Does sparkling water break a fast?

Sparkling drinks compared

Drink	Calories	While fasting
Sparkling mineral water, seltzer, soda water	0	Fine
Flavoured sparkling water, unsweetened	0	Fine
Flavoured sparkling water with sweeteners	Close to 0	Grey zone: see sweeteners
Sparkling water with juice or sugar	Check the label	Breaks your fast if there's sugar
Tonic water	About 124, with 32 g of sugar	Breaks your fast
Diet or light tonic	Close to 0	Grey zone, like diet soda

Why tonic water catches people out

It looks like soda water and sits next to it on the shelf, but tonic is sweetened to balance the bitterness of quinine. It has about 9 g of sugar in every 100 ml ¹, and sugar is the clearest fast breaker there is: it raises insulin, the signal that tells your body to store fuel rather than burn it ². If you want a mixer-style drink during a fast, soda water with a slice of lime does the job.

Does it count as water?

Yes. Carbonated water is water with carbon dioxide dissolved in it, and it hydrates you just the same. Count it towards your daily water goal: in Fasting Tracker you can log it from your iPhone, a widget or your Apple Watch.

Some people find the bubbles fill them up and help them through a hunger wave. Others find them bloating on an empty stomach. Both are normal: drink whichever feels better.

MYTH

The bubbles break your fast.

FACT

Carbon dioxide has no calories and doesn't raise insulin. Bubbles change how a drink feels, not your fast.

What about your teeth?

Carbonation makes water slightly acidic. In a laboratory study with extracted human teeth, sparkling mineral waters dissolved a little more enamel than still ones, but about a hundred times less than soft drinks did ³. Flavoured waters weren't part of that test, so plain is the safest choice for all-day sipping.

Ways to make it more interesting

• Add slices of lemon, lime, orange or cucumber (see lemon water).
• Add a few mint leaves, a sprig of rosemary or a slice of fresh ginger.
• Choose unsweetened flavoured waters, where the ingredients are just water, carbon dioxide and natural flavour.
• Have a cold one when you'd usually reach for a snack, then see if the hunger wave passes.

Hungry or thirsty?

Hunger on a fast tends to come in waves around the times you usually eat. Your hunger hormone, ghrelin, rises before a meal you're used to ⁴, and when people fast it still falls again on its own, without food ⁵. A big glass of water, still or sparkling, is a good way to wait one out: drink it, wait 20 minutes, then decide whether you really need to eat.

Sources

1. U.S. Department of Agriculture, Agricultural Research Service. FoodData Central: Beverages, carbonated, tonic water (FDC ID 171869); Beverages, carbonated, club soda (FDC ID 174842). SR Legacy. fdc.nal.usda.gov/
2. Holt SH, Miller JC, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. Am J Clin Nutr. 1997;66(5):1264-76. doi.org/10.1093/ajcn/66.5.1264
3. Parry J, Shaw L, Arnaud MJ, Smith AJ. Investigation of mineral waters and soft drinks in relation to dental erosion. J Oral Rehabil. 2001;28(8):766-72. doi.org/10.1046/j.1365-2842.2001.00795.x
4. Cummings DE, Purnell JQ, Frayo RS, et al. A preprandial rise in plasma ghrelin levels suggests a role in meal initiation in humans. Diabetes. 2001;50(8):1714-9. doi.org/10.2337/diabetes.50.8.1714
5. Natalucci G, Riedl S, Gleiss A, et al. Spontaneous 24-h ghrelin secretion pattern in fasting subjects: maintenance of a meal-related pattern. Eur J Endocrinol. 2005;152(6):845-50. doi.org/10.1530/eje.1.01919