The $64,000 Question

I've been obsessed with this question. It all started after reading the literature of pre-insulin treatment of diabetes and insulin-free animal models of the disease. Feeding fats and restricted protein, with no or minimal carbohydrate, gives the best prognosis without insulin; also fasting, which tends towards a similar mix of substrates. Then I read the literature showing inferior prognosis of type 2 diabetes with higher-carbohydrate, post-1977 diets; the longer carbohydrate is fed, the more fasting glucose climbs. Most of the glucose in the blood of diabetics comes from hepatic GNG, not dietary carbohydrate (I'm grateful to Carbsane for pointing this out to me originally - it's an important point).
I read the Richard K. Bernstein paper which describes tight control of glucose using low doses of insulin and a low carb diet, and then I watched the Robert Unger lecture I linked to in the previous post, and saw a slide of blood glucose levels in a mouse with no beta cells, given insulin normally (wide fluctuations ranging into hypo- and hyperglycaemia) or given insulin plus a glucagon antagonist.


Also compare the recent case study "Type 1 diabetes mellitus successfully managed with the paleolithic ketogenic diet" by  Tóth and Clemens.

"He was put on insulin replacement therapy (38 IU of insulin) and standard conventional diabetes diet with six meals containing 240 grams carbohydrate daily. He followed this regime for 20 days. While on this regime his glucose levels fluctuated between 68–267 mg/dL.
Average blood glucose level while on the standard diabetes diet with insulin was 119 mg/dL while 85 mg/dL on the paleolithic-ketogenic diet without insulin. Fluctuations in glucose levels decreased 
as indicated by a reduction of standard deviation values from 47 mg/dL on the standard diabetes diet to 9 mg/dL on the paleolithic-ketogenic diet. Average postprandial glucose elevation on the standard diabetes diet was 23 mg/dL while only 5.4 mg/dL on the paleolithic-ketogenic diet." 

Again the question - why does LCHF (or fasting) act like the glucagon receptor antagonist? Why does feeding glucose worsen hyperglycaemia and ketoacidosis, and fat improve them, when fat, and protein, not glucose, are the gluconeogenic and ketogenic substrates?
Could it be that in diabetes - when there is no insulin present, or when the cells of the liver are highly insulin-resistant, or when subcutaneous insulin fails to give attain an adequate concentration in the portal vein feeding the liver - glucose itself in some way promotes gluconeogenesis and ketogenesis?
Consider first that in uncontrolled diabetes blood glucose is very high and becomes even higher after carbohydrate feeding. This is especially so in the portal vein feeding the liver. Hepatocytes without insulin are not resistant to glucose, especially at high concentrations. The Glut2 receptor is not wholly controlled by insulin, though the metabolism of glucose within the cell is.

Concentrations of glucose approaching 10 mM are pre-diabetic levels. Concentrations of glucose above 10 mM are analogous to a diabetic condition within the cell culture system. This is important because the same processes that can affect cells and molecules in vivo can occur in vitro. The consequence to growing cells under conditions that are essentially diabetic is that cells and cell products are modified by the processes of glycation and glyoxidation. These processes cause post-translational secondary modifications of therapeutic proteins produced in cell cultures. [Sigma cell culture guide]
This excess glucose is getting into the cell, and is modifying its metabolism in ways that promote and increase the hormonal action of glucagon.

For example, in this mouse study.

Glucotoxicity Induces Glucose-6-Phosphatase Catalytic Unit Expression by Acting on the Interaction of HIF-1α With CREB-Binding Protein, A. Gautier-Stein et al. 2012.

We deciphered a new regulatory mechanism induced by glucotoxicity. This mechanism leading to the induction of HIF-1 transcriptional activity may contribute to the increase of hepatic glucose production during type 2 diabetes.

If that's true in humans (and I have to say it's very unlikely that glucotoxicity will do anything good for you) then minimising post-prandial glucose spikes is going to help keep a lid on fasting glucose levels as well.

There's also the concept of reductive stress; the metabolism of excess glucose will result in a buildup of NADH and a relative deficiency of NAD+. The cell copes with this by a number of mechanisms. Ketogenesis itself helps, because the conversion of acetoacetate to Beta- hydroxybutyrate generates NAD+. Under conditions of high glucose, glyceraldehyde-3-phosphate will build up in the cell unless cytoplasmic NADH is continuously re-oxidized. Cells oxidize cytoplasmic NADH by a combination of three pathways, the aspartate:malate shuttle, the glycerol:phosphate shuttle and during the conversion of pyruvate to lactate.Pyruvate may not enter the mitochondria. It may be reduced to lactic acid by lactic acid dehydrogenase. This reaction is driven when the cell’s need to oxidize NADH to NAD for use as a substrate to keep glycolysis working. Pyruvate reacts with hydrogen peroxide and forms water, carbon dioxide and acetic acid. This non-enzymatic reaction helps the cell defend itself from oxidative intermediates.

Now, in our model, pyruvate will not enter the mitochondria, because that step is controlled by insulin. This means that lactate will either be recycled to glucose or exported. So what is the link between lactate and diabetes?
Plasma lactate predicts type 2 diabetes here.
And lactic acidosis is a common finding in cases of diabetic ketoacidosis, here.
In starvation (very good account here, thanks to Ash Simmonds for the link), pyruvate, lactate, and alanine are exported to the liver for conversion into glucose. So, glucose is a gluconeogenic substrate. Meanwhile the poor hepatocyte is trying to oxidise fatty acids, making some ketone bodies in the process, but also struggling with the need to fend off, by metabolizing, devastatingly high glucose concentrations.I speculate that the liver's ATP needs are not being met under these conditions (of futile cycling), and that this is a trigger that increases sensitivity to the lipolytic effect of glucagon in adipocytes (as it is supposed to increase appetite in the liver homeostasis model of appetite regulation, how no-one knows).
And that ketogenesis is also increased by glucotoxicity. But the mechanism of all this is beyond me at present, I'm just sayin' that these are possibilities.

I don't feel that I've answered the $64,000 question yet. But I do think that idea of a glucose -> gluconeogenesis vicious cycle has merit in the type of imbalanced systems we've been looking at, where adding glucose has been a bad idea, and removing it a good one, since history began.

Now it may be that the answer is very obvious and doesn't need any of these baroque explanations.
In which case, please feel free to tell me. All I want is a formula that's consistent with every fact. Is that too much to ask?