When exercising for a prolonged period of time or at a higher intensity, the body loses a significant amount of water, either through sweating or whilst breathing. That process is called dehydration and happens normally in order to cool down the body during exercise and keep its temperature normal. To prevent any negative effects on health and performance, we need to maintain a balance in the body’s water levels by consuming fluids either during or shortly after exercising.
So far, water and sports drinks have been considered to provide the best options for replenishing water losses during exercise, whereas caffeinated drinks like coffee/tea or beverages that contain alcohol were thought to result in more frequent “bathroom stops” and possibly dehydrate us further.
A recent study put different drinks under the microscope to assess which ones could be best for rehydrating the body and which should be avoided. The researchers used a score called Beverage Hydration Index (BHI) to assess each drink, which is showing how much of a drink is retained in the body 2 hours after ingesting it (by assessing the volume of urine passed) compared to the same amount of still water. The higher the BHI, the more fluid is kept within the body and is more likely to support a healthy water balance and hydration level. The study was conducted to 72 active healthy males and they have assessed 13 known drinks, including sports drinks, coffee and tea (hot and cold), cola, milk (full fat and semi skimmed), beer and orange juice. The drinks and their BHI score is shown below:
BHI for still water is equal to 1 and any drink scoring higher has better hydrating properties, whilst BHI lower than 1 shows that the drink is passed faster from the body compared to water
(*shows statistical significance).
(Source: Maughan et al, Am J Clin Nutr 2016 Mar;103(3):717-23 )
What the results showed:
There seems to be no difference between still and sparkling water in their hydrating properties, so it is up to personal preference which one to choose whilst exercising.
Slightly better options for rehydration than water seem to be milk (both full fat and skimmed), orange juice and oral rehydration solution. All three had a BHI of almost 1.5, meaning about 50% more of those drinks seems to be retained within the body 2 hours after ingestion compared to the same amount of water. The specific drinks could provide an excellent choice following a prolonged event like a marathon, cycling or rowing event when the water losses are significantly high (and plain water does not seem too appealing anymore). Drinks that contain more calories (fat, sugar) or electrolytes are digested slower from the stomach which can lead in more fluid being retained in the body.
An interesting finding was that the standard sports drinks do not seem to have greater hydration properties than water, even though they have been often used as a gold standard.
On the other side, drinks known to be more "diuretic" like caffeine or alcohol beverages, did not perform as bad as expected. They seem to result in slightly greater urine output than water, however the difference between them and water was not found to be significant (not as "diuretic" after all). It is, however, worth to mention that both the lager that was used and the coffee did not contain a significant amount of alcohol or caffeine in them, therefore higher contents might lead to different results.
The specific study only assesses drinks based on their hydration properties. Other compounds within the drinks (eg, the electrolyte content of sport drinks, the carbohydrate content of orange juice or the protein content of milk) can also play different roles in health and performance and should be taken into consideration when choosing what to drink during or after exercise.
For further help and tips on hydration strategies, feel free to contact HP Nutrition here .