Carbohydrate metabolism isn’t as simple or easy to understand as pop-media and even sports nutritionists imply. The classic version: carbs get into the bloodstream as sugar, which hits the pancreas and causes a release of insulin. Insulin rushes through the body and shuttles sugar into cells. This is the 300 ft view.
Looking closer, it’s not insulin that carries sugar into cells; specialized transporters exist within each cell that bring sugar across the cell membrane, transporters called, not surprisingly, glucose transporters (GLUTs). The class I GLUTs—GLUT1 through GLUT4—are the best understood. (There are two more classes that contain GLUTs 5-12, but—besides the fructose transporter, GLUT5—science is still deciphering their function, and some, like GLUT6 and GLUT8 actually block glucose transport.)
Different tissue contains different transporters. Tissue with GLUT1s, GLUT2s or GLUT3s use sugar whether insulin levels rise or not. Cells of the pancreas, kidney, small blood vessels and nervous system, including those in the brain, contain GLUTs 1 through 3. That doesn’t mean these cells need sugar, only that they can always use it regardless of the presence or absence of insulin.
GLUT4, however, sits tucked within the surface of the cell membrane until the cell senses insulin, at which point the GLUT4s move to the surface and start grabbing sugar and pulling it in. Fat cells and muscle cells contain GLUT4 receptors. When the experts say the body is most sensitive to insulin in the morning, they mean GLUT4 tissue—body fat and skeletal muscle.
The plus side to this information: fat cells can’t store as much sugar as fat in the evening. The minus side: muscles can’t use carbs effectively either. There is, anyhow, a way to keep the plus and eliminate the minus. It’s something everybody reading this already does: RT—resistance training.
RT does three things. 1) It increases the number of GLUT4 receptors per cell—muscles can then absorb and use sugar more rapidly. 2) RT makes muscles hyper-responsive to insulin—fat cells may not respond well in the evening to insulin, but muscles will. 3) RT moves GLUT4s to the cell surface without insulin—cells can now start soaking up sugar for quicker recovery after a workout, even in the evening. Effects (1) and (2) last about 48 hrs, and effect (3) is immediate and short-lived, perhaps a few hours at most.
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Looking closer, it’s not insulin that carries sugar into cells; specialized transporters exist within each cell that bring sugar across the cell membrane, transporters called, not surprisingly, glucose transporters (GLUTs). The class I GLUTs—GLUT1 through GLUT4—are the best understood. (There are two more classes that contain GLUTs 5-12, but—besides the fructose transporter, GLUT5—science is still deciphering their function, and some, like GLUT6 and GLUT8 actually block glucose transport.)
Different tissue contains different transporters. Tissue with GLUT1s, GLUT2s or GLUT3s use sugar whether insulin levels rise or not. Cells of the pancreas, kidney, small blood vessels and nervous system, including those in the brain, contain GLUTs 1 through 3. That doesn’t mean these cells need sugar, only that they can always use it regardless of the presence or absence of insulin.
GLUT4, however, sits tucked within the surface of the cell membrane until the cell senses insulin, at which point the GLUT4s move to the surface and start grabbing sugar and pulling it in. Fat cells and muscle cells contain GLUT4 receptors. When the experts say the body is most sensitive to insulin in the morning, they mean GLUT4 tissue—body fat and skeletal muscle.
The plus side to this information: fat cells can’t store as much sugar as fat in the evening. The minus side: muscles can’t use carbs effectively either. There is, anyhow, a way to keep the plus and eliminate the minus. It’s something everybody reading this already does: RT—resistance training.
RT does three things. 1) It increases the number of GLUT4 receptors per cell—muscles can then absorb and use sugar more rapidly. 2) RT makes muscles hyper-responsive to insulin—fat cells may not respond well in the evening to insulin, but muscles will. 3) RT moves GLUT4s to the cell surface without insulin—cells can now start soaking up sugar for quicker recovery after a workout, even in the evening. Effects (1) and (2) last about 48 hrs, and effect (3) is immediate and short-lived, perhaps a few hours at most.
fOR MORE CLICK HERE
