I’ve been on a low-calorie diet for a long time. I started getting these ridges in my fingernails so I was thinking maybe I’m not getting enough protein. So, I tried to look it up on the net but can’t find any conclusive answer. I found a site for people who have had a gastric by-pass and the diet recommended 50-60 grams a day. I do some weight training and I want to be sure I’m getting enough for me to benefit. I am a senior citizen as well; so I’m wondering if that would affect how much I need. Right now I’m eating about 56 grams a day; I use soy powder to keep it above 30. 
I recently started working with a personal trainer, and he has me eating every 2- 4 hours, 20 grams of protein, medium fat, and low carb. I’m not quite a senior -
I have had ridges in my nails for many years, as does my mom. She’s inquired of her dr’s and they can’t tell her what causes them. I know it hasn’t affected the strength of my nails, though.
Depending upon your blood type (Eat Right 4 your type) soy protein may or may not be the right type of protein. I have B+, my daughter is A - she eats a higher non-meat protein diet and flourishes. I find I need to eat more meat (red, fish) or I start craving higher protein foods - and they usually are higher in carbs, too.
I would talk with a nutritionist to confirm how much protein and what type, to verify the best course for you.