We last left off rounding off the mini-series on dietary fats by discussing their effect on exercise performance. Today we are starting a discussion on a part of nutrition that is often overlooked, yet can have palpable effects on daily living and exercise performance: hydration. Hydration is an essential tool in the arsenal of any individual, athlete or otherwise. Its importance stems from the varied roles that fluid plays in our bodies and the large proportion of our bodies that is made of water. So, what does being hydrated actually mean, and how can we gauge our hydration levels?
Three hydration states
Firstly, we should introduce the three main states an individual can find themselves in:
- Euhydration — the state of appropriate hydration.
- Hyperhydration — being over-hydrated after consuming too much fluid.
- Hypohydration — when significant body water has been lost, likely due to insufficient fluid intake and/or excessive water loss.
At this point, you may notice these descriptions and ask: “but why does everyone say we should avoid dehydration?” And that, dear reader, is because dehydration describes the process of losing body water that leads to hypohydration.
In any regard, we should avoid substantial body water losses, as losses equivalent to 2% of our body mass can negatively affect both physical and cognitive performance (Evans et al., 2017; Maughan & Shirreffs, 1997). For a 75 kg person, that is only about 1.5 kg. That being said, in daily life we may find it difficult to consistently monitor body water losses — and therefore our risk of hypohydration.
Method 1: urine colour
Monitoring hydration very closely can be difficult in daily life — few people want to weigh themselves before and after every training session. Admittedly, for most people detailed monitoring is unnecessary. It becomes useful during prolonged, strenuous exercise, especially in warm environments. And even for high-level athletes who benefit from this level of detail, daily pre- and post-training weighing is not always practical.
The easiest alternative is observing urine colour (Ricci et al., 2025). Using a scale previously standardised in research, we can estimate our hydration status in that moment:
- Pale yellow — generally associated with adequate hydration.
- Darker shades — can indicate hypohydration.
- Very clear — can indicate that fluid intake has been excessive.
Even so, there is a thin line in evaluation: urine colour alone cannot determine hydration status or sodium balance. It is an easy, quick estimate — but only a snapshot of a constantly changing system.
Method 2: the scale (and your sweat rate)
Hydration is not static — it can change rapidly, with water losses during exercise being an important contributor. That is why weighing yourself before and after exercise is a valuable tool, both to assess sweat rate and to plan rehydration.
The weight lost during exercise, corrected for any fluid consumed during the session, gives you your sweat rate for those conditions. Naturally, sweat rate changes with temperature, humidity, and even clothing choices (Baker, 2017) — so tracking it across different scenarios builds a useful personal picture.
💧 Rule of thumb for rehydration: drink about 1.5 × the weight lost during exercise. Lost 1 kg? Aim for roughly 1.5 litres over the following hours. Replacing around 150% of fluid lost supports adequate rehydration after exercise (Evans et al., 2017; Maughan & Shirreffs, 1997; Ricci et al., 2025).
The bottom line
Hydration status is a constantly changing system, but maintaining euhydration matters for both well-being and performance. Importantly, simply drinking more is not always the best approach. For estimating fluid losses during exercise, weighing before and after training is one of the most useful methods; throughout the day, a quick check of urine colour does the job.