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A diet of French fries and soft drinks is certainly vegetarian but hardly full of nutrition. It's important to eat a variety of fruits, vegetables, legumes, grains, and soy products, paying close attention to protein, vitamin B12, omega-3 fatty acids, vitamin D, calcium, iron, and zinc–nutrients which are sometimes harder to consume on a meatless diet.
This isn't a big deal for most vegetarians because other than fruits, almost every other food of plant origin contains protein, even if it's in small amounts. The quality of plant protein is generally lower than protein from animal sources, but it's still adequate to meet the body's needs–just be sure to eat a varied diet that includes soy products, legumes, nuts, seeds, grains, and vegetables.
This vitamin, which helps produce red blood cells, is widely available in animal-based foods and isn't a problem for vegetarians who eat dairy products or eggs. But vegans should take a supplement or eat vitamin B12-fortified foods such as cereals, soy or rice beverages, or veggie burgers.
Vegetarians need to consume alpha-linolenic acids because they convert to omega-3 fatty acids, which help keep the brain and nervous system functioning and may also offer protection from heart disease. Plant-based sources of alpha-linolenic acids include canola oil, soy oil, walnuts, ground flaxseed, and soybeans. Flexitarians who consume fish can get omega-3s from fatty varieties like salmon.
Although fish, liver, and egg yolks are the only foods that naturally contain vitamin D, it's added to most milk in the United States. Your body also makes its own when your skin is exposed to sunlight, so simply drinking milk and getting outdoors can provide enough vitamin D to assist in calcium absorption and help maintain strong bones. Vegans may need a supplement or other vitamin D-fortified foods.
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If you consume dairy products, calcium intake is usually not a problem. Without dairy, it takes a little planning to consume the recommended amount of 1,000 milligrams per day. Consider taking a supplement and eat lots of calcium-containing plant foods: soybeans, fortified soy products, broccoli, kale, collards, mustard greens, okra, rutabaga, bok choy, dried figs, and fortified juices, cereals, cereal bars, and breads.
Lacto-ovo vegetarians can get iron from eggs, but others should eat plenty of legumes, fortified cereals and breads, spinach, beet greens, seeds, tempeh, prunes, raisins, and blackstrap molasses. Because our bodies don't absorb plant-based iron (nonheme iron) as well as iron from animal products, eat vitamin C-rich food with every meal to help increase absorption of nonheme iron. Also, if you cook in a cast-iron skillet, some of the iron from the pan will pass into the food.
When you don't eat meat, poultry, or seafood, you may come up short on zinc, a nutrient that helps the formation of proteins. Dairy products and many plants also contain this important nutrient, but the zinc from plant foods isn't absorbed as well as the zinc from animal products. However, if you eat plenty of whole-grain breads, legumes, tofu, seeds, and nuts, you can get an adequate amount.