Ten things about weight loss: Part 8

Nearly done with these now!!

9. Exercise goes on burning fat - even while you sleep

According to the programme, new research shows that we burn fat while we asleep..... Michael, our TV doctor, takes part in an experiment. He does a fairly exhausting treadmill exercise. After a full 90 minutes, he has burned off a mere 19 grammes of fat. Not surprisingly, after all that effort, he is a little disappointed! However, the next day, he takes part in a second series of tests.

First, he has to lie down on a couch and rest for about 45 minutes, while breathing into a large bag-thing. This enables another doctor to measure Michael's Basal Metabolic Rate (BMR). Now, remember that since the previous days treadmill exercise, Michael has had no activity. I am not entirely clear about how this was done, but from the BMR, they were able to determine that since the previous day, Michael had burned off an additional 49 grammes of fat (i.e. in addition to the 19 grammes burned the previous day). This is known as 'afterburn'.

In fact, it would appear that more fat is burned after a period of activity than during. Why is this? Well, because during exercise, our muscles mainly get their energy from using readily-available carbohydrates - these are easier for the body to burn. Once the store of carbohydrates is used up, it takes the body some 22 hours to replace it. The use of carbohydrates during exercise in this way, is why marathon runners use 'carbo-loading' before a race - to try and boost the amount of carbs available in the body. Now, if the body takes 22 hours to replace the used carbohydrate, how is it going to get energy in the meantime? Simple, it feeds on the body's fat stores. This will keep the basic bodily functions going (digesting, sleeping, heart beating etc). This is the so-called 'afterburn' effect. Calories burned from fat in the afterburn phase are considerably more important than calories lost through carbohydrate usage (not least beause there are more than twice as many calories in a gramme of fat than in a gramme of carbohydate).

There, simple!