Impact of Sodium Bicarbonate Prior to Exercise in the Heat on Gastrointestinal Injury and Endotoxemia

Sodium bicarbonate (NaHCO 3 ) is used by athletes to improve performance during high-intensity exercise as it enhances blood buffering capacity. Given that the dose required to increase buffering capacity is relatively high (i.e., ~ 25 g for an 80 kg individual), a common side effect of NaHCO 3 is GI distress, with symptoms such as bloating, diarrhea, and belching. Physical work in the heat and associated hyperthermia is also known to increase gastrointestinal (GI) distress and induce GI injury, which can result in increased intestinal permeability. As a result, endotoxemia may occur, where lipopolysaccharides from the intestinal lumen translocate into circulation, and can contribute to exertional heat stroke. However, it is unknown if NaHCO 3 exacerbates GI distress, GI injury, or endotoxemia during exertional heat stress. OBJECTIVE & HYPOTHESIS: We tested the hypothesis that NaHCO 3 would exacerbate GI symptoms and increase markers of GI injury and endotoxemia. METHODOLOGY: In a randomized double-blind, crossover design, eight participants (three females) completed two experimental trials consisting of walking two hours on a treadmill at 65% of their maximum heart rate in a heat chamber (40 °C, 20% relative humidity). One hour prior to exercise, participants ingested identical number of capsules containing either NaHCO 3 (0.2 g/kg of body weight) or a corn starch placebo (PLA) after a high carbohydrate meal (1.5 g/kg of body weight). Serum samples from pre-ingestion and post-exercise were analyzed using ELISA kits for markers of GI injury (intestinal fatty acid binding protein, I-FABP) and endotoxemia (lipopolysaccharide binding protein, LBP; and soluble cluster of differentiation 14, sCD14). GI symptoms via a validated questionnaire were assessed pre-, one hour-, and post-exercise. Mixed effects models were conducted to assess the effects of time (pre, post), condition (NaHCO 3 , PLA), or time x condition interaction on serum markers. A Wilcoxon signed-ranked test was used to compare the incidence of GI symptoms between NaHCO 3 and PLA groups. A significance level was set at p ≤ 0.05. RESULTS: There were no significant differences in GI symptoms between conditions (p=0.13). There was a significant decrease in I-FABP (p=0.03) from pre- to post-exercise, but no effect of condition (p=0.58) or interaction (p=0.76), as the change (Δ) for PLA (Δ - 412 ± 327 pg/mL) and NaHCO 3 trials (Δ -382 ± 416 pg/mL) were similar. There was no effect of time (p=0.37), condition (p=0.68), or interaction (p=0.32) for LBP (PLA Δ: 1.73 ± 4.53 μg/mL, NaHCO 3 Δ: 0.92 ± 2.65 μg/mL). For sCD14, there was no significant main effect of condition (p= 0.84), time (p=0.11), or interaction (p=0.12) (PLA Δ: 19.7 ± 174.1 ng/mL, NaHCO 3 Δ: 198.9 ± 209.6 ng/mL). CONCLUSION: Our findings indicate that acute NaHCO 3 supplementation (0.2 g/kg) taken with a high carbohydrate meal does not increase GI distress, markers of GI injury, or endotoxemia during two hours of treadmill walking in the heat. These results suggest that this dose of NaHCO 3 may be safely used during physical activity in the heat without exacerbating endotoxemia. University of New Mexico’s Graduate and Professional Student Association’s New Mexico Research Grant This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.