# Is beer hydrating? What a 500 ml glass counts for

A 500 ml beer at 5% is 20 g of pure alcohol and 215 calories. It still counts as 500 ml of fluid, and a controlled trial measured why.

## Numbers the app uses

| Field | Value |
| --- | --- |
| Default serving | 500 ml |
| Hydration factor | 1.00 |
| Counts toward the daily goal | 500 ml per serving |
| Calories | 43 kcal per 100 ml (215 kcal per serving) |
| Alcohol | 5% ABV (20 g per serving) |

## Weak and wet beats strong and small

A pint of lager is about 95% water. The controlled trial behind the hydration
factors in this app included a 4% lager among its thirteen drinks. Volunteers
drank a full litre of it. The researchers then weighed everything they produced
for four hours. The lager finished level with still water. It did not beat
water, and it did not lose to it.

That is why the hydration factor here is 1.00 rather than a penalty. The volume
of fluid arriving is large enough to cover the extra urine the alcohol causes.
Concentrate the same alcohol into a small glass and the arithmetic flips. That
is why the catalog discounts wine and spirits but not beer.

## What the diuretic effect actually depends on

The follow-up detail is the one almost nobody quotes. The same research group
later gave men a litre of beer with 4% alcohol or with none. The difference in
urine output depended on how hydrated the men already were. In well-hydrated
volunteers the alcoholic beer produced about 1279 ml of urine. The alcohol-free
version produced 1121 ml. That is a real difference, but a small one against a
litre of intake. Other volunteers had exercised in the heat and were already
dehydrated. In them there was no measurable difference at all. The body's own
water-saving hormones overruled the alcohol.

Read it as a dose effect, not a switch. One beer in an evening is a net gain of
fluid. Six beers is a large alcohol dose spread over hours. The hangover that
follows is not mainly a water problem anyway.

Source for that second study: Hobson RM, Maughan RJ. "Hydration status and the
diuretic action of a small dose of alcohol." *Alcohol and Alcoholism*,
2010;45(4):366-373. [PubMed](https://pubmed.ncbi.nlm.nih.gov/20497950/).

## The number that matters more than hydration

500 ml at 5% ABV is 20 g of pure alcohol and 215 calories. That is more than a
can and a half of cola. The app keeps that alcohol on its own track instead of
hiding it inside the water total. A week of "just a beer with dinner" adds up
somewhere you can see it. On iPhone the app also writes those grams to Apple
Health. On Android it syncs the water to Health Connect, but the alcohol figure
stays inside the app.

## Source

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. https://pubmed.ncbi.nlm.nih.gov/26702122/

Page: https://waterchamp.app/drinks/beer/