If one in three women in Britain are always on a diet and billions of pounds are spent on slimming products, why on earth are we all getting fatter?

This is the puzzle that led Dr Paula Baillie-Hamilton, author of The Detox Diet: Eliminate Chemical Calories and Restore Your Body's Natural Slimming System, to research some of factors that might explain our failure to get thinner. Her conclusions are shocking. The solution to our ever-expanding waistlines is to be found in the form of 'chemical calories', which 'lurk in every bite of food we eat, every sip of liquid we drink and in the very air we breath'. Sounds pretty scary.

Why chemicals are making us fat
Baillie-Hamilton gives a detailed explanation of why chemical calories are responsible for wide-scale weight gain. Farmers feed their livestock growth-promoting additives that force animals to gain weight fast.

These chemicals improve the efficiency of food by changing the animal's metabolism in such a way that less food goes further. Our metabolism is then affected by the animal products we consume. According to Baillie-Hamilton, synthetic chemicals impact on our bodies in a variety of ways.

They damage the natural appetite 'switch', which tells us when to stop eating, and they make us store fat more effectively. If any vegetarians out there are breathing a self-satisfied sigh of relief, then prepare yourself for some bad news: it's not just meat that's contaminated.

The same chemicals that promote weight gain in animals and humans are sprayed on vegetables and used in medicines, cosmetics, toiletries, metals, plastics and household products.

The Detox Diet is full of terrifying-looking graphs that show the 'fat epidemic' moving in tandem with the increasing use of chemicals in food production. It is estimated that each of us has roughly 300-500 industrial chemicals in our bodies. The presence of chemical calories means that we can no longer diet according to the conventional rules; the normal calorie content of food is distorted by the presence of chemical calories. Lettuce, for example, can be more fattening than the high-calorie avocado because it is a fragile crop that is sprayed often with preservatives and pesticides.

The omnipresence of fat-inducing chemicals begs the valid question, if everyone is absorbing these dangerous chemicals, why isn't everyone fat? Baillie-Hamilton argues that all bodies are different and some people have a more pronounced reaction to these chemicals.

Our natural slimming system
So far, so gloomy. At this stage of the book I was all set to put it down and raid the fridge in the happy knowledge that eating a few more sandwiches wouldn't make any difference to my weight - I can't help inhaling chemical calories.

Fortunately, Baillie-Hamilton provides a solution to our plight in the second half of the book.

All people are endowed with a natural 'slimming system', which is made up of a variety of factors: appetite, metabolism, hormone levels, fat burning, body heat and exercise. Each person's body tries to attain its own ideal weight in time of need or plenty by adjusting these mechanisms.

By eating fewer chemical calories that distort this process and consuming more 'slimming' nutrients, Baillie-Hamilton claims we can enhance our capacity to maintain a healthy weight.

Apparently, if we eat more organic food we can lose weight. To minimise the intake of chemical calories she suggests ways to store foods - keep them in glass or ceramic (not plastic) containers and make sure they stay cool.

If, for whatever reason, you can't or won't go organic, there is advice for lessening the quantity of chemical calories in normal food. And if you're convinced by her argument, there is a comprehensive detox eating plan at the end of the book, with an entire chapter of menus and recipes to get you started on a chemical-free, slimmer life.

Be warned: charcoal and clay play a large part in the recommended daily requirements.

So is it pie in the sky?
Baillie-Hamilton's research is compelling and she presents her arguments clearly and with passion. There is no doubt that too much processed food is bad for us but is that really the answer to our increased girth?

Isn't it simply that we eat more and move less than we used to? As she presents her argument, the constant refrain is that our collective weight gain in the west is 'incomprehensible'. But when you look at the volume of food on sale and the portion sizes in most restaurants it doesn't seem that baffling.

Baillie-Hamilton argues that 'if traditional dieting methods really worked, the fat epidemic should have been stamped out long ago', but what is a traditional diet and who's doing it? There are countless quirky diets that claim you can eat certain foods in abundance and as long as you omit meat/wheat/dairy/carbohydrates/fruit/sugar you'll lose weight.

Even if they seem successful in the short term, frustrated dieters tend to regain the weight they lost, plus extra. Although many of the ideas put forward in Detox are worth thinking about, an eating plan that limits so many common foods and recommends a daily dose of clay is reminiscent of just another faddy diet.