Insulin glucagon and protein

Again from dissertante's query: How can chicken be found to raise blood glucose, acutely?

Many years ago, as a beginner at treating diabetic animals, I tried to balance insulin dose rate/timing against carbohydrate intake. Owners always asked if there was anything they could feed as treats etc. I used to suggest meat and fat as they shouldn't need insulin for processing.

This was a mistake. Dogs are, by the time we diagnose them, functionally type 1 diabetics. While fat is perfectly OK, protein certainly isn't.

Eating protein, for a type 1 diabetic, produces an immediate rise in blood glucose. This is nothing to do with gluconeogenic amino acids, the effect of which would expect to be delayed for several hours, if it occurs at all. While protein for an normal human being/animal is neutral on systemic blood glucose it never the less produces an immediate spike (by around 60 minutes) in blood insulin.

Dandona measured insulin and glucose, although not glucagon, after casein ingestion as we saw in the last post:

Eating 75g of casein protein more or less triples your blood insulin level but doesn't budge blood glucose down any more than cream does, which leaves insulin pretty well alone. Under normal conditions the casein induced spike in insulin is counterbalanced by a rise in glucagon. If the insulin rise does not occur (through beta cell failure) the glucagon will still rise and is unopposed, so hyperglycaemia is the net result, coming from a rise in hepatic glucose output.

This took me years to realise. Slow, I know but ah well.... It's now common knowledge and Dr Unger's glucagonocentric view of diabetic hyperglycaemia makes a great deal of sense.

So protein will provoke hyperglycaemia in the absence of an insulin response, via glucagon, in a type 1 diabetic. I would guess that the same would apply to an advanced type 2. It very recently occurred to me that an elevated blood glucose after protein intake might be a useful supplementary test for certain oddities in OGTTs.

I had an email a few weeks ago about OGTT results in long term, non diabetic low carb eaters. I don't know the exact details of duration of LC eating or the period of carb loading before the OGTT, but the end result after glucose ingestion was a sustained hyperglycaemia with profoundly depressed C-peptide levels.

The worry here is that long term LC might have led to endocrine pancreatic insufficiency. My initial thought was to wonder what the response to exogenous insulin might be, but this was probably the wrong line of thought.

What would be far more interesting would be to run an oral protein response test, looking at blood glucose, insulin, glucagon and C-peptide. Although, at a pinch, all you need is the blood glucose result. If a person has developed a significant loss of beta cells then the unopposed alpha cell glucagon response to this protein would produce hyperglycaemia. A normal insulin reaction in response to protein would produce normoglycaemia after said protein load.

We all know that after a month or two of LC eating that three days at 150g/d of carbs will restore a normal response to glucose. But the question is what time scale of carb loading is needed after several years of LC eating. The regulation of insulin secretion in response to glucose requires active glycolysis, regulated by glucokinase in the pancreas. Glucokinase gene expression is controlled by dietary glucose supply. If long term glucokinase down regulation takes longer than a few days of carbohydrate loading to reverse, this would produce intolerance to glucose but would have no effect on insulin secretion when driven by amino acids. It would be quite simple to differentiate between down regulation of the pancreatic glucose sensor from newly acquired type 1 diabetes during LC eating.

Summary: Elevated blood glucose after an oral protein load suggests genuine diabetes. Poor responsiveness to glucose after sustained LC eating simply reflects a mothballed glucose sensor, provided response to protein is normal.

Peter