I lost a stone in three weeks eating crisps and drinking beer. Here's how.

Do you want to lose weight, but enjoy junk food too much, and haven't got time to exercise? Try this.

#1: Understand that your body is a machine.

The first step is to realise that your body is actually a finely-tuned biological machine with one purpose; to sustain life. Everything you eat and drink is meticulously processed and stripped down into component parts. The parts that can be used as-is, straight away, will be. Mostly everything else will be converted into energy. Your body then uses as much of that as it can and packs the rest of it together (into fat) to use later. This is the bit that sucks -- we can't change how this works.

#2: Know that you're always burning calories, even when you sleep.

Energy is essential. Everything you do, even the things you don't control, like your heartbeat for example, require energy -- calories. So, just being alive actually burns calories, and it's a good idea to know how many. In fact, you can get a good estimate by punching some details into online calculators like this one over at fitnessfrog.com. If you head over there now, make a note of the number the calculator gives you, this is your total daily energy expenditure, or TDEE for short.

#3: Realise that you don't need to exercise to lose weight.

When your body doesn't have enough energy available to do what it needs to, it's forced to break down fat to get that energy. It doesn't matter if the energy is needed for jogging or for simply keeping you alive, if it's not available your body will break down fat to get it. So, if you know how many calories your body needs every day, and you eat less than that, you'll lose weight -- even without exercising.

#4: Reduce your calorie intake, but don't go hungry.

Hunger kicks in if you go too long between meals, or if you eat far less than you need. Plus, if you're used to reaching for a snack every time you get a little peckish, and you suddenly stop that, you're going to feel it. Hunger sucks, and it'll kill your motivation faster than anything else. So, here's a few pointers to help get it right:

• Don't make any sudden changes to your diet. Ease changes in over a number weeks.
• Don't eat too little. If you need 2000 calories a day, aim to eat 1500.
• Don't forget that the calories in drinks count too.
• Do eat absolutely anything you want. Just don't exceed your calorie goal each day.
• Do space your calories out. A quater of your calorie goal every 4 hours works great.
• Do change things up. Routine can be great, but you don't need it. Experiment!

It can be dangerous to drop your daily calories too low. 500 calories less than what you need each day is a reasonable limit for most people, so really keep this one in mind.

#5: Remember to be healthy too.

Losing weight and being healthy are not the same thing. While staying on top of your calorie intake it's possible to eat junk food for every meal, drink beer, do zero exercise, and still shed the pounds. Really. And... there's nothing wrong with this, from time to time. Go nuts. But, please don't do this all of the time. Better food choices and regular exercise will always make you healthier than just losing weight alone -- strike a balance and you'll win all round.