Short answer: For muscle, whey did better in a head-to-head trial: in 22 older women, whey raised muscle protein building at rest and with exercise, while collagen did not raise longer-term building.1 Collagen lacks tryptophan, so it is an incomplete protein.2 Collagen's main evidence is for skin hydration and elasticity.3
| Collagen peptides | Whey protein | |
|---|---|---|
| Protein type | Incomplete: lacks tryptophan2 | Complete: all essential amino acids4 |
| Muscle protein building (22 older women, 30 g twice a day for 6 days) | Rose only with exercise in the short term; not above baseline over 6 days1 | Rose at rest and with exercise, short and longer term1 |
| Main studied use | Skin: better hydration, elasticity and wrinkles (19 trials)3 | Meeting protein needs around training4 |
| Amounts in studies | 2.5 to 15 g a day2 | Labels vary; NIH RDA for protein is 0.8 g/kg a day4 |
| Allergen | Depends on the animal source | Milk is a major food allergen5 |
In a double-blind trial, 22 healthy women around 69 years old took 30 g of whey or collagen twice a day for 6 days and did leg exercise on one side. Whey raised muscle protein building in both the rested and exercised leg, in the short term and over the 6 days. Collagen raised it only in the exercised leg in the short term, and not above baseline over the 6 days. Whey beat collagen on every measure.1
A dietary analysis found collagen could replace up to 36% of protein in a typical Western diet while still meeting essential amino acid needs, because the rest of the diet fills the gap.2
These are study protocols, not personalized advice; confirm any dosing with your prescriber.
A 2021 meta-analysis of 19 randomized trials (1,125 people, 95% women) found better skin hydration, elasticity and wrinkle scores with hydrolyzed collagen than placebo, mostly over about 90 days.3
More detail: Whey vs casein protein: what is the difference?, Whey vs pea protein: does plant protein build muscle as well?, and the Collagen Peptides and Whey Protein guides.