Greger went to college at Cornell University School of Agriculture, where as a junior he wrote informally about the dangers of bovine spongiform encephalopathy, commonly known as mad cow disease, on a website he published in 1994. In the same year, he was hired to work on mad cow issues for Farm Sanctuary, near Cornell, and became a vegan after touring a stockyard as part of his work with Farm Sanctuary. In 1998, he appeared as an expert witness testifying about bovine spongiform encephalopathy when cattle producers unsuccessfully sued Oprah Winfrey for libel over statements she had made about the safety of meat in 1996.
In 2004, the American College Of Lifestyle Medicine was formed in Loma Linda, and Greger was a founding member as one of the first hundred people to join the organization.
In 2005, he joined the farm animal welfare division of the Humane Society as director of public health and animal agriculture. In 2008, he testified before Congress after the Humane Society released its undercover video of the Westland Meat Packing Company, which showed downer animals entering the meat supply, and which led to the USDA forcing the recall of 143 million pounds of beef, some of which had been routed into the nation's school lunch program.
In 2011, he founded the website NutritionFacts.org with funding from the Jesse & Julie Rasch Foundation.
In his lectures, videos, and writings about nutrition, he tries to persuade people to change their eating habits from a Western pattern diet to a whole-food, plant-based diet, which he says can prevent and reverse many chronic diseases.:10 He is critical of some other doctors for not encouraging their patients to adopt plant-based diets and to avoid animal-based products:1–12 and criticizes the US government for giving watered-down advice about healthy eating in its guidelines, in order to protect the economic interests of food producers—especially those who make junk food and animal-based food.
Bird Flu: A Virus of Our Own Hatching received a favorable review which said it was "interesting and informative to both scientists and lay persons", but public health expert David Sencer was critical of the book, writing that it "focuses heavily on doomsday scenarios and offers little in terms of practical advice to the public" and that "a professional audience would quickly put [the book] aside for more factually correct sources of information".
Retired physician Harriet A. Hall, who is known as a skeptic in the medical community, has written that, while it is well-accepted that it is more healthy to eat a plant-based diet than a typical Western diet, Greger often overstates the known benefits of such a diet as well as the harm caused by eating animal products (for example, in a talk, he claimed that a single meal rich in animal products can "cripple" one's arteries), and he sometimes does not discuss evidence that contradicts his strong claims.
Heart Failure: Diary of a Third-Year Medical Student (2000)
Carbophobia: The Scary Truth Behind America's Low Carb Craze (2005).
Bird Flu: A Virus of Our Own Hatching (2007)
How Not To Die: Discover the Foods Scientifically Proven to Prevent and Reverse Disease (Hardcover) (2015) (with Gene Stone) ISBN1250066115
^"Mad cow disease; USDA misleads public on beef safety." Washington Times [Washington, DC] 2 Jan. 2004: A17. Infotrac Newsstand. Web. 1 Sept. 2016.
^Davidson, S. (2004, Jan 29). MIT to hold forum on mad cow disease; local physician to give keynote address. Jewish Advocate. Retrieved from Proquest. Quote: "Consumers concerned about mad cow disease and other issues about safeguarding the food supply may want to attend the Jan. 29 lecture at MIT by Michael Greger, M.D., entitled "Mad Cow Disease: Plague of the 21st Century?" ... Greger was raised in a small Arizona town, "the only Jewish family within 30 miles." His parents were New York natives; his mother taught Biblical Hebrew at the community college. Following his parents' divorce, he moved with his mother and brother to Binghamton, N.Y., where she taught Hebrew school at the orthodox Beth Israel synagogue."
^"Confused About Mad Cow? New Ad Exposes Scaremongers and Dispels Myths." PR Newswire 5 Jan. 2004. Academic OneFile. Web. 1 Sept. 2016.