Watch the full story tonight on "Nightline" at 11:35 p.m. ET
Click HERE for a slide show of how acai is produced, from harvest to market.
The scenes along the Amazon were unforgettable: grown men shimmying up huge palm trees in search of what has become the most-sought-after new food in the world.
"This is the skinny palms, you know; the black fruit there is the acai," said Monteiro.
The trees do not grow big and thick like the palm trees most people know.
Acai grows in the wild in clusters at the top of the skinny palm trees. It's bigger than a blueberry, smaller than a grape. People call it a berry, but it has just one seed ... so it's actually a fruit.
It's like a rock to bite.
"Actually, you need to take off the skin, and the skin makes the puree or the pulp we mix with water," Monteiro said. "It has kind of a coconut inside."
In the Amazon, a common site is a man scooping acai from a bucket and putting it into a juicing machine.
You don't eat acai, you drink it. The bland pulpy purple juice is not new to the people who live in the villages and cities of the Amazon. Almost everyone in this part of the Amazon seems to drink it. They say it's full of vitamins and gives them energy.
The signature red flag of an acai stand can be seen on almost every corner.
Brazilian athletes first helped turn acai into a sensation across the country a decade ago. ABC News stopped by a very humble jiu-jitsu gym in the Amazon city of Belem to see just how common acai is here.
Asked whether they drink acai, many of the athletes raised their hands.
Martial artist Rafael Andrade told "Nightline" he'd been drinking acai since he was a little boy. He said he drinks it before and after practice and that if he didn't drink it he would have less energy.
"I would fall asleep," Andrade said. "I would be much more tired."
But in the U.S., acai is being pitched by some as much than an energy drink. The Internet is filled with Web sites promoting acai pills for miracle weight loss. Others say it can offer added push to your sexual potency, or even a cure for cancer. It's hard to know what to believe.
To separate fact from fiction, ABC News spoke to some of the top food scientists in the U.S., at Texas A&M University.
Husband-and-wife team Steve Talcott, a biochemist, and Susanne Talcott, a food chemist, first began looking at acai in 2004. Although the scientific studies are not complete, what is clear is that acai does have extraordinarily high levels of antioxidants, which can help combat the effects of aging and heart disease.