This article was published six years prior to the discovery of insulin. The link below describes a doctor's method of starving diabetic patients until they were sugar free. Then a carefully structured diet was used to keep the patients relatively free of sugar. The diet was low in carbs, and high in fat. Several case histories are presented so we can see exactly how effective the diet was. Very impressive!!
Apparently a LCHF diet was the only way of staying alive and healthy before insulin was discovered.