It's a curious phenomenon. People will sometimes express concern about the consequences of eliminating meat from the diet, fearing that they will suffer some deficiency if they fail to use an appropriate substitute. Yet no one ever expresses a similar concern about switching from a vegetarian diet to a meat-containing one. Does meat contain nutrients that are unavailable otherwise? No. Are vegetarians more prone to deficiency than meat-eaters? No. Then why the concern? The concern stems from a lifetime of indoctrination emanating from classrooms, commercials, advertisements, and health care professionals beholden to certain industry groups. Some foods are richer in certain nutrients than others, but paying attention to basic nutritional principles assures nutritional adequacy.
Aside from the question of nutrition, the concern also relates to a change in the way we view a meal. The traditional concept is that of a main course, consisting of meat or other animal flesh, accompanied by one or more side dishes, "the vegetable." We need to change the way we think about a meal. Vegetables and whole grains, often combined in innovative ways, need to be moved to the center of the plate. Anything else becomes merely a condiment. There is a learning curve involved, but the question of "what do I eat?" soon becomes moot.
Despite their unjustified concerns, more and more people are reducing or eliminating red meat from their diets, and sometimes chicken and fish as well. They have the desire to keep their cholesterol levels low, and they want to eliminate the cholesterol sources from their diet. Beef, chicken, and fish all contain about the same amount of cholesterol, although chicken and, to a greater extent, fish, are lower in the saturated fats that our bodies use to manufacture cholesterol.
Many people have also heard of the studies linking meat consumption to certain cancers, including colon cancer, which is second only to lung cancer as a cause of death due to cancer in the U.S., prostate cancer, and lymphoma. Although a cause and effect relationship has not been proven, some but not all studies do show such a relationship.
The nutritional concerns often relate to protein, iron, and zinc, so we will consider each of these in turn. Meat, of course, is muscle, so aside from fat, protein is the main macronutrient. Protein, however, is really a non-issue. All whole foods, including grains, vegetables, and fruit contain protein. Yes, even fruit. A medium size California navel orange contains almost 1.5 mg of protein. Therefore, if the average woman consumed nothing but 35 oranges in a given day, she would meet her protein requirements! Other plant foods contain a much higher percentage of protein. In the optimal diet, no more than 15% of the calories need to be derived from protein, yet 16% of the calories from whole wheat flour, 22% of the calories from chickpeas, and 50% of the calories from spinach and mushrooms come from protein.
People who do not eat meat do not need to "combine" any foods. The occasionally heard term "complete protein," which implies that the protein in some foods do not contain some of the essential amino acids, the building blocks of protein that must be supplied by the diet, is misleading and should be abandoned. The protein in every whole plant food contains all of the essential amino acids. True, some vegetable proteins may have relatively more of some amino acids than of others, but there is nothing that says we have to consume amino acids in the exact proportion used by our bodies (as if we even knew what that was). In addition, if a person's diet is a little low in certain amino acids, the body adapts and retains more of those amino acids. In fact, if you ate enough of any one vegetable's protein to meet your daily protein needs, you would also be meeting your requirement for each of the essential amino acids.
It is clear then, that if one simply consumes a healthful diet, embracing a variety of whole foods and avoiding refined, nutritionally bereft "junk foods," and the calorie content is enough to maintain one's weight, one should obtain more than enough protein without difficulty. Consuming too much protein may actually be harmful. An overabundance of protein acidifies the blood, resulting in liberation of calcium from bone and an increased risk of kidney stones. Not surprisingly, animal flesh consumption is a major risk factor for kidney stones, which have become an epidemic in Western countries.
Red meat is undeniably an excellent source of well-absorbed iron. But, again, any well-planned diet containing a good variety of whole foods should provide adequate iron. Iron from plant foods is less well absorbed than that from meat, but when one consumes foods rich in vitamin C at the same time, the absorption of iron is greatly increased. Some plant foods, in fact, are good sources of both iron and vitamin C. These include many dark, leafy green vegetables (chard, spinach, kale, broccoli), potatoes, watermelon, and strawberries. Other plant-derived iron sources include grains, lentils, chickpeas, almonds, blackstrap molasses, and seitan (a wheat analogue made from the gluten fraction of wheat). Note that dried fruits are no longer considered good sources of iron; they are now dried on plastic rather than iron racks). Cooking in iron pots and pans (but not stainless steel) imparts iron to the foods being cooked.
Iron, like protein, is a two-edged sword. Too much iron in the body has a prooxidant (the opposite of antioxidant) effect, increasing the risk of chronic disease. This is mainly a problem for people who are carriers of the gene for the disease hemochromatosis, in which iron stores in the body become too high. About 10-15% of the population carries this gene.
As for zinc, it is indeed an important mineral for maintenance of the immune system and health of the retina, among other things. And meat is indeed a good source of zinc. It is worth noting that the National Research Council has lowered the Recommended Dietary Allowance (RDA) for zinc. Although it formerly stood at 15 mg for men and 11 mg for women, the current values are only 11 mg for men and 8 mg for women. Because of fiber and phytate, components of plant foods that inhibit zinc absorption somewhat, zinc from plant sources is not quite as well absorbed as that from animal products. However, consuming a good variety of healthful whole plant foods will easily allow sufficiency. Such foods include whole grains (especially rye), black-eyed peas, sesame and pumpkin seeds, most kinds of beans, lentils, peas, peanuts, pecans, almonds, cashews, chestnuts, pine nuts, asparagus, spinach, and mushrooms.
Vitamin B-12, on the other hand, a vitamin that is essentially found only in animal products, is a legitimate source of concern for those who are greatly reducing their consumption of animal products, and I address that concern in another section of this web site: Vitamin B-12.