“‘Obesity,’ and sometimes even ‘overweight,’ are claimed to ‘cause’ or ‘lead to’ CVD [cardiovascular disease], T2DM [type 2 diabetes], some types of cancer, and osteoarthritis. As with mortality, many studies have demonstrated an association between these morbidities and body weight, though others have not. Similar to studies showing associations between fatness and mortality, studies that have shown associations between fatness and morbidities are criticized for failing to control for potential confounding factors. Physical activity, fitness, weight cycling, and diet history have all been demonstrated to be associated with adiposity, and are therefore confounding factors in any analyses of the relationship between adiposity and mortality or morbidity. A range of social factors such as poverty, social class, and income are also associated with adiposity, and are therefore additional potential confounding factors in mortality and morbidity analyses. The Whitehall II Study of British civil servants demonstrated a strong inverse association between employment grade and the risk of metabolic syndrome, with only 10% of metabolic syndrome being explained by traditional risk factors. The biologically plausible explanation for this is that stress results in chronic inflammation. Chronic inflammation has been demonstrated to be an important risk factor for the development of T2DM, independent of body weight.”

- http://journals.sagepub.com/doi/full/10.1177/2158244018772888