The term vegetarianism was coined by the British Vegetarian Society in the mid 1800s, but the idea of excluding meat from the diet started thousands of years earlier.
Many anthropologists believe most early humans who lived as hunter gatherers ate a plant based diet because of the structure of the human digestive system.
Yet vegetarianism was not very common in the US until around 1971, when Frances Moore Lappé's groundbreaking bestseller Diet for a Small Planet was published.
The book encouraged people to eat meals without meat to decrease the world's food waste, and thus the popularity of vegetarian diets started to grow among Americans.
In 2016, an Australian survey conducted by Roy Morgan Research discovered 11.2 percent of those questioned declared themselves to be vegetarian.
As of that year, the highest number of Australian's adopting a meat-free diet live in New South Wales.
In 2018, approximately 25 percent of the world's population was found to be following a vegetarian or vegan diet.
What are the benefits of not eating meat?
Harvard Health Review reports there are many reasons why people choose to follow a vegetarian or vegan lifestyle.
Factors include health, religious beliefs, concerns about animal welfare or the use of chemicals and antibiotics in animal products, as well as a desire to avoid excessive use of environmental resources.
Recent studies seem to confirm the health benefits of meat-free eating, particularly in relation to the reduction of chronic illnesses.
According to the American Dietetic Association, "appropriately planned vegetarian diets, including total vegetarian or vegan diets, are healthful, nutritionally adequate, and may provide health benefits in the prevention and treatment of certain diseases".
Vegetarian diets have been linked to the reduction and improvement of conditions including heart disease, cancer, type 2 diabetes and urinary diseases.
Possible downsides to following a vegetarian diet
When considering switching to a vegetarian or vegan lifestyle, many people voice concern about getting sufficient amounts of protein, iron, vitamin B and zinc.
However Harvard Health studies show that lacto-ovo vegetarians generally get the recommended daily amount of protein, which is easily obtained from eggs and dairy products.
Likewise, vitamin B - espeically B12 - is only found in animal products, but those include dairy foods and eggs so most vegetarians get the required amount with minimal effort.
Vegan dieters should supplement their intake with foods fortified with vitamin B12, including soy products, rice based drinks and some breakfast cereals.
In terms of iron, studies have shown that in Western countries vegetarians tend to get the same amount of iron as meat eaters.
What is the difference between a vegan and vegetarian diet?
In simple terms, vegetarians are people who don't eat meat, poultry or seafood.
But in recent decades, many many variations of the vegetarian diet have emerged including:
Vegans - total vegetarians who do not eat meat, poultry, fish or any animal products including eggs, dairy products and gelatin.
Lacto vegetarians - do not eat meat, poultry, fish or eggs, but do consume dairy products.
Ovo vegetarians - do not eat meat, poultry, fish or dairy, but do eat eggs.
Lacto-ovo vegetarians - do not eat meat, poultry or fish, but do eat eggs and dairy products.
Partial vegetarians are people who avoid meat but eat fish - known as pescatarians - or poultry - known as pollo-vegetarians.
Like vegetarians, vegans do not eat any animal flesh. But in addition to not consuming animal meat, a vegan does not eat eggs, dairy products or any other product derived - even in small part - from an animal.
So now you understand the terms and jargon, let's start looking at 11 of the world's most famous celebrity vegetarians.
Taking things one step on from vegetarian eating, Natalie Portman is one of the world's most famous vegans.
The Black Swan star produced a documentary called Eating Animals - based on the book by Jonathan Safran Foer - which questions the practice of raising animals to slaughter for food.
Portman is also passionate about the environmental damage cause by eating meat.
The Oscar winner switched to a vegetarian diet late into adulthood, but Kate has been an active advocate PETA for many years.
Winslet also narrated a series of videos about boycotting restaurants that serve foie gras, a product made from the liver of a duck, according to Harper's Bazaar.
The ex wife of Magic Mike star Channing Tatum has been a committed vegetarian from a young age, previously revealing she felt traumatised after watching a documentary about slaughterhouses age 10 or 11.
Jenna was later diagnosed as lactose intolerant which prompted her to change her diet to a vegan lifestyle.
She has credited veganism for clearing her skin, giving her "tonnes" more energy and improving her mental clarity.
Oscar winning actor Jared Leto is a longterm vegetarian and more recent vegan.
When he turned 41, Leto credited his plant-based diet (as well as lots of sleep) for his youthful appearance, telling GQ Magazine: “It’s probably just down to sleep and diet. If you travel long haul a lot or don’t sleep much, it’s not going to last very long, that’s for sure. I’m pretty healthy so I think that helps a lot. I’ve been that way for a long time – 20 solid years of eating vegetarian/vegan and taking care of myself. That probably helps the preservation process.”
Leto officially refers to himself as a 'cheagan', which he says is a cheating vegan.
"I don’t eat meat ever. But if someone’s mom made a cookie and handed it to me, I’d probably take a bite, or if I’m in Alaska and there’s wild salmon out of the river, I’d probably eat it," he once told Rolling Stone.
System.ArgumentNullException: Value cannot be null. Parameter name: input at System.Text.RegularExpressions.Regex.Match(String input) at System.Text.RegularExpressions.Regex.Match(String input, String pattern) at ASP._Page_app_plugins_pacembedly_pacembedly_cshtml.Execute() in c:\inetpub\wwwroot\site\App_plugins\PacEmbedly\PacEmbedly.cshtml:line 12 at System.Web.WebPages.WebPageBase.ExecutePageHierarchy() at System.Web.Mvc.WebViewPage.ExecutePageHierarchy() at System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) at Umbraco.Core.Profiling.ProfilingView.Render(ViewContext viewContext, TextWriter writer) at System.Web.Mvc.Html.PartialExtensions.Partial(HtmlHelper htmlHelper, String partialViewName, Object model, ViewDataDictionary viewData) at ASP._Page_Views_Partials_grid_editors_base_cshtml.Execute() in c:\inetpub\wwwroot\site\Views\Partials\Grid\Editors\Base.cshtml:line 20
Legendary singer-songwriter Paul McCartney is a long-time vegetarian and continued animal rights campaigner with PETA.
The former Beatle revealed he decided to change to a vegetarian diet during a fishing trip.
"Many years ago, I was fishing and as I was reeling in the poor fish, I realised - I am killing him - all for the passing pleasure it brings me. Something inside me clicked, and I realised as I watched him fight for breath that his life was as important to him as mine is to me."
American country superstar Shania Twain cites a vegetarian diet as the reason for her radiantly youthful appearance.
The singer follows a carb-free meal plan which includes a mixture of raw, whole-food products with an emphasis on dark green vegetables and nuts, according to Harper's Bazaar.
Australian actress Ruby Rose follows a vegetarian diet and tries to be vegan whenever she can.
The star previously urged her followers on Twitter to make a stand for the environment and for animal rights by giving up meat and following a whole-food, plant-based regime.
In March, Ariana Grande announced she was collaborating with Starbucks to create a new drink called the Cloud Macchiato, an espresso shot and milk with fluffy foam that comes in caramel or cinnamon flavour.
The ingredients of the Cloud Macchiato caused controversy because of the inclusion of butter, heavy cream and milk - meaning the beverage is not vegan.
This sparked a storm of criticism because Ariana herself has professed to follow a strictly vegan lifestyle since 2013, causing many to wonder if Grande is vegetarian rather than fully vegan.
In an interview with The Mirror in 2014, the Thank U Next hitmaker said she "loves animals more than people" and believes "eating a full plant-based, whole food diet...can expand your life length and make you an all-round happier person".
Irish-born Harry Potter star Evanna Lynch has been a committed vegetarian since childhood because, as she told Vegan Food and Living, she was "viscerally repelled by the idea of eating animal flesh and there was no way to avoid the fact that someone had been killed for that piece of meat."
Evanna transitioned to a fully vegan lifestyle in 2015 after reading Jonathan Safran Foer's Eating Animals, just like Natalie Portman.
She is now a vegan activist and regularly posts sweet images of her furry friends on Instagram.
Victoria's Secret model Lily Aldridge is just one of the VS catwalk queen's who swears by a vegetarian diet.
The Angel says she eats clean by using a vegetarian delivery service called Sakara, and previously told Peaceful Dumpling she feels healthier when following a plant-based diet.
Cowboys and Aliens star Olivia Wilde has been a vegetarian since the age of 12, according to Veganuary.
The actress has been following an almost vegan lifestyle for the past four years, except during her pregnancy when she returned to vegetarian eating.
Wilde caused controversy in the animal rights community by returning to vegetarianism after her divorce, leading many critics to say she was merely jumping on a fashionable bandwagon.
Wilde told Cosmopolitan at the time, "I actually really like healthy food. I was hardcore vegan for years. When everything in my life became a little hectic, going through the divorce and everything afterward, I was like 'I need some goddamn cheese'. And so I had some cheese."