In the paper that has been published in the reputable scientific journal "Diabetes", Gordon I. Smith and colleagues describe an experiment the results of which clearly suggest that whey doesed at 0.6g/kg fat free mass has a sign. insulin-desensitizing effect in twenty-two sedentary (<1.5 hour of exercise/w) and weight-stable (<2 kg change for at least 6 months), 50-65y old postmenopausal women who participated in this acute response study.
Acute response? Yes, there it is, the first in a line of problems that reduces the significance of the results. After all, testing the acute response to a certain health cannot tell you anything about the long-term effects on said parameter... especially if your subject group due to being sedentary and in an age where the parameter in question is deteriorating, anyway.
But let's not be the "it's not bros, so it's not valid for bros"-guys. Let's rather take a look at (a) the procedures and (b) the results and make up our minds later. And let's first take a look at a handful of important parameters of the study design: To determine the insulin sensitivity, the scientists used two hyperinsulinemic-euglycemic clamp sessions with the subjects being randomly assigned to do the procedure with vs. without whey protein first.
During the "whey trials", the subjects consumed 0.6 g of whey protein (unflavored Unjury®, ProSynthesis Laboratories, Inc, Reston, VA) per kg FFM dissolved in 360 ml water or the same volume of water alone. In addition, the researchers conducted a trial in which the subjects consumed the same amount of leucine.
"Before each clamp procedure, subjects were instructed to adhere to their usual diet and to refrain from vigorous physical activities for three days. Subjects were admitted to the Clinical Research Unit in the late afternoon, where they consumed a standard dinner between 1800 and 1900 h, and then fasted, except for water, until the next morning. At 0600 h, a catheter was inserted into an arm vein for the infusion of a stable isotope labeled glucose tracer; catheters for blood sampling were inserted into the radial artery of the opposite arm and in retrograde fashion into the femoral vein of one leg. At ~0645 h, a primed, constant infusion of [6,6- 2 H2]glucose (priming dose: 22 µmol·kg body wt-1, infusion rate: 0.22 µmol·kg body wt-1·min-1), purchased from Cambridge Isotope Laboratories Inc. (Andover, MA), was started and 4 h later the hyperinsulinemic-euglycemic clamp procedure was initiated with two 5-minute priming doses (first 200 mU·m-2 body surface area (BSA)·min-1 then 100 mU·m-2 BSA·min-1) of human insulin (Novolin R, Novo Nordisk, Princeton, NJ); for the remaining 230 min, insulin was infused at a rate of 50 mU·m-2 BSA·min-1. Euglycemia (at blood glucose concentration ~5.6 mM) was maintained by variable rate infusion of 20% dextrose (Baxter, Deerfield, IL) enriched to 2.5% with [6,6-2H2]glucose" ().
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increase the same insulin levels you're keeping stable, anyway... not to speak of its effects on satiety. What? Yeah, I call that bogus.To figure out if any effect they would observe was induced by whey, i.e. a complex protein, or just the most-applauded whey ingredient, i.e. leucine, the scientists ran a follow-up test (1-4 weeks later) in which the subjects consumed either 0.0684 g/kg FFM of pure leucine (that's equivalent to the amount of leucine in the whey protein) dissolved in 360 ml Kool-Aid® (Kraft 94 Foods, Inc, Northfield, IL) or the same volume of the Kool-Aid® solution alone during the clamp procedure. I don't have to tell you that this was a mistake that makes the results of this follow-up useless for comparisons to the previous trial, in which the whey protein was mixed with water - Kool-Aid is after all all-carbohydrate - with 0.9g carbohydrates per ml of junk... ah, I mean per ml of the soft-drink.
manufacturer claim) whey protein vs. water in the previous trial, they would probably have found no significant effect of whey protein on muscular glucose uptake, because the test wouldn't have been unfairly thwarted in favor of the water control which came without the additional glucose load from the whey-induced gluconeogenesis in the liver.
|Figure 3: Both, acute and chronic realistic and thus relevant studies show beneficial effects of whey on glycemia (Petersen. 2009) and insulin sensitivity (Pal. 2010) - you decide which studies to trust ;-)|
- Akhavan, Tina, et al. "Effect of premeal consumption of whey protein and its hydrolysate on food intake and postmeal glycemia and insulin responses in young adults." The American journal of clinical nutrition 91.4 (2010): 966-975.
- Frid, Anders H., et al. "Effect of whey on blood glucose and insulin responses to composite breakfast and lunch meals in type 2 diabetic subjects." The American journal of clinical nutrition 82.1 (2005): 69-75.
- Layman, Donald K., and Jamie I. Baum. "Dietary protein impact on glycemic control during weight loss." The Journal of nutrition 134.4 (2004): 968S-973S.
- Morifuji, Masashi, et al. "Dietary whey protein increases liver and skeletal muscle glycogen levels in exercise-trained rats." British journal of nutrition 93.04 (2005): 439-445.
- Pal, Sebely, Vanessa Ellis, and Satvinder Dhaliwal. "Effects of whey protein isolate on body composition, lipids, insulin and glucose in overweight and obese individuals." British journal of nutrition 104.05 (2010): 716-723.
- Petersen, Brent L., et al. "A whey protein supplement decreases post-prandial glycemia." Nutr J 8.47 (2009): 1475-2891.
- Smith, Gordon I., et al. "Protein ingestion induces muscle insulin resistance independent of leucine-mediated mTOR activation." Diabetes 64.5 (2015): 1555-1563.