The study investigates the impact of a low-microbiota-accessible carbohydrate (MAC) diet on the gut microbiota over multiple generations. The researchers used humanized mice to model the effects of a Western diet, which is rich in MACs, on microbial diversity. They found that while changes in the microbiota due to a single generation of low-MAC diet consumption were reversible, over multiple generations, the microbiota showed a progressive loss of diversity that could not be fully recovered even after returning to a high-MAC diet. The loss of diversity was particularly pronounced in the Bacteroidales order, and the reintroduction of dietary MACs alone was insufficient to restore the lost taxa. The study suggests that the Western diet's low MAC content may contribute to the reduced microbial diversity observed in industrialized populations compared to traditional lifestyles. The findings highlight the need for strategies that incorporate both dietary MACs and the reintroduction of specific taxa to restore the gut microbiota to its original state.The study investigates the impact of a low-microbiota-accessible carbohydrate (MAC) diet on the gut microbiota over multiple generations. The researchers used humanized mice to model the effects of a Western diet, which is rich in MACs, on microbial diversity. They found that while changes in the microbiota due to a single generation of low-MAC diet consumption were reversible, over multiple generations, the microbiota showed a progressive loss of diversity that could not be fully recovered even after returning to a high-MAC diet. The loss of diversity was particularly pronounced in the Bacteroidales order, and the reintroduction of dietary MACs alone was insufficient to restore the lost taxa. The study suggests that the Western diet's low MAC content may contribute to the reduced microbial diversity observed in industrialized populations compared to traditional lifestyles. The findings highlight the need for strategies that incorporate both dietary MACs and the reintroduction of specific taxa to restore the gut microbiota to its original state.