According to the table above, the stricter a diet is in terms of limiting animal protein sources, i.e., fish, poultry, eggs and dairy products, the more acute the problems due to nutrient deficiencies might be. A careful combination of legumes with nuts or cereals, such as a lentil and rice dish, can provide high biological value protein. Since vegetarian diets do not allow the consumption of meat, the daily requirements of protein intake can be met by a variety of plant sources. Rich sources of plant-based protein are cereals, legumes and nuts.
While vegetarian diets are rich in omega-6 fatty acids, they often lack omega-3 fatty acids, which our bodies cannot synthesize and need to be obtained from dietary sources. When fish is excluded from vegetarian diets, the intake of essential omega-3 fatty acids, such as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), decreases. These fatty acids are important for cardiovascular function, cognitive health, and visual acuity. However, some plant foods, such as flaxseed, walnuts and soy, can provide alpha-linolenic acid, which the human body uses to synthesize the long-chain fatty acids EPA and DHA. Omega-3 fatty acid fortified foods, like margarine spreads, are other sources of EPA and DHA for people following a vegetarian diet.
Furthermore, the abstention from meat and dairy products and the presence of plant foods in vegetarian diets hinder the required intake of essential minerals and trace elements. Red meat is the best source of absorbable iron. Vegetarian diets that include animal protein, such as poultry meat, shellfish and some fish (perch, sardines, swordfish), offer some important amounts of absorbable iron. Plant sources of iron include legumes, mushrooms, peas, artichokes and cherries. However, iron from plant foods is not as easily absorbed from the body. To increase the level of iron absorption, it is recommended that plant foods be combined with a food source of vitamin C or animal iron source. Dishes such as chicken with mushrooms, artichokes ala polita with plenty of lemon juice (vitamin C) or a fruit salad with cherries, kiwis and strawberries (vitamin C sources) enhance iron absorption. On the other hand, iron-containing food should not be consumed with dairy products as calcium blocks iron absorption.
Dairy products are a main source of calcium so if the vegetarian diet excludes such foods, calcium has to be found in other sources. Eating fish with bones provide good amounts of calcium. Though calcium is present in legumes and some vegetables, it is not readily absorbed since the presence of phytic acid and oxalic acid prevent good absorption from the body. Vegetarians can generally meet their nutritional needs for calcium by consuming a variety of plant sources rich in calcium. Even though their bioavailability of calcium is rather low, nuts and seeds can contribute to calcium needs. Fortified with calcium food such as wholegrain breakfast cereals, biscuits, fresh juices or non-dairy milks fortified with calcium, like soymilk and almond milk, can also contribute a significant amount of calcium requirements.
Finally, vitamin B12 is only found in animal foods and has particular nutritional value, especially for the development of the nervous system. While vitamin B12 is not present in plant foods, vegetarians can meet their dietary needs from fortified foods such as breakfast cereals and soy products.