A study published earlier this year suggests that fat people can be as healthy as thin people. A group of medical doctors tracked the weights and habits of 12,000 people over several years. They found that the people who are most at risk of dying young are those who are obese but do not engage in any "healthy activities" like exercising or eating vegetables. Obese people with healthy habits had roughly the same risks as thinner people of dying young.
Over at Sociological Images, Lisa Wade explains this chart (pictured) of the group's findings:
The "hazard ratio" refers to the risk of dying early, with 1 being the baseline. The "habits" along the bottom count how many healthy habits a person reported. The shaded bars represent people of different BMIs from "healthy weight" (18.5-24.9) to "overweight" (25-29.9), to "obese" (over 30).
The three bars on the far left show the relative risk of premature death for people with zero healthy habits. It suggests that being overweight increases that risk, and being obese much more so. The three bars on the far right show the relative risk for people with four healthy habits; the differential risk among them is essentially zero; for people with healthy habits, then, being fatter is not correlated with an increased relative risk of premature death. For everyone else in between, we more-or-less see the expected reduction in mortality risk given those two poles.
This data doesn't refute the idea that fat matters. In fact, it shows clearly that thinness is protective if people are doing absolutely nothing to enhance their health. It also suggests, though, that healthy habits can make all the difference. Overweight and obese people can have the same mortality risk as "normal" weight people; therefore, we should reject the idea that fat people are "killing themselves" with their extra pounds. It's simply not true.