Tuesday, October 8, 2013

Pre-Meal Protein Ingestion to Improve Glucose Tolerance: Insulin, GIP, GLP-1 - That's the Whey(!) it Works! Plus: Even Pure Glucose Can "Improve Your Insulin Tolerance"

Can a whey protein appetizer really undo the damage of greasy fast food? Probably not, but it's still interesting to see how it affects the postprandial glycemia.
Insulin resistance is the #1 contributing factor to the obesity epidemic and despite the fact the solution is already out there (read more about the necessary lifestyle modifications), it probably won't hurt to know if something as simple as having a high protein "appetizer" before a junky meal could improve blood glucose management even further, right? "Right, 'cause protein is always, good!" Ah, no... I guess the answer is a little more complex than that... Nevertheless, I still suspect that the results, Tina Akhavan and her colleagues from the University of Toronto present in their soon-to-be-published paper in the Journal of Nutritional Biochemistry will be of interest to you.

The study results are interesting, to say the least...

... and that's not despite but rather because the researchers did not use the usual subjects (rodents, obese individuals or elderly people), but young men (aged 18-29) with a BMI of 18.5-29.4 kg/m². In a randomized cross over design (cross over means that every subject got each treatment - obviously in seperate testing sessions), the subjects drank either...
  • 300ml of a 10g or 20g whey protein solution, 
  • 300ml of a 10g or 20g glucose solution, or
  • 300ml of flavored zero calorie water 
The test drinks were consumed four hours after a standardized (junk = Honey Nut Cheerios + Skim Milk + Orange Juice) "breakfast". 30 min later the subjects were served even more junk in form of a *yummy* frozen Pizza from McCain Foods Ltd.

"Cereals", skim milk, pizza... whey alone won't help to counter that

The Pizza had been prepared "according to manufacturer‘s directions". This means that the reduction in glycemia the scientists observed in response to the protein preload were not because the pizza was still frozen... ok, before I produce even more nonsense, let's take a look at what the whey protein and glucose pre-loads did to the subjects blood glucose responses, right?
Figure 1: Glucose and insulin levels after pre-load and after meal (mean of 30-230min); all values expressed relative to water control, i.e. +85% would mean "85% higher than during control trial" (Akhavan. 2013)
If that's not your first visit to the SuppVersity, I probably won't have to explain the mechanism by which the pre-ingestion of whey (and glucose) reduces the Pizza-induced glycemia - do I? Well, I guess I better repeat it briefly:
  1. The ingestion of the whey protein triggers a significant increase in insulin - 127% for the 10g and 191% for the 20g dosage.
  2. Contrary to the glucose infusion there is no exogenous glucose that could lead to a rapid elevation of blood glucose (cf. figure 1, left → pre-values); the minimal increase you see is produced by gluconeogenesis in the liver.
  3. With the elevated insulin levels, the mean glucose levels in the postprandial phase (30min-230min after the pizza ingestion) is lower with both the glucose and whey preload. The effect is however more pronounced with whey than with glucose. The reason should be obvious: The overall amount of glucose that's got to be stored away is lower.
I know it sounds counter-intuitive, but aside from (2) the mechanism is absolutely identical for the glucose trial - with the insulin already being around low (10g) glucose preload can actually lead to lower postprandial glucose levels than the water control (this is probably only true for healthy individuals).

Insulin? Is that all, or is there more to it?

Now that we have gotten the fundamental mechanism by the means of which "glucose-" and "whey-preloading" before eating pizza can ameliorate the blood glucose surge after the meal, let's take a look at the auxiliary data.
Figure 2: GLP, GIP, PYY, CCK and Ghrelin levels before eating the pizza; all values expressed relative to water control, i.e. +85% would mean "85% higher than during control trial" (Akhavan. 2013)
As the data in figure 2 tells you the increased insulin release was brought about and accompanied by profound increases in the production of the satiety hormones GLP-1 and CCK, as well as the "insulin trigger" GIP (all these changes occured in the pre-meal = pre-pizza phase, only). Ghrelin and PYY, which play an even more important role in the regulatory process that's supposed to control our energy intake, did not show significant treatment dependent differences, though.
What's the practical relevance of these findings? Honestly, I am not sure how relevant the findings from the study at hand actually are. I mean, from a "do this" or "don't do this" point of view - not from a "understanding how things work" perspective.

SuppVersity Suggested Read: "The Satiating Truth About Proteins and Why High Protein and Low Amounts of Low GI Carbs May Not Mix As Well As Most People Think" | read more
For those who would benefit most from reductions in postprandial glycemia, i.e. the obese type II diabetic, it is questionable whether (a) the mean 7% decrease is actually making a difference and whether it would (b) even occur in someone who is having a hard time producing enough insulin to have his / her body react to it.

For the lean individual, on the other hand, the 7% reduction in gylcemia probably doesn't matter at all and the insulin spike before the onslaught of a the "perfect storm" of carbs and fats from a greasy frozen pizza could (worst case scenario) increase the chance of fat storage - I mean the glucose can go to the muscle (learn more), the fat, on the other hand must end up in your adipose organ.

I would thus strongly advice everyone to stick to my "get 30g of quality protein with every meal" recommendation, instead of turning it into a "get 30g of protein before every meal". Aside from the questionable benefits of having the protein before your meal, having it with / as part of your mwal will also direct you away from pizza and towards healthier food choices. After all, you will be hard pressed to find a pizza with 30g+ of protein in it... and I bet the novel "pizza on a stick" I told you about on Facebook, recently, probably doesn't qualify either ;-)
  • Akhavan T et al. Mechanism Of Action Of Pre-Meal Consumption Of Whey Protein On
    Glycemic Control In Young Adults. The Journal of Nutritional Biochemistry. October 2013 [accepted manuscript]