# Peptides instead of protein: why molecule size sets the pace

> A «fast» protein is not richer in protein, just cut into smaller pieces. What PepT1, absorption kinetics and the leucine rise have to do with it - and how WOO® Lachs Protein is set up.

Not every protein source reaches the bloodstream at the same speed. The difference between a "fast" and a "slow" protein is not the protein content printed on the tub, but molecule size - and which route the fragments take through the gut wall.

## Two routes through the gut wall

A protein has to be broken down before any of it arrives in the blood. Two systems handle the uptake: specific transporters for free amino acids - and **PepT1 (SLC15A1)**, a proton-coupled transporter for di- and tripeptides.

PepT1 has broad substrate specificity and high capacity. Daniel (2004) summarised what follows from that: a substantial share of absorbed nitrogen crosses the gut wall not as free amino acid but as a short peptide. Feed the body a protein that has already been enzymatically split into peptides, and part of the digestive work is skipped.

## Fast and slow: the classic experiment

Boirie et al. (1997) compared two milk proteins in what is now a much-cited study. **Whey** drove the plasma amino acid level up steeply within about an hour and back down just as quickly. **Casein** clotted in the stomach and released its load slowly over seven hours.

The result was not "better or worse" but two profiles: the fast protein produced the stronger acute stimulation of protein synthesis, the slow one suppressed protein breakdown more durably. Hydrolysed proteins - salmon peptides among them - sit at the fast end of that spectrum, peaking in the blood as early as 20 to 30 minutes after intake.

## Why the rate of rise matters

Muscle protein synthesis responds not only to the amount but to the dynamics: a rapid rise in leucine concentration is a stronger trigger than a flat plateau. Witard et al. (2014) showed that synthesis rates rose with increasing protein dose and levelled off at around 20 g per meal.

That comes with a caveat. The meta-analysis by Morton et al. (2018) shows that total daily protein has a clearly larger effect on muscle mass and strength than source or timing. Kinetics is the fine-tuning, not the foundation.

## Lactose-free without detours

Whey comes from milk and, depending on processing, carries residual lactose plus milk protein allergens. For many adults that is a practical problem: bloating after a shake is rarely imagination.

Marine protein sources bypass this structurally: no milk sugar, no whey proteins, no gluten.

## How WOO® Salmon Protein is set up

**[WOO® Salmon Protein](/en/shop/woo-salmon-protein-can)** is built on salmon peptides (Salmen Peptide®) with a protein content of 80% and less than 1% sugar. A 30 g serving delivers 24 g of protein at 104 kcal; the 600 g tin covers 20 servings. It also contains ascorbic acid and the lemon verbena extract Recoverben®, rounded off with orange and vanilla flavouring. 100% lactose- and gluten-free.

Recommended as a protein addition to meals or after resistance training.

## Frequently asked questions

**Is fish protein a match for whey?**
Fish protein is a complete protein containing all essential amino acids. The evidence base for muscle building is larger for whey - which says more about research history than about the quality of the source.

**How many servings a day make sense?**
A working guideline is 1.6 to 2.2 g of protein per kilogram of body weight daily, spread over three to four portions of roughly 20 to 40 g each. One serving covers part of that - food remains the base.

**Do I have to drink it right after training?**
The famous anabolic window is considerably wider than once assumed.

## Sources

Boirie Y et al. (1997), Proceedings of the National Academy of Sciences - Slow and fast dietary proteins differently modulate postprandial protein accretion.
Daniel H (2004), Annual Review of Physiology - Molecular and integrative physiology of intestinal peptide transport.
Witard OC et al. (2014), American Journal of Clinical Nutrition - Myofibrillar muscle protein synthesis rates subsequent to a meal in response to increasing doses of whey protein.
Morton RW et al. (2018), British Journal of Sports Medicine - A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength.

*WOO® Salmon Protein - in the NEMAPO shop.*