Protein

[Doc-t]

@KarenM 1st let me copy the abstract then I will follow that with my interpretation.

Abstract

Activation of the mechanistic target of rapamycin (mTOR)-controlled anabolic signaling pathways in skeletal muscle of rodents and humans is responsive to the level of dietary protein supply, with maximal activation and rates of protein synthesis achieved with 0.2 to 0.4 g protein/kg body weight (BW). In horses, few data are available on the required level of dietary protein to maximize protein synthesis for maintenance and growth of skeletal muscle. To evaluate the effect of dietary protein level on muscle mTOR pathway activation, five mares received different amounts of a protein supplement that provided 0, 0.06, 0.125, 0.25, or 0.5 g of crude protein (CP)/kg BW per meal in a 5 × 5 Latin square design. On each sample day, horses were fasted overnight and were fed only their protein meal the following morning. A preprandial (0 min) and postprandial (90 min) blood sample was collected and a gluteus medius muscle sample was obtained 90 min after feeding the protein meal. Blood samples were analyzed for glucose, insulin, and amino acid concentrations. Activation of mTOR pathway components (mTOR and ribosomal protein S6 [rpS6]) in the muscle samples was measured by Western immunoblot analysis. Postprandial plasma glucose (P = 0.007) and insulin (P = 0.09) showed a quadratic increase, while total essential amino acid (P < 0.0001) concentrations increased linearly with the graded intake of the protein supplement. Activation of mTOR (P = 0.02) and its downstream target, rpS6 (P = 0.0008), increased quadratically and linearly in relation to the level of protein intake, respectively. Comparisons of individual doses showed no differences (P > 0.05) between the 0.25 and 0.5 g of protein intake for either mTOR or rpS6 activation, indicating that protein synthesis may have reached near maximal capacity around 0.25 g CP/kg BW. This is the first study to show that the activation of muscle protein synthetic pathways in horses is dose-dependent on the level of protein intake. Consumption of a moderate dose of high-quality protein resulted in near maximal muscle mTOR pathway activation in mature, sedentary horses.

Interpretation

This is a brilliant find PLUS you were reading my mind! I am getting ready to do a podcast on Rapamycin and mTOR.

This abstract describes a study where sedentary horses were fasted and then a baseline blood sample and a 90 minute post protein meal sample was made for blood glucose, blood insulin and blood amino acid concentrations. A muscle biopsy was also obtained from the upper hind limb and analyzed for evidence of mTOR activity as a sign of muscle building. The abstract correlated an increase of a target of mTOR but did not show causation between protein intake and muscle growth. The “P value” showed significance that the mTOR pathway was activated with protein consumption.

mTOR is a large protein in every cell of every multicellular organism. This includes humans, horses, insects, and virtually every animal on the planet.The purpose of this protein is to measure availability of nutrients for cells. When there are nutrients then the cell will be allowed to grow. When there are no nutrients then the cell stops growing and goes into clean up mode through autophagy.

Rapamycin is a bacteria found in the 1970’s that when applied to cells causes them to shut down. I’ll go into this in the podcast. Time restricted eating also does this in humans.

What was of interest to me was that the range of high quality protein fed was from 0.13=g per pound body weight up to 1.1g per pound body weight. I have suggested 0.5 to 1.0g per pound of body weight. There was a direct and significant rise in blood glucose, blood insulin, blood amino acid concentrations as well as an increase in mTOR activation and downstream activity of mTOR all corresponding to the graded increase in the amount of protein fed. However, the statistical difference between 0.5 and 1.0g per pound of body weight was not significant for mTOR activation.

Why did the blood glucose and blood insulin rise with a protein only diet? I would guess it is because these were described as sedentary horses and that their diet up until fasting was most likely high in sugar. Based on what I know, the horses would need to be on a restricted carbohydrate diet before performing this study. I would also add data from muscle growth and strength development and not just make a correlation of mTOR activity. You need mTOR activity for any cell to grow (including cancer cells).

While this study was significant for showing a response of mTOR in the muscle cells from feeding a high quality protein to sedentary horses it did not alter (for me) my experience that horses consuming high quality protein in a non-inflammatory environment improve all their protein tissues. As of yet, I have not found information of how inflammation affects mTOR.

Thank you again for finding this and asking me for an interpretation. I hope this doesn’t confuse things. mTOR is confusing at first. I think my podcast on this will be out towards the middle of August. Doc T

[KarenM]

Cool. Looking forward to the podcast. Funny that my wandering through the interwebs intersected with a topic already in consideration. Excellent.