Introduction: Body weight influences the GI response to meals. Studies have demonstrated post-prandial GI symptoms and dysfunction at the extremes of the BMI scale. More specifically, underweight individuals (BMI < 18.5) often report post-prandial bloating, nausea, and fullness as a result of delayed gastric emptying, as well as prolonged oro-cecal transit time (OCTT). Conversely, individuals with obesity (BMI > 30) may experience impaired satiety and fullness cues. Previous studies had linked higher BMI with elevated methane (CH₄) on conventional fasting breath tests. In this real-world study, post-prandial breath hydrogen (H₂) and CH₄ were measured to investigate the influence of body weight on GI motility and activity of the gut microbiome.

Methods: We studied 3,809 individuals with varying BMI (< 18.5, 18.5-25, 25-30, and 30+) and self-reported GI and non-GI symptoms (bloating, flatulence, abdominal pain, and fatigue). Post-prandial breath H₂ and CH₄ levels and symptoms were measured from an app-connected, personalized H₂and CH₄device (FoodMarble, Ireland) daily for 1 week while consuming their habitual diet. To assess the association between the diurnal pattern of post-prandial breath gases (H₂ and CH₄)_, and BMI, linear regression was applied.

Results: Average age was 44.2 ± 13 years, average BMI was 24.1 ± 5.6, with 35% male and 65% female. By BMI category, 255 (7%) had BMI < 18.5, 2101 (55%) had BMI of 18.5-25, 977 (26%) had BMI of 25-30, and 476 (12%) had BMI of 30+. The top 4 GI and non-GI symptoms at baseline (median, IQR) measured on a scale of 0-10 were bloating (4.4, 3.5-5.6), flatulence (2.9, 0.7-4.5), abdominal pain (1.97, 0.5-3.7) and fatigue (2.44, 0.7-4.5). Those with a higher BMI (25-30 and 30+) on average produced more breath H₂ in comparison to those with a normal (18.5-25) or low BMI (< 18.5) (Figure 1). However, the opposite relationship was observed for average CH₄ levels over the day, whereby those with a lower BMI (< 18.5) had elevated levels of CH₄ and those with the highest BMI produced lower average CH₄. More specifically, there was a negative association between BMI and CH₄, averaged by the individual (r = -0.99, p-value = 0.01), and a positive association between BMI and H₂, averaged by the individual (r = 0.98, p-value = 0.02) in symptomatic individuals.

Conclusions: Recent studies have shown that post-prandial breath H₂ is influenced by short-term dietary changes. Here we show that BMI is positively correlated with post-prandial H₂ production (r = 0.98, p-value = 0.02), perhaps driven by substrate availability for bacterial fermentation, and post-prandial CH₄ production was negatively associated with BMI (r = -0.99, p-value = 0.01). Measuring these gases in real time after meal consumption—as opposed to the fasting state—may offer clinical benefits in monitoring interventions relating to BMI-associated dysmotility.

<i>Average Hourly Breath Hydrogen (H<sub>2</sub>) and Breath Methane (CH<sub>4</sub>) in symptomatic individuals (n=3,809) with varying BMI: (< 18.5) n=255, (18.5-25) n=2101, (25-30) n=977 and (> 30) n=476.</i>

Average Hourly Breath Hydrogen (H₂) and Breath Methane (CH₄) in symptomatic individuals (n=3,809) with varying BMI: (< 18.5) n=255, (18.5-25) n=2101, (25-30) n=977 and (> 30) n=476.

FoodMarble Breath Test Device and Associated Smartphone App

Aonghus Shortt

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