Body fat is essential for life.
White fat, or the lipid-storing depots found under our skin and around our organs, serves an important energetic and homeostatic role. Dozens of hormones and other factors are secreted from our fat tissue into the circulation, where they serve important physiological roles. Recent studies have also shown white fat to be important for immune function.
Brown fat, or the thermogenic (calorie-burning) fat, was recently identified in adult humans, although previously scientists had believed it was only found in babies (Identification and importance of brown adipose tissue in adult humans. Cypess AM, Lehman S, Williams G, Tal I, Rodman D, Goldfine AB, Kuo FC, Palmer EL, Tseng YH, Doria A, Kolodny GM, Kahn CR. N Engl J Med. 2009 Apr 9;360(15):1509-17).
These facts are not disputed. However, the correct or optimal or 'best' amount of body fat for humans to have, is still hotly-contested.
See these two recent findings:
From Doehner et al. 2009, you can see that BMIs considered overweight or mildly obese are actually NOT correlative with higher risk for mortality:
Another recent publication has come to an important clinical agreement in terms of diagnosing the metabolic syndrome - the cluster of metabolic phenotypes (including obesity) which lead to greater health risk. The most important finding is that obesity should not be considered an obligatory component of the diagnosis:
"A cluster of risk factors for cardiovascular disease and type 2 diabetes mellitus, which occur together more often than by chance alone, have become known as the metabolic syndrome. The risk factors include raised blood pressure, dyslipidemia (raised triglycerides and lowered high-density lipoprotein cholesterol), raised fasting glucose, and central obesity. Various diagnostic criteria have been proposed by different organizations over the past decade. Most recently, these have come from the International Diabetes Federation and the American Heart
Association/National Heart, Lung, and Blood Institute. The main difference concerns the measure for central obesity, with this being an obligatory component in the International Diabetes Federation definition, lower than in the American Heart Association/National Heart, Lung, and Blood Institute criteria, and ethnic specific. The present
article represents the outcome of a meeting between several major organizations in an attempt to unify criteria. It was agreed that there should not be an obligatory component, but that waist measurement would continue to be a useful preliminary screening tool. Three abnormal findings out of 5 would qualify a person for the metabolic syndrome. A single set of cut points would be used for all components except waist circumference, for which further work is required. In the interim, national or regional cut points for waist circumference can be used."