eating late at night does not pile on the weight – as long as your daily calorie needs match your body’s requirements.

A calorie is a calorie, it doesn’t matter when you eat it – but the total number of calories eaten daily does matter. If you eat late at night there’s a temptation to fit in an early-evening snack to control hunger, so boosting daily energy intake overall. But an identical meal eaten at 5pm or at 10pm has exactly the same effect, calorie-wise, in the body.

You should not exercise immediately after eating

After a meal some 10 to 15 per cent of our usual hourly blood flow is directed to the gut to aid digestion. When we exercise, muscles require more blood, too, to supply oxygen and nutrients. Both exercise and eating make competing demands on our circulation – the basis of this myth.

It’s fine to exercise immediately after eating, so long as it is not so intense that the muscles take so much oxygen that the stomach struggles – leading to cramps.

So, no need to delay that after-dinner brisk walk or swim, although probably best not to start heavy exercise immediately after Sunday lunch. It will slow digestion and the food will slosh around in your stomach for longer.

Vitamin C will stop you getting flu and colds

People believe this vitamin promotes good health like no other. It is linked to cell protection and is readily absorbed into white blood cells, and has long been thought of as a crusader against infection.

Supplements have been shown to reduce infection risk in those who have a pre-existing deficiency or who are undertaking extreme physical activity known to hamper immunity (such as elite athletes and military personnel). For the rest of us, Vitamin C supplements at 200mg+ a day reduce cold symptoms by just eight hours and have proved useless in stopping us catching colds or flu.

Coffee/caffeine is a diuretic, dehydrating rather than rehydrating you

Coffee contains caffeine, which has a weak diuretic (water-losing) effect if you normally avoid caffeine. If you regularly consume coffee, tea, chocolate or energy drinks (such as Red Bull), your liver learns to process caffeine quickly, neutralising this effect. Research shows the key factor influencing the diuretic effect of coffee is not related to its caffeine content but to the size of the drink.

We should all drink two litres of water a day

Research in the Forties found adult men needed two litres of fluid a day to stay hydrated. But this includes water content of food, which is more significant than you may imagine. Even toasted bread is a quarter water. The amount of fluid needed depends on activity and body size. If you are hydrated, you will produce a decent amount of urine, the colour of light straw, two to three times a day. Any excess just passes out. You don’t get extra benefit from drinking more than you need.

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