National Geographic Explorer and author Sarah Marquis has evaded harassing horsemen in Mongolia’s steppes. She spent three days in the Laos jungle with one leg tied to a tree to keep her from falling into water while suffering a fever. But perhaps her biggest challenge on her journeys is finding enough food every day.

That’s because Marquis is an extreme global trekker. For more than 20 years, the Swiss woman has dedicated her life to walking alone for months at a time and lives almost exclusively off the land while she’s doing it. Plus, she’s a vegetarian, which makes places like meat-centric Mongolia particularly difficult to navigate. (Finding buckwheat in the desert there made her day, she says.)

We caught up with her shortly after she completed a three-month walk through the wilds of Australia, surviving on crickets (an exception to her vegetarian rule), lily bulbs, and wild passionfruit. She gave us her tips for surviving in the wilderness.

View Images Sarah Marquis walks in Kimberly, Australia. Photograph by Krystle Wright, NG Creative.

Before she even leaves on an expedition, Marquis is focused on food. She packs on about 40 pounds—40 healthy pounds, that is. To Marquis, that means “quinoa, buckwheat, pasta, a lot of grain and vegetables,” plus fresh dates between meals. She doesn’t drink or smoke.

“My body is my salary. It’s like a sports car… You need to put the best fuel in it,” Marquis says.

“Every time I go to a country, I research the plants,” she says. She needs to know which plants are edible, which plants are medicinal, and which plants are deadly. Even if she can’t identify an exact plant, if she knows the family, she can usually tell if it’s safe to eat.

First, “if you see the animals around don’t eat it, it’s not a good sign.”

If the plant seems OK, she mashes a little of it on her wrist. “If it’s getting a little red or itchy, don’t eat it.”

View Images Sarah Marquis checks out a tree. Photograph by Krystle Wright, NG Creative.

Her second test is to touch the plant with her tongue. If there’s no reaction, then she starts chewing a small piece.

She avoids things that are red because they tend to be poisonous, and always has a little back up food in her bag, just in case. In drought-stricken Northern Australia, she brought along 3 oz. of flour a day to supplement her foraging—enough to make a little hand-sized flatbread, she says.

Another key tip is to listen to you body: “Fear is a good thing.” That electricity that runs up your spine to the top of your head? You need to pay attention to that, Marquis says.

While all of this experimentation may seem scary to those of us used to buying food from a store, Marquis says she has honed these skills over years of research and observation. “When you spend so much time in nature, you become nature. My instincts are really sharp.”

In fact, she says, that connection with nature is why she will never stop walking. “You lose your sense of identity. It’s amazing. It’s like a little ice cube melting in the desert —suddenly you’re part of everything. You are the wind, the sun, the elements.”