I suspect the ideas of "insulin resistance" (and it's inverse "insulin sensitivity") are entirely explained by muscle mass and muscle glycogen (and liver glycogen).

I may be wrong; this is my current opinion; I'm not an expert; But this is informed by experts, in particular Roy Taylor, a prominent diabetes researcher from Newcastle University.

If you have a lot of muscle mass and it is depleted of glycogen (generally your liver is also depleted) you are very insulin sensitive. Your muscles will suck up sugar greedily. This happens after fasting, after exercise, and when on the keto diet (essentially a sugar fast). On the other hand, if your muscle and liver glycogen is full then you are insulin resistant. They have no room to suck up any more sugar. You can change your insulin sensitivity quickly, within hours, by eating or fasting. There is a longer-term component and a genetic component, which I presume has to do with how much glycogen your liver and muscles can hold. If you train a lot, they can hold more. But this is also partially genetically determined where some people even after training don't hold much glycogen in their muscles and are thus genetically at least somewhat "insulin resistant" all the time.

People trying to work on their "insulin sensitivity" to avoid type-2 diabetes are IMHO probably misguided. They should just try to be a healthy weight, to not overeat, and to do some exercise to keep their glycogen from filling up and spilling over into body fat.... and ignore this new mysterious thought-to-be-independent factor.

People wearing continuous glucose monitors who aren't diabetic, and even people trying to avoid "blood sugar spikes" by avoiding fruit like bananas, are IMHO also probably misguided. Blood sugar is supposed to spike - that is what insulin is for. Blood sugar spikes don't cause diabetes... it is only high blood sugar that remains high that *signals* diabetes (high blood sugar is an effect of diabetes, not a cause). We evolved to eat fruit and honey for god sake. Epidemiological research shows people that eat a lot of complex carbs live the longest. Gut bacteria need fiber (a carbohydrate) to produce the chemicals that our health seems to depend on.

Diabetes is caused by (based on Roy Taylor's research):

1. Your propensity to store fat viscerally (mostly genetically determined, and widely ranging)

2. Your beta cell tolerance to visceral fat (this also ranges widely and is apparently genetically determined),

3. Based on 1 & 2, if you are over your personal weight threshold such that enough viseral fat has entered your pancreas to cause those beta cells to stop functioning.

Diabetes can be reliably reversed by losing weight... and eating sugar if you want, as long as you lose weight. Roy Taylor reversed diabetes in people by feeding them a complete nutritional supplement (these tend to be 60% carbohydrate) that wasn't enough to meet daily caloric needs, so they lost weight.

There was some clear research based on MRI scans of pancreatic fat that determined that yes, thin people with type-2 diabetes have fat pancreases, even though they don't appear to be fat. And fat people without diabetes don't have fat pancreases. So the connection is pretty clear.

#DontFearTheCarbohydrate