Introduction
Greens are generally high in vitamins A and C, calcium, and iron. The darker the leaf, the more vitamin A it provides. There can be as much as fifty times the amount in dark leaves as in pale ones. Ounce for ounce, greens will have as much calcium as whole milk, with some having more. However, some greens contain oxalic acid (spinach, rhubarb, sorrel, and Swiss chard), which inhibits the absorption of calcium and iron and encourages the formation of kidney stones. Some of it is destroyed by cooking the food in plenty of water or by blanching it, but there is always some left. Oxalic acid is easily detected in the mouth as it sets the teeth on edge and causes a slight numbness of the tongue. It is wise to avoid feeding children these otherwise nutritious vegetables too often and in excessive quantities -- something kids have instinctively known all along!
In addition, many greens contain nitrates that convert naturally into nitrites in the stomach. This causes a reaction with the amino acids in proteins, forming nitrosamines, some of which are known, or suspected to be, carcinogens. These do not pose a problem to the healthy adult; but, when they are cooked and left to stand at room temperature, bacterial enzymes rapidly convert nitrates to nitrites, which are especially hazardous to young children.
On the plus side, greens have chlorophyll, the green pigment in plants. Chlorophyll enables sunshine to combine carbon dioxide with water to create carbohydrates and oxygen. By utilizing light, chlorophyll is the primary source of plant energy, and its chemical structure is similar to hemoglobin, the red blood pigment that carries oxygen in humans. This is why chlorophyll is often used in the treatment of certain anemias as it has the ability to promote growth, metabolism, and respiration, while at the same time, having the ability to stimulate tissue growth and wound healing.
