For years it has been claimed that sparkling water may aid weight loss by helping you feel fuller – reducing your desire to snack and overeat.
Now, a recent hypothesis has suggested that sparkling water may help you lose weight by boosting your body’s blood sugar (glucose) uptake and metabolism.
But before you go and stock your fridge up with fizzy water, it’s important to actually take a look at the study itself and how it was conducted. This publication makes it clear that it isn’t new research – rather, it’s a new hypothesis formed by referencing the results of a study published in 2004 — alongside additional supplementary research to support the theory.
It should be noted that the old study was not even looking at the effect of fizzy water on body weight. It was actually an observation of what happens to blood when it goes through a kidney dialysis machine (haemodialysis) and how it might lower blood glucose. No fizzy water was consumed as part of this study either.
The effect of haemodialysis is said to mimic the effect of carbon dioxide in the blood – which increases the pH or alkalinity inside red blood cells. This then encourages the red blood cells to metabolise more glucose.
Using the figures from the 20-year-old paper, it’s estimated that a four hour dialysis session seems to increase glucose use by 9g – only around 36 additional calories burned.
But the study the hypothesis was based on wasn’t looking at the effects of carbon dioxide in the blood. Rather, it was looking at how haemodialysis changes the pH of red blood cells — and how that affects blood glucose. This makes it difficult to compare how the carbon dioxide in fizzy water may affect blood glucose when it enters the bloodstream.
So why the fuss?
The paper itself contains a valid scientific idea worthy of discussion. But unfortunately, some of its nuance has been lost in the way the study has been promoted – with media headlines exaggerating the paper’s findings.
To understand whether this hypothesis stands, research will need to be done which investigates whether a significant amount of carbon dioxide actually does enter our bloodstream when we drink sparkling water, and how quickly this is absorbed by the body – which will tell us how long the potential effects last.
But a glass of sparkling water contains less than a gram of carbon dioxide – and this will be absorbed in minutes. This amount of carbon dioxide is a tiny fraction compared to the kilogram our body naturally produces in an average day) through respiration – how our body uses energy.
Looking at these numbers, fizzy water will probably not have a measurable effect on blood carbon dioxide levels – and therefore no effect on metabolism and weight.
The hypothesis’s author itself is careful to state in the paper that carbonated water is not a standalone solution for weight loss and that healthy diet and physical activity are both key.
Does fizzy water at least help with appetite?
Another claim that has sometimes been made about fizzy water in the media and in other studies (though not by the author of this latest hypothesis) is that it can help you feel fuller for longer, which may aid in weight loss. However, the evidence here is not conclusive.
While some studies have found that people who drank carbonated water reported it helped them feel fuller for longer, other studies have actually shown it may have the opposite effect. Research in rats that looked specifically at weight and appetite hormones found that sparkling water increased both weight and levels of the hunger hormone ghrelin. In a parallel study these researchers conducted on 20 men, it was shown that fizzy water also increased their ghrelin levels. This suggests fizzy water could actually make people more hungry.
It seems the data is not conclusive about the effect of fizzy water on hunger. In theory, fizzy water might help to stretch our stomach causing us to feel full. However, the data does not seem to agree with this theory.
In order for fizzy water to do this, it would need to stay in the stomach longer than still water – and science suggests this isn’t the case. A study which compared drinking fizzy water versus drinking still water after a meal found both seem to leave the stomach at the same rate.
What’s more, drinking water with meals does not have a significant effect on appetite and feeling full. This is all down to the shape of the stomach and how it churns and breaks down our food. The bottom curve of our stomach has a channel called the Magenstrasse or “stomach road” which allows liquids to flow quickly into the small intestine where it can be absorbed.
While we might wish a glass of sparkling water could help support weight loss or at least help us feel fuller for longer, there’s currently little to no data to support this. The only real effect that drinking fizzy water (or even still water) has on body weight seems to be that when people use it to replace sugary drinks, it means they consume fewer calories on average.
The Conversation has spoken with Akira Takahashi, doctor of medicine and head of department at Tesseikai Neurosurgical Hospital, the author of the hypothesis. He writes that based on the 2004 study’s findings, it would be difficult to simulate the effect of haemodialysis through drinking carbonated water – and that it’s unlikely fizzy water alone could lead to weight loss.
He states that the mechanism shown in the haemodialysis study, by which CO2 can reduce blood sugar levels, may behave similarly to the CO2 absorbed from drinking fizzy water — and that this may result in glucose consumption in the blood near the stomach. However, he says more research will be needed to measure blood sugar levels before and after drinking carbonated water to validate this effect. Takahashi also thinks the feeling of fullness caused by drinking carbonated beverages warrants further research, as carbon dioxide releases bubbles that stimulate the stomach’s stretch receptors – creating a sensation of fullness.
Takahashi writes: “It is important to note that carbonated water alone is unlikely to contribute significantly to weight loss. A balanced diet and regular exercise remain essential for effective weight management.”
Duane Mellor, Visiting Academic, Aston Medical School, Aston University
This article is republished from The Conversation under a Creative Commons license. Read the original article.