This is literally just the plot to Cannibal Holocaust, don't bother reading.
4 brave Americans went on a mission to go to the Amazon Jungle, where the majority of the population was Native American Cannibals. Their mission was observe and analyze the cannibals, by blending in with their tribes. But sadly, these 4 young American RESEARCHERS never came back.
Prior to this, a rescue team is sent to there to hopefully find the missing researchers and bring them back home with all the needed footage of this important mission.
But, what the rescuers found were quite disturbing.
After several days of trekking through the jungle, the group encounters the Yacumo tribe. They arrange release of their hostage in exchange for being taken to the Yacumo village. Once there, the group initially meets hostility, and learns that the film had caused great unrest among the people. The next day, Monroe and his rescue team head deeper into the rain-forest to locate two warring cannibal tribes, the YanoMamo and the Shamatari. They encounter a group of Shamatari warriors and follow them to a riverbank where they save a smaller group of Yanomamo from certain death. Grateful, the Yanomamo invite Monroe and his team back to their village, yet they treat the outsiders with suspicion. To gain their trust, Monroe bathes naked in a river. A group of Yanomamo women emerge to take him to a shrine where he discovers the remains of the missing American Filmmakers. Angry, Monroe confronts the Yanomamo, during which time he plays a tape recorder for them. The intrigued Natives agree to trade it for the first team's surviving reels of film during a cannibalistic ceremony, in which Monroe has to take part it. He bites into a Human heart to please the natives.
Back in New York, executives of the Pan American Broadcast Company invite Monroe to host a broadcast of the documentary to be made from the recovered film. Monroe insists on seeing the raw footage first. They would proceed to do so.