Abstract
Miller and Colagiari proposed that our human ancestors may have selected for insulin resistance during the last ice age when diets were high in protein and low in carbohydrates.1 During that time, it may have been beneficial to have insulin resistance, which enabled ongoing gluconeogenesis from the liver. As human diets have increased in carbohydrate load, insulin resistance has become detrimental, leading to hyperglycemia and type 2 diabetes.2
Bottlenose dolphins (Tursiops truncatus) ingest very high protein, very low carbohydrate diets, and it has been demonstrated that overnight fasted bottlenose dolphins (Tursiops truncatus) have multiple changes that mimic those reported in people with diabetes. These changes include increased platelet count; increased serum gamma-glutamyl transpeptidase and alkaline phosphatase; movement toward a metabolic acidic state; and decreased serum uric acid.
We hypothesized that, like humans with insulin resistance, if dolphins were fed sugars, they would develop a sustained, postprandial hyperglycemia. Nine healthy adult bottlenose dolphins were fasted for 12 hours, then fed either 2.5-4.5 kg Spanish mackerel or 2-3L 10% dextrose in Ionosol. Blood and urine solutes were tracked hourly for 24 hours. Significant changes in plasma glucose were detected in both the mackerel and dextrose feeding studies. A significant change in urine glucose concentration was found among dolphins fed dextrose but not those fed mackerel. Bottlenose dolphins appear to have adapted to maintain normal plasma glucose levels by ingesting protein, but develop a sustained hyperglycemia and hyperglucosuria after ingestion of sugars.
References
1. Miller CB, Colagiuri S. 1994. The carnivore connection: dietary carbohydrate in the evolution of NIDDM. Diabetologia 37:1280-1286.
2. Venn-Watson S, Ridgway SH. 2007. Big brains and blood glucose: Common ground for diabetes mellitus in humans and healthy dolphins. Comp Med 57:390-395.