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

Evidence level: single-case observation (n=1)

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

Evidence level: established (mechanism)

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

Evidence level: established (mechanism) + n=1

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

Evidence level: plausible (evidence) + n=1

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.