Overeating and lack of physical activity are the main causes of obesity, especially in combination. But many factors contribute to obesity.
The number of overfed people on the planet is at its highest level. For the first time in history (year 2000) the world's total of overweight people equals the total of those who are underfed. Up to 1.2 billion people eat more than they need, and as many go hungry each day.
Obesity is a chronic disease. It develops over a period of years. Obesity becomes a health problem when it leads to disability, illness or increased risk of death, and these effects are difficult to separate or quantify. Some of the consequences of obesity are controversial. However, serious overweight appears to reduce life expectancy. Obesity strongly predisposes to maturity-onset (type 2) diabetes because it can lead to insulin resistance and glucose intolerance, conditions that often precede the onset of type 2 diabetes. The evidence linking it to hypertension is somewhat controversial but obesity is considered to be a major risk factor for coronary heart disease. It also causes disabilities, including osteoarthritis of weight-bearing joints, musculo-skeletal complaints such as backache, potential loss of vision (via diabetes), varicose veins, breathing difficulties (including sleep apnoea), increased surgical, obstetric and cancer risks (liver, kidney, oesophagus, gallbladder, pancreas, colon and rectum, cervix, ovary, uterus, breast (in postmenopausal women), prostate, and stomach (in men) as well as non-Hodgkin's lymphoma and multiple myeloma), and numerous psycho-social problems. Overweight and obese people reportedly have slower cognitive abilities, increased pain and limited mobility.
Huge resources are spent on fat and fat research. There are also a multitude of anti-obesity pills that control metabolism and feelings of satiety. Surgical removal of fat, for example by liposuction, is increasingly perfected as a surgical technique but may bring complications. Also the remaining fat may redistribute. Fat is now considered a vital organ of the body, not just a surplus energy store, and the implications of its redistribution are not well understood.
A person puts on weight when his/her consumption of food exceeds energy expenditure. Frank obesity is defined as being 30% overweight for one's height and build. Morbid obesity is 50% above ideal body weight, or more.
Waist size is the critical factor in defining obesity according to some specialists. As a rule of thumb, a waist measurement of more than 94 cm doubles the risk of developing diabetes, hypertension and high cholesterol. Pinching subcutaneous fat is also a measure of overweight. However, abdominal fat is only one type of fat laid down by the overweight. Typically, ageing men lose muscle mass and accumulate fat on the sides of their waist (love handles) and in their stomach (beer belly). Women in their prime, with oestrogen levels high, tend to store fat in their hips and thighs; but after menopause, a slowdown in metabolism coupled with reduced physical activity contribute to a fat distribution pattern more similar to the middle-age male, with thickening waist and belly fat. Such superficial fat does carry some increased risk of cardiovascular disease. But it is mainly the visceral fat, deposited deep inside the abdominal cavity, that is linked to high cholesterol, high blood pressure, diabetes and heart disease. This is best monitored by body mass index (BMI).
Body mass index is a more precise measure of obesity than waist size. It is the ratio of the body weight in kilograms and the square of the height in metres. A body mass index of 21 is ideal; greater than 25 is classified as overweight by some doctors; greater than 27 means overweight according to other doctors; greater than 30 is obese. People with a body mass index exceeding 27-28 are already carrying significantly increased risk of ill health. With a body mass index of 32, people 30 to 54 years of age double their risk of premature death.
Factors that increase a person's risk of carrying more weight than is healthy include:
[Diet] Regular consumption of high-fat foods and sugary foods and beverages, which are dense in calories.
[Inactivity] Sedentary people are more likely to gain weight because they don't burn calories through physical activities.
[Psychological factors] Some people overeat to cope with problems or deal with difficult emotions.
[Genetics] Genes may affect the amount of body fat stored and where that fat is distributed. Children of obese parent have a 25-30% percent greater chance of being obese.
[Sex] Men have more muscle than women; because muscle burns a greater number of calories than fat burns, men expend up to 20 percent more calories than women do even at rest.
[Age] The amount of muscle in the body tends to decrease with age and fat accounts for a greater percentage of body weight. This lower muscle mass leads to a decrease in metabolism. Metabolism also slows naturally with age. Together, these changes reduce calorie needs.
[Cigarette smoking] Smokers tend to gain weight after quitting. This weight gain may be partially due to nicotine's ability to raise the rate at which your body burns calories (metabolic rate). When smokers stop, they burn fewer calories. Smoking also affects taste. Former smokers often gain weight because they eat more after they quit. Their food tastes and smells better.
[Pregnancy] After each pregnancy, a woman's weight increases an average of 2 to 3 kilograms over her pre-pregnancy weight.
[Medications] Corticosteroids and tricyclic antidepressants, in particular, can lead to weight gain.
[Illnesses] Medical problems that lead to decreased activity can result in weight gain.
[Medical problems] Less than 2 percent of all cases of obesity can be traced to a medical cause such as low thyroid function, Cushing's syndrome (excess production of hormones by the adrenal glands) or other hormonal imbalances. A low metabolic rate is rarely a cause of obesity.
Paradoxically the energy intake of people living today may be less than that of their parents and grandparents at the same age. They are more inclined to put on weight because their lifestyles are less physically active. Inactivity, not gluttony, is the main factor responsible for adult obesity doubling between 1987 and 1997 in Europe. Technology has made it easier to get by on less work. Around the world, cars replace bikes, television replaces outdoor activity, and it has almost become unavoidable to be lazy. Other contributors are lack of education and a lack of money in poorer societies; however in richer societies self-indulgence and sedentary lifestyles are blamed. Thus money and education do not eradicate obesity.
Generally, obesity was recognized as a serious health problem during the 1970s in industrialized countries and among affluent groups elsewhere, and its prevalence appears to be increasing in most western-style countries. The average body weights in industrialized countries have increased by 4 to 9 kg over the last 30 years.
In 1995 in Europe, the incidence of overweight people was around 33%, and had risen steadily since 1980. Cultural differences may be marked: Eastern Europe, Britain, Benelux and Germany have higher proportions of fat people than the Mediterranean countries, Scandinavia, and Finland. In Czechoslovakia there was a striking increase in the incidence of obesity in men and women between 1956 and 1972. In 1996, there were more overweight men (one in four) than women (slightly over one in five) in the European Union as a whole. The record in this respect was held by Greek men. In the UK, body fat increased by about 10% in all age groups over the last four decades of the twentieth century. In 1991, in the UK the percentage of obese men and women had risen to 13% and 15% respectively, compared to 7% and 12% in 1987; there was a 30% increase in individual obesity in the last two decades. This trend may be encouraged by the ever larger official recommended weights for people that doctors and insurers accept.
People in non-developed countries are also gaining weight. China, where famine recurs in history, is an example. Since 1993, the proportion of overweight men in China tripled. In 2001, fifteen percent of China's adult population was overweight.
One national survey in Canada estimated that more than 60% of people of both sexes aged over forty were overweight. This was called middle-age spread. Another estimate made in 2001 is that one out of every seven Canadians is obese. This survey found that weight seems to have a bigger impact on women than on men. Women view their own health state as poor if they are overweight while men perceive their health to be compromised once they become morbid obese. Men rated the severity of obesity alongside migraines, but women said it is more serious than being diabetic or having a stroke.
Americans are the heaviest society in the world, and probably in the history of the world. The incidence figures for overweight vary greatly, from 30% to 60% of the population, depending on the source and the definition of overweight. Undeniable is the recent massive rate of increase in overweight, a jump of nearly 50% from 1991 to 1998. According to the Centers for Disease Control and Prevention in 2001, more than 50% of American adults are overweight and approximately 20% are obese. A government estimate in 1999 was that more than 60% of adults were overweight or obese. These numbers translate into at least 70 million obese people, including more than a third of all adults and one in five children. One in 200 people are morbidly overweight.
At the same time, only 39% of US adults considered themselves overweight. Women are affected slightly more than men. Mexican-American women and black women have a higher weight than the average for American women; American males show little variation for race. Nearly 30% of patients diagnosed as overweight in 2000 have been 35 years old or younger. Between 1989 to 1999, the obesity rate among Americans aged 18 to 29 more than doubled from 5 percent to 12 percent.
In 1988 the US Surgeon General declared being overweight the most significant nutrition problem in the USA, and it has remained so. Obesity and related conditions were the second leading preventable cause of death in the USA in 1997, according to some medical experts. As of 1998, an estimated 300,000 people die prematurely each year of conditions brought on by obesity, but this figure is contested. The weight problem is estimated to cost the health care industry an estimated $70 billion annually. In 1995, one third of the women's cancer deaths in one study, particularly breast, colon and endometrial cancers, were due to being overweight. Implicated were bile acids from dietary fat and oestrogen in the body fat.
In the Netherlands in 1997, the medical costs for overweight patients were estimated to be $500 million per year.
Dietary changes may be responsible for rising obesity in some countries in the South Pacific region. Especially the consumption of refined carbohydrates has increased, and the incidence of hypertension, diabetes and gout rose in parallel.
The increase in seat size and strength in cars and public transport over the past 20 years tacitly acknowledges the increased average size of people.