I agree with Kamya. We can't simply assume that a vegetarian diet will do no harm, especially when many ecosystems (including animals) are destroyed daily from growing rice, wheat, corn, soy and other crops on a large scale. Ecological and organic farming, gathering food from the wild and hunting are all sources of food that can be the basis of a healthier and more ethical diet, whether it includes meat or not. In these ways we can contribute to the health of the planet, rather than add to harm being done every day.
Being vegetarian doesn't alone achieve ahimsa. You are still taking the milk that belongs to a calf, supporting the industry that kills male chicks to get your eggs, and eating the stomach content of copies in your dairy. True ahimsa is being cruelty free. Vegan. Even if its just your diet for the longest time, that alone saves many animals lives and truly sports non harming as a lifestyle.
Ahimsa does not mean vegetarianism as this article suggests. The Yama Ahimsa is non-violence and gentleness and is meant to be applied towards everything, not just animals raised for food. I would argue that some forms of industrial monoculture are much more violent to the environment and farmers than small-scale local farms raising livestock and chickens. Perhaps ahimsa calls us to make honest informed food choices and to always know exactly where our animals and vegetables come from rather than forgoing all animal flesh in order to consume corn, soy, and wheat that is destroying our land and the lives of many Americans.
If you are eating a variety of whole, unprocessed foods, you will easily consume all the nutrients you need. The only real deficiency in a vegan diet is vitamin B12, which comes from bacteria found in the waste of animals (therefore, meat). However, the daily requirement is only 3 micrograms (not milligrams) a day, so this is easy to acquire. Soy, like all foods, is fine in moderation, provided you are not allergic, but there are also a large amount of protein alternatives.
I agree with the plant based diet although I also think that in today's day and age, Soy is not the best option to get your nutrients. Soy as it is grown as a commodity vegetable, fed to commodity raised cattle, is not good for human consumption because our bodies can not process it. So I highly suggest for people to start turning away from soy as a backup protein source. You would be amazed to know how many people actually test positive for soy allergies because they can not process it.