3.1 Participant Characteristics and Psychosocial Measures
Psychosocial and behavioral characteristics of the 92 individuals who are overweight or obese (mean BMI=33.22kh/m2, mean age=32.84 years) are summarized in Table 1. Based on the IPAQ scoring guidelines for determining PA levels, the average total PA in the high (n=43), moderate (n=32), and low (n=17) groups were 13,432.84 METs, 1,822.953 METs, and 5,081.70 METs respectively (p<0.001).
The high PA group had greater average BRS resilience scores (p=0.04) and ability to cope through acceptance of reality (p=0.04), and a significant difference compared to the low PA group. A trend in the anxiety scores were also seen with the HAD measures, with highest anxiety scores seen in the low PA groups, even though these did not reach significance.
Based on PA, there were also significant differences in multiple food addiction measures, as assessed using the Yale Food Addiction Scale (YFAS), with food craving scores being lowest with high PA group. When comparing between high vs. low PA groups, significant differences were found with the following YFAS measures: continued use (p=0.025), giving up (p=0.005), time spent (p<0.001), loss of control (p=0.01), and symptom count (p<0.001). Significant differences were also seen between moderate vs. low PA for the following YFAS measures: tolerance (p=0.04), continued use (p=0.04), time spent (p=0.002), loss of control (p=0.02), and symptom count (p=0.003; Table 1).
3.2 PA Differentiates Brain Functional Connectivity
After adjusting for confounding variables such as age, sex, BMI, and diet, a sPLS-DA of brain functional connectivity displayed significant clustering based on PA level (Figure 2A). Connectivity between 73 pairs of brain regions were significantly associated with PA (p<0.05), and after correcting for multiple comparisons 67 pairs and 3 pairs of regions remained significant (q<0.05) for the high vs. moderate and moderate vs. low PA groups respectively. The brain networks involved included the salience (SAL), central autonomic (CAN), central executive 40, emotional regulation (ERN), sensorimotor (SMN), default mode (DMN), and occipital networks 41. The specific brain regions are summarized in Table 2.
Compared to moderate PA individuals, those with high PA have significantly increased functional connectivity in 52 pairs of brain connections, involving the default mode, central executive, sensorimotor, occipital, central autonomic, emotional regulation, and salience network (q<0.05). In contrast to high PA participants, those with moderate PA had significantly increased functional connectivity in 15 pairs of brain regions, and including brain regions involving the DMN, CEN, OCC, ERN, and CAN networks (q<0.05) (Figures 2B, 2D, Table 2).
When comparing moderate versus low PA, there were 3 pairs of connections that were significantly different (q<0.05) in functional connectivity involving the networks CEN, DMN, and OCC. Moderate PA individuals had increased connectivity between the left superior parietal lobule and left cuneus compared to low PA individuals. However, low PA individuals had increased functional connectivity between the right middle temporal gyrus and angular gyrus as well as left supramarginal gyrus and superior parietal lobule (Figures 2C, 2E, Table 2).
3.3 PA and Gut Microbiome Composition
When comparing the three PA groups after adjusting for covariates such as age, sex, BMI and diet, significant differences in beta diversity were seen. The low PA group had a significantly different beta diversity compared to the high and moderate group, which had similar beta diversity signatures (Figure 3A). Significant differences in relative abundance were also seen when comparing both the high versus low and moderate versus low PA groups with the MaAslin2 analysis, after adjusting for covariates. When comparing high and low PA participants as seen in Figure 3B, three genera (Fournierella, Acidaminococcus, and Prevotella) were positively associated and two genera (Lachnospira, Riminococcus gnavus) were negatively associated with high PA. Fournierella demonstrated the greatest positive fold change when comparing high versus low PA. In the moderate versus low comparison, one genus (Prevotella) showed a positive association and seven genera (Blautia, Faecalibacterium, Bacteroides, Fusicantenibacter, Lachnospiraceae, Lachnospira, and CAG-56) showed a negative association with moderate compared to low PA (Figure 3C). Prevotella showed the greatest positive fold change in the moderate versus low comparison and is increased in relative abundance in a dose-dependent fashion, as it also demonstrated a positive fold change in the high PA group compared to low (Figure 3B, 3C).
3.4 Fecal Metabolites Associated with PA
27 fecal metabolites were significantly correlated with PA level. Amongst the significant lipid metabolites, the high PA group displayed higher levels of myoinositol (high vs. low: q=0.03 ; high vs. mod: q=0.05) and 5alpha-androstan-3beta,17alpha-diol monosulfate (high vs. low: q=0.03; high vs. mod: q=0.02) when compared to both low and moderate PA (Table 3, Figure 4A, 4B). Taurochenodeoxycholate was another metabolite belonging to the lipid super-pathway that was elevated with more PA when comparing moderate versus low PA (q=0.03) (Table 3, Figure 4C). The other 7 lipid metabolites were seen to be increased with less PA when comparing either low versus moderate, moderate versus high, or low versus high (Table 3, Figure 4A-C).
Within the 7 significant metabolites belonging to the amino acid super-pathways, 4-hydroxyphenylpyruvate (q=0.03), 3-methyl-2-oxovalerate (q=0.03), and 4-methyl-2-oxopentanoate (q=0.04) were increased in high PA versus low PA participants (Figure 4A), while 2,3-dihydroxy-5-methylthio-4-pentenoate (DMTPA) (q=0.05), N-formylmethionine (q=0.05), and hydroxy-N6,N6,N6-trimethyllysine (q=0.03) were elevated with low PA versus either high or moderate PA participants (Figure 4A, 4C).
The metabolites belonging to the xenobiotics super-pathway were seen to be either significantly increased or decreased with PA. Digalacturonic acid (q=0.05), 7-methylurate (q=0.040), and 3,7-dimethylurate (q=0.05) were significantly increased with more PA, specifically when comparing high versus moderate PA (Figure 4B). 5-acetylamino-6-amino-3-methyluracil was seen to be highest in moderate PA participants when compared to both high (q=0.04) and low (q=0.01) PA individuals (Figure 4B, 4C). 3-(3-hydroxyphenyl) propionate was also significantly increased in the moderate PA when compared to the high PA group (1=0.05) (Figure 4B).
A summary of the significant associations identified between psychosocial variables, metabolites, and pairs of connected brain regions across all PA group comparisons can be found in Table 4.