Nails are similar to hair in that they are both made from the same protein, keratin. Thus the nutritional recommendations for healthy hair apply to nails as well.
The nail grows from the cells in the nail matrix at an average rate of 0.1 mm per day or 2-3 mm per month. Because new nail tissue is constantly being produced, nails are a good indicator of health and provide clues about our diet. Brittle nails that grow slowly are usually indicative of inadequate blood flow or low nutrient levels.