The health advantages of the vegan diet have been confirmed by numerous doctors and nutritionists. A vegan diet strengthens the immune system and promotes longevity, health, intelligence and balance. It has a preventative effect against cancer, as well as coronary disease, osteoporosis, high blood pressure and diabetes.
https://www.provegan.info/en/general-information/vegan/

Dr. Claus Leitzmann, Professor Emeritus of Nutritional Sciences at Germany’s Justus Liebig University Giessen and member of the German Nutrition Society on the topic of the vegan diet: “Studies of those who adhere to a vegan diet conducted around the world as well as our own studies show that vegans are significantly healthier on average than the general population. Body weight, blood pressure, blood and cholesterol levels, kidney functions as well as overall health are more often within the normal range. […] If everyone were vegan, individual health as well the environment and public health would be better. We should take advantage of this potential.”
http://www.vebu.de/alt/nv/nv_2001_4__Prof_Dr_Claus_Leitzmann__Statement_zum_Veganismus.htm

Dr. T. Colin Campbell is Project Director of the China-Oxford-Cornell Diet and Health Project known as the China Study, the most comprehensive research on health and nutrition ever conducted. The study shows that pure vegan nutrition is optimal for humans. Dr. Campbell says: “Plant-based diets create health, prevent disease and the benefits are enormous, especially in terms of controlling health care costs. Health care costs can be reduced substantially for example if everyone switches over to a whole food, plant-based diet.”
http://www.thechinastudy.com

Dr. Neal Barnard, president of the Physicians’ Committee for Responsible Medicine, says in his book Eat Right, Live Longer, “I strongly suggest avoiding meats and dairy products completely. They contain so many ingredients that accelerate free radical and chemical attacks, artery deterioration, hormone shifts, bone loss, and weight problems that there is no reason to include them ever.”
http://www.pcrm.org/media/experts/neal-barnard
http://www.vegparadise.com/news27.html

Thanks to its health advantages, the vegan diet tremendously increases physical fitness and endurance. That is why many high performance athletes prefer plant-based nutrition and choose veganism. Some vegan athletes are: Katharina Wirnitzer (Cyclist from Austria), Alexander Dargatz (Bodybuilder, 2005 World Champion – from Germany), Patrik Baboumian (Armenian-German strongman), Michael Griesmeier (German extreme athlete), Andreas Hänni (Hockey player for SC Bern, Switzerland), Brendan Brazier (Triathlete, Winner of the Canadian 50 km Ultra Marathon 2006), Scott Jurek (Winner of the Badwater Ultra Marathon 2006), Georges Laraque (NHL Hockey player), Kenneth G. Williams (Bodybuilder), Dave Zabriskie (World class cyclist), John Salley (NBA Basketball player), Keith Holmes (Boxer), Pat Neshek (Baseball player for Minnesota Twins), Ruth Heidrich (Ironman, Marathon runner), Mac Danzig (Professional mixed martial artist and instructor), Martina Navratilova (Top ranking tennis player for many years), Pat Reeves (Weightlifter, multiple winner of the British Master's Championship Powerlifting title) etc.

In order to produce one kilo of meat, six to ten or more kilos of grain are necessary. Every sixth human being suffers from hunger and malnutrition, some 25,000 people die every day from the consequences – more than at any other time in history. More than half of the fatalities are children under five years of age – this is because up to 40 percent of grain harvests around the world are fed to animals!
https://www.huffingtonpost.com/entry/cutting-back-on-meat-consumption-could-help-end-hunger-by-2030-experts_us_55f3424ee4b077ca094f27a5
https://prime.peta.org/2013/08/hunger
http://www.onegreenplanet.org/environment/world-hunger-population-growth-ditching-meat/

Energy from alternative sources, saving water, and limiting car travel etc. – these are all very important, but we can positively affect the environment even faster and more effectively when we change our diet.

An individual who just once gives up one pound of beef saves more water than not showering for six months.

Moreover, according to a report by UNESCO up to 15,000 liters of water are necessary to produce one kilo of beef. That corresponds to 80 bathtubs of water! Today, 1.1 billion people have insufficient access to clean drinking water. Climate change along with growing populations will increase scarcity in the foreseeable future.
http://www.unesco.org/new/en/natural-sciences/environment/water/wwap/wwdr/wwdr3-2009/downloads-wwdr3/

Cattle raising is responsible for approximately four-fifths of deforestaion of the Amazon Rainforest (cutting trees for pasture and raising feed crops.) Concentrated animal livestock operations produce huge amounts of carbon dioxide which is released into the atmosphere. Meanwhile, the deforested terrain is no longer able to absorb carbon dioxide, which leads to a worsening of global warming.

Domesticated animals are the single largest source of methane, a greenhouse gas that (over a 20 year time span) traps at least 72 times more heat than CO₂. Carbon dioxide stays in the atmosphere for thousands of years; methane for around 12 years only. Therefore in the short term, methane does much more damage but, ending intensive animal agriculture will quickly bring global warming in check.

Because concentrated animal livestock is responsible for over 50 % of greenhouse gases in the world, a vegan diet could reduce those emissions by half!
http://www.worldwatch.org/files/pdf/Livestock%20and%20Climate%20Change.pdf

Organic farming uses less energy and water than conventional methods of growing foods. It does not use pesticides or chemical fertilizer; it is much more sustainable for the environment and protective for our health.

Organic agriculture also uses less fossil fuels: this in turn lowers the production of greenhouse gases.

A vegan diet with food that is grown organically is the most effective contribution to ending climate change.
https://www.foodwatch.org/fileadmin/foodwatch_international/campaigns/climate/foodwatch_report_on_the_greenhouse_effect_of_farming_05_2009.pdf