If you want to boost immunity, look to the gut

70% of the immune system is located in the gut, where diverse bacteria is best.

You likely know that what you eat can affect your weight and energy level throughout the day. But you might not realize the extent to which diet affects the immune system.

“Seventy percent of the immune system is located in the gut,” says David Heber, MD, PhD, professor emeritus of medicine at UCLA Health. “Nutrition is a key modulator of immune function.”

Immune cells in the gut interact with the microbiome, the diverse array of bacteria and fungi that live in the gastrointestinal tract and are directly influenced by an individual’s diet and lifestyle.

The foods we eat affect the diversity and composition of bacteria in the gut, which in turn affect immune cells. Those gut bugs are healthiest and support strong immunity when their hosts (that’s us) consume plant foods that are high in fiber.

“The microbiome and the immune system are critically intertwined,” says Jonathan Jacobs, MD, PhD, a professor of digestive diseases at the David Geffen School of Medicine at UCLA. “What’s present in the gut determines what education immune cells get.”

Dietary diversity and microbial diversity go together, Dr. Jacobs says. The typical Western diet, which is high in animal proteins, sugar, processed foods and saturated fat, results in less-diverse gut bacteria and promotes inflammation and chronic disorders, he says.

A fiber-rich diet, on the other hand, supports the microbiome and reduces inflammatory response.

“Gut bacteria subsist on complex carbohydrates and fiber that our own cells are unable to digest,” Dr. Jacobs says. Those fibrous sources are plant foods, from apples and broccoli to yams and zucchini.

Carrying extra weight also affects immune function, says Dr. Heber, founding director of the UCLA Center for Human Nutrition. Fat stores, once thought to be inert tissue, actually secrete hormones and chemicals that stimulate inflammation. Medically known as adipose tissue, fat is now understood to be a “metabolically active endocrine organ,” says Vijaya Surampudi, MD.

“Obesity affects the immune system directly,” she says. The low-grade inflammation obesity stimulates is an immune-system response.

Maintaining a healthy weight through a plant-based diet boosts the microbiome and the immune system. Here are some strategies doctors recommend:


Eat plenty of plants. Dr. Heber recommends seven servings a day of colorful fruits and vegetables. “From a health standpoint, plant-based eating is what you need to do,” he says.

Eat good fats. “Healthy fats support immune function,” Dr. Heber says. He suggests cooking with olive oil, avocado oil or canola oil. He also adds avocado slices to salads in lieu of dressing and uses olive oil in a spray bottle when cooking. Good fats such as these should comprise 20% to 40% of daily caloric intake, he says.

Eat wild-caught fish. Dr. Heber says wild-caught fish are healthier than farmed varieties. He aims to eat fish three times a week and takes a daily, 1,200-milligram fish-oil supplement.

Eat protein at every meal. The typical American diet features a big serving of protein at dinner, in the form of a hearty steak, perhaps, but the immune system fares better on more regular protein servings. “We are doing our bodies a disservice when we do not have enough protein with each meal,” says Michael C. Garcia, MD. Like fat, muscle is an endocrine organ that directly affects the immune system, he says, and muscle is made from protein. Dietary protein can come from animal products, but plant sources are better for the microbiome.

Use natural spices and herbs in food preparation. Not only do herbs and spices add flavor to foods, they’re rich in phytochemicals that may support gut-bug diversity.

For more information on the importance of a healthy diet, visit the UCLA Center for Human Nutrition.