Altered immunometabolic response to fasting in humans living with obesity

Abstract

Fasting and ketosis are gaining interest for treating obesity-related immunometabolic dysfunction. We aimed to (1) characterize systemic and T cell immunometabolic responses to a 48-h fast in humans and (2) determine if responses differed between individuals with (O-BMI) and without (L-BMI) obesity (n = 16 per group). Despite similar increases in systemic fat oxidation, increases in blood β-hydroxybutyrate (BHB), BHB-amino acid conjugates, and lysine β-hydroxybutyrylation were blunted in obesity. T cells from the L-BMI group upregulated their relative capacity for fat oxidation while the O-BMI group did not. The O-BMI group had a greater proportion of Th17 cells and secreted more interleukin-17 (IL-17), even after fasting. CD8 expression decreased in both groups and CD4 expression only decreased in the L-BMI group. The balance of anti-to pro-inflammatory cytokines increased less in the O-BMI group. Collectively, these findings show that humans living with obesity have a blunted systemic and T cell immunometabolic response to fasting. NCT05886738.

Keywords: human metabolism; immunology.

Graphical abstract

Figure 1

Summary of participant flow and study design (A) CONSORT diagram. ∗Participants were eligible but wait-listed once recruitment had closed but data collection was not yet completed. (B) Schematic depicting the study design across the 48-h fast. Participant baseline measurements were collected 2 h after a standardized breakfast. Participants returned to the lab after 24 and 48 h of fasting and repeated each measurement.

Figure 2

Systemic metabolism and hormones throughout a 48-h fast in individuals with L-BMI and individuals with O-BMI (A) Respiratory exchange ratio (RER) derived by indirect calorimetry. (B) Free fatty acids (FFA) from serum. (C) Capillary beta-hydroxybutyrate (BHB) from finger prick. (E–G) BHB-amino acid conjugates from serum. (H) Representative western blot of beta-hydroxybutyrylated lysine histone residues (Kbhb) from PBMCs and delta of Kbhb normalized to Ponceau stain from PBMCs. (I) Capillary glucose from finger prick. (J) Insulin concentration in serum. (K) Leptin concentration in serum. Large circles or triangles are estimated marginal means and black vertical bars are 95% confidence intervals derived from a linear mixed effects model. Orange circles represent the lean BMI (L-BMI) group and teal triangles represent the obese BMI (O-BMI) group. Small circles or triangles represent individual participant data. N = 32; 8 males/8 females per BMI group. ∗Group × time interaction, p < 0.05; ‡main effect of time, p < 0.05; †main effect of group, p < 0.05; ^abaseline vs. 48 h, p < 0.05; ^bbaseline vs. 24 h, p < 0.05; ^cL-BMI vs. O-BMI at baseline, p < 0.05.

Figure 3

Mitochondrial respiratory states measured in isolated human T cells at baseline and after a 48-h fast in individuals with L-BMI or O-BMI (A) Routine T cell respiration representing respiration in the basal state. (B) T cell respiration due to fat-supported respiration. (C) Maximum oxidative phosphorylation capacity. (D) Uncoupled respiration representing maximum OXPHOS capacity. (E) Proportion of respiration due to fat-supported respiration as a percentage of maximum OXPHOS capacity. Large circles or triangles are estimated marginal means and black vertical bars are 95% confidence intervals derived from a linear mixed effects model. Orange circles represent the lean BMI (L-BMI) group and teal triangles represent the obese BMI (O-BMI) group. Small circles or triangles represent individual participant data. N = 32; 8 males/8 females per BMI group. ∗Group × time interaction; ‡main effect of time, p < 0.05; †main effect of group, p < 0.05; ^abaseline vs. 48 h, p < 0.05; ^cL-BMI vs. O-BMI at baseline, p < 0.05.

Figure 4

Cell counts and T cell subsets at baseline and after a 48-h fast in individuals with L-BMI or O-BMI (A) Total white blood cell count. (B) Absolute lymphocyte counts in whole blood. (C) Proportion of white bloods cells that were lymphocytes in whole blood. (D) Proportion of isolated T cells derived from whole blood that were CD4⁺/CD8⁻, CD4⁻/CD8⁺, or double-negative (CD4⁻/CD8⁻). (E) Proportion of CD4⁺ T cells that were either Th1, Th2, Th17, Th22, or Treg cells. Large circles or triangles are estimated marginal means and black vertical bars are 95% confidence intervals derived from a linear mixed effects model. Orange circles represent the lean BMI (L-BMI) group and teal triangles represent the obese BMI (O-BMI) group. Small circles or triangles represent individual participant data. N = 32; 8 males/8 females per BMI group. ∗Group × time interaction, p < 0.05; ‡main effect of time, p < 0.05; †main effect of group, p < 0.05; ^cL-BMI vs. O-BMI at baseline, p < 0.05.

Figure 5

Markers of T cell function before and after a 48-h fast in individuals with L-BMI or O-BMI (A) Expression of CD4 on isolated human T cells. (B) Expression of CD8 on isolated human T cells. (C) Intracellular secretion of IFNγ in isolated human T cells following a 24-h activation culture. (D) Intracellular secretion of IL-17 in isolated human T cells following a 24-h activation culture. Large circles or triangles are estimated marginal means and black vertical bars are 95% confidence intervals derived from a linear mixed effects model. Orange circles represent the lean BMI (L-BMI) group and teal triangles represent the obese BMI (O-BMI) group. Small circles or triangles represent individual participant data. N = 32; 8 males/8 females per BMI group. ∗Group × time interaction, p < 0.05; ‡main effect of time, p < 0.05; †main effect of group, p < 0.05; ^cL-BMI vs. O-BMI at baseline, p < 0.05. MFI, median fluorescence intensity.

Figure 6

Plasma cytokines before and after a 48-h fast in individuals with L-BMI or O-BMI. Plasma cytokine responses (A) Monocyte chemoattractant protein (MCP)-1. (B) Growth/differentiation factor (GDF)-15. (C) Interleukin (IL)-8. (D) Fibroblast growth factor (FGF)-21. (E) Interleukin (IL)-1 receptor antagonist (RA). (F) Interleukin (IL)-6. (G) Interleukin (IL)-10. (H) Tumor necrosis factor (TNF)-alpha. Large circles or triangles are estimated marginal means and black vertical bars are 95% confidence intervals derived from a linear mixed effects model. Orange circles represent the lean BMI (L-BMI) group and teal triangles represent the obese BMI (O-BMI) group. Small circles or triangles represent individual participant data. N = 32; 8 males/8 females per BMI group. ∗Group × time interaction, p < 0.05; ‡main effect of time, p < 0.05; †main effect of group, p < 0.05; ^abaseline vs. 48 h, p < 0.05; ^cL-BMI vs. O-BMI at baseline, p < 0.05. MFI, median fluorescence intensity.