Stone-ground cornmeal, as with other whole grain flours, is ground with both the germ and bran left in, which results in a higher nutrient content than flours that have these removed before grinding.
In Europe and the United States, cornmeal and polenta are usually made from yellow corn, but white corn is also used as the basis for bread, polenta, tortillas, and many other specialties. In countries where corn is not a common food, it is simply ground before using. However, where corn is a staple food, it is specially treated or enriched to make it easier to process and improve the nutritional content. Cornmeal made from corn kernels that have been previously soaked in a water and lime solution, is marketed as masa harina and used to make tortillas
From Wikipedia: Cornmeal is a meal (coarse flour) ground from dried maize (corn). It is a common staple food, and is ground to fine, medium, and coarse consistencies, but not as fine as wheat flour. In the United States, very finely ground cornmeal is also referred to as corn flour. When fine cornmeal is made from maize that has been soaked in an alkaline solution, e.g., limewater (a process known as nixtamalization), it is called masa, which is used for making tamales and tortillas. Boiled cornmeal is called polenta in Italy.
There are various types of cornmeal:
- Blue cornmeal is light blue or violet in color. It is ground from whole blue corn and has a sweet flavor. The cornmeal consists of dried corn kernels that have been ground into a fine or medium texture.
- Steel-ground yellow cornmeal, which is common mostly in the United States, has the husk and germ of the maize kernel almost completely removed. It is conserved for about a year if stored in an airtight container in a cool, dry place.
- Stone-ground cornmeal retains some of the hull and germ, lending a little more flavor and nutrition to recipes. It is more perishable, but will store longer if refrigerated. However, it too can have a shelf life of many months if kept in a reasonably cool place.
- White cornmeal (mielie-meal), made from white corn, is more common in parts of Africa. It is also popular in the Southern United States for making cornbread.
From “https://en.wikipedia.org/wiki/Maize”: Raw, yellow, sweet maize kernels are composed of 76% water, 19% carbohydrates, 3% protein, and 1% fat (table). In a 100-gram serving, maize kernels provide 86 calories and are a good source (10-19% of the Daily Value) of the B vitamins, thiamin, niacin, pantothenic acid (B5) and folate. In moderate amounts, they also supply dietary fiber and the essential minerals, magnesium and phosphorus whereas other nutrients are in low amounts.
Maize has suboptimal amounts of the essential amino acids tryptophan and lysine, which accounts for its lower status as a protein source.
Eating a diet based completely on corn dishes would cause a protein deficiency, which is why it is important to make sure that you are getting enough protein from other dishes. This is why the Incas ate corn together with beans.