Gut microbiome changes and cancer immunotherapy outcomes associated with dietary interventions: a systematic review of preclinical and clinical evidence Original paper

What was reviewed?

This paper is a systematic review that examined how dietary interventions shape the gut microbiome and, in turn, influence responses to cancer immunotherapy. The authors reviewed both preclinical and clinical evidence to clarify whether diet-driven microbiome changes alter the efficacy, durability, and toxicity of immune checkpoint inhibitors, particularly therapies targeting PD-1, PD-L1, and CTLA-4. Rather than testing a single dietary strategy, the review synthesized findings across fiber-rich diets, probiotic and prebiotic supplementation, caloric modulation, and Western-style dietary patterns to understand how nutrition modifies host–microbiome–immune interactions relevant to cancer treatment.

Who was reviewed?

The review encompassed animal models of cancer immunotherapy alongside human cancer patients receiving immune checkpoint inhibitors across multiple tumor types, including melanoma, lung cancer, and gastrointestinal malignancies. The human studies included patients exposed to defined dietary patterns or interventions before and during immunotherapy, as well as observational cohorts linking habitual diet to treatment outcomes. By integrating preclinical and clinical populations, the review aimed to bridge mechanistic insight with translational relevance for oncology practice.

What were the most important findings?

The review demonstrated that diet-induced alterations in gut microbiota composition strongly associate with immunotherapy responsiveness. High-fiber diets consistently promoted microbial diversity and enrichment of taxa such as Bifidobacterium, Akkermansia muciniphila, Faecalibacterium prausnitzii, and other short-chain fatty acid–producing bacteria, which correlated with improved tumor control, enhanced CD8⁺ T-cell infiltration, and stronger interferon-γ signaling. In contrast, Western-style diets high in saturated fat and low in fermentable fiber reduced microbial diversity and favored inflammatory or immunosuppressive profiles that impaired checkpoint inhibitor efficacy.

Preclinical models showed that fiber-driven increases in butyrate and propionate enhanced antigen presentation and T-cell memory, while antibiotic-like disruptions of the microbiome blunted treatment response. Clinical studies mirrored these findings, reporting higher response rates and longer progression-free survival in patients with fiber-rich diets, whereas probiotic use without dietary context sometimes reduced microbial diversity and was associated with poorer outcomes. Across studies, the microbiome emerged as a modifiable mediator linking diet to systemic antitumor immunity rather than a passive biomarker.

What are the greatest implications of this review?

For clinicians, this review underscores diet as a clinically relevant, low-risk lever that may optimize immunotherapy outcomes by shaping the gut microbiome. It suggests that dietary counseling, particularly promoting diverse, fiber-rich foods, could complement immunotherapy regimens and potentially improve response durability. The findings also caution against indiscriminate probiotic use during immunotherapy. Overall, the review positions nutritional modulation of the microbiome as a promising adjunct strategy in precision oncology.