Sparkling Water and Intermittent Fasting

Sparkling water and intermittent fasting are a common combination, but many people are unsure whether carbonated drinks could break their fast. Plain sparkling water contains no calories, no sugar, and no macronutrients, making it compatible with most fasting protocols in the same way as still water. This article explains whether sparkling water breaks a fast, any potential downsides, which other drinks are safe during a fasting window, and practical tips for staying well hydrated throughout your fasting plan.

Does sparkling water break a fast?

Plain sparkling water does not break a fast because it contains zero calories and no macronutrients. Always check labels, as added flavourings or sweeteners can introduce calories that interrupt a fast.

Plain sparkling water does not break a fast, provided it contains no added sugars, sweeteners, calories, or flavourings. The carbonation in sparkling water comes from dissolved carbon dioxide gas, which has no caloric value. Because plain carbonated water provides zero calories and no macronutrients, it is generally considered compatible with fasting in the same way as still water.

Intermittent fasting works by restricting caloric intake to a defined eating window, allowing insulin levels to fall and supporting processes associated with metabolic health.^[9] The human evidence for specific mechanisms such as autophagy (sometimes described as cellular repair) is still developing, and most robust data come from animal studies; the practical benefit for most people is the reduction in overall calorie intake during the fasting window. Because plain sparkling water contributes no calories or macronutrients, it does not interrupt these processes. This applies whether you are following a 16:8 protocol, a 5:2 approach, or any other structured fasting pattern.

It is worth checking the label carefully before drinking sparkling water during a fast. Many commercially available sparkling waters contain added fruit flavourings, citric acid, natural sweeteners, or small amounts of sugar. These additions may introduce calories that could interrupt a fast. Always choose a product labelled as plain or unflavoured carbonated water, with zero calories and no additives, to be confident your fast remains intact.

Some people ask whether the carbonic acid formed when carbon dioxide dissolves in water could affect digestion or gut function during a fast. There is no evidence that carbonic acid at the concentrations found in sparkling water has any meaningful effect on fasting outcomes at typical intakes. The key principle remains simple: if a drink contains no calories or macronutrients, it is generally considered compatible with fasting.

Are there any downsides to drinking sparkling water while fasting?

Sparkling water can cause bloating, belching, or worsen acid reflux when the stomach is empty. Frequent sipping also carries a mild risk of dental enamel erosion due to its mild acidity.

For most people, drinking plain sparkling water during a fast is well tolerated, but there are a few practical considerations worth being aware of. The most commonly reported issue is bloating or increased feelings of fullness caused by the carbonation. During a fasting window, the digestive system is relatively quiet, and swallowing carbonated water introduces gas into the stomach, which can cause temporary discomfort, belching, or a sensation of pressure in some individuals.

People who experience acid reflux or gastro-oesophageal reflux disease (GORD) may find that sparkling water worsens their symptoms, particularly when the stomach is empty. The NHS lists fizzy and carbonated drinks among the triggers that can aggravate heartburn and reflux.^[1] Carbonated drinks can increase gastric pressure, potentially allowing stomach acid to travel upwards.^[1][2] If you have a history of reflux, it may be worth switching to still water during fasting periods and discussing your symptoms with your GP if they persist.

There is also a question about dental health. Sparkling water is mildly acidic due to the formation of carbonic acid, and frequent sipping throughout the day could, over time, contribute to enamel erosion.^[3] This risk is considerably lower than that associated with fizzy soft drinks, which are far more acidic and often contain sugar, but it is not entirely absent. NHS dental guidance advises avoiding frequent sipping of acidic drinks and waiting at least one hour before brushing your teeth after consuming them.^[3][4] Drinking sparkling water at mealtimes rather than sipping it continuously is a sensible precaution.

Finally, some flavoured sparkling waters contain citric acid or natural fruit extracts, which make them more erosive than plain sparkling water and may also stimulate appetite. Choosing genuinely plain, unflavoured varieties avoids these concerns and keeps your fasting window as clean as possible.

Which drinks are safe to have during intermittent fasting?

Plain still or sparkling water, black coffee, and unsweetened plain or herbal teas are the safest choices during a fasting window. Drinks containing calories, milk, sugar, or alcohol should be avoided.

Several zero-calorie drinks are widely considered compatible with intermittent fasting, with plain still water and plain sparkling water being the most straightforward choices. Beyond water, black coffee and plain tea (without milk, sugar, or sweeteners) are commonly consumed during fasting windows. Because they contain no calories and no added macronutrients, these drinks are acceptable for most fasting protocols.

Herbal teas are another popular option, provided they are unsweetened and do not contain added honey, fruit syrups, or caloric ingredients. Green tea, peppermint tea, and chamomile tea are frequently chosen for their mild flavour. It is important to read ingredient lists, as some herbal blends include dried fruit pieces or natural sweeteners that add a small caloric load.

Drinks to avoid during a fasting window include anything containing calories, sugar, milk, cream, fruit juice, or alcohol. Bulletproof coffee (coffee blended with butter or MCT oil) is popular in some fasting communities but does provide calories and fat, which would technically break a strict fast, even if proponents argue it preserves some metabolic benefits. Bone broth similarly contains protein and calories and is not suitable for a strict fasting window, though some modified fasting approaches permit it.^[9]

Diet fizzy drinks and artificially sweetened beverages are a more contested area. While they contain no calories, the UK Scientific Advisory Committee on Nutrition (SACN) has noted that evidence on whether low or no calorie sweeteners influence gut microbiota or appetite in humans remains inconclusive.^[5] If you are following intermittent fasting for metabolic health reasons, sticking to plain water, sparkling water, black coffee, and plain tea is the most straightforward and evidence-consistent approach.

Tips for staying hydrated on an intermittent fasting plan

Aim for six to eight glasses of fluid daily in line with NHS guidance, spreading intake throughout the day. Watch for signs of dehydration such as headaches, dark urine, or fatigue, which are sometimes mistaken for fasting side effects.

Staying well hydrated during intermittent fasting requires a little planning, particularly because food itself contributes a meaningful proportion of daily fluid intake.^[6][7] When you are not eating for extended periods, you lose that dietary source of water, making it important to drink consistently throughout both your fasting and eating windows.

A practical starting point is to aim for six to eight glasses of fluid per day, in line with NHS guidance on water and drinks, adjusting upwards in hot weather or when exercising.^[6] Spreading your fluid intake across the day, rather than drinking large amounts in one sitting, helps maintain steady hydration and avoids the discomfort of a very full stomach during a fasting window. Keeping a reusable water bottle nearby is a simple but effective prompt.

If you find plain water unappealing over long fasting periods, alternating between still and sparkling water can add variety without compromising your fast. Adding a slice of cucumber or a sprig of fresh mint to still water provides a subtle flavour without introducing calories. Be cautious with citrus slices, as the juice released is mildly acidic and, with frequent sipping, may contribute to enamel erosion over time.

Pay attention to signs of dehydration, which can include headaches, difficulty concentrating, dark urine, and fatigue. These symptoms are sometimes mistakenly attributed to fasting itself, when inadequate fluid intake is the actual cause. If you experience persistent headaches or dizziness during fasting, contact your GP to rule out other causes and to discuss whether your fasting approach is appropriate for your individual health circumstances.

Intermittent fasting is not suitable for everyone. The British Dietetic Association advises that people who are pregnant or breastfeeding, under 18, underweight, older or frail, living with an eating disorder, or managing diabetes with insulin or sulfonylureas (which carry a risk of hypoglycaemia during fasting) should seek medical advice before starting any fasting plan.^[10][11] People with kidney conditions or other significant health conditions should also speak to their GP or a registered dietitian before making changes to their eating pattern.

Frequently Asked Questions