Exercising to control my weight

When we're away from home, we usually eat more than normal, but we usually exercise more than normal as well. The result is that we - also usually - put on quite a bit of weight. It often puts me in mind of people who say something like "I had a giant meal out with a bottle and a half of wine, then we stopped for a kebab on the way home - whoops! I'll be hitting the gym tomorrow!"

I have seen information about how much exercise you have to do to work off a cheese sandwich, but I thought I would calculate it for my own situation. Once a geek, always a geek. The first thing is that my exercise is almost all steps - my knees won't tolerate running, and I am a poor swimmer, so steps are the thing for me. How many calories we burn depends on our body size, gender and age, but for me 1,000 steps burns about 70 calories, and that takes me about 10 minutes. So if I walk for an hour, I burn 420 calories.

Now the interesting bit. If I eat out and have an extra pint of beer, I will need to walk for 25 minutes to burn it off. If I have a Tesco cheese and pickle sandwich, I will need to walk for over 50 minutes. If I had garlic mushrooms, fish and chips, two pints of beer and a chocolate sundae (a big meal, but not dramatically so), then I would be faced with a six-and-a-half hour walk - just a little fifteen-mile stroll!

So the damage if I eat too much is much more than any benefit I would realistically get from the sort of exercise I might do to undo the harm. And worse than that, I can do the damage quickly and just on the spur of the moment - it seems like a good idea to scoff a big meal, and an hour later the damage is done. But it doesn't work the other way - I rarely (let's be honest, never) get an irresistible and urgent craving to get my trainers on and walk for six hours.

Some people may find they can hit the gym so hard that they can undo any excess calories. But the message I take from my bits of arithmetic is that I am not one of them - exercise is fine for me to feel good, to help my body to work better, and so on, but it is not at all a good tool for undoing eating indiscretions.