Health and Obesity
The state of obesity is definitely correlated with exacerbation of several disease states. Several systemic reviews and/or meta-analysis' noted that the state of obesity is associated with worsened symptoms and signs of Polycystic Ovarian Syndrome (PCOS), Pulmonary Function and Cardiovascular Risk, Asthma, Obstructive Sleep Apnea, Kidney function, Schizophrenia, Bipolar Disorder, Alzheimer's, worsened Breast Feeding potential and heightened risk of Pregnancy complications as well as preeclampsia, and increased risk of Colorectal Adenocarcinoma.
Several Meta-analysis' indicate that obesity is correlated with disease states and appears to be further correlated with worsened disease progression over time (when compared to leaner subjects with the same disease state)
Conversely, BMI appears to be inversely related to success of suicide attempts (although attempts in women only are positively correlated) and the evidence of BMI influencing cancer survival during chemotherapy is mixed.
The above studies establish a relationship between obesity and several disease states, but do not per se establish a causative link. However, unless the (obese/overweight) person being assessed is not the statistical norm it is possible these results would apply to them
Obesity and Activity
Sumo wrestlers tend to be a hot topic in regards to 'Health at Every Size®' due to their body mass exceeding the standards of obesity yet the strength and activity level of an average Rikishi exceeding most of the population.
In sumo wrestlers, the large amount of daily physical activity conducted in accordance with a high calorie diet and state of obesity does not appear to be enough to normalize some health parameters; Type II diabetes, triglycerides, and hypertension are still higher in highly active sumo wrestlers when compared to age-matched controls of normal BMI status. This study noted no significant differences in blood glucose or total cholesterol but worsened parameters otherwise, and it should be noted that the difference in average weight was a mere 12.2kg (88kg in control, 100.2kg in Rikishi) which is not the size many associate with a 'sumo wrestler'.
The risk of premature death is higher in sumo wrestlers when comparing the heaviest weight class against lower weight cohorts; an increase in risk of death was very significant when compared against age-matched controls, although it is hard to delineate if this is due to obesity or due to professional contact sports, some evidence towards it being weight related is an association between weight and premature cardiovascular death in NFL players of heavier weight but to a lesser extent in lighter weight NFL players. Retired NFL players also appear to be at greater risk for metabolic syndrome if their BMI is greater, and the state of obesity in athletes of this caliber is associated with hepatic damage, assessed by ALT levels.