Semi-vegetarian diets primarily consist of vegetarian foods, though occasional exceptions are made for some non-vegetarian foods, including fish, poultry and red meat. These diets may be followed by those who choose to reduce the amount of animal flesh consumed as a way of transitioning to a vegetarian diet or for health, environmental, or other reasons. The term "semi-vegetarian" is contested by most vegetarian groups, who believe that vegetarianism must exclude all animal flesh. Many individuals describe themselves as "vegetarian" while practicing a semi-vegetarian diet.

The Vegetarian Society, founded in 1847, claims to have "created the word vegetarian from the Latin 'vegetus' meaning 'lively' (which is how these early vegetarians claimed their diet made them feel) ..." However, the Oxford English Dictionary and other standard dictionaries state that the word was formed from the term "vegetable" and the suffix "-arian".

The Oxford English Dictionary also gives evidence that the word was already in use before the foundation of the Vegetarian Society:

but notes that "The general use of the word appears to have been largely due to the formation of the Vegetarian Society at Ramsgate in 1847."

The earliest records of (lacto) vegetarianism as a concept and practice amongst a significant number of people come from ancient India. Vegetarianism was also practiced by the ancient Greek civilisation in Southern Italy and in Greece in the 6th century BCE. In both instances the diet was closely connected with the idea of nonviolence towards animals (called ahimsa in India) and was promoted by religious groups and philosophers.

Following the Christianisation of the Roman Empire in late antiquity, vegetarianism practically disappeared from Europe. Several orders of monks in medieval Europe restricted or banned the consumption of meat for ascetic reasons, but none of them eschewed fish. Saint Genevieve, the Patron Saint of Paris, is mentioned as having observed a vegetarian diet — but as an act of physical austerity, rather than out of concern for animals.

Vegetarianism re-emerged somewhat in Europe during the Renaissance. It became a more widespread practice in the 19th and 20th centuries.

In 1847, the first Vegetarian Society was founded in England; Germany, the Netherlands and other countries followed. The International Vegetarian Union, a union of the national societies, was founded in 1908. In the Western world, the popularity of vegetarianism grew during the 20th century as a result of nutritional, ethical, and more recently, environmental and economic concerns.

Vegetarianism is considered a healthy, viable diet. The American Dietetic Association and the Dietitians of Canada have found a properly planned vegetarian diet to satisfy the nutritional needs for all stages of life, and large-scale studies have shown that "Mortality from ischemic heart disease was 24% lower in vegetarians than in nonvegetarians" Necessary nutrients, proteins, and amino acids for the body's sustenance can be found in vegetables, grains, nuts, soymilk, eggs and dairy.

Vegetarian diets can aid in keeping body weight under control and substantially reduce risks of heart disease and osteoporosis. Non-lean red meat, in particular, has been found to be directly associated with dramatically increased risk of cancers of the esophagus, liver, colon, and the lungs. Other studies, in contrast, have shown no significant differences between vegetarians and nonvegetarians in mortality from cerebrovascular disease, stomach cancer, colorectal cancer, breast cancer, or prostate cancer, although the sample of vegetarians was small and included ex-smokers who had switched their diet within the last five years.

The American Dietetic Association and Dietitians of Canada have stated: "Vegetarian diets offer a number of nutritional benefits, including lower levels of saturated fat, cholesterol, and animal protein as well as higher levels of carbohydrates, fibre, magnesium, potassium, folate, and antioxidants such as vitamins C and E and phytochemicals." Vegetarians tend to have lower body mass index, lower levels of cholesterol, lower blood pressure, and less incidence of heart disease, hypertension, type 2 diabetes, renal disease, osteoporosis, dementias such as Alzheimer’s Disease and other disorders

Plants are not generally significant sources of Vitamin B12. However, lacto-ovo vegetarians can obtain B12 from dairy products and eggs, and vegans can obtain it from fortified foods and dietary supplements. Since the human body preserves B12 and reuses it without destroying the substance, clinical evidence of B12 deficiency is uncommon. The body can preserve stores of the vitamin for up to 30 years without needing its supplies to be replenished.

The only reliable vegan sources of B12 are foods fortified with B12 (including some soy products and some breakfast cereals) and B12 supplements. The research on vitamin B12 sources has increased in the latest years.

A 1999 metastudy combined data from five studies from western countries. The metastudy reported mortality ratios, where lower numbers indicated fewer deaths, for fish eaters to be .82, vegetarians to be .84, occasional meat eaters to be .84. Regular meat eaters and vegans shared the highest mortality ratio of 1.00. The study reported the numbers of deaths in each category, and expected error ranges for each ratio, and adjustments made to the data. However, the "lower mortality was due largely to the relatively low prevalence of smoking in these [vegetarian] cohorts". Out of the major causes of death studied, only one difference in mortality rate was attributed to the difference in diet, as the conclusion states: "vegetarians had a 24% lower mortality from ischemic heart disease than nonvegetarians, but no associations of a vegetarian diet with other major causes of death were established."

In "Mortality in British vegetarians", a similar conclusion is drawn: "British vegetarians have low mortality compared with the general population. Their death rates are similar to those of comparable non-vegetarians, suggesting that much of this benefit may be attributed to non-dietary lifestyle factors such as a low prevalence of smoking and a generally high socio-economic status, or to aspects of the diet other than the avoidance of meat and fish."

The Adventist Health Study is an ongoing study of life expectancy in Seventh-day Adventists. This is the only study among others with similar methodology which had favourable indication for vegetarianism. The researchers found that a combination of different lifestyle choices could influence life expectancy by as much as 10 years. Among the lifestyle choices investigated, a vegetarian diet was estimated to confer an extra 1–1/2 to 2 years of life. The researchers concluded that "the life expectancies of California Adventist men and women are higher than those of any other well-described natural population" at 78.5 years for men and 82.3 years for women. The life expectancy of California Adventists surviving to age 30 was 83.3 years for men and 85.7 years for women.

The Adventist health study is again incorporated into a metastudy titled "Does low meat consumption increase life expectancy in humans?" published in American Journal of Clinical Nutrition, which concluded that low meat eating (less than once per week) and other lifestyle choices significantly increase life expectancy, relative to a group with high meat intake. The study concluded that "The findings from one cohort of healthy adults raises the possibility that long-term (≥ 2 decades) adherence to a vegetarian diet can further produce a significant 3.6-y increase in life expectancy." However, the study also concluded that "Some of the variation in the survival advantage in vegetarians may have been due to marked differences between studies in adjustment for confounders, the definition of vegetarian, measurement error, age distribution, the healthy volunteer effect, and intake of specific plant foods by the vegetarians." It further states that "This raises the possibility that a low-meat, high plant-food dietary pattern may be the true causal protective factor rather than simply elimination of meat from the diet." In a recent review of studies relating low-meat diet patterns to all-cause mortality, Singh noted that "5 out of 5 studies indicated that adults who followed a low meat, high plant-food diet pattern experienced significant or marginally significant decreases in mortality risk relative to other patterns of intake."

Statistical studies, such as comparing life expectancy with regional areas and local diets in Europe also have found life expectancy considerably greater in southern France, where a low meat, high plant Mediterranean diet is common, than northern France, where a diet with high meat content is more common.

A study by the Institute of Preventive and Clinical Medicine, and Institute of Physiological Chemistry looked at a group of 19 vegetarians (lacto-ovo) and used as a comparison a group of 19 omnivorous subjects recruited from the same region. The study found that this group of vegetarians (lacto-ovo) have a significantly higher amount of plasma carboxymethyllysine and advanced glycation endproducts (AGEs) compared to this group of omnivores.[69] Carboxymethyllysine is a glycation product which represents "a general marker of oxidative stress and long-term damage of proteins in aging, atherosclerosis and diabetes." "Advanced glycation end products (AGEs) may play an important adverse role in process of atherosclerosis, diabetes, aging and chronic renal failure."

Libby Sande argued in a blog for USA Today that Vegetarianism reduces E. coli infections, and in a piece for The New York Times linked E. coli contamination in food to industrial scale meat and dairy farms. E. coli infections in the US during 2006 were traced to spinach and onions.

Transmission of pathogenic E. coli often occurs via fecal-oral transmission. Common routes of transmission include unhygienic food preparation and farm contamination. Dairy and beef cattle are primary reservoirs of the E. coli strain O157:H7, and they can carry it asymptomatically and shed it in their feces. Food products associated with E. coli outbreaks include raw ground beef, raw seed sprouts or spinach, raw milk, unpasteurized juice, and foods contaminated by infected food workers via fecal-oral route. In 2005, some people who had consumed triple-washed, pre-packaged lettuce were infected with E. coli. In 2007, packaged lettuce salads were recalled after they were found to be contaminated with E. coli. E. coli outbreaks have been traced to unpasteurised apples, orange juice, milk, alfalfa sprouts, and water.

Salmonella outbreaks have been traced to peanut butter, frozen pot pies & puffed vegetable snacks. BSE, also known as mad cow disease, is linked by the World Health Organization to Creutzfeldt–Jakob disease in humans.

There have been reports of fears of foot-and-mouth disease in sheep, PCBs in farmed salmon, mercury in fish, dioxin concentrations in animal products, artificial growth hormones, antibiotics, lead and mercury, pesticide contamination of vegetables and fruits, banned chemicals being used to ripen fruits. In 2005, fears that "bird flu" could be caused by eating chicken were featured in a PETA call for vegetarian diets.

The consumption of meat can cause a transmission of a number of diseases from animals to humans. The connection between infected animal and human illness is well established in the case of salmonella; an estimated one-third to one-half of all chicken meat marketed in the United States is contaminated with salmonella. Only recently, however, have scientists begun to suspect that there is a similar connection between animal meat and human cancer, birth defects, mutations, and many other diseases in humans. In 1975, one study found 75 percent of supermarket samples of cow's milk, and 75 percent of egg samples to contain the leukemia (cancer) virus. By 1985, nearly 100 percent of the eggs tested, or the hens they came from, had the cancer virus. The rate of disease among chickens is so high that the Department of Labor has ranked the poultry industry as one of the most hazardous occupations. 20 percent of all cows are afflicted with a variety of cancer known as bovine leukemia virus (BLV). Studies have increasingly linked BLV with HTLV-1, the first human retrovirus discovered to cause cancer. Scientists have found that a bovine immunodeficiency virus (BIV), the equivalent of the AIDS virus in cows, can also infect human cells. It is supposed that BIV may have a role in the development of a number of malignant or slow viruses in humans.

The proximity of animals in industrial-scale animal farming leads to an increased rate of disease transmission. Transmission of animal influenza viruses to humans has been documented, but illness from such cases is rare compared to that caused by the now common human-adapted older influenza viruses, transferred from animals to humans in the more distant past. The first documented case was in 1959, and in 1998, 18 new human cases of H5N1 influenza were diagnosed, in which six people died. In 1997 more cases of H5N1 avian influenza were found in chickens in Hong Kong.

Whether tuberculosis originated in cattle and was then transferred to humans, or diverged from a common ancestor infecting a different species, is currently unclear. The strongest evidence for a domestic-animal origin exists for measles and pertussis, although the data do not exclude a non-domestic origin.

According to the 'Hunter Theory', the "simplest and most plausible explanation for the cross-species transmission" the AIDS virus was transmitted from a chimpanzee to a human when a bushmeat hunter was bitten or cut while hunting or butchering an animal.

Historian Norman Cantor suggests the Black Death might have been a combination of pandemics including a form of anthrax, a cattle murrain. He cites many forms of evidence including the fact that meat from infected cattle was known to have been sold in many rural English areas prior to the onset of the plague.

Hinduism, Buddhism and Jainism teach vegetarianism as moral conduct. Buddhism in general does not prohibit meat eating, while Mahayana Buddhism encourages vegetarianism as beneficial for developing compassion. Other denominations that advocate a fully vegetarian diet include the Seventh-day Adventists, the Rastafari movement and the Hare Krishnas. Sikhism does not equate spirituality with diet and does not specify a vegetarian or meat diet.

Most major paths of Hinduism hold vegetarianism as an ideal. There are three main reasons for this: the principle of nonviolence (ahimsa) applied to animals; the intention to offer only "pure" (vegetarian) food to a deity and then to receive it back as prasad; and the conviction that non-vegetarian food is detrimental for the mind and for spiritual development. Hindu vegetarians usually eschew eggs but consume milk and dairy products, so they are lacto-vegetarians.

However, the food habits of Hindus vary according to their community and according to regional traditions. Historically and currently, those Hindus who eat meat prescribe Jhatka meat.

Theravadins in general eat meat. If Buddhist monks "see, hear or know" a living animal was killed specifically for them to eat, they must refuse it or else incur an offense. However, this does not include eating meat which was given in alm or commercially purchased. In Theravada cannon, Buddha did not make any comment discouraging them to eat meat (except specific types, such as human, elephant, horse, dog, snake, lion, tiger, leopard, bear, and hyena flesh) but he specifically refuse to institute vegetarianism in his monastic code when a suggestion has been made.

In Mahayana Buddhism, there are several Sanskrit texts where the Buddha instructs his followers to avoid meat. However, each branch of Mahayana Buddhism selects which sutra to follow and some branches of Mahayana Buddhists including majority of Tibetan and Japanese Buddhists do eat meat while most of Chinese Buddhists do not eat meat.

The tenets of Sikhism do not advocate a particular stance on either vegetarianism or the consumption of meat, but rather leave the decision of diet to the individual. The tenth guru, Guru Gobind Singh, however, prohibited "Amritdhari" Sikhs, or those that follow the Sikh Rehat Maryada (the Official Sikh Code of Conduct) from eating Kutha meat, or meat which has been obtained from animals which have been killed in a ritualistic way. This is understood to have been for the political reason of maintaining independence from the then-new Muslim hegemony, as Muslims largely adhere to the ritualistic halal diet.

"Amritdharis" that belong to some Sikh sects (eg Akhand Kirtani Jatha, Damdami Taksal, Namdhari, Rarionwalay, etc.) are vehemently against the consumption of meat and eggs (though they do consume and encourage the consumption of milk, butter, and cheese). This vegetarian stance has been traced back to the times of the British Raj, with the advent of many new Vaishnava converts. In response, to the varying views on diet throughout the Sikh population, Sikh Gurus have sought to clarify the Sikh view on diet, stressing their preference only for simplicity of diet. Guru Nanak said that over-consumption of food (Lobh, Greed) involves a drain on the Earth's resources and thus on life. Passages from the Guru Granth Sahib (the holy book of Sikhs, also known as the Adi Granth) say that it is "foolish" to argue for the superiority of animal life, because though all life is related, only human life carries more importance.

"Only fools argue whether to eat meat or not. Who can define what is meat and what is not meat? Who knows where the sin lies, being a vegetarian or a non-vegetarian?"

The Sikh langar, or free temple meal, is largely lacto-vegetarian, though this is understood to be a result of efforts to present a meal that is respectful of the diets of any person who would wish to dine, rather than out of dogma.

A number of medieval scholars of Jewish religion (e.g. Joseph Albo) regard vegetarianism as a moral ideal, not just because of a concern for the welfare of animals, but because the slaughter of animals might cause the individual who performs such acts to develop negative character traits. Therefore, their concern was with regard to possible harmful effects upon human character rather than with animal welfare. Indeed, Rabbi Joseph Albo maintains that renunciation of the consumption of meat for reasons of concern for animal welfare is not only morally erroneous but even repugnant.

One modern-day scholar who is often cited as in favour of vegetarianism is the late Rabbi Abraham Isaac Kook, the Chief Rabbi of Pre-State Israel. It is indeed the case that in his writings, Rabbi Kook speaks of vegetarianism as an ideal, and points to the fact that Adam did not partake of the flesh of animals. In context, however, Rabbi Kook makes those comments in his portrayal of the eschatological (messianic) era.

According to some Kabbalists, only a mystic, who is able to sense and elevate the reincarnated human souls and "divine sparks", is permitted to consume meat, though eating the flesh of an animal might still cause spiritual damage to the soul. A number of Orthodox Jewish vegetarian groups and activists promote such ideas and believe that the halakhic permission to eat meat is a temporary leniency for those who are not ready yet to accept the vegetarian diet.

Having ties with both ancient Judaism and Christianity, members of the ancient Essene religious group practiced strict vegetarianism sharing a similar belief with the Hindus'/Jains' idea of Ahimsa or "harmlessness".

Translation of the Torah's Ten Commandments state "thou shalt not murder." Some people argue that this can also be taken as meaning not to kill at all, animals nor humans, or at least "that one shall not kill unnecessarily," in the same manner that onerous restrictions on slavery in the Bible have been interpreted by modern theologians as to suggest banning the practice. Although it should be noted that the very same Torah also commands people to ritually slaughter animals when killing them, and goes into precise detail on the rituals of animal sacrifices.

While it is neither required nor prohibited for Jews to eat meat, the choice must be made in regard to the ethics and ideals of Judaism"The Vegetarian Mitzvah". http://www.brook.com/jveg. 

Ancient Greek philosophy has a long tradition of vegetarianism. Pythagoras was reportedly vegetarian (and studied at Mt. Carmel, where some historians say there was a vegetarian community), as his followers were expected to be. Socrates was reportedly vegetarian, and in his dialogue of what people, or at least Philosopher-rulers, in an ideal republic should eat, he described only vegetarian food. He specified that if meat-eating was allowed, then society would require more doctors.

Roman writer Ovid concluded his magnum opus Metamorphoses, in part, with the impassioned argument (uttered by the character of Pythagoras) that in order for humanity to change, or metamorphose, into a better, more harmonious species, it must strive towards more humane tendencies. He cited vegetarianism as the crucial decision in this metamorphosis, explaining his belief that human life and animal life are so entwined that to kill an animal is virtually the same as killing a fellow human.

Everything changes; nothing dies; the soul roams to and fro, now here, now there, and takes what frame it will, passing from beast to man, from our own form to beast and never dies...Therefore lest appetite and greed destroy the bonds of love and duty, heed my message! Abstain! Never by slaughter dispossess souls that are kin and nourish blood with blood!

Jesus ordered his apostles to catch and prepare meals with fish and he famously fed 5000 people with five loaves of bread and two fish. Since no other kind of meat is mentioned, and since some of the apostles (and possibly Jesus) may have taken the Nazarite vow, it is surmised that Jesus was a pescetarian.

While vegetarianism is not a common practice in current Christian culture, except by traditional monastics and by other Orthodox at least during 'fast' times, the concept and practice have scriptural and historical support. According to the Bible, in the beginning, humans and animals were vegetarian.(Genesis 1:29–30) Immediately after the Flood, God permitted the eating of meat. (Genesis 9:3)

There is also a strong association between the Quaker tradition within Christianity and vegetarianism dating back at least to the 18th century. The association grew in prominence during the 19th century, coupled with growing Quaker concerns in connection with alcohol consumption, vivisection and social purity. The association between the Quaker tradition and vegetarianism, however, becomes most significant with the founding of the Friends' Vegetarian Society in 1902 "to spread a kindlier way of living amongst the Society of Friends."

Followers of Islam, or Muslims, have the freedom of choice to be vegetarian for medical reasons or if they do not personally like the taste of meat. However, the choice to become vegetarian for non-medical reasons can sometimes be controversial. Though some more traditional Muslims may keep quiet about their vegetarian diet, the number of vegetarian Muslims is increasing.

Vegetarianism has been practiced by some influential Muslims including the Iraqi theologian, female mystic and poet Râbi‘ah al-‘Adawîyah of Basrah, who died in the year 801, and the Sri Lankan sufi master Bawa Muhaiyaddeen who established The Bawa Muhaiyaddeen Fellowship of North America in Philadelphia.

In January 1996, The International Vegetarian Union announced the formation of the Muslim Vegetarian/Vegan Society.

Many omnivore Muslims will select vegetarian (or seafood) options when dining in non-halal restaurants. However, this is a matter of not having the right kind of meat rather than preferring not to eat meat on the whole.

Environmental vegetarianism is based on the concern that the production of meat and animal products for mass consumption, especially through factory farming, is environmentally unsustainable. According to a 2006 United Nations initiative, the livestock industry is one of the largest contributors to environmental degradation worldwide, and modern practices of raising animals for food contributes on a "massive scale" to air and water pollution, land degradation, climate change, and loss of biodiversity. The initiative concluded that "the livestock sector emerges as one of the top two or three most significant contributors to the most serious environmental problems, at every scale from local to global."

In July 2009 Nike and Timberland stopped buying leather from deforested Amazon Rainforest a few weeks after Greenpeace report demonstrated the destruction caused by Amazon cattle ranchers. According to Arnold Newman every hamburger sold results in destruction of 6.25m2 of rain forest.

In addition, animal agriculture is a large source of greenhouse gases and is responsible for 18 percent of the world's greenhouse gas emissions as measured in CO2 equivalents. By comparison, all of the world's transportation (including all cars, trucks, buses, trains, ships, and planes) emits 13.5 percent of the CO2. Animal farming produces 65 percent of human-related nitrous oxide and 37 percent of all human-induced methane. Methane has about 21 times more Global Warming Potential (GWP) than carbon dioxide and nitrous oxide has 296 times the GWP of CO2.

Animals fed on grain, and those that rely on grazing, need far more water than grain crops. According to the USDA, growing the crops necessary to feed farmed animals requires nearly half of the United States' water supply and 80 percent of its agricultural land. Additionally, animals raised for food in the U.S. consume 90 percent of the soy crop, 80 percent of the corn crop, and a total of 70 percent of its grain.

When tracking food animal production from the feed trough to consumption, the inefficiencies of meat, milk and egg production range from 4:1 up to 54:1 energy input to protein output ratio. This firstly because the feed first needs to be grown before it is eaten by the cattle, and secondly because warm-blooded vertebrates need to use a lot of calories just to stay warm (unlike plants or insects). An index which can be used as a measure is the efficiency of conversion of ingested food to body substance, which indicates, for example, that only 10% is converted to body substance by beef cattle, versus 19–31% by silkworms and 44% by German cockroaches. Ecology professor David Pimentel has claimed, "If all the grain currently fed to livestock in the United States were consumed directly by people, the number of people who could be fed would be nearly 800 million." To produce animal based food seems to be, according to these studies, typically much less efficient than the harvesting of grains, vegetables, legumes, seeds and fruits. However, this would not apply to animals that are grazed rather than fed, especially those grazed on land that could not be used for other purposes. Nor would it apply to cultivation of insects for food, which may be more environmentally sustainable than eating food coming from cattle farming.[168] Meat produced in a laboratory (called in vitro meat) may be also more environmentally sustainable than regularly produced meat.

According to the theory of trophic dynamics, it requires 10 times as many crops to feed animals being bred for meat production as it would to feed the same number of people on a vegetarian diet. Currently, 70 percent of all the wheat, corn, and other grain produced is fed to farmed animals. This has led many proponents of vegetarianism to believe that it is ecologically irresponsible to consume meat. Rearing a relatively small number grazing animals is often beneficial, as observed by the Food Climate Research Network at Surrey University, which reports, "A little bit of livestock production is probably a good thing for the environment".

In May 2009, Ghent was reported to be "the first [city] in the world to go vegetarian at least once a week" for environmental reasons, when local authorities decided to implement a "weekly meatless day". Civil servants would eat vegetarian meals one day per week, in recognition of the United Nations' report. Posters were put up by local authorities to encourage the population to take part on vegetarian days, and "veggie street maps" were printed to highlight vegetarian restaurants. In September 2009, schools in Ghent are due to have a weekly veggiedag ("vegetarian day") too.

The "Appeal to nature" logical fallacy invites one to believe that something is good or right because it is natural.

A metaphor has been presented by Douglas Dunn: that if one gives a young child an apple and a live chicken, the child would instinctively play with the chicken and eat the apple, whereas if a cat were presented with the same choices, its natural impulse would be the opposite. Omnivorous and comparatively human-like species such as chimpanzees' offspring may not instinctively kill a prey animal, such as a Senegal Bushbaby, when presented with one and a piece of fruit either. In a similar assertion, vegetarian Scott Adams wrote humorously: "...a live cow makes a lion salivate, whereas a human just wants to say 'moo' and see if the cow responds."

This same non-predatory inter-species interaction can be seen in adult chimpanzees, which have been seen toying with other animals without regarding them as prey and even occasionally socialising with other species.

People may choose vegetarianism because they were raised in a vegetarian household or because of a vegetarian partner, family member, or friend.

Limited vegetarianism has appeal for some young people in Western societies. A 2007 University of Michigan Medical School experiment on the diffusion of memes included an attempt to encourage limited vegetarianism.

A 1992 market research study conducted by the Yankelovich research organisation claimed that "of the 12.4 million people [in the US] who call themselves vegetarian, 68 percent are female while only 32 percent are male."

At least one study indicates that vegetarian women are more likely to have female babies. A study of 6,000 pregnant women in 1998 "found that while the national average in Britain is 106 boys born to every 100 girls, for vegetarian mothers the ratio was just 85 boys to 100 girls." Catherine Collins of the British Dietetic Association has dismissed this as a "statistical fluke".

There is speculation that diets high in soy, due to high isoflavone content, can have a feminising effect on human infants due to their action as phytoestrogens. Proponents of this theory claim that diets high in isoflavones promote earlier onset of female puberty and delayed male puberty. However, a 2001 study conducted by the University of Pennsylvania found no significant differences in the later onset of puberty between infants raised on soy-based formula and cow milk formula.

Vegetarianism is viewed in different ways around the world. In some areas there is cultural and even legal support, but in others the diet is poorly understood or even frowned upon. In many countries food labelling is in place that makes it easier for vegetarians to identify foods compatible with their diets.

In India, which has more vegetarians than the rest of the world combined (399 million as of 2006), not only is there food labelling, but many restaurants are marketed and signed as being either "Vegetarian" or "Non-Vegetarian". People who are vegetarian in India are usually Lacto-vegetarians, and therefore, to cater for this market, the majority of vegetarian restaurants in India do serve dairy products while eschewing egg products. Most Western vegetarian restaurants, in comparison, do serve eggs and egg-based products.