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After assessing the evidence, he stopped taking vitamin C, vitamin D, and omega-3 supplements.

"The science doesn't back up any of these as definitely working, so people are just wasting their money," he told Business Insider.

The jury is still out on supplements -- some studies suggest supplements could be beneficial for healthy aging, among other things. However, some experts, such as supplement researcher Dr. Andrea Myer and writer Michael Pollan, have previously told BI that they get their nutrients from food and don't bother with supplements.

Spector thinks that 99.9% of all supplements are "completely worthless."

"Unless you have a medical condition, you really don't need these supplements," he said. "Evidence shows that we only need tiny amounts of these substances, and getting extra doesn't help."

That being said, Spector has continued to take two supplements (on top of eating a gut-healthy diet) that he said research supports.

Spector eats a mostly plant-based diet, so he takes a B12 supplement most days. He skips it on the one or two days a month he eats meat and fish.

People who don't eat meat can struggle to get enough B12 in their diets because it's mostly found in meat, eggs, and dairy, but we need it to make DNA and to keep blood and nerve cells healthy.

BI previously reported that vegans and vegetarians can also increase the amount of B12 in their diets by eating algae.

Spector also uses a scoop of ZOE's new "Daily 30" mix to supplement his healthy diet.

Daily 30 is a minimally processed mixture of whole foods, including eight types of mushrooms, seven fruits and vegetables, six types of seeds, five herbs, three types of nuts, and two legumes and whole grains. It's meant to be added to meals to increase the diversity of plants people eat each day.

Spector previously told BI that eating 30 plants a week is key for a healthy gut, because the more diverse a person's diet, the better their gut health. The number 30 comes from a 2018 study called The American Gut Project by researchers at the University of California, San Diego. Samples from over 11,000 participants showed that those who ate more than 30 plants a week had much more diverse gut microbiomes than those who ate fewer than 10.

You can also make your own version of the Daily 30. BI previously reported on Spector's "diversity jar," which is a similar mix of nuts, seeds, and other plants that can be added to meals.