The CDC has found that obesity is the single strongest risk factor for severe COVID-19 illness.Complications are either directly caused by obesity or indirectly related through mechanisms sharing a common cause such as a poor diet or a sedentary lifestyle. The strength of the link between obesity and specific conditions varies. One of the strongest is the link with type 2 diabetes. Excess body fat underlies 64% of cases of diabetes in men and 77% of cases in women.Health consequences fall into two broad categories: those attributable to the effects of increased fat mass (such as osteoarthritis, obstructive sleep apnea, social stigmatization) and those due to the increased number of fat cells (diabetes, cancer, cardiovascular disease, non-alcoholic fatty liver disease). Increases in body fat alter the bodys response to insulin, potentially leading to insulin resistance. Increased fat also creates a proinflammatory state, and a prothrombotic state. Metrics of health
Newer research has focused on methods of identifying healthier obese people by clinicians, and not treating obese people as a monolithic group. Obese people who do not experience medical complications from their obesity are sometimes called (metabolically) healthy obese, but the extent to which this group exists (especially among older people) is in dispute. The number of people considered metabolically healthy depends on the definition used, and there is no universally accepted definition. There are numerous obese people who have relatively few metabolic abnormalities, and a minority of obese people have no medical complications.
In 2005, the medical costs attributable to obesity in the US were an estimated $190.2 billion or 20.6% of all medical expenditures, while the cost of obesity in Canada was estimated at CA$2 billion in 1997 (2.4% of total health costs). The total annual direct cost of overweight and obesity in Australia in 2005 was A$21 billion. Overweight and obese Australians also received A$35.6 billion in government subsidies. The estimate range for annual expenditures on diet products is $40 billion to $100 billion in the US alone.The Lancet Commission on Obesity in 2019 called for a global treaty—modelled on the WHO Framework Convention on Tobacco Control—committing countries to address obesity and undernutrition, explicitly excluding the food industry from policy development. They estimate the global cost of obesity  $2 trillion a year, about or 2.8% of world GDP.Obesity prevention programs have been found to reduce the cost of treating obesity-related disease. However, the longer people live, the more medical costs they incur. Researchers, therefore, conclude that reducing obesity may improve the publics health, but it is unlikely to reduce overall health spending. Obesity can lead to social stigmatization and disadvantages in employment. When compared to their normal weight counterparts, obese workers on average have higher rates of absenteeism from work and take more disability leave, thus increasing costs for employers and decreasing productivity. A study examining Duke University employees found that people with a BMI over 40 kg/m2 filed twice as many workers compensation claims as those whose BMI was 18.5–24.9 kg/m2.