"Ask the Coach" is the column in which Wolfgang Unsöld answers your questions about training and nutrition. The book of the same name was published by Riva Verlag and Available right here on Amazon.
Question: According to this article, whey has a big effect on blood sugar. You can read a lot on the internet about the effect of the amino acid leucine on blood sugar. Since whey is very high in leucine then it makes a lot of sense that the leucine in whey is responsible for this spike in blood sugar, right? Facebook users
WU: That sounds logical at first glance. However, it is not correct. Leucine has a large effect on blood sugar, but primarily in two specific circumstances. However, neither is the case in the case of a pure whey shake.
On the one hand, if we compare the absolute and relative leucine content of whey protein (also often referred to as whey protein) with meat/fish, the following is noticeable:
Whey contains about 10g or 10% leucine per 100g.
Meat and fish contain about 2g or 2% leucine per 100g.
Whey contains about 80-85g protein per 100g, ie. about 8% of the protein content is leucine.
Meat and fish contains about 20-25g of protein per 100g, ie. 8-10% of the protein content is leucine.
Thus, a 30-60g portion of whey contains approx. 3-6g leucine.
And a 200-300g serving of meat or fish contains around 4-6g of leucine.
However, meat and fish have a much lower effect on blood sugar than whey. I have also proven this in practice with dozens of blood sugar reaction analyzes through CGM measurements over the past year. Whey and water protein shakes have a big effect on blood sugar levels for most people. Meat and fish have a small effect. Thus, it is clearly not the leucine portion of the protein that is responsible for this blood sugar response.
Looking at the history of leucine, it was Manninen et al in 2006(1) who published one of the first major studies/articles on leucine and blood sugar. In one of these studies, three different post-workout shakes and their effect on blood sugar management were compared:
Shake 1: High glycemic carbohydrates
Shake 2: High glycemic carbohydrates plus protein hydrolyzate
Shake 3: High glycemic carbohydrates plus protein hydrolyzate and leucine
Shake 2 compared to Shake 1 had a 66% greater blood glucose response.
However, shake 3 compared to shake 1 had a 221% higher blood glucose response.
Note: Leucine is part of a protein hydrolyzate. In the case of the study, 8% of the protein hydrolyzate was leucine.
Bottom Line: Protein (including leucine) increases blood sugar response by 66%. However, when isolated leucine is added to this mixture, the response is increased more than 3-fold. Thus, it is not leucine as part of a protein or a peptide chain that is responsible for the primary insulinogenic property, but leucine in isolated form as an amino acid.
It is important to note that one of the most common misconceptions about protein metabolism is the shape of the protein when it is absorbed in the small intestine. Protein is not digested from long peptide chains into amino acids and then absorbed as is often assumed. They are primarily di- and tri-peptides, which are chains of 2 to 3 amino acids that are absorbed in the small intestine. Thus, leucine as part of a peptide found in meat, fish and whey does not have the insulinogenic effects of leucine as an isolated amino acid.
Leucine is a branched chain amino acid (BCAA). The primary benefit of BCAAs is that they don't need to be metabolized by the liver, but are made available directly to the muscle. However, this effect is primarily present when BCAAs are taken in isolation, as in an amino drink, and not as a protein or peptide chain, as in meat, fish and whey.
Another study (2) showed that the primary effect of leucine on blood sugar depends on the concomitant consumption of glucose. And so the consumption of leucine without glucose has a significantly lower effect on blood sugar.
Thus, leucine has a significant effect on blood sugar primarily under two distinct circumstances. When leucine is consumed in isolation as an amino acid and in combination with glucose or high glycemic carbohydrates.
However, this still doesn't answer the question of why the whey leads to a strong blood sugar response in so many people. The answer to this is that along with carbohydrates, protein in general also has an effect on blood sugar. And one of the biggest advantages of whey is that it digests very quickly. Conversely, this leads to a very rapid increase in protein in the blood (3). This very rapid digestion, absorption and increase in protein in the blood results in an increased blood sugar response, largely independent of the leucine present.
So it is not the leucine but the fast-digesting whey protein that is responsible for the rise in blood sugar.