I have always had strong nails, but about 2 years ago I cut the heck out of one of my fingers while making dinner. The knife went across the top of my finger and permanently damaged my nail bed. My nail has grown with a large ridge in it ever since and I guess it always will. The annoying part is that my nail will split like crazy along that ridge.
Anyway, a few weeks ago I decided to try to eat more like my DH, who is diabetic. I quit eating cereal, which I had been eating for breakfast and as a snack. I replaced it with a yogurt that's similar to Greek yogurt. It's Siggi's Icelandic Skyr, if anyone's interested. Each little yogurt cup has 14 grams of protein in it. I've been eating two of those a day. My nail still has the ridge in it, but it has quit splitting. It is just as strong as the rest of my nails. The only thing that I can think is that the added 28 grams of protein a day has made a real difference.
Just thought I'd share, since I've seen quite a few posts on here about supplements for weak nails.