More about protein...

In last week’s discussion, the Cooke study was used to demonstrate how whey protein supplements enhance performance.  The Cooke study states that protein supplements providing “exogenous amino acids, especially within the first 4 hours after resistance exercise (as implemented in the study), increases protein synthesis, decreases protein breakdown, and produces a positive protein balance, thus providing an environment for muscle growth” (Cooke et al, 2010).  This week, the search was for studies that supported the use of milk-based protein, such as whey, for muscular anabolism. 

Tipton et al set up a study to examine the response of muscle protein balance when subjects consume whey proteins either before or after resistance exercise (Tipton et al, 2007).  There were both male and female subjects; seventeen total.  None of the subjects had done regular resistance training for at least five years prior to the study, and all were young and healthy (Tipton et al, 2007).  The volunteers were randomly assigned to two groups:  Group A consumed a 300-ml solution of 20g whey proteins before exercise (PRE); Group B consumed the same amount of whey protein post exercise (POST) (Tipton et al, 2007).  There was no placebo group.  Each group conducted ten sets of eight leg extension exercises. 

The researchers sampled the subjects before protein ingestion and four hours after to measure the amino acid uptake.  The researchers found that the timing of the protein ingestion had no effect; however, it was the combination of the free amino acids and carbohydrates that did have an effect on the measurements (Tipton et al, 2007).  Phenylalanine concentrations increased immediately after ingesting whey protein for both PRE and POST groups, but there was no significant difference between the PRE and the POST groups (Tipton et al, 2007).

Elliot et al set out to discover if whole foods would have an effect on muscular anabolism.  Again, the twenty-four subjects had not participated in regular resistance training in at least five years prior to the study (Elliot et al, 2006).  The subjects were randomly assigned to three groups:  1)  237g fat free milk (FM), 2) 237g whole milk (WM), and 3) 393g fat-free milk isocaloric with the whole milk (IM).  There was no placebo group.  Each group ingested their protein one hour after leg exercises, and researchers measured amino acid balance across the leg to determine net muscle protein balance (Elliot et al, 2006).  The groups were tested just before exercise and 55 minutes post-exercise; as well as, immediately prior to consuming their drink (Elliot et al, 2006).

The researchers discovered that the amino acid uptake was higher for the WM group (Elliot et al, 2006).  The threonine exchange was present in all three groups; this was measured in arterial concentrations.  The phenylalanine in muscular concentrations was present in all three groups; this was measured via biopsy of the muscular tissue (Elliot et al, 2006).  The researchers concluded that the milk ingestion stimulates phenylalanine and threonine net uptake and promotes muscular anabolism.

Both the Elliot and Tipton studies determined free amino acid concentration via GCMS and used muscle biopsies to analyze for intracellular amino acid concentrations.  All three studies used non-athletes as their subjects.  All three studies demonstrate that it is best to combine the carbohydrate with the amino acid source to stimulate net muscle protein synthesis and muscle growth, which is why the whey protein and whole milk are useful to athletic performance.

Cooke, Matthew; Rybalka, Emma; Stathis, Christos; Cribb, Paul; Hayes, Alan. Whey protein isolate attenuates strength decline after eccentrically-induced muscle damage in healthy individuals.  Journal of the International Society of Sports Nutrition 2010; 7:30

Elliot, Tabatha A; Cree, Melanie G; Sanford, Arthur P; Wolfe, Robert R.; Tipton, Kevin D.  Milk Ingestion Stimulates Net Muscle Protein Synthesis Following Resistance Exercise.  Medicine and Science in Sports and Exercise  2002; 38: 667-674

Tipton, Kevin D; Elliot, Tabatha A.; Cree, Melanie G; Aarsland, Asle A; Sanford, Arthur P; Wolfe, Robert R.  Stimulation of net muscle protein synthesis by whey protein ingestion before and after exercise.  American Journal of Physiology-Endocrinology and Metabolism  2007; 292: E71-E76