Protein fasting & blood sugar: my self-test (shake + a light session)

What is “protein fasting” (WPF)?

Briefly for context, so it’s clear what I’m writing about here: WPF stands for “Wolfs Protein Fasten”, a concept popularised by the entrepreneur and co-founder of the brand More Nutrition, Christian Wolf. The idea combines intermittent fasting with a high protein intake: instead of fasting completely during the food-free hours, one to two protein portions (often as a shake) are planned in, plus two protein-rich meals.

The appeal for many: it’s meant to keep you full, protect muscle mass and fit into everyday life more easily than classic diets. But the honest placement matters to me: this is a marketing and diet concept of a fitness brand, not a therapy programme recommended by professional societies. I’m testing it out of curiosity for my own metabolism: not because it’s “proven”.

My test setup this morning

Concretely: early on an empty stomach I drank a protein shake (More Protein Iced Coffee, flavour Brownie Marshmallow), per my CGM note with around 3 g of carbs, so almost carb-free. Right after, I rode a 45-minute, light endurance session on the Peloton, a “low-impact ride” at low intensity (level 2), heart rate in zone 1. It’s exactly this combination I want to follow with the CGM.

The starting point

Before the test I was at 123 mg/dl with a flat trend. The night was calm: the curve stayed largely in the target range. A good, clean starting point.

Why protein on an empty stomach can slightly raise blood sugar

Now the interesting part that many aren’t aware of: a protein shake contains hardly any carbs, yet blood sugar can rise slightly afterwards. The reason lies in the hormonal effect of protein.

Protein provides amino acids, and these stimulate the release of the hormone glucagon: the counterpart to insulin.¹ Glucagon prompts the liver to release glucose: from stores (glycogenolysis) and by new formation from, among other things, amino acids (gluconeogenesis).² Result: blood sugar can move upward, although hardly any carbs were involved. In type 2 diabetes this effect is often more pronounced, because glucagon regulation can be disturbed.³

And the movement? The counterpart

This is where the light bike session comes in. Moderate endurance effort lets the muscles take up glucose: partly insulin-independent. So it counteracts the small protein-driven rise. My expectation: the low-impact ride buffers the morning rise and keeps the curve calm.

An honest addition from my own experience: moderate, aerobic effort tends to lower for me, while very intense sessions can even briefly raise the value. Why that is, I’ve described in detail in “Exercise: down first, then up”. The light ride is deliberately chosen here.

Satiety until noon

An effect I clearly notice myself: the protein shake keeps me full for a long time. That protein is more satiating than the same amount of carbs or fat is well documented. For me in everyday life that means: after the shake I usually make it to noon without hunger. That’s my personal experience: for others it can be different.

Honest placement: opportunities and criticism

To keep this article fair, the other side belongs here. “Protein fasting”/WPF isn’t only celebrated but also criticised.⁴ The main points I take seriously:

• At its core, calorie reduction. The weight-loss benefit comes above all from the calorie deficit, the fixed structure and the satiating protein – not from “magic” of the concept.
• A lot of substitute products. Building the day heavily on one brand’s shakes and light products makes for a one-sided diet. There are reports of people for whom this focus on substitute products wasn’t good.
• I keep the rest of the day real: I make sure the rest of the day contains real, wholefood foods, not just powder.

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