"The new study began several years ago when the investigators used national data to look at death risks according to body weight. They concluded that, compared with people of normal weight, the overweight had a decreased death risk and the underweight and obese had increased risk."
Let's contrast this with last week's "being fat causes cancer" headlines: "[C]ontrary to expectations, the obese did not have an increased risk of dying from cancer [comparison of different types of cancer and effect of weight] ... In the end, the increases and decreases in cancer risks balanced out."
It did say this: "The higher death rate in obese people, as might be expected, was almost entirely driven by a higher death rate from heart disease." And there was a diabetes tie-in here, too.
Also, exercise is good for your brains. So can we stop obsessing about being fat (per the BMI calculator I am, FYI), and get some exercise and be happy, now?