Hot chocolate: hydration, calories, theobromine

• Default serving240 mlDairy & milk
• Counts toward goal324 mlhydration factor 1.35
• Calories168 kcal70 kcal per 100 ml

Milk is the best hydrating drink in the trial

The trial compared thirteen beverages by weighing urine output for the four hours after a litre of each. Only three finished clearly ahead of still water: an oral rehydration solution, skimmed milk and full-fat milk. Milk wins on two mechanisms at once. It carries sodium and potassium, which is what signals the kidneys to hold on to fluid. Its protein, fat and lactose also slow the rate at which the stomach releases it. The water arrives as a trickle your body can absorb rather than a flood it flushes.

A mug of hot chocolate is milk with cocoa and sugar stirred into it, so it inherits most of that behaviour. The app rates it at 1.35, meaning a 240 ml mug counts as 324 ml toward the day's goal. Only milk itself, kefir and chocolate milk score higher in the catalog. Made with water instead of milk, none of this holds. That version is a hot sweet drink with a hydration factor closer to 1.00. Edit the drink to say so.

The stimulant in cocoa is not mainly caffeine

Cocoa contains a few milligrams of caffeine per mug. That is why the catalog figure is zero and the app does not treat hot chocolate as a caffeinated drink. What it does contain in quantity is theobromine, caffeine's chemical cousin. It is a milder stimulant, and it works more on the heart and blood vessels than on alertness. The body clears it more slowly than caffeine. That is the reason a mug in the evening feels harmless and a bar of dark chocolate at midnight sometimes does not.

Theobromine is also the reason chocolate is dangerous for dogs. They metabolise it several times more slowly than we do. A dose that gives a person a mild lift accumulates in a dog to something toxic.

168 calories is the price

Seventy calories per 100 ml puts a mug of hot chocolate above cola and above beer. It is level with a small meal's worth of sugar and milk fat. The hydration is real and so are the calories. Treating it as the day's water is a decision rather than an accident. The app logs both figures against the same drink so the trade is visible at the point you make it.

Hydration factors follow the Beverage Hydration Index: Maughan RJ, Watson P, Cordery PA, et al. “A randomized trial to assess the potential of different beverages to affect hydration status: development of a beverage hydration index.” American Journal of Clinical Nutrition, 2016;103(3):717-723. Read the paper on PubMed. In WaterChamp a hot chocolate holds water in the body better than plain water.