In the 1890s, Mr.
and Mrs.
Charles Knox made gelatin by boiling leftover slaughterhouse waste, and devised a method of drying it into sheets and grinding it into a powder.
In one of advertising history's most successful campaigns, they claimed that this waste product would make fingernails stronger, presumably because cow hooves are strong.
You can still buy Knox's gelatin, and many people still believe the old claims, even though there is no evidence that gelatin has any effect on nails.
Gelatin does not contain any special nutrients.
It contains protein, but lack of protein is not the cause of brittle and cracked nails.
Even if protein deficiency caused brittle nails, gelatin would be a poor choice, because it is very low in two of the protein building blocks tryptophan and lysine.
You can meet your needs for protein by eating any ordinary food source of protein such as beans, meat, fish or chicken.
If you have deformed nails, check with a dermatologist to see if you have a fungus infection that can be treated.
If you have nails that peel, crack and break, you probably have a genetic condition that causes your nails to lose moisture.
The most effective treatment is to use nail polish to slow the loss of moisture, and to keep the nails very short.