From the wikipedia page on Vilhjalmur Stefansson
Stefansson is also a figure of considerable interest in dietary circles, especially those with an interest in very low-carbohydrate diets. Stefansson documented the fact that the Inuit diet consisted of about 90% meat and fish; Inuit would often go 6 to 9 months a year eating nothing but meat and fish—what was perceived to have been a no-carbohydrate diet. He found that he and his fellow explorers of European descent were also perfectly healthy on such a diet. While there was considerable skepticism when he reported these findings, they have been borne out in later studies and analyses. In multiple studies, it was shown that the Inuit diet was a ketogenic diet although a percentage of its calories are derived from the glycogen found in the raw meats, although the native Eskimo ate a diet of primarily stewed (boiled) fish and meats. When medical authorities questioned him on his findings, he and a fellow explorer agreed to undertake a study to demonstrate that they could eat a 100% meat diet in a closely observed laboratory setting for the first several weeks, with paid observers for the rest of an entire year. Stefansson was compensated for his efforts by the American Meat Institute. The results were published, and K. Andersen had developed glycosuria during this time, which is normally associated with untreated diabetes. But unlike the pathology of diabetes, in this particular study, glucosuria was present in K. A. for 4 days and coincided only with the giving of a 100 gm of glucose for a tolerance test and with the first 3 days of his pneumonia, where he received fluids and a diet rich in carbohydrate. Once that situation resolved, the glucosuria disappeared. However, Stefansson and Andersen's doctors admitted that their subjects were unable to survive on the significantly higher protein diet that had been observed in the early stages of the dietary experiment. This was due to the doctors insistence on "normal cuts" of meat that were higher in protein and lower in fat as compared to their earlier experiences on the Inuit diet, and the two white explorers could only complete the experiment by eating their own choices of meat which in effect restricted the higher protein and significantly increased the fat intake.
I've also read that the Inuit diet worked because they ate the whole animal, in particular the fat, offal and bones/marrow and less muscle meat.