The Fat Cell 11: Insulin and Exercise
Cats, Cows and Sciatica
Exercise helps cells become more sensitive to insulin. The evidence for this across populations of different ages, weights, and conditions is overwhelming. Pinpointing the exact mechanism that ends with such a positive result is, as usual with biological mechanisms, problematic; but one hypothesis gathering steam is based on TBC1D proteins in the muscle cell.
Muscle cells during exercise deactivates a protein TBC1D1 by adding phosphorus atoms to a precursor. At rest, muscle and fat cells will use a slightly different mechanism to withdraw glucose from the blood, by deactivating a TBC1D sibling, TBC1D4.
Both proteins when active inhibit the production of GLUT 4 (the molecule that rises to the surface of the cell and captures glucose), but exercise works like a gag on the TBC1D siblings. When the inhibition is decreased so the cell produces more GLUT 4.
Recap! Food becomes glucose in the bloodstream which clues the pancreas to produce insulin. The insulin rides the blood stream until it finds a fat or muscle cell and then inserts itself into an insulin receptor on the surface of the cell. The insulin kicks off a series of molecular reactions inside the cell which includes TBC1D. GLUT 4 molecules rise to the surface and snags the glucose riding the bloodstream. The less GLUT 4, the more glucose stays in the bloodstream and the more it ends up in other areas of the body where it does not belong. Over time there may even be permanent damage. Not good. Keeping the cells highly responsive to insulin is obviously crucial to the functioning of the body. It appears that exercise helps the cells sensitivity by the phosphorylation (adding phosphorus atoms) to a molecule, Akt, just upstream from TBC1D.
The dampening of TBC1D1 happens immediately but dampening TBC1D4 has an especially interesting result. The response is delayed. The phosphorus molecules do not gag TBC1D4 until later, after the initial glucose has been scavenged from the bloodstream; but the late response means the cell is primed to capture more glucose when it does arrive again, resulting in more insulin sensitivity.
Exactly what type, intensity and length of exercise is the most beneficial is still under investigation, although there is good evidence that high intensity interval training increases GLUT 4 and insulin sensitivity the most compared to moderate continuous training. Many but not all studies show that the biggest improvements are seen with a combination of both aerobic and resistance training. Astonishingly, even one average exercise episode creates molecular changes leading to more insulin sensitivity and lasts up to five days. 
Long before the difference appears on the scale or the blood pressure monitor, the cells know. “Who knows what evil lurks in the hearts of men (and women)?” Forget The Shadow, The Cell knows.
Weighing in at 183.6. Since week one, 13.4 lbs lost, she says nonchalantly. Ha! I wanted to throw confetti when I got on the scale. I am still overweight. According to the charts I have fourteen more pounds to lose before I can officially claim “not fat,” but I don’t feel fat anymore. For a while, I felt like I was pouring myself out of the car, onto the couch, into my clothes, like butter in Death Valley.
Actually, the molecular composition between the butter and the weight I lost has a distasteful similarity.
I am surprised that thirteen pounds makes such a big difference. I am hardly lean, and yet, I am moving through space much more easily, less like butter melting, more like a panther in motion - or at least, that’s the image in which my overactive-serotonin-dosed brain indulges. The truth may be more along the lines of a dancing bovine.
That was until I hurt my back. Again. Only some of my habits have been turned around. I have not exercised since I re-injured my back months ago for fear of injuring it again, but the caution failed. I hurt it again - perhaps because I have not exercised. Now that I know a few more details of the effect of exercise on the cells, I am kicking myself (weakly, due to being out of shape) for not taking steps, aerobic or otherwise, to prevent this. Just as soon as I can pull myself out of this chair without being in pain, I am ramping up my activity level. My inner panther requires it. Growl.
 Bird SR, Hawley JA. Update on the effects of physical activity on insulin sensitivity in humans. BMJ Open Sport Exerc Med. 2017 Mar 1;2(1):e000143. doi: 10.1136/bmjsem-2016-000143. PMID: 28879026; PMCID: PMC5569266.
About the Creator
D. Thea Baldrick
By wedding two strange bedfellows, bachelor degrees in Biology and Literature, the resulting chimeric offspring are stories laced with science. I publish with thecollector.com and Underland Arcana. Unearth at dthea.com
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