When you consume proteins, your body breaks them down to their constituent amino acids. These amino acids can then be recombined in numerous ways to create the various proteins that your body needs for its regular functions. Of the 20 amino acids that your body needs, nine are called "essential" because you can obtain them only from dietary sources. Although animal products, such as beef, chicken and tuna, are the best sources of lysine, most vegetarians do not lack in this essential amino acid.
Also known as "complete proteins," high-quality proteins are foods that provide a source of all essential amino acids. Although the majority of these are not suitable for vegetarians, a few vegetarian foods are high-quality proteins. Legumes account for most of these, with tofu, tempeh, edamame and lentils all exceeding your essential amino acid needs in as little as 2 to 3 cups, or 4 to 6 servings, per day. Although not suitable for all vegetarian diets, eggs and 2 percent milk also provide all of your essential amino acids in less than 6 servings, which is equivalent to 6 cups of milk or six large eggs. As long as you regularly eat a source of these foods, your vegetarian diet will not lack in lysine or any other essential amino acid.
Some foods contain large amounts of lysine despite not being a source of all essential amino acids. Grains that are high in lysine include quinoa, buckwheat and oatmeal, which meet your daily needs in 5.5, 7.7 and 8.4 cups, respectively. Although fruits and vegetables are generally low in protein and amino acids, you can meet your lysine needs by eating 9.2 medium-sized potatoes in their skins or 10.3 cups of broccoli. A number of nuts and seeds also contain large amounts of lysine, with 2.5 cups, or 10 servings, of cashews, pistachios and sunflower seeds all exceeding your daily needs. As these foods are suitable for all vegetarians, a well-planned diet can easily meet your lysine needs.
In its 2009 position paper on vegetarian diets, the American Dietetic Association -- now the Academy of Nutrition and Dietetics -- states that vegetarian diets generally do not lack in protein or essential amino acids. However, this may not be true if you have allergies or other dietary restrictions. For example, your vegetarian diet may lack in lysine if you are allergic to soy. The ADA notes that some vegans may also suffer from insufficient lysine intake because they abstain from such high-lysine animal foods as eggs and dairy products. Because of this, registered dietitian Jack Norris of Vegan Health suggests that it is more important for vegans to monitor their lysine intake than total protein intake.
Your liver is capable of storing essential amino acids, so you do not need to work particularly hard to meet your body's amino acid needs. Because most plant proteins contain small amounts of all essential amino acids, dietitian Dr. Reed Mangels of The Vegetarian Resource Group states that it is possible to meet your daily needs even if you eat only one food. However, this would require that you eat an unreasonably large number of servings -- for example, more than 15 cups of cooked rice or nearly 90 tomatoes per day. As this would also result in nutrient overconsumption and deficiencies, the best way to meet your essential amino acid needs is to eat a balanced vegetarian diet with a variety of protein sources.
Matthew Lee has been writing professionally since 2007. Past and current research projects have explored the effect of a diagnosis of breast cancer on lifestyle and mental health and adherence to lifestyle-based (i.e. nutrition and exercise) and drug therapy treatment programs. He holds a Master of Arts in psychology from Carleton University and is working toward his doctorate in health psychology.