Figure 1. Circulating lactate and 3-hydroxybutyrate feed the gut microbiome. See also^{Figure S2}.

(A) Schematic of intravenous infusion of isotope-labeled nutrients to identify circulating metabolites that feed gut microbiome.

(B) Circulating lactate rapidly enters the feces. Mice were infused with ¹³C-lactate and serum and fresh feces enrichment were compared. Mean±s.e., N = 3.

(C) Circulating citrate does not enter the feces. As in (B), for ¹³C-citrate. Mean±s.e., N = 3.

(D) Passage of circulating ¹³C-labeled nutrients into the feces. Mice were infused with labeled nutrients for 2.5 h, and labeling fraction in feces was normalized to labeling fraction in serum. Mean±s.e., N = 3 except for lactate (N = 8) and 3-hydroxybutyrate (N = 7).

(E) Pharmacological inhibition of MCT1 transporter decreases the passage of circulating lactate to feces. Mice were injected i.p. with saline or 100 mg/kg AZD3965, and fresh feces lactate enrichment measured. Mean±s.e. N = 6 for saline and N = 5 for AZD3965. ***P<0.001 by two-sided Student’s t-test.

(F) Passage of circulating ¹⁵N-labeled nutrients into the feces. As in (D), for ¹⁵N-lableing. Mean±s.e. N = 3 except for urea (N = 4) and ammonia (N = 5).