Vitamins and minerals are quite varied in structure and amount in the foods you eat. They can be found in food in a free form, chemically bound to a larger molecule, or tightly encased inside a food aggregate. In most cases, they are liberated during eating by the mechanical process of grinding. They may also be liberated during the breakdown of the large molecules like proteins and starch, in which they may be encased.

Since your body requires specific amounts of these key nutrients, most vitamins and some minerals have active transports in place for absorption and are taken into the body in very specific ways. These active transports act as shuttles, picking up the vitamin or mineral and taking it through the intestinal cell wall into the body, where it may be directly released or transferred to another transport molecule. Since vitamins and minerals are small and are usually found in much lower levels than amino acids, carbohydrate, and fats, these active transports must select and pull these important molecules out of the food and take them into your body. Active transports require energy to function properly.

Calcium and iron are examples of minerals that are taken into the body by active transport. Most of the water-soluble vitamins have an active transport in place as well, and these active transports are primarily found in the middle section of the small intestine, the jejunum. Some minerals, like iron and calcium, are absorbed in the first part of the small intestine as well as the jejunum. The fat-soluble vitamins (vitamins A, D, K, and E), as discussed above, are absorbed with fat miscelles, and therefore require fat to be present for their full absorption.

Magnesium is a mineral of tremendous importance for bone health, energy production, and overall healthy functioning throughout the body since it activates more than 300 cellular enzymes. Like calcium, magnesium must be constantly supplied to maintain optimal function. Magnesium doesn't have an active transport, but depends entirely on dietary intake and a healthy intestinal lining for its absorption, and can be absorbed throughout the entire small intestine and even in the colon. Low intakes of magnesium, or loss of ability of the intestinal tract to absorb magnesium due to intestinal inflammation or disease, can result in a variety of problems such as muscle twitching or tremors, weakness, irritability and restlessness, depression, and weak bones. Magnesium is found at highest levels in whole foods such as grains but is often removed during processing. Whole grain bread and cereals will have a much higher amount of magnesium than white bread, which is made from refined flour.

Vitamin B12 is also absorbed differently from the other vitamins and minerals. First, it is most commonly found attached to proteins, and therefore requires protein breakdown to be liberated. Then, it requires a protein made in the stomach, called intrinsic factor, for its absorption, but is not absorbed until the vitamin B12-intrinsic factor complex reaches the final part of the small intestine, the ileum. Optimal digestion of vitamin B12 is dependent on your ability to make a healthy amount of stomach acid, since protein breakdown requires stomach acid and research has shown that intrinsic factor is also not secreted in adequate levels when stomach acid is low.

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