There are three main types of vegetarian diet. The most common form is lacto-ovo-vegetarianism in which meat and fish are omitted from the diet, but eggs and dairy products are not. Pro-animal vegetarianism excludes meat while a vegan diet excludes all animal products, i.e. not only meat and fish but also dairy produce and eggs.
There is no reason why a vegetarian diet cannot be as healthy as a diet containing meat, provided that, for example, the protein that non-vegetarians obtain from meat is obtained from some other source, such as nuts, cereals or pulses. Vegetarians also need to ensure they get adequate supplies of iron, zinc and calcium, which are found in good supply in meat and milk. Women in particular have double the iron needs of men and should take care to avoid iron deficiency. Women also seem to suffer more from loss of calcium. Generally an adequate supply of these minerals can be obtained from dairy products, but if these are not included in the diet, substitutes must be found. A vegan diet is likely to be deficient in vitamin B12, and supplements may need to be taken to avoid this.