David F. Williamson, a senior epidemiologist with the Centers for Disease Control and Prevention whose research is cited by the paper, raised some issue with the numbers used. He felt the researchers did not explain how accurate their numbers might be.
"Even political polls always report a margin of error," he said, explaining that he did not know how accurate the three quarters of a year lost to obesity (listed as .71 years) might be. "They present it as though it's a fixed number and we know that it's not."
He noted that the number might be accurate or might reflect that a possible reduction in lifespan is close to no effect.
"The estimate may be very reliable and it may be compatible with no," he said. "I just don't know what to make of this."
Stewart responded that the researchers used a number of models to make their predictions, and so while the possible variance in age was not definite, a number of possibilities were considered.
Williamson also said he did not believe an ideal scenario of all nonsmokers of normal weight presented in the paper could be achieved, so he did not see why that model was shown.
"We know we're not going to get a population where everyone is normal weight," he said. "I just question why you would show that scenario."
Normal weight for everyone may also not be ideal. Recent research has suggested that being slightly overweight may help increase lifespan, especially as someone gets older and is more prone to fall ill.
"When you gain weight, you not only gain fat but you gain muscle mass and bone," said Williamson. "I think there's a fairly wide range of body mass, adjusted for height, that are compatible with good health. The extremes are to be avoided."
Williamson however praised the discussion in the paper for talking about ways in which obesity can be dealt with.
He noted that attention to the problems of obesity may already be having an effect, as there has been some suggestion that the rise of recent years is tapering off.
"We don't know why it's leveling off," he said, noting that it could also be related to genetics.
"Maybe we just hit the ceiling. I mean, how much more can we eat?" he said, adding, "I'm hoping that it is leveling off, because I don't believe that obesity, however it's defined, is [making] us better off."