Scientists from Deakin University in Australia and the University of Auckland in New Zealand report that ingestion of a single breakfast with about 30 grams of protein from dairy activated mTOR in healthy middle-aged men, whereas an equivalent soy protein-rich breakfast did not.
“We report that when matched for total protein, fat, and similar in carbohydrate content dairy and soy based meal result in very similar blood glucose and insulin responses but that the dairy meal results in a more sustained BCAA concentration in the plasma and a larger branched-chain amino acids area under the curve (BCAA AUC),” wrote the researchers in Nutrition & Metabolism.
“The more sustained BCAA response is likely a result of the greater BCAA content in dairy meal and a slower release from the gut.”
The study, which was funded by the Australian Dairy Health and Nutrition Consortium, also found that middle-aged men with metabolic syndrome had impaired mTOR signaling in response to both protein-rich breakfasts.
'More study needed'
Commenting independently on the study's findings, Ralf Jäger, PhD, President of Milwaukee-based consultancy Increnovo, told NutraIngredients-USA: "Gran et al showed that certain markers of muscle protein synthesis are impaired in middle aged men with metabolic syndrome. Dairy protein seemed to be more effective in activating markers of protein synthesis in comparison to soy protein. The authors attributed difference to a 20% higher leucine content in the dairy protein.
"Acute anabolic signalling measurements throughout the mTOR pathway do not always translate in actual increased muscle protein synthesis. A follow-up study needs to include actual measurements of body composition to conclude that different protein sources actually have different physiological meaningful effects in this specific population."
Led by Petra Gran from Deakin University, the researchers recruited 10 healthy men and 10 men with Metabolic Syndrome. MetS is characterized by central obesity, hypertension, and disturbed glucose and insulin metabolism. The syndrome has been linked to increased risks of both type-2 diabetes and cardiovascular diseases.
The men were randomly divided to consume energy-matched breakfasts made with either dairy-protein or soy-protein foods in a single-blinded randomized cross-over design study. “The primary novel aspect of this study was the ingestion of a complete breakfast consisting of whole foods rather than an isolated liquid protein supplement,” explained Gran and her co-workers.
Muscle biopsies taken two and four hours after feeding indicated that only the dairy meal was associated with increases in mTOR phosphorylation two hours after feeding, but only for the healthy men. Ribosomal protein S6 phosphorylation also increased following the dairy meal only. Ribosomal protein S6 is also a downstream target within the mTOR pathway, explained the researchers.
No differences between the groups were observed for mTOR phosphorylation in the men with MetS.
“There are many conflicting reports in the literature concerning anabolic resistance of protein synthesis and anabolic signaling deficits in ageing; even less is known about anabolic resistance or signaling deficits in middle aged men with obesity and metabolic syndrome,” wrote the researchers. “We report that MetS is associated with impaired downstream signaling in the mTOR pathway in response to two different high protein mixed meals. Secondarily, we report that other mTOR pathway targets are activated to a greater degree following dairy mixed consumption compared with a soy based meal matched for protein.
“Future work should look to use measurements of muscle protein synthesis to directly assess differences in anabolic sensitivity in subjects with MetS using mixed meals rather than amino acid infusions and clamp methodology,” they concluded.
Source: Nutrition & Metabolism
“Muscle p70S6K phosphorylation in response to soy and dairy rich meals in middle aged men with metabolic syndrome: a randomised crossover trial”
Authors: P. Gran, A.E. Larsen, M. Bonham, et al.