This randomized, double-blind, placebo-controlled trial will assess the clinical effects of Akk09 in adults with functional constipation. Participants will receive Akk09 or placebo for 4 weeks. The study will evaluate changes in bowel habits and symptom burden, as well as alterations in host inflammatory status, immune modulation, microbial ecosystem dynamics, neuroendocrine signaling related to the gut-brain axis, and systemic metabolic responses, to characterize the overall physiological impact of BC09 supplementation.

Inclusion Criteria:

1. Men and women aged between 18 and 65 years;
2. Participants presenting with constipation, characterized by <3 spontaneous bowel movements per week or BSFS stool types 1-2;
3. Capable of following the study protocol and completing all required assessments; Individuals who have voluntarily signed the informed consent form;
4. No plans for pregnancy from at least 14 days prior to screening through 6 months after the study, with agreement to use reliable contraception methods.

Exclusion Criteria:

1. Intake of similar functional products within a short period prior to enrollment that could influence study results;
2. Participants who significantly alter their habitual diet during the trial;
3. Individuals with severe allergic conditions or impaired immune function;
4. Women who are pregnant, lactating, or intending to conceive;
5. Patients with serious underlying diseases affecting major organs or metabolic systems;
6. Antibiotic treatment within 2 weeks before enrollment;
7. Individuals with severe mental or psychological disorders;
8. Non-compliance with study requirements, including improper intake or missed follow-ups;
9. Other subjects considered inappropriate for participation by the investigator.