Eating 20 grams of whey protein and 20 grams of a plant-based protein with added leucine both build muscle at about the same rate in young, healthy people—even though whey makes your insulin spike higher. That means insulin probably isn’t the main reason your muscles grow after protein.

We analyzed one assertion on this question and found that 20 grams of whey protein and 20 grams of leucine-fortified pea and canola protein led to similar muscle-building results in young, healthy people [1]. This suggests that, at least in this group, the source of protein—whether animal-based like whey or plant-based with added leucine—may not make a big difference in how well muscles grow over time. Whey protein caused a stronger rise in insulin, a hormone involved in how the body uses sugar and nutrients. But since muscle growth was about the same despite this difference, it’s possible that insulin spikes aren’t the main driver of muscle gains after protein intake [1]. This doesn’t mean insulin doesn’t play any role—it just means, based on what we’ve seen so far, it might not be the key factor separating these two proteins in terms of muscle outcomes. We only reviewed one assertion, and it focused on a specific group: young, healthy individuals. We don’t yet know if these results apply to older adults, people with different activity levels, or those with health conditions. We also don’t have data on long-term effects, different doses, or how these proteins affect recovery or strength gains beyond muscle size. What we’ve found so far is that, under these specific conditions, both proteins appear to support muscle growth similarly. That doesn’t mean one is better or worse—it just means, for now, the added leucine in the plant-based blend may help it match whey’s effect. For someone choosing between them, this could mean plant-based options with added leucine are a viable alternative if you’re avoiding dairy or prefer plant foods.