Page:Popular Science Monthly Volume 83.djvu/353

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It will be clear from what has been said above that the requirements of the body for muscular labor in winter will depend on whether a person works indoors or out. Lumbermen who work in the north woods in winter probably require more food than any other class of laborers. At the opposite extreme, so far as external conditions are concerned, stand the men who work in factories, beside furnaces, etc. Their muscular work may be just as heavy as that of the lumberman, but their bodies are kept warm by artificial heat. The problem for them, as for ordinary laborers outdoors in hot weather, is rather that of removing the extra heat of muscular work.

Between these two extremes, naturally, are people who are subjected to conditions of all degrees of severity It is impossible to prescribe a day's dietary which will fit all of them. We select a teamster and a foundryman of average weight. The former we suppose not only does the heavy muscular work of lifting boxes and cases, but is exposed to cold winds and rains. The latter does heavy work but is kept warm at his task.

A person who follows his natural craving will find himself eating more meat, especially more fat meat, in winter than in summer. This is not merely because fat meat contains more energy for the same weight than starchy foods, but because foods rich in protein and fat stimulate the processes of combustion by which heat is produced. For example, a day's diet consisting of nothing but lean meat would increase the heat production by about 30 per cent. The same diet consisting exclusively of starchy foods would increase it only about 5 per cent. This is the reason why laborers in the open crave meats more than do those who work indoors.