We are continually bombarded with news stories about how the nation, and indeed the world, is getting bigger. Obesity is reaching epidemic proportions.

In the 1960's, 13% of the population was obese. By the year 2000 this figure had grown to 31%.

Obesity is defined as having a Body Mass Index over 30. Overweight is categorized as having a BMI over 25. The figure for overweight Americans was 63% in 2000. It is likely to be over two thirds of the population by now.

Obesity is receiving so much attention as it is a risk factor for just about everything................... Heart attack, stroke, diabetes, cancer, osteoarthritis..... the list goes on.

A lot of research is being done due to the size of the problem and the likely future strain it will put on the health system.

 The laws of physics apply to our bodies. One such Law states: 'Energy cannot be created or destroyed'

This means that in order to stay the same weight, the energy our body burns in everyday functions and movement must equal the energy we put into our system in the form of food.

This is very unlikely to balance out each day so our body has a system to store energy when we have surplus in order to provide for the times of deficit. This is what our body fat is for.

If , on average over time, we use more energy than we provide our body - we lose weight.

If we provide excess, and continue to regularly, we put on weight.

Sounds simple? But what about metabolism?

Metabolism is often blamed for weight gain. Without going into the technical side too much it can be though of as the rate we burn energy to perform the functions necessary to sustain life. Many overweight people blame their condition on having a 'slow metabolism', implying an inevitability about their weight.

 It is true that obese people often have a slower metabolism than healthier individuals, but generally it is a result of their weight gain, not the cause.

Metabolism is related to muscle mass. The more muscle you have, the more energy is required to maintain the body. This leads to a 'fast' metabolism.

Obese people tend to have a lower proportion of muscle and so can idle at a lower rate - they have a slower metabolism.

Physical activity also increases metabolism. Which group does more of that?

 To find what is to blame for obesity we need to look at the reason for our high energy intake and low energy output:

• Calorie dense food - Modern manufactured food achieves a very high calorie to weight ratio.
• Sedentary lifestyle - We are not designed to work at a desk and drive a car.
• Behavioral factors.

 There is a reason we call it "comfort food". We get a feeling of comfort or satisfaction from eating when we are hungry. The brain associates the act of eating with the sensation of comfort and subconsciouly encourages you to eat to lift your mood when you are feeling down.

Depression of course is a complicated condition and there is much variation. Some people with depression lose their appetite completely and lose weight, but many people form the link between food and satisfaction.

Both depression and obesity have been increasing at alarming rates. There is likely to be a link but at this stage it is not understood or well defined.

 With nearly 10% of the American adult population on antidepressants it is hard not to think they may be being over prescribed. One of the common side effects of antidepressants is weight gain.

This raises an interesting question. If depression can lead to weight gain, are we treating it with medication that can lead to further weight gain? Is depression and its medication a contributing factor in the modern obesity epidemic?

The sooner we focus on the psychological reasons behind our eating behaviour and our sedentary lifestyle, the sooner we will effectively address the problem