Veganism is the strictest form of vegetarianism. Vegans do not eat milk, eggs, gelatin, and other animal products such as honey. Vegans find the meat industry to be repulsive and barbaric, and almost always fight strongly against it. Vegans will find animal products hidden in everything--for instance, carmine, a red dye in some foods, is obtained by crushing carmine beetles. A vegan will refuse to dissect (although many other vegetarians will do the same thing) and will attend the local fur protest. And, a vegan will never "eat it to please his mother." A vegan feels that the animal's life is more meaningful than someone's ego, and, if necessary, will politely make this known

The term "animal product" in a vegan context refers to material derived from animals for human use. Notable animal products include meat, poultry, seafood, eggs, dairy products, honey, fur, leather, wool, and silk.Common animal by-products include gelatin, lanolin, rennet, whey, beeswax and shellac.Most vegans refrain from supporting industries that use animals directly or indirectly, such as circuses, rodeos, and zoos, and will not use products that are tested on animals.

Animal ingredients can be found in countless products and are used in the production of—though not always present in the final form of—many more;many of these ingredients are esoteric, also have non-animal sources,and especially in non-food products may not even be identified. Although some vegans attempt to avoid all of these ingredients, Vegan Outreach argues that "it can be prohibitively expensive and time-consuming to shun every minor or hidden animal-derived ingredient," and therefore that doing what is "best for preventing suffering" is more important than identifying and excluding every animal ingredient.
People who adopt a vegan diet to reduce resource consumption or ecological footprint extend the idea of environmental vegetarianism to all animal products. The fundamental rationale is that each additional trophic level in a food chain passes on only a fraction of the energy it consumes, so a diet that consists of plant products rather than animal products will generally use less of some resources, and indirectly may cause less environmental damage. In 2006, the Food and Agriculture Organization of the United Nations found that livestock destruction is responsible for 18 percent of greenhouse gas emissions measured in CO2 equivalent, which is directly affecting global climate change.

Specific nutrients

Vitamin B12, a bacterial product, cannot be reliably found in plant foods.While it may take one to five years to exhaust some individual's reserves of vitamin B12, many people do not have such reserves and serious health consequences are a risk as a result of B12 deficiency.Additionally, mild B12 deficiency can develop even with such reserves.In a 2002 laboratory study, more of the strict vegan participants' B12 and iron levels were compromised than those of lacto- or lacto-ovo-vegetarian participants. The Vegan Society and Vegan Outreach, among others, recommend that vegans either consistently eat foods fortified with B12 or take a daily or weekly B12 supplement. Tempeh, seaweed, spirulina, organic produce, soil on unwashed vegetables, and intestinal bacteria have not been shown to be reliable sources of B12 for the dietary needs of vegans.
Adequate amounts of vitamin D may be obtained by spending 15 to 30 minutes every few days in the sunlight, although this may be difficult for vegans in areas with low levels of sunlight during winter.
A 2007 study showed that vegans have an increased risk of bone fractures than both meat eaters and vegetarians, likely due to lower dietary calcium intake, but that vegans consuming more than the UK's estimated average requirements for calcium (525 mg/day) had risk of bone fractures similar to other groups.It is recommended that vegans eat three servings per day of a high calcium food, such as fortified soy milk and take a calcium supplement as necessary.