Why do some people get fat while others don't?

There is a strong genetic tendency to obesity. This is why fatness runs in families. Studies have been done of identical twins who were adopted out at birth and they always ended up being almost exactly the same weight even though eating differently and brought up in separate families. People are born with the tendency to be fat or lean. To try to fight against this and be something else is very difficult. If one parent is fat you have a 50% chance of being likewise. If both parents are fat then there is an 80% chance of being fat too.

Appetite and hunger are behind the problem of obesity. It has nothing at all to do with greed or gluttony as some people think. Fat people are just plain hungry even when they have eaten enough for their energy needs. Their stomachs just keep sending messages to the brain that they are hungry and hunger is one of the hardest feelings to ignore. The story about people having bottomless pits is pretty close to the truth and a lot of big people have never had the sensation of fullness – until they have surgery! The bottom line is that obese people eat much more than thin people because they have a much bigger appetite.

What is obesity?

Obesity is always due to consumption of more calories than needed by the body for energy. These extra calories are then converted by the body into fat which is the body's way of storing energy for a rainy day. When there is plenty of food available, we don’t need this stored energy and so it stays with us as fat. It may come on quickly if large amounts of food are eaten over a few weeks, or slowly over many years if there is only a small excess of calories.

What is morbid obesity?

Morbid obesity is a disease of excess energy stores in the form of fat. Clinically this correlates with a Body Mass Index (BMI) of 40kg/m2 or with being 40kg. overweight. The biological basis for morbid obesity is unknown, though recent work has demonstrated a genetic component of 25 to 50 per cent. The genetically determined protein found in gastric cells called leptin has a place in the control of satiety through central nervous system. This confirms that morbid obesity is a disease and not a disorder of will–power, as sometimes implied.