Hydration - a balancing act

About 60% of the adult human body is water and around 65% for children. And a whooping 75% of our brain is water! That's why dehydration even as little as 2% loss can have a negative impact on our brain functions. That can look like poor coordination, losing focus, increase in perception of effort and feeling really tired. Not to mention you'd feel really thirsty!

Here are some signs and symptoms of dehydration (severe in red):

• Increased thirst

• Dark urine + low volume and frequency

• Loss of body weight (>2% compared to well-hydrated state)

• Headaches

• Dry skin / dry and cracked lips / dry mouth

• Increase in perceived effort

• Disorientation/confusion

• Rapid breathing and heart rate

• Loss of consciousness/collapse

How do we know if we are hydrated enough?

Our body is in a constant state of homeostasis - the continuous act of trying to maintain balance in our various body systems through feedback loops. To aim to be 'well-hydrated' or euhydration in scientific terms, we are aiming for normal total body water balance. We are targeting the sweet spot between hypohydration (below normal hydration) or hyperhydration (above normal hydration). Imagine holding a tray filled with water and trying to walk from point A to B trying to maintain balance and not spill any water. Same with your hydration, you are aiming for that ball park state of being hydrated enough (i.e. water can slosh around on the tray but not spilling it) to prevent undesirable consequences of either hypo- or hyperhydration.

The weight, urine colour and thirst (WUT) Venn diagram is a practical hydration assessment tool to guide us. This tool was first proposed by Chevront and Sawka (2005) to assess hydration status in athletes looking at colour of first pee in the morning, weight changes and thirst as indicators. A recent study by Keefe et al (2023) demonstrated the possibility of using of the Venn diagram in broader populations and situations such as in free living individuals and at afternoon timepoints and not limited to athletes or first morning pee. In other words, it's a tool that is widely applicable and easy to use at an individual level. Just bear in mind it is a guide only and not a diagnostic assessment tool.

Figure 1. WUT Venn diagram (Source:Keefe et. al. 2023)

Interpreting the Venn diagram, you are likely hypohydrated if you have 2 or more of the indicators overlapping and very likely if all 3 indicators are present:

• Weight: Body weight 1% or more below what you consider to be euhydrated

• Urine colour: Colour 4 and above indicate you are likely hypohydrated

• Thirst: Level of thirst. The more thirsty you are, the more likely you may be hypohydrated in consideration of the other 2 indicators as well.

Figure 2. Urine colour chart (Source: https://www.healthdirect.gov.au/urine-colour-chart)

So, how much fluid should one be aiming for every day?

For the every day individual, estimated fluid requirements are often calculated using these formulae**:

• 18-64 years old: 35-45ml/kg body weight/day

• 65 years old and above: 30-40ml/kg body weight/day

• **if you have no other existing health conditions requiring you to follow a fluid restriction (e.g. kidney disease or heart conditions). This provides a ball park amount to aim for across the day.

• you may need to increase your fluid intake if you have increased fluid losses either through sweat, vomit or diarrhoea. Please seek medical advice.

Additional fluid considerations for the active individual:

Before a race/event/exercise:

For the active individual participating in a race/event, aim for 5-10ml of fluid/kg body weight 2 to 4 hours prior to optimise your hydration (and preferably with food or high sodium fluids as this helps to retain more fluid in your body). If you are short on time with only 2 hours to go, aim for 3-5ml/kg body weight instead.

During exercise:

It depends on the sport activity, the temperature, the intensity and the duration. And most importantly, fine-tuning with practice. Individuals should aim to keep total body water loss to <2%. An accredited sports dietitian can support your hydration and fuelling needs by exploring the factors impacting on hydration during exercise as well as understanding your fuelling needs to come up with an individualised plan for you to fine-tune throughout your training.

Knowing your sweat loss (across a variety of settings) is useful when you need to purposefully and aggressively replace your fluid losses. This data can take time to collect (i.e. across seasons) during training but can provide a good insight to help guide your hydration plan.

Post race/event/exercise:

Again, it depends on a few factors. In most circumstances, normal eating and drinking should replace fluid losses. See below decision tree to help guide you. If you are needing to aggressively replace your hydration, typically aim to restore fluid balance by drinking ~1.25-1.5L of fluid (not just water) for every 1kg of body weight lost.

Figure 3. Decision tree for post-exercise fluid replacement (credit: Dr Alan McCubbin, Adv Acc Sports Dietitian)

Electrolyte supplements vs sports drink - know the difference!

Did you know that electrolyte supplements such as Hydralyte Sports is different from sports drinks such as regular Gatorade/Powerade (not the zero sugar versions). The difference lies in their carbohydrate content. Below is a great infographic by the Australian Institute of Sport (AIS) on sports drinks, showing the various types available on the market.

Figure 4. AIS Sports Supplement Framework - Sports Drinks (types available and their differences)

Commerical sports drinks tend to have both electrolytes and carbohydrates which are ideal for fuelling endurance events lasting more than 1 hour. Electrolyte supplements (mainly sodium chloride) are generally not necessary in short exercise periods but they are helpful in replacing fluids quickly in situations where rehydration is crucial and targeted. This is because sodium chloride helps to retain fluid in the body and can be particularly helpful if the individual is unable to tolerate large volume of fluids and/or if they have limited time for rehydration and not needing to top-up fuel from carbohydrates during their sport/event.

If you have identified a need to use electrolyte supplements, ensure you choose products that are batch-tested and safe for use. Look out for the HASTA or Informed-Sport certified logos.

There are lots to consider when it comes to hydration. Working with an Accredited Sports Dietitian can help you navigate the many nuances and considerations when it comes to your hydration (and of course, fuelling). You don't have to do this alone. Get the support you need and book in an appointment today! :)

Disclaimer: Information on this post does not replace individualised nutrition therapy. Please consult an accredited practising dietitian/sports dietitian for advice. (www.sportsdietitiansaustralia.com.au).

References:

Cheuvront, SN & Sawka, MN (2005) Hydration assessment of athletes. Sports Sci Exchange 18, 1–5.

Keefe, MS et. al. (2023) The weight, urine colour and thirst Venn diagram is an accurate tool compared with urinary and blood markers for hydration assessment at morning and afternoon timepoints in euhydrated and free-living individuals. British Journal of Nutrition, First View, 1-8.