Maughan 2016

Staying hydrated is important to us all. Following an intense workout or long run a high volume of water will have been lost through sweat. Keeping well hydrated has been shown in studies to help with brain function, recovering from injury, muscle growth, improving sleep and mental health.

What’s your go to drink to keep hydrated?

There was a study published in 2016 by Ron Maughan, investigated the beverage hydration index. Fluids that are consumed need to be retained. If you’re drinking a big glass of water but the peeing the same volume out, this is not effective hydration.

Maughan was looking at several different fluids, using water as the base to compare the other drinks from. Following the consumption of fluid, urine was measured over 2 hours and then compared with the volume consumed. There were some obvious results like coffee having a poor hydration index. Some surprising results with milk being one of the better fluids retained, results close to expensive electrolyte drinks. It is thought that the milk content slows down the absorption of water, which results in less fluid extracted by the kidneys.

Important to consider when trying to rehydrate. Other than just drinking water consider putting in some lemon or a small amount of sea salt (the potassium and sodium help slow down the water absorption). This was the first study of its kind. Hopefully there’ll be future studies about post exercise related hydration drinks.

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Original Abstract

BACKGROUND: The identification of beverages that promote longer-term fluid retention and maintenance of fluid balance is of real clinical and practical benefit in situations in which free access to fluids is limited or when frequent breaks for urination are not desirable. The postingestion diuretic response is likely to be influenced by several beverage characteristics, including the volume ingested, energy density, electrolyte content, and the presence of diuretic agents.

OBJECTIVE:This study investigated the effects of 13 different commonly consumed drinks on urine output and fluid balance when ingested in a euhydrated state, with a view to establishing a beverage hydration index (BHI), i.e., the volume of urine produced after drinking expressed relative to a standard treatment (still water) for each beverage.

DESIGN: Each subject (n = 72, euhydrated and fasted male subjects) ingested 1 L still water or 1 of 3 other commercially available beverages over a period of 30 min. Urine output was then collected for the subsequent 4 h. The BHI was corrected for the water content of drinks and was calculated as the amount of water retained at 2 h after ingestion relative to that observed after the ingestion of still water.

RESULTS: Total urine masses (mean ± SD) over 4 h were smaller than the still-water control (1337 ± 330 g) after an oral rehydration solution (ORS) (1038 ± 333 g, P < 0.001), full-fat milk (1052 ± 267 g, P < 0.001), and skimmed milk (1049 ± 334 g, P < 0.001). Cumulative urine output at 4 h after ingestion of cola, diet cola, hot tea, iced tea, coffee, lager, orange juice, sparkling water, and a sports drink were not different from the response to water ingestion. The mean BHI at 2 h was 1.54 ± 0.74 for the ORS, 1.50 ± 0.58 for full-fat milk, and 1.58 ± 0.60 for skimmed milk.

CONCLUSIONS: BHI may be a useful measure to identify the short-term hydration potential of different beverages when ingested in a euhydrated state.

Maughan et al, (2016) A randomized trial to assess the potential of different beverages to
affect hydration status: development of a beverage hydration index. Am J Clin Nutr

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