My Sump-Pump Analogy for the ß-Cell
I'm going to try to make this as short and to the point as possible. It's just me thinking out loud a bit, drawing on the massive amount of peer review research I've read on the topic -- a mere fraction of which I've formally blogged on -- but without any references so that I can just get this out there. No ... this is not some manifesto grand theory on diabetes and all that to be analyzed and picked apart as if I'm presenting this as fact. It's just a plausible analogy for what I think happens when metabolic mahem turns to "diabetes". I'm also going to simplify things and deal with only glucose and fatty acids here.
Our ß-cells metabolize glucose and fatty acids the same way our other cells like muscle cells do for energy. Essentially this metabolism is part of the mechanism by which the ß-cell senses the circulating levels of these energy substrates. This metabolism also produces ROS -- reactive oxidative species. While ROS are often seen as detrimental, due to the fact that they are in inappropriate amounts, the ROS molecules also play key signaling roles. The metabolism of glucose and fatty acids produce a different redox state and ROS so this is roughly how the cells can tell what's being metabolized, etc.
Insulin is secreted by ß-cells in response to both glucose and fatty acids. In response to a sharp rise in glucose (e.g. eating a carby meal), an insulin "spike" is mounted -- an acute secretion of insulin -- the GSIS = glucose stimulated insulin secretion. However we always have some basal level of circulating insulin (and it isn't as simple as some constant slow secretion) that is regulated to a significant degree by the levels of circulating free fatty acids, NEFA. The production of insulin can be simplified to modification of a precursor protein (proinsulin) to form insulin granules packaged in vesicles which eventually are released into circulation by the process of exocytosis. There is some evidence that high demand for basal insulin depletes the proinsulin stores so that the cell can no longer produce the larger amounts of insulin required for an appropriate GSIS.
The ß-cell takes up glucose via GLUT transporters -- proteins that allow glucose to pass through the membrane. While most are familiar with the insulin-stimulated GLUT4, the major transporters in ß-cells are GLUT2. Fatty acids do not require transporters, but there is evidence that NEFA uptake is a combination of both passive diffusion and membrane-protein (FA transporter) mediated. While it may be a bit of an oversimplification, since glucose requires transporters (though not necessarily insulin) for uptake while NEFA do not, the ß-cells, like other non-adipose cells, cannot refuse the delivery of fatty acids. Once inside the cell, that which is not oxidized is esterified -- converted to triglycerides -- for local storage. These local storage depots are called lipid droplets, and are perfectly normal. However once esterified, the NEFA concentration inside the cell is kept low, and if the circulating level is high, thanks to diffusion the cells keep taking up fatty acids and fatty lipid droplets grow.
We can think of the ß-cell as having a well that fills with fatty acids and glucose that are metabolized for energy or pumped out temporarily with a sump-pump and used in timely fashion. The level of the "float" on that automatic pump regulates how much insulin is produced in the basal state to try to suppress NEFA release from adipose tissue in the fasted state and keep glucose production in the liver in check to effectively lower the level in the well. Float up = hyperinsulinemia, float down = low basal insulin production. It's like that pump in a leaky basement. Slight trickles, the pump goes on a couple times a day. Big rain storm and the pump is going on every hour.
Now this analogy is tricky, because the ß-cells are not pumping out glucose and fatty acids, but rather insulin. So let's think of the insulin as a current requirement to power the pump. The more the pump is required to run, the greater the continual current requirement. A semi-renewable power source will work for this analogy -- e.g. a rechargeable battery with a slow recharge rate, so that if you run the pump on battery too long it can't keep up. In the normal pancreas, the battery charge rarely goes below, say, 75% in response to a surge in flow of glucose, and is recharged to 100% in between. But in the over-nourished state, the pump is working 24/7 to keep the well level down while still working well enough to deal with the intermittent deluges. Perhaps the well level gets closer to the overflow and the pump has to work for longer to get the level back down, but the ß-cells manage. Indeed in many "pre-diabetics", the pancreas compensates by putting more pumps (increased ß-cell mass) into the well. Still with the increased running times, the battery charge now barely makes it to 75% before it's drained again, and now the charge goes down below 50% or even lower when the surges come. The pump is still working.
All the while, some of the excesses from the well have been moved to overflow tanks and now these are full-up. Now the well fills and despite the pump going all the time, it can't keep the level down. The pump runs and runs, it can't recharge fast enough. The glucose flood comes and it tries to make enough insulin, but the battery is fully discharged by the attempt. Perhaps this is also analogous to a sump pump in the well where the flow in exceeds the pump's ability to pump out -- once the well is overflowed into the basement, the pump "float" no longer sees gushes. It just keeps running and running trying to get the level down but it doesn't "see" the periodic influx from the downpours any differently from the constant ground water trickle because the level is too high. At some point, this is your ß-cells. They are now malfunctioning. You are officially diabetic with chronic hyperglycemia.
If it's your basement, perhaps you do whatever it is you do (pray? an anti-rain dance?) to get the water flow to stop so your pump can eventually get rid of all the water. Otherwise you call in the fire department and the pump has long since been shut off to avoid burning out the motor. The FD comes in with their mega pumps and removes the water. You turn the pump back on and it's able to function again.
Over the past year I've blogged on *reversal* of the diabetic state by gastric bypass surgery (GBP), the "crash" diets (very low calorie VLCD) and early insulin therapy. All of these are generally poo-pooed in the low carb community because basically they are fixated on (a) lowering insulin and (b) reducing dietary carbohydrate contributions to blood glucose levels. Certainly there's utility in the latter for controlling hyperglycemia to a degree, but in my opinion, the insulin lowering strategy is ill-conceived as it is implemented. Let's look at the reversal strategies using our analogy.
1. Early Insulin Therapy, EIT: The progression of ß-cell malfunction seems to start with excessive fatty acids (lipotoxicity) and snowball with the combination of fatty acid and glucose excess (lipotoxicity + glucotoxicity = glucolipotoxicity). Although the majority of T2 diabetics have "functioning" ß-cells, once this function is insufficient to maintain glycemic control (the end of the line) and a diabetes diagnosis is made, it seems that the hyperglycemia per se makes matters even worse. EIT is analogous to calling in the fire department. The exogenous insulin is like bringing in the super pumps to bring down the flood waters of nutrients. EIT is also a bit like getting the prayer or whatever answered as well because the insulin will help trap the fatty acids in the fat cells (where they belong) and stem the incessant flow of glucose from the liver.
2. Crash Diets: The crash diets stop the inflow of BOTH fatty acids and glucose into the well and the significant calorie deficit allows the pancreas to drain the filled-to-the-gills overflow tanks -- e.g. pancreatic fat. In the recent study, we see that even without changes in the basal state, the acute response was already improved. The combination of virtually eliminating the added nutrients and draining the local overflow tanks seems to be enough to allow the ß-cell to resume functioning.
3. GBP Surgery: It may well be that this works largely by means of #2. There is additional (and perhaps longer term) evidence that improved incretin (GLP-1 specifically) responses that stimulate insulin secretion and other things, plays a role.
So what of low carb successes? Well, I submit that in the short term, the *normal* Atkins-induction style diet is successful largely by means of #2. Folks going on a low carb diet, especially VLC for the very first time (sung to the tune of Madonna) spontaneously reduce intake dramatically and don't "up the fat". But the results -- even with legit VLC like the touted Westman study -- are largely attained in the first few months with no further improvements, and seem to be mostly in the area of reducing insulin dosage. In other words, lower dietary carb = lower pp insulin dose needed. But even Wheat Belly describes his diabetes as in remission. One tiny carb dose sends his blood glucose soaring. Fat Head, who didn't have BG issues before going low carb, now describes similar if he were to eat starches. This is because those eating maintenance low carb high fat likely have their ß-cell fatty acid wells all full up and they've adapted their metabolisms to a lower insulin response. For those who have reversed their diabetes, many will never even know, I'm afraid, because they are slaves to their glucometers and hysteria over glucose "spikes" so they'll never know if they can be *normal*. Eating energy balance calories, with high levels of fats and low dietary carb only stops the periodic rain showers. It does nothing for the ground trickle and perhaps even increases it. Why? Because if VLC is effective in lowering basal insulin without improving hepatic/adipose sensitivity to insulin, the trickle may even increase due to (a) improper suppression of NEFA release from adipose tissue and/or (b) improper suppression of endogenous glucose production by the liver.
So there you have it. The ardent low carbers are trying to deal with flooded basements by putting an umbrella over their ß-cells and diverting the intermittent glucose downpours. Little do they realize that fatty acids permeate their umbrellas. They do nothing, absent substantial and sustained weight loss, about that ground flow, and may even increase it. The "crasher" or EIT'er has either called in the fire department or stemmed the downpours sufficiently to allow their sump-pumps the opportunity to return to "functioning". Perhaps this is analogous to the pump being reset a little higher up in the well after emergency measures get it within operating range. As things improve, the pump can be repositioned back where it belongs.