X-REAL-IP nginx reverse proxy spoofing

I have express js API where I need to obtain user IP address.
In nginx I have these settings:

location /api {  proxy_pass http://localhost:3000;  proxy_set_header X-Real-Ip $remote_addr;  }

In express I get ips like this

req.headers['x-real-ip']  

And it works, I really get some IP addresses, but my question is:
Is it real to fake x-real-ip?
Someone every 3 seconds create tnew user with new ip through API and I dont believe someone with 10.000 proxies registrate accounts..