It’s not just iron. If his iron levels are fine, you have much bigger fish to fry. Here’s the thing. If you have high iron levels beforehand, you won’t suffer from losing blood (the reason iron is the usual problem is that it takes the body longer to produce red blood cells than some other components of blood. Adequate preparation does away with this issue).
But the other thing in blood that your body can’t replace overnight, even if you’re eating all the right foods for the situation, is sugar, and * that’s* a problem. The right amount of sugar will not protect you from your body’s reaction to sugar loss, and when you lose blood, you lose sugar very fast.
I just donated blood again yesterday morning. I’m a regular donor, which in Canada means once every 56 days. We don’t get paid here, but I’m an athletic 20 year old in strapping good health and have a rare blood type, so I donate as soon as I’m eligible every time. I don’t have any health conditions, any markers for diabetes, anything else that might affect blood sugar.
My iron levels were about 10 points above the minimum, but I passed out in the chair due to sugar loss just as they were taking the needle out (the dizziness can sneak up on you really fast). I suddenly couldn’t see anything but a blur. My body temperature went through the roof, I poured out more sweat per second than I do during intense excercise, and I was instantly more nasueous than I have ever been in my life. It was the worst, ickiest physical feeling I’ve ever had in my life. Worse than the real flu by far.
I was calm, but the nurses panicked. Why? Well, there’s a risk of permanent damage to your guts and liver because your body diverts all the blood going there to the brain. If something really goes pair-shaped there’s a risk of brain damage. And at the very least, you will be dizzy for a long damn time.
They took excellent care of me, did everything they possibly could, and still, 36 hours later, I can’t stand up without getting dizzy. For all of yesterday, I couldn’t even sit up. I was dizzy just lying propped up on a pillow. I’m ordered to stay away from even moderate exercise for several days, away from strenuous exercise for a week, and a routine blood test my doctor ordered to check for potential physical causes of depression has to be moved to next month. So the answer is yes, very bad things can and will happen to your friend if he’s giving blood every week, even if he is lucky when it comes to iron absorption and has enough iron in his diet. Each time he gives without the proper recovery period, he’s increasing his risk of passing out and not being brought back fast enough to avoid long-term consequences.
Especially if, as you state in the OP, the nurses present don’t know that he’s been giving blood more often than is technically allowed. This is a disaster waiting to happen.
ETA: very little of the iron in iron supplements is absorbed by the body even in the best of circumstances. Compared to dietary sources, they’re practically useless.