The problem with eating a diet high in wheat and grains is that they squeeze out calories and nutrients from other foods without fully replacing them. The nutrients in milled/processed grains have low bioavailability, which means the body can't access and absorb them. Even unrefined grains are limited by the toxins the plant produces to fend off predators.
Plants are equipped with antinutrients called gluten, lectins, and phytates. Some animals can handle the toxins, but humans can't. Gluten, of course, causes intolerance-related symptoms in many people, even those who don't have full-blown celiac disease. Lectins bind to insulin receptors and the intestinal lining, causing GI distress. Phytates can bind to minerals and slow their absorption.
To see what this is all about, check out the following list of vitamin and mineral quantities in wheat and grains:
Vitamin A: None in grains. Only yellow maize contains beta carotene, which the body converts to vitamin A. Lack of vitamin A is a huge problem in developing countries because of their high wheat consumption; there, this deficiency is a major determining factor for childhood disease and mortality. Vitamin A deficiency exacerbates infectious disease symptoms.
Vitamin B: Vitamin B12 is found in animal products only. Generally, grains contain the rest of the B vitamins, but their bioavailability isn't very high.
For example, whereas your body can utilize 100 percent of the B6 available in meat, it can access only 20 to 25 percent of the amount in wheat. Vitamin B12 deficiency hinders the production of red blood cells, nerves, and DNA. Lack of other B vitamins, such as thiamine, riboflavin, and niacin, leads to all kinds of problems, including reproductive problems and the inability to synthesize insulin.
Vitamin C: None. Vitamin C is important for your bones, skin, and connective tissue, especially in the area of wound healing.
Vitamin D: None naturally. Many cereals are fortified with vitamin D. Lack of this vitamin contributes to rickets and poor bone health and may be a player in the development of diabetes, multiple sclerosis, and hypertension.
Vitamin E: None to speak of in wheat, with minimal amounts in other grains. Vitamin E deficiency contributes to neurological issues, gastrointestinal diseases, and reproductive issues.
Calcium: Very little. These low amounts combined with high levels of phosphorus and magnesium in wheat lead to increased calcium loss and thus bone loss.
Iron: Very little, which is a major issue because iron deficiency is the most common nutritional problem in the world, affecting about 30 percent of the population. Getting too little of this vitamin leads to fewer red blood cells and less oxygen throughout the body.
Zinc, copper, and magnesium: Very little of all three, resulting in decreased immune function and, in the case of magnesium, increased risk of heart disease and diabetes as well as muscle weakness and personality changes.