The relationship between what you eat and exercise is a simple one. Compare yourself to the fuel tank of your car. Imagine the tank is being filled at the top. At the same time, a pipe at the bottom which leads to your engine allows the fuel to leave. Provided fuel enters and leaves at the same rate, the amount of fuel within the tank remains unchanged.
Now imagine that the fuel entering the tank represents the calories you eat. The fuel leaving the tank being used up by your car’s engine is your energy expenditure. This is the amount of calories you burn up through exercise. If you have more calories going in than going out your tank is going to 'overflow'. The excess energy is converted into fat and will remain in your body.
Many who are overweight don't acknowledge that they eat more than they should. Perhaps they don't. It may well be that they expend less energy than they take on board. To achieve a happy balance and to lose weight we need to diet as well as exercise. If you are not very active you should restrict your diet as the excess energy will make you gain weight.
You do not have to ‘starve’ yourself to lose weight. If you reduce your intake of food by 250-500 calories a day you would lose 1-2 pounds a week. This is a ‘sensible’ rate of weight loss to aim for.
You would lose 26 pounds or nearly two stone at the rate of one pound a week if sustained over six months!
A pound of fat represents about three and a half thousand calories of stored energy. Compare this to a gallon of petrol in your car which can take you thirty miles. If you don't drive anywhere, the gallon of petrol will stay in your tank.
If you eat 2500 calories a day and expend 2000 calories your body retains 500 calories each day. Over the course of a month you would therefore retain (30 x 500 ) 15,000 calories which as we said before is equivalent to over 4 pounds of fat, as one pound of fat is about 3,500 calories.
The following table gives you an idea of how much work you have to do to get burn off excess energy.
Food |
Calories |
Exercise to ‘burn off’ |
Apple |
55 |
Doing nothing (sleeping) you will still use this much energy in an hour |
Cream Biscuit |
120 |
Cycle for half hour |
Bailey’s Irish Cream |
130 |
Swimming for twenty minutes |
Packet of Crisps |
180 |
Walk for half hour |
Pint of Beer |
180 |
Gardening for half an hour |
Doughnut |
300 |
Brisk walk for one hour |
Dr Nishan Wijenaike MD, FRCP
Consultant Physician (Diabetes and Endocrinology)
West Suffolk Hospital NHS Trust
Bury St Edmunds
August 2006