Affecting nail health. Nails are dead. Once they're out there, you can't do much to change them beyond delaying the decay with temporary fixes like nail hardeners.
While it is true that nail health begins before you ever see the nail itself--which means diet is quite important to producing healthy nails, some people will simply have weak, bendy nails, no matter what they eat.
I've always had super-fine hair, thus it's not a surprise that I have the nail equivalent, which is weak, bendy nails that chip and break easily. I use Nail-Aid's keratin-infused strengthener under my "good" base coat (Orly Bonder) to give my nails a boost, and that works great. Double base coats also means no stains from the high color saturation of these new polish formulas.
As for the gelatin, I'm not sure protein/keratin intake is a problem for me. I'm on a low carb diet out of necessity, so protein intake is plenty high. I even have to make my own "jell-o" from plain gelatin and real unsweetened juices as flavoring with stevia as the sweetener. Diabetes means no sugar, of course but stevia, because I'm allergic to most artificial sweeteners.
Now one thing that might be affecting my cuticle health is how I consume no dairy because I've developed an allergy to it in the past two years--right alongside my cuticle dryness. I'll be talking to my MD about whether dairy withdrawal is the cause, or merely a coincidence, at our next appointment in a couple of weeks.
I wish I could go to a good manicurist for advice, but I don't dare with so many people stupid about COVID where I am (red state).