So, you've likely heard that your collagen-loving friends are currently touting it as the new muscle-building powerhouse. Well, they’d better hold onto their collagen-infused smoothies because it isn’t as clear-cut as they'd hope.

A recent review published in the Aesthetic Surgery Journal Open Forum did show some promising links between collagen supplementation and a slight improvement in muscle health. This includes gains in muscle mass and strength when coupled with strength training. But before you ditch your protein shake for a bowl of collagen-rich bone broth, there's a catch.

This review based its findings on earlier systematic reviews that examined 113 random controlled trials with nearly 8,000 participants. However, the participants were already pumped up on resistance training, and almost anyone with a shred of fitness knowledge knows that resistance training alone does wonders for muscle building and strength increase. So, the big question remains: was it the collagen making all the difference, or was the resistance training the real hero of the story?

According to Alexander Leritz, a registered dietitian and sports nutritionist at JM Nutrition, it's probably the latter. “While collagen supplementation likely provided some benefit," he points out, "it is more likely that resistance training was a larger contributor to overall improvements in strength and muscle mass.”

It's also significant to note that collagen is an incomplete protein, lacking in several essential amino acids that play a significant role in muscle protein synthesis - the process responsible for muscle-rawing magic after exercise. This means, as Leritz suggests, that the evidence supporting collagen supplements for muscle building is still a lightweight contender compared to heavy-hitting complete proteins like whey.

That's because it’s had decades of rigorous scrutiny to prove it can consistently improve muscle mass and strength. Against such a muscular veteran, collagen remains a rookie fighter with much to prove.

In simple terms, Leritz wouldn't recommend choosing collagen over more established protein supplements, such as whey, if you're looking to become the next Hulk. Collagen might, however, have a role to play for those who don't get enough protein from their diet or need an additional source of protein while following a strength-training program.

So, before you go all-in on the collagen craze for muscle building, keep in mind this mantra - all that glistens is not muscle gold.