The health risks of obesity

As shown in Figure 6.1, people who are overweight are significantly more likely to die prematurely, and at 50% over desirable weight there is a twofold risk of premature death. Figure 6.4 shows the main causes of premature death that are associated with overweight and obesity, expressed as the ratio of that condition as a cause of death in obese people to the expected rate in lean people.

Obesity, and especially abdominal obesity (section 6.2.3), is strongly associated with insulin resistance and the development of non-insulin-dependent diabetes mellitus (section 10.7). This is largely the result of increased circulating concentrations of non-esterified fatty acids (released from plasma lipoproteins by lipoprotein lipase; section 5.5.6.2). Non-esterified fatty acids decrease muscle uptake and utilization of glucose and may also antagonize insulin action. Weight loss results in a considerable improvement in glycaemic control in patients with early non-insulin-dependent diabetes.

In addition to the diseases caused by, or associated with, obesity, obese people are considerably more at risk of death during surgery and post-operative complications. There are three main reasons for this:

  • Surgery is longer and more difficult when the surgeon has to cut through large amounts of subcutaneous and intra-abdominal adipose tissue.
  • Induction of anaesthesia is more difficult when veins are not readily visible through subcutaneous adipose tissue, and maintenance of anaesthesia is complicated by

digestive diseases diabetes

% over desirable weight

Figure 6.4 Cause-specific mortality with overweight and obesity. From data reported by Lew EA and Garfinkel L (1979) Journal of Chronic Diseases 12: 563-5 76.

coronary heart disease cerebrovascular disease digestive diseases diabetes

% over desirable weight

Figure 6.4 Cause-specific mortality with overweight and obesity. From data reported by Lew EA and Garfinkel L (1979) Journal of Chronic Diseases 12: 563-5 76.

the solubility of anaesthetic agents in fat, so that there is a large buffer pool in the body, and adjustment of the dose is difficult.

• Most importantly, anaesthesia depresses lung function (as does being in a supine position) in all subjects. Obese people suffer from impaired lung function under normal conditions, largely as a result of adipose tissue in the upper body segment; total lung capacity may be only 60% of that in lean people, and the mechanical workload on the respiratory muscles may be twice that of lean people. Therefore, they are especially at risk during surgery.

Because of their impaired lung function, obese people are more at risk of respiratory distress, pneumonia and bronchitis than are lean people. In addition, excess body weight is associated with increased morbidity from such conditions as:

  • arthritis of the hips and knees, associated with the increased stress on weight-bearing joints;
  • varicose veins and haemorrhoids, associated with increased intra-abdominal pressure, which possibly are due more to a low intake of dietary fibre (section 4.2.1.6 and section 7.3.3.2) and hence straining on defecation than a direct result of obesity.
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