Nearly half of Americans try to lose weight each year, and roughly 17% (about 43 million adults) follow a special diet like keto, vegan or Mediterranean, data shows.
With so many different diet plans and conflicting advice, it may be difficult to determine the right way to eat. Mark Hyman, M.D., says there isn’t any single plan that works for everyone.
“The truth is the best diet is the one that works for your biology,” he said on a recent episode of his podcast, “The Dr. Hyman Show.” “We’re all different. There isn’t a one-size-fits-all [diet].”
At the core of any healthy eating plan, according to Hyman, is the difference between real food and what he calls “food-like substances.”
“Food is something that helps support the health and development and growth of an organism,” he said in the episode. “Honestly, what most people are eating in America today is not definitionally food. It’s a food-like substance.”
Minimally processed foods — items that are recognizable and close to their original form — are fundamentally different from ultraprocessed products that are engineered for convenience and shelf life, Hyman emphasized.
He also offered his definition of food beyond energy, noting that “food is medicine.”
“It’s not like medicine. It is medicine,” he clarified, pointing to the thousands of bioactive compounds in plants that influence inflammation, detoxification and disease risk.
“Everything you put in your body is a drug that’s going to help you or harm you,” Hyman added, noting that every meal affects how the body functions.
One of the factors that determines how people respond to food is blood sugar regulation, the doctor said. Diets high in refined starch and sugar can disrupt metabolic health in ways that ripple throughout the body, he warned.
“If you don’t have balanced blood sugar, if you have high blood sugar or high insulin, this is going to screw up your blood sugar metabolism,” Hyman said, linking poor metabolic control not only to diabetes and heart disease, but also to mental health conditions.
Keto diets— which emphasize high-fat, moderate protein and low-carbohydrate intake, according to Mayo Clinic — are popular in part due to this connection.
By sharply reducing carbohydrates, keto shifts the body from burning sugar to burning fat. “When you switch into fat-burning [mode], that’s called ketosis,” Hyman said.
Hyman described ketones (small energy molecules the body makes when it doesn’t have enough available glucose) as a particularly efficient fuel for the brain, noting that the keto approach can stabilize blood sugar, reduce insulin levels and lower inflammation.
At the same time, he cautioned that keto is not inherently healthy if done poorly.
“People can make mistakes and it can be bad,” he said, emphasizing the difference between “crappy keto” and versions built around whole foods, vegetables and high-quality fats.
“For most people, it’s a tool, not a permanent lifestyle,” he added.
Other diets — like paleo, which consists of fruits, vegetables, lean meats, fish, eggs, nuts and seeds; and vegan, which contains no animal products — can be appropriate when done carefully and tailored to a person’s lifestyle.
“You can’t be a ‘chips and soda vegan,’” Hyman said, emphasizing the importance of whole foods.
The effectiveness of Mediterranean-style diets, often credited for longevity and heart health, also depend on how they are interpreted, the doctor noted.
Hyman distinguishes traditional versions rich in vegetables, olive oil, fish and legumes from modern imitations that are heavy on refined bread and pasta.
“It’s a good foundation, but it’s really about personalized diets,” he said.
Across all diet approaches, Hyman consistently returns to the same principle: paying attention to each individual’s response.
“How do you feel?” he asked. “Does your energy go up? Are your cravings down? Is your sleep better?”
Hyman referred to the body as “the smartest doctor in the room,” saying that it consistently signals whether a diet is helping or harming.
“Your biology always tells the truth,” he added.
Anyone looking to adopt a new dietary plan should first consult a healthcare professional to make sure it’s right for them.
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