He is the author of several books on nutrition and longevity, of which 15 have become New York Times bestsellers, including Food Fix, Eat Fat, Get Thin, and Young Forever.

[24][25] In 2009, Hyman testified before the United States Senate Committee on Health, Education, Labor, and Pensions about integrative medical care.

[39][40] In 2016, Hyman joined environmentalists and civil rights leaders in calling for federal investigations into U.S. fluoridation policy, writing that communities of color are at particular risk of adverse health impacts.

[41] In an episode of The Diary of a CEO podcast, Hyman claimed that autism could be caused by eating gluten or by childhood vaccines, contrary to widely accepted scientific evidence.

[44][45] Hyman was director of the Center for Functional Medicine at the Cleveland Clinic until some point in 2023, when cardiologist Dr. James E. Carter stepped into the position.

[49][48] The company partnered with health club Equinox Group to offer a personalized nutrition, sleep, and fitness coaching program.

[14][56] The pegan diet is gluten-free and encourages consumption of nonstarchy vegetables with grass-fed organic meats and low-mercury fish.

Hyman allows the occasional organic goat or sheep milk, yogurt, kefir, grass-fed butter, ghee or cheese.

[14][15] The diet's emphasis on vegetables and omega-3 fats is in accord to mainstream nutrition advice but has been criticized for limiting the consumption of beans and whole grains, which are associated with multiple health benefits such as reducing cardiovascular disease and cancer risk and supporting weight management.

[60] A review in Publishers Weekly commented that "Pegan is a silly, paradoxical misnomer: no diet can be simultaneously paleo (meat, fats, and few vegetables/fruit) and vegan (with no animal products whatsoever).

However, the diet’s recommendations are basically sound: fresh, locally sourced, preferably organic food; nothing refined or processed; and a focus on not raising blood sugar.

"[61] Dietitian Carrie Dennett has written that "while the pegan diet is more moderate - and potentially easier to follow - than either of its dietary parents, it does restrict many nutritious foods for reasons that aren't quite supported by science.

"[14] A downside to the diet is that it can be costly for those with low incomes who cannot afford the expensive "grass-fed" and "pasture-raised" animal source foods that Hyman recommends.

[14] Aisling Pigott, a dietitian and spokesperson for the British Dietetic Association, has suggested that the pegan diet is too restrictive to maintain and although some of its principles such as eating more plant-based foods and fewer processed foods are recommended for good health, "labeling this as a 'diet' is unethical and potentially dangerous and difficult to follow.