Kefir

Kefir is a fermented dairy product with higher microbial density than yogurt. Kefir microbes survive stomach acid more effectively than yogurt cultures and reach the intestinal microbiome intact. Unflavored, whole-milk kefir is recommended because flavored varieties contain added sugar that undermines the sleep benefit. Goat milk and sheep milk kefir are valid alternatives to cow's milk kefir. Combining kefir with polyphenol-rich berries enhances sleep quality because polyphenols feed gut bacteria that produce sleep-supporting compounds.