In 1910, thin was already in for both health and fashion. But Dr. George Niles has some really practical reasons why it might be good to be fat:

Suppose a ship went down in midocean and a few of the passengers and crew got off on a raft. Suppose on one of the rafters was a man of about 40 per cent fatty matter — the kind that has not seen his shoelaces for ever and ever so long — according to Niles’s theory he would outlive the whole crew, granting of course (which the doctor does not) that the raft does not ground on a cannibal island or the crew draw lots with stacked chips…

Dr. Niles explains it thus: “Fat is like a housewife who, though not apparently earning anything, by her care and industry conserves the fruits of her husband’s labor, enabling him not only to support the domestic establishment, but also lay aside a surplus.”

Furthermore, the doctor “also asserts in so many words that to be fat is to be genial in disposition and optimistic in temperament, while to be thin is to be restless, pessimistic, uncontented and temperamentally dissatisfied with life in general.” Therefore, he adds, “grow fat and rejoice in your fatness.”

BEING FAT IS LIKE HAVING MONEY IN THE BANK: At Last a Physician Rises Up and Seriously Defends Surplus Flesh; Which Should Comfort Thousands (PDF)

From May 15, 1910