It’s difficult to estimate the number of vegetarians out there, given the flexible nature of many people’s dietary patterns. It is challenging to conduct effective cross-cultural research into the issue, such as research into vegetarianism in urban Canada versus rural India). Consider the question of what really constitutes vegetarianism. Is it complete avoidance of all animal products? Is it avoiding red meat only? Is it eating no meat, but still making use of animal products, such as leather, wool and beeswax?

The question of why people abstain from eating meat may, surprisingly, be easier to address than the number of abstainers. Typical reasons for “going veg” generally include one or more of the following: ethical reasons (not wanting to cause animal suffering), health reasons (believing that a non-meat diet is more conducive to human health), and religious or spiritual reasons ( as is the case with Hindus, Buddhists, and Rastafarians). In addition, a significant number of vegetarians list environmental reasons as the prime motivator in shaping their dietary choices.

So what environmental factors influence people in this camp? One of the prime factors cited is the amount of land required to support farm animals. According to some sources, seven times more land is required to grow livestock feed, than would be needed to grow food directly for people. Much like the energy lost when converting, say, home heating fuels to actual heat, an animal’s conversion of food energy into meat for human consumption is not an entirely efficient process.

Given these two factors, the question becomes whether meat production makes environmental sense. The question gains relevance from an environmental standpoint given increasingly intense competition for scarce land resources and a global ecological scenario characterized by severe loss of natural habitat.

A second rationale some environmentalists give for becoming vegetarian is water quality. We’ve all heard of the pollution of waterways and groundwater sources by high-nutrient animal waste, particularly in the context of large-scale industrial agricultural operations. While nutrients in the water may sound a lot less concerning than, say, toxins spewed into a waterway from some industry, high nutrient levels in water are actually serious business. Eutrophication is the term used to refer to a water body suffering from excessive nutrient levels. High concentrations of nutrients, such as phosphorous and nitrogen, are taken advantage of by algae, which proliferate, sometimes in massive blooms. These algal blooms block light, preventing the growth of other plant species and use up the water’s oxygen supply to the extent that fish and other aquatic organisms can often no longer survive.

E-coli is among the most well known of the manure-related microorganisms that can also affect water quality. They can pose health risks to both people and other animals. The argument in this case is often not against livestock-based agriculture per se, but rather against industrial-scale agriculture. With the latter, the production of waste in a given area exceeds the capacity to deal with it in an environmentally responsible manner.

A third rationale is that meat eating contributes to global climate change in more ways than one. According to the United Nations, 18% of greenhouse gases (more than is produced by all the automobiles in the world) come from farm animals. Methane, one of the most efficient of the greenhouse gases in terms of heat-trapping capacity, is at the root of the issue. Indelicately put, the problem is animal farts. The large population of farm animals (that actually outweigh the earth’s human population) produces methane as a by-product of digestion. This methane is a significant contributor to the problems associated with climate change.

In addition, deforestation is common practice in some parts of the world in order to create new areas for livestock pasture or for the production of livestock feed. The problem is that the world’s forests are massive carbon sinks. The term sink is associated with trees that use carbon in their photosynthetic processes and incorporate it into their tissues, thus removing it from the atmosphere. With excess atmospheric carbon strongly linked to global climate change, and large-scale removal of these carbon sinks being at least partly due to meat production, climate considerations offer a strong rationale for going vegetarian.

Whatever the rationale, most of us constantly make choices about our diets and the dietary patterns of our families. Thinking about the rationale others use for determining their eating habits is, at the very least, interesting food for thought.