The investigators recruited $173$ people with a normal BMI $($range $21\mathrm{.}5$ to $25)$ and $150$ who they classified as "healthy underweight" $($with a BMI below $18\mathrm{.}5).$ They used established questionnaires to screen out people with eating disorders as well as those who said they intentionally restrained their eating and those who were infected with HIV. They also excluded individuals who had lost weight in the past six months potentially related toillness or were on any kind of medication. They did not rule out those who said they "exercised in a driven way," but only $4$ of $150$ said they did.