The microbiota of a group of hunter-gatherers in Tanzania undergo changes in composition depending on seasonal changes in their diets, a new study reveals. Furthermore, the composition of their microbiomes varies greatly from that of people consuming a Western diet. The Hadza are among the last remaining populations in Africa that live a hunter-gatherer lifestyle, with fewer than 200 people adhering to this traditional way of life. Their diet depends on the season: berry-foraging and honey consumption are more frequent during the wet season and hunting is most successful during the dry season. To better understand patterns between diet and the microbiome, Samuel Smits and colleagues collected 350 fecal samples from 188 Hadza people across different seasons, and thus diets. The data reveal that 70% of Bacteroidetes disappeared between the end of the dry season and beginning of the wet season, yet the majority of these strains reappeared at later points in time. In total the authors identified four families of bacteria in Hadza people that were particularly variable across seasons. Next, the team compared the microbiomes of Hadza to the microbiomes of 18 populations across 16 countries. They found that the microbiomes of industrialized populations were dominated by Bacteroidaceae, averaging 21% of the microbiome, compared to 0.8% of traditional biomes analyzed. As well, two prevalent bacterial families within the Hadza and other traditional groups were rare or completely undetected in people following non-traditional diets. The Hadza also possessed more enzymes to process plant carbohydrates than people consuming Western diets. Lastly, the authors report that the microbiota of U.S. populations exhibited substantially more antibiotic-resistant genes than the microbiota of the Hadza. Shyamal Peddada discusses these findings in a related Perspective.