New year, new you? Change your life

You wake up on New Year's Day feeling slightly uneasy. At the back of your mind, something's not quite right. At first, it feels like a vague sense of dread, and then, moments later, as your mind clears, you realise what it is.

Jesus!

It's worse than you thought.

Today, you are going to change your life. This is something you decided to do last month, or last week, or possibly even last night. At the time, it seemed like a good plan. You wanted to lose weight, or give up smoking, or sort out your relationship with alcohol or drugs. And now here you are, on the appointed day, and you don't quite know how to go about it. It's like turning up to an exam and realising, as you walk towards your desk, that you haven't done any revision.

You want to try, but you're afraid of failing, and your biggest fear is that, if you try and fail, it will be harder to succeed the next time.

And so, as you get out of bed, and walk towards the kitchen, you are struck by what seems like a perfectly clear, logical thought. It goes like this: giving up smoking, or going on a diet, or whatever, might not, in the circumstances, be the right thing to do. In fact, if you think about it a bit more, it's precisely the wrong thing to do. Because it won't work.

Why should it? It didn't work last time, did it? And you only have so many tries, don't you?

You survey your options. One: total denial. I did not say I was going on a diet. Two: I was joking. Three: New Year's Day itself doesn't count. It's sort of an honorary member of the year before, because you woke up so late, because you drank so much, because you want a cigarette, or because you must have toast and marmalade to deal with your hangover, or because you might have some drugs left over that you failed to snort before you passed out.

Four: you will cut down. And so on.

If you want to change your life, there are many, many ways to fail. In fact, there are millions, because everybody fails in their own unique way. Just to get this into perspective, of all the people who want to lose weight, and set a target, and achieve that target, 95 per cent put all the weight, or more, back on. Usually more.

And then there are all the people who don't hit the target in the first place. And the ones who make the decision to diet, but can't quite manage to start the diet. I once watched a daytime talk show in which a man said he was frustrated with his obese wife, who said she'd been on a diet, but hadn't lost a pound, had in fact gained weight; and one day he'd left the house, got to the station, then realised he'd forgotten his wallet, and walked back home, and there she was, sitting at the kitchen table, in flagrante. Fast food everywhere. She hadn't even started her diet. That's a pretty bad way to fail, but it's not uncommon.

As someone who spent many years trying to quell my raging appetites - for food, drink and drugs - I've had more than my share of failure. So let me tell you about the pitfalls. The first has to do with going on diets. Dieting sounds simple: you are fat because you have eaten too much. Your solution, therefore, should be to eat too little, thus redressing the balance. If too much food made you fat, too little, it seems obvious, must make you slim.

Of course, it does. But that's not the most important thing. As the great diet writer Geoffrey Cannon explains, when you eat too little, your body gets extremely good at transforming the food you do eat into fat. This is because, even though food is plentiful, your body does not think this is the case. Your body has not evolved in any significant way since more or less everybody was on the verge of starving to death most of the time. So when you eat too little, you may be thinking "diet", but your body is thinking "famine".

Of course, if you eat too little for ever, you'll stay slim. But if you relent, you'll find that your capacity to get fat has increased. And if you try to swing the pendulum back, and go on a reduced-calorie diet again, you'll compound the problem. Your body will get even better at turning the food you eat into body-fat. That's one reason why diets fail. That's why there are so many diets around. And that's why, when you put the weight back on, you end up heavier than you started.

Of course, there is one type of diet that will make you slim without making your body into an efficient fat-packing machine. This is the diet where you eat the right amount of healthy food - no sugar, no white bread, no doughnuts or bagels, and lots of fish and green vegetables. Without sugar, and without much refined carbohydrate, you'll feel less hungry. The salmon and spinach, or whatever, will make you feel full. I went on a diet like this, and lost two and a half stone.

So what's wrong with that? Not much, on the face of it. After a while, though, I started to crave other things. Having given up alcohol, I wondered if I could begin a new, more adult relationship with it. I bought a bottle of wine and removed the cork, and poured myself a glass of wine, and took a sip, and 16 hours later I woke up, fuzzy and nauseous, trying to piece together my fleeting memories of the night before, the streetlights and taxis, the bars, the kebab shop, the drugs.

That's another reason why diets don't work. Sometimes, food - or alcohol, or smoking, or whatever - isn't the problem. A lot of people give up smoking, and get through the period of physical withdrawal, but it's still no good - they go right back to smoking. Some people, like me, diet, and lose weight, and then start drinking. Sometimes, the real problem is emotional. If you do harmful stuff to yourself, it's not always because you enjoy the harmful stuff. Sometimes, it's because the harmful stuff is good at distracting you from your troubles.

Did you make a resolution to give up the bad stuff? And are you wondering, right now, if you were a little hasty? Well, maybe you were. The point to remember is that, if you've been using food or alcohol or drugs as an emotional crutch, the first thing to start thinking about is your emotions. Are you overeating or drinking or taking drugs to escape from a reality you can't face? So start facing it.

Where are you now? In the kitchen? In a café? Are you about to crack, and smoke that cigarette, or order that glass of wine, or that sticky pudding? Think about it. The tobacco or the wine or the food might not be the problem. They might be the symptoms. My advice: try to think about the actual problem. When you do that, you're much less likely to fail.

William Leith's 'The Hungry Years' is published by Bloomsbury at £10.99