Obesity - The Size of the Problem

A person is considered to be obese if he is so heavy that weight endangers health.¹ Obesity is a growing problem in most developed countries and is responsible for a significant degree of morbidity and mortality in the western world. Obesity in adults has been an increasing problem for many years but now there is a major and increasing problem of obesity in children too.

Body Mass Index

A diagnosis of obesity is most commonly made using body mass index (BMI) levels. BMI is calculated as weight in kilograms divided by height in metres squared. As a general rule, an ideal BMI is 20 to 25. Between 25 and 30 is overweight and over 30 is obese. A BMI in excess of 40 is called morbidly obese, meaning that weight is a real and imminent threat to health.

There are a few exceptions that are worthy of note:

• A person who is very muscular will have a great weight in muscles and bone to support the muscles and so may have a high BMI without an excess of fat. Many top sportsmen in rugby, football and other sports have a BMI in excess of 25.
• BMI per se is not a suitable way to assess children. In the article on centile charts and assessing growth the problems of diagnosing childhood obesity is discussed. BMI can be used provided than it is moderated by use of the UK90 charts² or the like.
• In the elderly, the lowest morbidity is in the group with a BMI of 25 to 30³ rather than 20 to 25.

Waist-Hip Ratio

An alternative measure of obesity is the waist-to-hip ratio (WHR). It indicates abdominal fat and is a more accurate predictor for cardiovascular risk than BMI in different ethnic populations as well as being more valuable in those over 75 years old.⁴ The upper limit for acceptable is 0.90 in men and 0.85 in women.

Obesity is a growing problem in many countries.

• In the United States it is estimated that as many as 64% of the adult population are overweight or obese with 4.7% having a BMI of 40 or greater.⁵
• In the UK in 1998 it was estimated that 21% of women and 17% of men were obese.⁶ However, rather more men were overweight and if overweight is added to obesity, it is now estimated that over half of women and over two thirds of men are overweight or obese.¹ This means that only half of women and a third of men have a BMI of 25 or less. The number overweight or obese rises with age. A very small excess of calorific intake over expenditure adds up to a marked gain in weight over time.
• Obesity is said to be approaching smoking as the major avoidable cause of premature death but as deaths from obesity are said to number 30,000 a year⁷ compared with 110,000 for smoking, it still seems to be a long way behind. Some people are obese smokers. Obesity is also said to cause 18 million days lost from work due to illness each year.
• Data from the MRC suggest that in 2002, 23% of men and 25% of women were obese.⁸
• The Health Survey for England 2002⁹ states that 16% of boys and girls aged 2 to 15 are obese with a total of 30% classified as either overweight or obese. A third of young adults are either overweight or obese (32% of young men and 33% of young women). In addition, 9% of young men and 12% of young women are actually obese.
• Several factors have now been shown to predict the development of obesity in individuals such as a family history of obesity, lifestyle, diet and socioeconomic factors.¹⁰

The medical profession is traditionally sceptical about claims that obesity 'runs in the family'. However, the recent mapping of the human genome, combined with evidence from single-gene mutation cases and animal cross-breeding experiments have identified a significant link between genetic factors and obesity. Over 600 genes, markers, and chromosomal regions have now been identified.¹¹ It is emerging that obesity is the result of a complex pathophysiological pathway involving many factors that control adipose tissue metabolism. Cytokines, free fatty acids and insulin all play a part, and genetic defects are likely to have a significant effect on the fine balance of this process.¹² For example, the metabolic syndrome, of which obesity is a feature, is thought to be linked with alleles at the glucocorticoid receptor gene.¹³

The link between ethnicity, genetics, and the concept of insulin resistance as a genetic advantage at times of food shortage, is a fascinating topic which could help to explain the obesity pandemic we are currently facing. ¹⁴ It is hoped that continued research into this field, and the development of such procedures as genetic engineering and the modulation of molecular food handling 'signals', could eventually yield significant advances in the management of obesity.

Just because obesity runs in families, this does not mean that it is genetic and it certainly does not mean that it is impossible to do something about it. Families eat together. They develop a common attitude towards food. The diet may be high in fat. Large, high calorie meals may be normal and everyone is expected to clear the plate. In some families the provision of sweets and cakes is an index of love. Being at risk of obesity does not make obesity inevitable. It means that the individual has to work harder to maintain an acceptable weight. Obesity is multifactorial.

An assessment of an obese patient should begin with history and examination.

History

• Physical or psychological problems associated with obesity.
• Ask, "Why do you want to lose weight?" The response may give an indication of motivation.
• Past medical history including history of dieting.
• Social history including diet, exercise, occupation, smoking.
• Family history including history of obesity, diabetes, heart disease.

Examination

• Weight, height and BMI.
• Blood pressure measurement - using appropriate sized cuff.
• Waist circumference should be no more than 88cms in women and 102 cms in men.
• Waist-to-hip ratio is likely to be used more often in the future.
• Bioelectrical impedance analysis gives a more accurate assessment of body fat and lean tissue mass. This is usually unnecessary and the other measures can all be made with simple equipment found in any surgery.

Other investigations

Other investigations which should be considered in the assessment of an obese patient include:

• Urinalysis - for glucose and protein
• Microalbuminuria screen. The value of this test is not limited to diabetics.¹⁵
• U&E and LFTs
• Fasting blood glucose unless already known to be diabetic
• Fasting lipid profile

In addition, a few other investigations may be required as indicated by history and examination.

• Hormone profile including sex hormones and cortisol. Hormonal causes of obesity are rare and cortisol may be slightly elevated simply by obesity.
• TSH. Hypothyroidism is a rare cause of obesity and does not cause gross obesity.
• Other investigations as suggested by co-morbidities eg. ECG, CXR.

The National Audit Office report included a calculation of relative risks of other diseases resulting from obesity. The risks are just averages and risks increase with increasing obesity.

Obesity also increases the risk of breast cancer¹⁷ and carcinoma of the endometrium. Polycystic ovary disease is usually a disease of the obese. Obesity impairs fertility, especially in the female. If the person develops a surgical condition, diagnosis is more difficult and almost every complication is more frequent including deep vein thrombosis, chest infection and wound dehiscence. Not only is osteoarthritis more common but treatments such as total hip replacement are more likely to be problematical in obesity.

There are 4 risk factors for type 2 diabetes.

• Family history of type 2 diabetes
• There is a linear association between BMI over 25 and risk
• Smoking
• Lack of exercise

Obesity may account for as much as 65% of type 2 diabetes.¹⁸ It also causes much unhappiness and poor social function.

If an obese person loses 10% of body weight, it is said to confer the following benefits:

• In those with hypertension there is a fall of 10mmHg in both systolic and diastolic pressure.
• In newly diagnosed diabetics, an abnormal fasting blood glucose falls in 50%.
• In impaired glucose tolerance:
  • there is >30% fall in fasting or 2 hours insulin levels
  • >30% rise in insulin sensitivity
  • 40% to 60% reduction in the rate of progress to overt diabetes
• Lipid profiles improve with:
  • 10% fall in total cholesterol
  • 15% fall in LDC
  • 8% rise in HDC
• Mortality improves with:
  • >20% fall in all cause mortality
  • >30% fall in mortality related to diabetes
  • >40% reduction in mortality related to obesity