Abstract
Background Carbonated water has been reported to induce satiety, gastric motility and lower serum glucose concentrations, but the mechanisms remain unclear.
Methods This report explores the physiological effects of carbonated water, referencing a study published in 2004 on the mechanisms of hypoglycaemia induced by haemodialysis.
Results Upon consumption of carbonated water, carbon dioxide (CO2) is absorbed into the bloodstream, and converted into bicarbonate by the enzyme carbonic anhydrase in erythrocytes. This process increases intracellular pH, stimulating anaerobic glycolysis in erythrocytes and leading to higher glucose utilisation. A comparison is drawn with haemodialysis, where CO2 absorption by the blood similarly enhances glucose metabolism. During haemodialysis, blood glucose levels decrease from an average of 118.3 mg/dL before entering the dialyser to 98.6 mg/dL after passing through, despite the glucose concentration in the dialysate being approximately 105.0 mg/dL.
Conclusion CO2 in carbonated water may promote weight loss by enhancing glucose uptake and metabolism in red blood cells. However, the amount is so small that it is difficult to expect weight loss effects solely from the CO2 in carbonated water. Drinking carbonated water may also affect blood glucose measurements. Further studies are needed to explore its long-term effects and potential side effects.
The consumption of carbonated water has become popular among health conscious individuals, leading to discussions about its potential effects on weight loss. While many advocate for its benefits, it is important to explore the underlying mechanisms more closely. It has been reported that distension of the gastric antrum due to the release of dissolved gas from carbonated water induces satiety,1 which may cause further satiety and gastric motility,2 thereby reducing hunger.3 Additionally, carbonated water that is high in sodium has been shown to lower blood glucose levels.4 However, the specific mechanism behind the reduction in blood glucose levels is not yet fully understood. This short report explores the physiological effects of carbonated water, particularly its impact on glucose metabolism, discussed in a study published in 2004,5 and how these effects might contribute to weight management.
When carbonated water is consumed, carbon dioxide (CO2) is absorbed through the stomach lining. This process can be compared with the dynamics seen in haemodialysis, where blood passes through a dialyser. The dynamics of CO2 and glucose in the haemodialysis dialyser are shown in figure 1. In haemodialysis, blood shifts from acidosis to alkalosis, but the key substance delivered to the blood from the dialysate is primarily CO2, not bicarbonate (HCO3−).5 Just as CO2 enters the blood from the dialysate in the dialyser, CO2 from carbonated water enters the bloodstream through the stomach capillaries. It easily penetrates the lipid bilayer membrane of red blood cells and is rapidly converted to bicarbonate (HCO3−) by the enzyme carbonic anhydrase within these cells. Red blood cells are rich in buffering systems, such as haemoglobin, causing the interior of the cells to quickly become alkaline. This alkalinisation accelerates glycolysis6 by activating key enzymes, including hexokinase and phosphofructokinase.7
Dynamics of carbon dioxide (CO2) and glucose in the dialyser. The HK-PFK system, which is the rate limiting enzyme of anaerobic glycolysis in red blood cells, is promoted by an increase in pH. As a result, anaerobic glycolysis is promoted and the glucose concentration in red blood cells decreases, which promotes the uptake of glucose from plasma into red blood cells and reduces blood glucose levels. GLUT1, glucose transporter 1; HCO3−, bicarbonate; HK, hexokinase; PFK, phosphofructokinase.
A similar mechanism occurs in cells that have abundant carbonic anhydrase and hydrogen (H+) extrusion systems, such as H+ pumps and Na+/H+ exchangers, specifically in the proximal tubule cells of the kidney. A transient increase in intracellular pH (pHc) occurs within the first 30 s due to respiratory alkalosis when the PCO2 (partial pressure of carbon dioxide) of the surrounding peritubular fluid decreases.8 Although the initial pHc is significant, raising the basolateral PCO2 leads to an increase in HCO3− levels due to the action of carbonic anhydrase, subsequently also raising pHc.9 In red blood cells, the H+ produced by the action of carbonic anhydrase, when PCO2 rises, is buffered by haemoglobin or excreted outside the cells by the Na+/H+ exchanger or H+ pump. Hence, HCO3− is more likely to remain within red blood cells compared with proximal tubule cells.
When PCO2 increases, the HCO3− concentration in red blood cells also increases, leading to a rise in pHc. If a change in PCO2 results in a higher pHc, it is believed that anaerobic glycolysis is promoted,6 enhancing the uptake of glucose from plasma into red blood cells. Clinical observations during haemodialysis support this mechanism, showing a significant decrease in blood glucose levels (from an average of 118.3±18.0 to 98.6±5.7 mg/dL, p<0.05) as blood passes through the dialyser, despite a higher glucose concentration (approximately 105.0 mg/dL) in the dialysate.5
Further studies have indicated that inhibiting carbonic anhydrase with acetazolamide reduces CO2 induced glucose consumption,10 reinforcing the hypothesis that CO2 stimulates glycolysis by alkalising the intracellular environment. This process leads to increased glucose consumption within red blood cells, resulting in greater glucose uptake from plasma and, consequently, lower overall blood glucose levels.
While these findings suggest that carbonated water may indirectly promote weight loss by enhancing anaerobic glycolysis and glucose utilisation, it is crucial to approach these effects in context. Carbonated water is not a standalone solution for weight loss. During haemodialysis, glucose concentrations decrease by an average of 19.7 mg/dL as blood passes through the dialyser. In a typical 4 hour haemodialysis session with a blood flow rate of 200 mL/min, approximately 48 000 mL of blood flows through the dialyser. This results in approximately 9.5 g of glucose being consumed during the session. Given this minimal glucose reduction, the impact of CO2 in carbonated water is not a standalone solution for weight loss. A balanced diet and regular physical activity remain crucial components of sustainable weight management.
Also, drinking carbonated water can have some effects on the digestive system, particularly for individuals with sensitive stomachs or pre-existing gastrointestinal conditions. The primary concerns include bloating, gas and, in some cases, exacerbation of certain symptoms associated with digestive disorders, such as irritable bowel syndrome11or gastro-oesophageal reflux disease.12 Moderation is key to avoiding discomfort while still enjoying the possible metabolic benefits of carbonated water.
Recent reports have shown that there is a clear positive correlation between the concentration of carbon dioxide in the breath and blood glucose levels.13 Therefore, although the calorie consumption from CO2 is small when drinking carbonated water, there is a possibility of a temporary decrease in blood glucose levels, and there may be an effect if blood glucose levels are measured while drinking carbonated drinks.
In conclusion, the CO2 in carbonated water may support weight loss by converting to HCO3− in red blood cells and increasing pHc to enhance glycolysis. However, because this glycolysis due to CO2 consumes fewer calories, it should be integrated into a broader strategy of healthy living rather than relied on as a primary weight loss tool. Further research is necessary to better understand its long term effects and optimise its role in dietary interventions.
Contributors: AT was involved in the conceptualisation, design, original draft preparation, and manuscript editing. AT takes responsibility that this brief report has been reported honestly, accurately, and transparently, and accepts account for the ability of the overall work by ensuring that questions on the accuracy or integrity of any portion of the work are appropriately investigated and resolved.
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests: None.
Provenance and peer review: Not commissioned; externally peer reviewed by: Addae Yaw Hammond, Kpembe Nursing & Midwifery Training College, Kpembe, Ghana.
Data availability statement
The data that support the findings of this study will be made available by the corresponding author upon reasonable request.
Ethics statements
Not applicable.
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