Nutrition, proteins, collagen intake - does it matter for PE? Probably not so much. Here's why.

Good nutrition is hugely important for everyone's well-being - especially in the long run. Eating a clean diet, getting adequate exercise - these are two components of living a good life. Being fit is important for sexual performance, erection quality, but also for longevity. Also, a low body fat percentage decreases your fat pad and causes your penis to look larger in proportion to your body. I recently lost about 70 lbs by eating clean, fasting and doing time restricted feeding (alternate day fasting). It's been hugely beneficial for my erection quality (thereby making my penis fuller and therefore larger), and it has reinvigorated my sex life and given me a boost in free testosterone. So I ain't throwing shade on nutrition, that's not why I write this.

With that preface done - does nutrition status and collagen (or amino acids, protein) intake matter for actual penis enlargement, if we look only at the penis itself and not the whole system? I see variations of that question asked all the time. Here's my attempt at an in-depth answer, adapted from a comment I made in another thread a while back:

The tiny, ^tiny amounts of building blocks necessary per day for growing your penis by minute fractions of a gram per day, are insignificant compared to what your body turns over. Far more important than nutrition is to make sure you are metabolically healthy and that you get a good blood supply going to the fibroblasts in your tunica albuginea, which do not have easy direct access to nutrients from the blood. You want to get frequent erections, especially nocturnal erections, perhaps do feeder sets of pumping, perhaps do some edging for an hour or two a couple of times per week, etc. Any junk food that causes atherosclerotic build-up to occur over time should be a no-no if you prioritise long-term penile health and function, and smoking is one of the worst things you could possibly do since it's vasoconstrictive. Vasodilation is what you want. As long as you get plenty of blood flowing, you needn't be concerned with eating any special nutrients since we're talking extremely slow growth here. This is why you often see the recommendation to use L-Citrulline (and sometimes L-Arginine) - it boosts nitric oxide metabolism and helps with vasodilation, improving erection quality.

The amino acids most important for collagen synthesis are glycine, proline and lysine - you always have a sufficient (for PE) supply of those in the blood unless you're extremely protein deficient for some reason. Vitamin-C is a co-factor for many of the enzymes involved in collagen synthesis - but who in this day and age is vitamin C deficient?

One should think of PE more in terms of causing a growth stimulus:

Certain growth factors, such as Transforming Growth Factor-beta (TGF-β), Platelet-Derived Growth Factor (PDGF) and Fibroblast Growth Factor (FGF), play a part in signalling fibroblasts to synthesise collagen. The stretching action of PE will trigger the production of these growth factors. Fibroblasts really "love" stretching stimulus. Local low-grade inflammatory processes started by pro-inflammatory cytokines like interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-α) can enhance collagen production - they trigger the "healing response", so to speak. Hypoxia and changes in tissue pH can also influence fibroblast activity. This is why we do hypoxic clamping to stimulate growth. Hypoxia in particular will stimulate fibroblast hyperplasia. It would be a misnomer to call collagen production hypertrophy, since it's not fibroblasts themselves that grow, but the extracellular collagen matrix they support.

Prostaglandins play an important part in the balance of collagen synthesis and breakdown because they modulate the expression of matrix metalloproteinases (MMPs), which are key enzymes in collagen breakdown, and tissue inhibitors of metalloproteinases (TIMPs) which inhibit said breakdown. Edging sessions will stimulate the production of PGE-1 in the penile tissue, which has a local effect on the balance of collagen synthesis and breakdown. Remember we don't want to synthesise too much collagen - we don't want to become too adapted to tensile load. We more want to reconfigure the tunica - to remodel it - not make it a lot thicker and stronger. What we want is the sliding action of collagen fibril over each other, and locking them into a new and more extended configuration. This is where heat helps a lot by making it more easy to break hydrogen bonds between collagen molecules to allow them to slide. PE needs to be a balance of remodeling the collagen matrix and building more and stronger tissue, else it will stall.

On a side note, here is some speculation which I can't support with reference to literature, since none exist, but it makes sense to me from first principles:

It is probably beneficial for PE to have a very low degree of systemic inflammation (we always have some amount of it, and especially so if we eat a junk diet), so that any local signal in the tunica albuginea of TNF-α and IL-1 will rise significantly above baseline and be picked up. Therefore, it might be a good idea to occasionally do some medium duration water fasting three to five days or so, and to do intermittent fasting more often - which will lower systemic inflammation and generally be good for metabolic health. End of side note.

Summary and tl:dr? Nutrition doesn't really matter for PE. But it matters a whole lot for quality of life and for erection quality, so do eat a clean diet anyway! We want our penises to work well for laying pipe, not just be large.

And if you want to take supplements, go for L-Citrulline (and some L-Arginine doesn't hurt, they are synergistic, but arginine is broken down much quicker). Don't focus on things like collagen and glycine - they're wasted money. Eating proteins in general gives you all the building blocks you need for PE. The important part is delivering nutrients to your fibroblasts, and for that you need lots of local blood flow, so ... stay erect for as long as possible and as often as possible, within reason :)