Beverage Hydration Index

Why Coca-Cola may be better than water.

#health

What is hydration?

Being hydrated is having enough water and electrolytes in your body. When you sweat, breath, and urinate, you lose water in your body.

Hydration is the process of re-adding water into your body so that it can continue to use and circulate water throughout your body.

Electrolytes help regulate the body’s usage and retaining of fluids. If the body has sufficient levels of electrolytes, it helps combat dehydration. Elecrolytes help make this happen by regulating the amount of water that is expelled from your body. This is why sport drinks like Gatorade are so popular for athletes: they have high levels of electrolytes, which help them retain fluids in their body.

We drink water to hydrate. We know that water is of crucial importance to our bodies - obviously - but what if water isn’t the best way to rehydrate your body? Specifically, is “pure” water all we need?

Beverage Hydration Index

The Beverage Hydration Index (BHI) was developed by researchers from the University of Stirling in Scotland. The concept was introduced in a study published in The American Journal of Clinical Nutrition in 2016. The BHI evaluates the hydrating potential of different beverages compared to water by measuring how much and how quickly a liquid is absorbed and retained in the body over time.

The BHI and studies covering it look at how different types of beverages contribute to your level of hydration. This happens by tracking urination. If you drink a drink X versus drink Y, you can compare the urine content and see how a human body stays hydrated by measuring the mass of urine being expelled.

Coca-Cola versus water

This leads to a funny fact that I saw mentioned on 𝕏 over the weekend: Coca-Cola is better than water for rehydration:

I spent some time researching it and found the source:

Here’s the full abstract of the study:

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. This trial was registered at www.isrctn.com as ISRCTN13014105.

It seems counter-intuitive to say Coca-Cola is objectively better than water at rehydration - although very amusing, taken at face value1). However, we can see from the chart in the study (which I screenshotted in my post) that Coca-Cola does lead to more fluid retention than plain water. Drinks like orange juice and milk can lead to even more fluid retention! But how does it work? Why do some drinks, like Coca-Cola or milk, more effectively rehydrate the body?

Glucose and electrolytes

The answer is two-fold: glucose, and electrolytes. To recap biology class, glucose is a sugar that your body uses for energy. When you eat food, particularly carbohydrates, your body converts them into glucose and either uses it immediately, or stores it for use later. In your intestines, glucose helps water transport more effectively by triggering sodium absorption. This is called sodium-glucose co-transport.

In the case of Coca-Cola, the presence of glucose through sugar - particularly in the excellent Mexican coke variety, which uses cane sugar2 instead of high-fructose corn syrup - effectively provides sugar that can help the body take water and transport it through your body. Amazing!

Milk scores even better on the Beverage Hydration Index. The reason is the high electrolyte, protein, and fat contents. Milk has high level of sodium and potassium, therefore helping the body stay hydrated after drinking fluids. The protein and fat slow the absorption of fluids, also helping with hydration.

This is a fun study that challenges some of the assumptions people have about rehydration. It is worth noting that caffeine is a known dieuretic, so I would still argue that if you’re on the hunt for rehydration specifically, drinking fruit juices or milk may be more effective. Coca-Cola in particular does have its uses (Ray Peat has written a lot about this), but I’ll classify this whole thing as a fun factoid that I dug into this weekend as I enjoy a nice Mexican coke. Biology is fun!

Footnotes

  1. This falls under the “funny factoids that I enjoy sharing in conversation” category - it seems crazy, has science to back it up, and is a fun thought exercise. Cool! ↩

  2. Cane sugar is an excellent form of sugar. It contains sucrose, which is made up of roughly 50% glucose and 50% fructose. ↩