Hyperthyroidism is accompanied by an increased metabolism which causes the body to burn up first its available carbohydrates, then its superfluous fat and later its protein. The exact source of the energy that goes into the production of the excess heat is obscure. Carbohydrates are, in normal persons, an important source of heat production. In hyperthyroidism the glycogen content of the liver is greatly depleted, if not completely exhausted, as was shown by Cramer and Krause,1 Kuriyama,2 Fukui3 and Coggeshall and Greene.4 Yet in this condition Denis, Aub and Minot,5 Gardiner-Hill, Brett and Smith6 and Sanger and Hun7 observed reduced tolerance for sugar. Boothby and Sandiford,8 as a result of extensive experiments, concluded that "there is no measurable increase in the endogenous protein metabolism in exophthalmic goiter; therefore it can not be the cause of the increased basal metabolism in this disease."
HEPLER OE. FAT TOLERANCE IN HYPERTHYROIDISM. Arch Intern Med (Chic). 1935;55(6):979-996. doi:10.1001/archinte.1935.00160240108006