January 21, 2025

expert reaction to a brief research report suggesting fizzy water can aid in weight loss by boosting glucose uptake and metabolism

A study published in BMJ Nutrition, Prevention & Health looks at carbonated water and weight loss. 

Catherine Collins, Intensive care unit dietitian, NHS, said:

“Can carbonated water support weight loss? is bound to be of interest at this time of the year, but – spoiler alert – the short answer from this UK dietitian is a robust ‘NO’

“Dr. Takahashi, a kidney specialist from Japan, revisits his 20-year-old research on how red blood cells increase glucose usage during dialysis sessions in people with severe kidney failure, and this publication discusses in detail the metabolic processes around these findings.

“For context, people in ‘end stage’ kidney failure must rigidly control diet and fluid intake. Dialysis – typically three times a week – removes retained water, electrolytes and protein metabolites that make blood more acidic and helps re-establish the natural alkalinity of blood essential for good health. This is achieved by using fluids in dialysis machines that are rich in ‘buffering’ agents – such as bicarbonate – to re-establish normal blood alkalinity.

“Dr Takahashi explores the tiny increase in glucose use by red blood cells when bicarbonate is absorbed from the dialysis fluid during dialysis. He considers whether this slight increase in glucose use by red blood cells during dialysis would increase energy expenditure sufficient to help control weight. This has not been researched. 

“Without empirical data, Dr Takahashi’s suggestion that the bicarbonate generated from carbon dioxide in fizzy water would exert a similarly sized effect on glucose use to that of haemodialysis to boost red blood cell metabolism and generate weight loss is purely speculative.

“In healthy people, drinking a fizzy drink will have very little effect on blood pH, because typically their bodies are easily buffering blood pH to keep it in the healthy pH 7.35-7.35 range. The kidneys are key regulators, but our breathing rate also controls oxygen and CO2 levels in the bloodstream. Blood levels of ammonia and phosphate can also be used to support a health blood pH.

“However, substituting zero calorie fizzy water to replace calorific drinks may aid weight loss as part of a calorie-controlled diet, by reducing calorie intake. Taking a fizzy drink with meals has in some research reduced calorie intake by inducing feelings of ‘fullness’, but in other studies have shown to increase appetite.

“Bottom line? Carbonated (fizzy) water is a low-calorie way to rehydrate. But its natural acidity derived from dissolved CO2 bubbles, is not as ‘tooth friendly’ as plain water varieties.”

Prof Keith Frayn, Emeritus Professor of Human Metabolism, Emeritus Fellow at Green Templeton College, University of Oxford, said:

“This is a short theoretical report with no experimental data to support a claim that fizzy drinks may aid weight loss.  I am sceptical of the claimed mechanism.  Even if it were possible to show that the carbon dioxide in fizzy drinks increases the use of glucose by red blood cells, that will not necessarily lead to weight loss, however minimal.  Red blood cells cannot fully ‘burn’ the glucose, and it will be recycled by the liver.  If fizzy drinks were to be shown to lead to weight loss, it would much more likely be through effects on feelings of fullness.  In the meantime, however, sugar-sweetened fizzy drinks are recognised as a source of excess calories and likely to do just the opposite.”

Can carbonated water support weight loss?’ by Takahashi was published in BMJ Nutrition, Prevention & Health at 23:30 UK time on Tuesday 21^st January.

DOI: 10.1136/bmjnph-2024-001108

Declared interests:

Catherine Collins: “No conflicts of interest declared”

Prof Keith Frayn: “I have no commercial interests related to this topic. I am the author of books on metabolism including ‘A Calorie is a Calorie’, Piatkus, Jan 2025”