Short-term animal product dietary restriction alters metabolic profiles and modulates immune function

Abstract

Background: Dietary interventions are powerful tools for disease prevention and health promotion, yet the molecular mechanisms by which diet influences health remain incompletely understood. Investigating the effects of diet in healthy individuals enables characterization of molecular and physiological responses in the absence of disease-related confounders and facilitates the identification of diet-responsive pathways underlying physiological regulation.

Methods: We investigated the metabolic and immune effects of short-term dietary restriction of animal products in a unique group of apparently healthy individuals (N = 200) who alternate between omnivory and animal product restriction for religious reasons. We profiled clinical biomarkers and immune parameters during both dietary states, alongside a control group of continuously omnivorous individuals (N = 211).

Results: Short-term restriction is associated with reductions in total and non-high-density lipoprotein cholesterol, urea, creatinine, alanine aminotransferase, and gamma-glutamyltransferase, and a concurrent 73% reduction of normal-range C-reactive protein levels. Immune profiling reveals reductions in frequencies of non-classical monocytes, CD56⁺ natural killer cells, and CD8⁺ memory T cells, accompanied by an increased response of cytokine IL-10, suggesting enhanced immune regulation against inflammation. Although most changes are in a direction suggesting beneficial health effects, levels of alkaline phosphatase increase upon restriction, implying possible negative effects on bone turnover or liver function.

Conclusions: Short-term animal product restriction mostly improves systemic metabolic and immune health markers and may lower chronic inflammatory disease risk. Our findings highlight the value of studying diet in the absence of disease to reveal adaptive molecular changes and emphasize the translational potential of short-term dietary interventions in altering health-related risks.

Fig. 1. Study design.

A Dietary restriction of animal products is practiced during four extended periods throughout the year, as well as on Wednesdays and Fridays of each week, for a total of 180–200 days annually. Participant profiling was carried out in autumn (T1: both dietary groups on an omnivorous diet) and in spring (T2: the PR group had abstained from meat, fish, dairy products, and eggs for 3–4 weeks). B Two hundred participants practicing periodic restriction of animal products (PR group, red) and 211 continuously omnivorous, nonrestricted participants (NR group, blue) were profiled for blood biomarkers and complete blood counts (CBC) at two time points. T1: both dietary groups were on an omnivorous diet. T2: the PR group had practiced animal product restriction for 3–4 weeks. C For a subset of participants at both time points, we isolated PBMCs and: i) performed ex vivo profiling of immune cells through flow cytometry (left panel), ii) quantified production of cytokines by PBMCs at 6 h following stimulation with LPS and R848 to capture effects on innate immunity (central panel), and iii) quantified production of cytokines by PBMCs at 48 h following stimulation with PHA to capture effects on adaptive immunity (right panel). Created in BioRender. Palaiokrassa, K. (2025) https://BioRender.com/i18jw70. LPS lipopolysaccharide; R848 resiquimod; PHA phytohemagglutinin.

Fig. 2. Effects of short-term dietary restriction of animal products.

Changes in measured traits associated with short-term animal product restriction (PR individuals, red) were mostly beneficial for health. Fewer changes, likely capturing seasonal effects, were found in the continuously omnivorous group (NR individuals, blue) from T1 to T2. The changes in measured traits between timepoints were estimated using linear mixed effects models with random effects, and Tukey’s correction was performed for all associations. Mean values of the measured traits for each time point are summarized in Supplementary Table 3. Created in BioRender. Palaiokrassa, K. (2025) https://BioRender.com/97ty2ig. ALT alanine aminotransferase; ALP alkaline phosphatase; BMI body mass index; CRP; C-reactive protein; DBP diastolic blood pressure; HDL-C high-density lipoprotein cholesterol; LDL-C low-density lipoprotein cholesterol; MCH mean corpuscular hemoglobin; MCHC mean corpuscular hemoglobin concentration; MCV mean corpuscular volume; NR nonrestricted; PR periodically restricted; RBC red blood cells; RDW SD red cell distribution width standard deviation; WBC white blood cells; γ-GT gamma-glutamyltransferase.

Fig. 3. Immune cell population fold changes across dietary patterns (T1 vs T2).

Each dot represents an immune cell type in PR (top) and NR (bottom) individuals. Blue dots indicate reduced cell frequency at T2, while red dots indicate increased cell frequency at T2. In the PR group, blue dots are shown first to highlight cell types whose frequency decreased following animal product restriction, with results from the NR group shown in the same order as the PR group. We tested for changes in frequencies using two-sided paired sample t-tests. Significant changes are indicated by P * < 0.05 and ** < 0.01. Dot sizes are scaled by −log10P. Exact P-values are mentioned in the text. NK natural killer; NR nonrestricted; PR periodically restricted.

Fig. 4. Magnitude of change in cytokine production between T1 and T2 following immune cell stimulation.

A Magnitude of change in cytokine production between T1 and T2 following 6-h stimulation with bacterial ligand LPS. B Magnitude of change in cytokine production between T1 and T2 following 6-h stimulation with viral ligand R848. C Magnitude of change in cytokine production between T1 and T2 following 48-h stimulation with PHA. Significant changes are indicated by P * < 0.05 and ** < 0.01. Significance was calculated by two-sided paired sample t-tests. Exact P-values are provided in Supplementary Table 13. Sample sizes ranged from 14 to 22 with the exception of MCP-1, for which N = 10 in PR individuals and N = 4 in NR individuals (Supplementary Table 8). LPS lipopolysaccharide; R848 resiquimod; PHA phytohemagglutinin.