The number of people who are obese is rising rapidly throughout the world, making obesity one of the fastest developing public health problems. The World Health Organisation has described the problem of obesity as a “worldwide epidemic”. It is estimated that around 250 million people worldwide are obese, about 7% of the adult population Obesity develops gradually over a period of time as weight is gained.
Weight gain occurs when the amount of energy (calories) consumed as food and drink exceeds the energy which is used for exercise and other metabolic processes of the body. This is known as positive energy balance. The excess energy is stored principally as fat. Each kilogram of fat stores approximately 9000kcal. This fat can only be lost when the body requires more energy than is available from food and thus draws upon its energy stores. This is known as negative energy balance.
Energy balance is tightly regulated in most people and does not usually require conscious control. A change in life circumstances that alters either the diet (and thus energy intake) or activity (and thus energy expenditure) can lead to weight gain or loss. It is often difficult to identify these changes as only a small imbalance can lead gradually, but perceptibly, to changes in body weight and fatness Factors which increase the likelihood of obesity There are a number of factors which seem to predispose an individual to obesity. It is clear that obesity runs in families, is more common in some ethnic groups and is seen more frequently in developed countries where there is an inverse relationship between socioeconomic status and obesity. These observations provide some clues as to why some individuals become obese.
Genetics
Obesity tends to run in families. Children with two obese parents have about a 70% risk of becoming obese compared to less than 20% in children with two lean parents. This could be explained by environmental factors since families usually share the same diet, lifestyle and cultural influences. These habits tend to persist into later life. However, studies of adopted children have revealed weight patterns similar to those of their natural rather than their adopted parents and so obesity does have some genetic basis. However the degree to which obesity is genetically determined is still under discussion. Detailed studies of genetic transmission, including studies of mono- and dizygotic twins, have placed the influence of genetic factors from as low as 5% to more than 50%.
Over 50% of adults in the UK now weigh more than the medically recommended level. The prevalence of obesity (severely overweight) has doubled in the past decade and now affects more than 15% of the adult population. Obesity raises the risk of a whole range of physical diseases – including coronary heart disease, hypertension, diabetes, degenerative joint diseases, and some cancers. A fat cell does not function alone, it requires help from a complex enzyme system. Enzymes facilitate the transport of fat in and out of the fat cell. The enzymes that help store fat are called the lipogenic enzymes, and the enzymes that help release fat are the lipolytic enzymes.
Men and women have roughly the same number of fat cells but the difference is the enzyme systems and the size of the fat cells. Women have more lipogenic enzymes for the storage of fat, and the more you can store, the bigger the fat cell. Men have more lipolytic enzymes for the release of fat, and therefore have smaller fat cells. Why do people get fat? The reasons for this are quite complex and it’s not possible to give one definite answer.
Some people, probably only about 5% of those who are obese (the technical term for people who are between 20 and 25% over their ‘normal’ body weight) have body imbalances, usually caused by damage to the hypothalamus, the part of the brain which controls hunger. In most people, however, it is due to them more food than they actually need. We all need to gain energy from the food that we eat for the activities we carry out. If we take in more energy than we expend over a long period of time, we will gain weight, as the excess energy is stored as fat.
To lose weight involves taking in less energy than we expend: the best way to do this is to eat a healthy, balanced diet, and to take plenty of exercise. It should come as no surprise that obesity is only really a problem in ‘developed’ countries where people have a high standard of living. In the USA, for example, between 50 and 70 million people are obese and about 65% of 50-60 year old women and 38-48 year old men are 10% heavier than they should be.