What Juicing Does to Your Brain

Is it time to retire your juicer?

“A human being has a natural desire to have more of a good thing than he needs.” –Mark Twain

Ever since Norman Walker invented the modern juicer in the 1930s, people have been feeling like they stumbled upon the fountain of youth. But is juicing too much of a good thing?

Walker’s machine was big. It used a grinder to pulp the fruits and veggies and then a large hydraulic press to extract the juice. It was not a home appliance. So, he set up a juice bar in San Francisco. Yes, amazingly, the precursor to Jamba Juice started some 90 years ago.

Walker was a big proponent of the health advantages of juicing, but he was also a bit of a grifter, awarding himself multiple degrees and doctorates to help sell his brand.

A lot of people who hate raw foods were introduced to fruits and veggies this way, so there were some benefits. People got vitamins, minerals, a little protein, and a lot of sugar. Plus, it was occasionally tasty.

Although Walker may have been less than honest in his juicy promotions, he was at least encouraging Americans to eat more fruit and veggies in a convenient quaff. So, big win, right?

Indeed, juicing has picked up considerable steam in the last 90 years. Today’s juicers fit nicely on the kitchen counter. But when you clean out the juicer, you see something remarkable: The best part of the fruit or veg is left behind. It gets scraped out and thrown away.

That’s the fiber and the polyphenols that cling to them. For your gut microbes, that’s the best part of the fruits and veggies. From their point of view, juicing is a starvation diet.

Walker would endorse that, feeling that fermentation in the colon caused toxemia. But fermentation is exactly what the colon is meant to do. The microbes we starve are the healthy ones.

The juice goes on

In the 1990s, Jay Kordich introduced a new generation to the wonders of juicing. Like Walker, Kordich was not above a little elaboration on the truth. He claimed that juicing could cure cancer. The American Cancer Society demurs, saying, "there is no convincing scientific evidence that extracted juices are healthier than whole foods."

Kordich promoted the concept that juicing could detoxify your body. But detoxing isn’t really a thing that diets can do. That’s up to your liver, which does a terrific job of it.

A recent study from Northwestern University brings some sobering news about juicing. The researchers found that oral and gut microbes were significantly perturbed by the practice. One of their first observations was that sugar-loving microbes bloomed. After all, juicing frees up and concentrates the natural sugars in fruit and veggies.

These sugar-loving bacteria may increase gut permeability, potentially creating a “leaky gut” and allowing toxins or bacteria to pass through the gut lining. Ironically, rather than “detoxing,” juicing might actually increase bodily toxins.

The researchers found that pro-inflammatory microbes also increased on a juice diet, setting the immune system on edge.

Perhaps most importantly, they found that microbes associated with cognitive decline seemed to thrive on a juice diet. This is the gut-brain axis in action. Thus, a drink that is supposed to be uber-healthy may actually lead to inflammation and cognitive impairment.

Furthermore, the researchers warn that “many of the microbes that increased in relative abundance in response to the juice diets have been identified as potential critical risk factors for their involvement in increasing inflammatory markers, colorectal cancer, cardiovascular disease, gingivitis, and periodontal disease.”

None of this is great.

Missing the good stuff

This subpar situation is due to the missing polyphenols and fiber in juice. Polyphenols in whole fruits and veggies are metabolized by microbes in the colon to produce antioxidants and molecules that tell the immune system to chill out. When microbes consume fiber, they produce butyrate, a molecule that is both food and medicine for the cells lining the gut, preventing leaky gut syndrome. In addition, butyrate makes it all the way to the brain, where it supports both the health and the growth of nerve cells, improving cognition.

The study was fairly small and only involved three days of juicing. They noted that two weeks after resuming a normal diet, the microbiome largely recovered from the juice diet. But an extended period of juicing was not explored in this study, so we don’t know if that might lead to more lasting damage.

To be on the safe side, rather than juicing, make smoothies instead. That way you get the fiber and polyphenols that are like ambrosia to the microbes living in your gut. The fiber prevents the sugar spikes that pure juice induces. It’s still a convenient way to consume your veggies and fruit, but without eliminating the fiber.

It was fun while it lasted, but in an era when people are starting to wake up to the manifold health benefits of fiber, it may be time to retire the juicer.

References

Sardaro, Maria Luisa Savo, Veronika Grote, Jennifer Baik, Marco Atallah, Katherine Ryan Amato, and Melinda Ring. “Effects of Vegetable and Fruit Juicing on Gut and Oral Microbiome Composition.” Nutrients 17, no. 3 (January 27, 2025): 458.