19 min read

Fluids, Hydration and Fitness

Here's how hydration (fluid intake) like drinking water influences training and your fitness outcomes. It's probably not how you think!
Fluids, Hydration and Fitness


Hydration doesn’t actively contribute to weight loss or muscle mass gain.

However, indirectly staying well hydrated improves mood, energy, cognition, digestive function, renal health and exercise performance. Even slight dehydration lowers sport/exercise performance. This primes you to make better food/exercise choices and contributes to better quality training sessions. It also heavily contributes to your daily happiness and health.

Drinking a larger amount of water (250-500ml) before you eat a meal may also help lower the total energy intake during that meal. As water has no caloric value but increases the volume of the stomach, contributing to the feeling of fullness.

This is a skill consideration if weight loss is your goal.

Absolute recommendations for water, such as two liters or eight glasses each day are misguided because people are different sizes. They also live in different climates/ environments. People in hot humid climates will need more water than people in more moderate climates.

If your urine is consistently clear, you’re over-hydrated. You can stop drinking water until a slight yellow tinge reemerges. If you’re consistently dark yellow, you’re dehydrated, drink more water. Consistently brown/reddish urine means you should seek medical treatment.

I Recommend: Drink enough fluid to yield approximately five large off-clear, yellow tinge pees each day is an ideal hydration level. This means looking in the toilet when you’re done. More specific recommendations below along with a urine chart to assess the proper colour..

Alright, I’ve talked about protein and vegetables (they’re awesome!). I talked about fat and I talked about carbs too.

One of which you have some minimum requirements but both will probably round out any person’s diet to some extent.

Yes I don’t really care if you eat ‘high’ fat or ‘high’ carb because outside of protein both work for different folks. What did I miss though?

Water on the table and in the ocean. Yes, I live in a beautiful place…

I’ll give you a hint, it makes up about 55-60% of an adult’s body weight.

It’s about 75% of a babies bodyweight.

Stumped still?

It’s 2/3’s of the earth’s surface…

Now we’re on the same page…


What is hydration?

Basically it’s the process of absorbing water. So in the human body it’s the balance between what you excrete every day and how much water you absorb or take in.

You could also say it’s the opposite of dehydration?

Dehydration occurs when the loss of body fluids exceeds the amount that is taken in. On a cellular level more water is moving out of each cell than is being absorbed via the water you’re drinking.

Basically a water imbalance, typically measured as a percentage.

Why Does It Matter?

Good water balance basically ensures good cellular function and that’s a true, if-not-hidden benefit.

Hydration does not directly contribute to muscle mass gains or fat loss.

The only way to gain muscle is to create a slight energy surplus combined with consistent progressive resistance training stimulus. You gain good weight by stimulating muscles regularly and having the energy (and sufficient protein remember) available to build those muscles.

The only way to lose weight is to create an energy deficit. You maintain weight by creating an energy balance, that’s what does it. Not water intake.

Water has no inherent caloric or energy value to the human body but it’s still a very important consideration. Especially for ‘healthy living’ and ‘sport or exercise performance.’

At a mere 2% dehydration[1][2] you will statistically lower strength, power and sport performance outcomes.

Hydration is highly important for renal (kidney) health.[3] A moderate consistent dehydration is a known contributor to painful kidney stones.

And of course dehydration at ~10% can cause death! Yikes…

Don’t try to go a few days without water. Mmm..kay? We’d all like you to stay alive.

Good consistent hydration levels are associated with[4]:

  • Maybe an increase in Thermogenesis
  • Non-Caloric Substitution
  • Better Neurological Function
  • Improved Skin Barrier Function
  • Better Renal (kidney) Function
  • Improved Digestion (Gastrointestinal Function – Better pooping mostly)
  • Heightened Cognition
  • Improved Mood
  • Reduced Fatigue Levels

Hydration Thermogenesis

I scoured this research only to find rather mixed results. The best and most recent work actually used a control group. The majority of the other research had no control group and was of lower quality.

That research suggests that previous experiments completely over-estimated the benefits of water consumption thermogenesis.

The best research found <3% increase in resting energy expenditure and a drop in respiratory quotient. Ultimately they determined that there was a sham effect for body composition and metabolic increases.

The effect is next to nothing. Not worth writing home to mom over.

The best effect of 500 ml of water consumption before eating is likely that it leads to fewer calories consumed at that meal. Along with better satiety.

Thermogenesis is basically the amount of energy it takes to digest something. Energy lost as heat, hence ‘thermo.’ When I talked about protein I talked quite a bit about the thermic effect of that type of food.

Basically a similar thing here but to a much lesser extent and more specific to the body’s temperature regulation, than the cost of digestion.

When you digest cold or hot water, even room temperature water, digestive processes may have some work to do to make that water the same temperature as your body (~98ºF or ~37ºC).

Initial and older research[5] showed some promise but the numbers are a bit misleading. A 24% increase in total metabolism when you consume 500 ml of water sounds bigger than it actually is.

That increase in total metabolism only lasts for 60 minutes, so the net total effect on metabolism is actually rather small.

Also only large amounts of water (~500 ml) at a time appear to have the effect. Smaller amounts of water like ~50ml at a time, do not appear to have the same effect on metabolism.

Another research paper[6] found that 500 ml of water ingested increased metabolism 30%, but it took 10 minutes for that to kick in, and it peaked within 30-40 minutes.

Again this number is somewhat misleading. 30% sounds huge!

In reality, this boost in metabolism amounted to a mere 100 kj or 23 kcal of energy utilized that day.

Again, only larger amounts of water appear to have this effect. 2 liters of water a day might yield an extra 400 kJ (95 kcal) in energy expenditure but there is reason to doubt that number.

Many propose that you have to drink this water above and beyond your actual requirements. Yet the majority of that research has only ever been done on those with obesity.

I’d argue that consuming too much water has risk associated relative to size. Leaner individuals may run more of a risk of hyponatremia at those quantities. I discuss that below under ‘Risks.’

Updated Research

Newer and higher quality research suggests that much of this older water thermogenesis research is poorly done or simply inaccurate.

Another better study[7] found that only cold water (3ºC) led to an increase in metabolism. The net effect was far smaller, only a 4.5% increase in total metabolism for 60 minutes. Maybe an extra 20 kcal for 2l of water, which is peanuts.

I say it’s a better study because it used a specific amount of water relative to the person’s size (7.5ml/kg).

This is a far better way to approach water intake and arbitrary recommendations like 2L a day are meaningless. They don’t factor a person’s size into the equation.

Maybe the metabolic increase is merely a sympathetic response.[8]

Maybe it’s blood pressure.[8][9]

Maybe (most likely) it’s a combination of all of those things…

However, the best and most recent paper[10] I could find suggests all that initial support is likely exaggerated.

They used updated methods and a control group, which none of the other research I could find utilized.

This research suggests that the thermogenesis effect is <3% combined with a drop in respiratory quotient. Indicating a bit of a contradiction and likely a cancelling out.

If the 30% research indicated a 100 kj (23 kcal) increase in metabolic rate per 500 ml of ingestion. Then this research indicates less than a 10 kj (2.3 kcal) increase per 500 ml of ingestion.

Basically next to absolutely nothing. Not worth your time. Don’t bother worrying about it.

Outdated research (5-9) is still being used to justify something that likely doesn’t work.

A Better Explanation

A better explanation for weight loss from drinking water before you meal is simple caloric displacement. Caloric displacement is when you displace higher calorie foods with lower or no calorie foods.

Consider that caloric beverages account for a significant portion of the US diet[11] (at least as of 2006). Reducing 5.4% of the average person’s energy intake by replacing high calorie sodas with non-caloric fluids like water, or plain black coffee/tea certainly helps people lose weight.

The other better explanation for weight loss is substitution via an increase in stomach volume. [12][13]

Consuming 500 ml of a non-caloric beverage before you eat improves your odds of eating less overall food.

Stomach stretching contributes to a feeling of fullness. Resulting in less food eaten during the meal and subsequently lower energy intake.

That could be population specific though as the effects don’t appear statistically relevant in young adults.[14]

Nervous System and Skin

A lot of people online will claim that hydration improves your skin health. Whatever that means…

It’s likely subjective. However, objectively staying well hydrated does improve your skin barrier function. Making a well hydrated individual’s skin more protective from the elements.

It also means less dry skin. However, this evidence is rather weak. [15]

Nervous system function is related to sport, exercise and cognitive performance. [16][17]

Good fluid balance contributes to better neurological function and firing. That means your muscles contract better when you want them to and your brain functions better when you need it to.

This is especially important for the elderly and the young.

Kidneys, Digestion & Hydration

Staying hydrated substantially lowers your risk for kidney stones and other related kidney (renal) issues.[18]

It also substantially lowers your risk of constipation. However, those with pre-existing constipation do not get a benefit from increased water intake.

We can get constipation for a variety of reasons, so low fluid intake isn’t always the culprit. Most of this research however is also done in children.[19]

Better Mood, Energy and Cognition

As already discussed improved neurological function improves neurological function and consequently cognition.[20]

Making you “smarter” and more capable of high capacity learning and work.

However, better mood and energy levels are also highly associated with good hydration. Less overall fatigue as a result.[21]

These have highly indirect benefits to body composition/weight and overall health.

When you’re in a good mood, you’re more likely to make better overall food choices and exercise choices.

When you have more energy, you’re more likely to want to be physically active. You’re also likely to sleep better.

One of the benefits of exercise alone, is that the improved mood/energy from it, indirectly improves food choices. Subconsciously, we eat better.

This often yields a lower energy intake and better weight loss outcomes.

Good mood = better food choices.

Good Energy Levels = more exercise, and a better mood

Less Fatigue = better decision making

Who feels like eating well or exercising when they are tired? Nobody…

Body Weight and Composition

There is a ton of misinformation on water consumption out there and it’s relevance to fitness, health and body composition.

The biggest misconception is that it somehow directly influences calories in some way shape or form.

Most research indicates that simply drinking more water (non-caloric fluids) doesn’t work on it’s own. Not without substitution, displacement or other indirect effects on energy intake.

The greatest impact of non-caloric fluid intake is indirect. The biggest impact is likely the calories it displaces from other sources.

It’s not the water intake so much as the food or sugary drinks it prevents you from eating and drinking. Or the reduction of total food you consume, after a large amount of water before your meal.[22]

Water preloading effects are most notable in people who are overweight or have obesity.[23]

Preloading with 500 ml before your main meals may be something to consider if weight loss is your objective. Especially if you are in that demographic.

However, leaner people are less likely to battle with caloric beverages and have smaller stomach volumes.

This preloading strategy doesn’t work for everyone trying to lose weight. It may not work for certain meals either. [24][25]

If you’re the kind of person who doesn’t drink calorie rich beverages. Then you won’t a direct effect on your weight simply from drinking more non-caloric fluids.

IF there is no substitution effect, then no energy deficit is created.

If you’re the kind of person who doesn’t eat a ton of food in one sitting. Then the added volume of 500 ml of water before food intake, might not help at all either.

‘Normal’ weight individuals tend to have smaller stomach volumes to begin with.

There may be one last indirect benefit. Thirst and hunger signals could be confused by your rational brain.

As a result some people might interpret thirst signals for hunger. Instead of drinking, you could end up eating more than you need.

Some hunger is a natural part of creating an energy deficit. It’s to be expected.

However, managing it is an important aspect for those with weight loss goals. Too much of it can undo a lot of your hard work with intense cravings.

Hunger is a big reason I recommend lean protein-rich foods with most meals or meeting your minimum fiber intakes. These things help manage hunger.

Staying hydrated is yet one more tool in your toolbox for managing hunger. If you’re hungry but you ate recently, try drinking some fluids. Maybe it’s thirst.

A person of a “normal” BMI/body fat % trying to lose ten or fifteen more pounds may not see any direct benefits from increased water consumption.

However, the improved mood/energy and minimized fatigue will still likely lead to better outcomes when practicing other skills.

It’s just important to know who benefits the most from pre-loading and caloric displacement. Before you go integrating the approach into your routine. Only to discover it may not be appropriate for you later.


Hydration has become a hot topic in the last ten or fifteen years. Tons of large public companies from Powerade to Gatorade are making a fortune on hydration.

These drinks may be applicable for athletes participating in sport for >60-90 minutes but the majority aren’t appropriate for the average person engaging in <60 minutes of exercise.

Even in athletic populations there are likely better options. Use sports drinks with care. Many are loaded with sugar, which is increases energy intake and lower satiation due to the liquid form.

Use caution with such drinks if weight/fat loss is your objective, or opt for the zero calorie versions if available.

A WORD OF CAUTION: You can consume too many fluids. It’s not just being dehydrated that is a potential issue.

Athletes, especially many amateur athletes were being told to stay hydrated were drinking too much water. As a result quite a few people died during long-distance endurance sports in the recent past.

The problem isn’t consuming too much water directly, it’s in the mineral imbalance too much water intake can create combined with physical exertion.

It’s called Water Intoxication (often resulting specifically in hyponatremia) or an imbalance of electrolytes.

Hyponatremia is specifically low sodium concentration of the blood. It’s more common in the heat or during prolonged exertion. Typically you see it in amateur endurance athletes.

Too much water, not enough minerals (electrolytes) can lead to some serious problems and yes, even death. Don’t assume you can totally off-set huge water intakes with increased electrolyte consumption either.

If your urine is perfectly clear all the time, you’re over-hydrated and you can stop drinking some water until your next urination.

Just as chronic dehydration could help you develop kidney stones or possibly something even worse.

If you regularly have dark yellow or even brown (reddish) urine you’re dehydrated. Drink more water. If it persists, seek medical treatment.

It’s about finding the right intake for you consistently. See my recommendations below…

Your summer intakes may be higher than your winter intakes. Consider the climate/weather and adjust daily, rather than just using an absolute number all the time. Greater protein consumption could also yield higher need for water.

General Recommendations

I hate the common water recommendations you see online:

  • Drink 8 glasses of fluids
  • Drink 2 litres of fluid a Day

These are far too generic. It’s like telling everyone to consume 2000 kcal a day.

If it helps you as a starting point, cool. However, don’t just stop there, you could drink 2 litres of fluid everyday and still be dehydrated or overhydrated.

Depending on where you live and your size they could be too much or not enough.

If you have a diet high in fruits/vegetables, these foods have a higher water content, so you may need less fluids in a day. People who consume more protein relatively speaking will likely need more fluids.

Any alcohol consumption can throw your fluid intake for the day off too. You may need more following intake or during intake.

Finally, you may also want to vary your intake throughout the day. There may be a high need to hydrate first thing in the morning but going to bed slightly dehydrated may reduce any late night peeing.

*I don’t often recommend drinking water before bed, unless of course you’ve had too much alcohol to drink. That’s another story altogether.

There can be quite a bit of variance as a result from person to person. You have to cater your fluid intake to your needs. Those needs change from day-to-day and week-to-week.

The best way to do this is to observe the colour of your urine regularly.

Yep, I’m sorry but get into a habit of checking the toilet bowl out when you’re done peeing. Look for these colours:

If you’re brown consistently for a while, please see a medical doctor.

Clear is too hydrated, you can stop drinking fluids for a while.

Brown or Reddish brown is a problem, you should drink a lot of water soon (up to a liter or perhaps even more). If that persists, see your doctor.

I prefer a more practical recommendation from physiologist Lyle McDonald.

Ideally most people have five solid pees in a day that are in the hydrated range. Just off-clear, with a slight yellow tinge.

Smaller people may urinate more frequently than that, a by-product of their size. And it’s possible that very big people urinate less frequently than that as a by-product of their size.

Doesn’t have to be perfect, just ballpark.

Further Considerations

I’d add that most people will pee first thing in the morning. Use the scale above to determine how much fluid you should immediately consume upon waking.

This is a rough recommendation and people are different. You may need more or less, so experiment with the quantity based on the colour.

I recommend having a good large drink first thing in the morning to rapidly elevate your hydration levels.

It says ‘sip water’ but truthfully any non-caloric (non-energy) form of beverage will do.

Particularly if weight loss is your objective. For weight gain, I’d make an exception for milk or a shake.

That means plain tea/coffee, even artificially sweetened beverages — I know…I know…you may have an opinion about those, but they still contribute to hydration.

After that, you should ideally have those five solid pees. If you have a smaller bladder, they may be more frequent, if you have a larger bladder maybe slightly less frequent.

To repeat what I said above: You just want to be in the ballpark.

Towards bed, if you want to stop drinking water a couple hours from bedtime, go for it. I’d even recommend it.

Especially if you wake up frequently during the night to pee. Slight dehydration and the fatigue it yields may even help you sleep better.

Please note that all fluids and high water content foods (fruits/vegetables) contribute to hydration status.

I apologize for anywhere I’ve used ‘water’ instead of the more ambiguous ‘fluids’ as all fluids contribute to hydration, not just water.

Despite popular opinion or the online myth that they dehydrate you, even caffeinated beverages contribute positively to hydration status. The small amount of fluid lost from the caffeine intake is still substantially less than the hydrated status gained from the fluid intake.

Lastly, thirst is actually a poor indicator of hydration status. I wish I could tell you just to drink when you’re thirsty. By the time you’re thirsty though, you’re likely already dehydrated.

It’s better to find a schedule or routine of sipping fluids throughout the day that works for you. Combined with monitoring your urine status.

This can be a process, but it’s worth it.

Trust me in the long run, it’s actually easier than worrying about how many glasses or liters of water you drank in a day.

You just observe and adjust.

Exercise or Sport Performance Hydration Recommendations

If you’re not an amatear athlete of some kind please ignore this section, it probably doesn’t include you.

The simplest thing to do to manage fluid loss with exercise or sport participation is to weigh yourself before and after participation.

Then you just drink the equivalent weight of fluids that you’ve lost. In such a short amount of time any weight lost will be water weight.

If you’re 1 kg lighter (2.2 lbs), then you need to drink at least 1 litre of fluid to replenish those lost fluids. If you’re 0.5 kg lighter, you need 500 ml of fluid.

1 g = 1 ml, or 1 kg = 1 l

For the metrically impaired: 2.2 lbs = 1 kg, 1 lb = 454 g/ml

If you’re exercising for longer than 60-90 minutes you may need to increase your fluid intake above your normal intakes. Especially in warm environments.

It’s unlikely that you’ll dehydrate yourself substantially during exercise less than that duration, so long as you keep with your consistent intake.

However, at longer durations or distances, fluid loss can outpace normal intakes. This can lead to levels of dehydration that decrease performance, without replenishment during that sport or exercise.

They may also impact recovery after training. The longer the sport/training, the greater the fluid considerations.

You will need to experiment with how much water you should typically drink during your training, depending on your sport. i.e. have a sip every few minutes or a few sips every 10 or 15 minutes.

Too much fluid at one time during exercise can lead to an upset stomach in some people. Anecdotally I find small consistent amounts best at a greater frequency.

Ideally you use a scale (before and after training) to determine right pattern of fluid intake for you, the training conditions and your performance.

If you weigh the same before and after exercise, then you maintained good hydration during training. Weigh less, and you likely did not hydrate well. If you weigh more obviously you hydrated too much.

Following exercise/sport performances most people will likely be a little dehydrated, even when well planned. Similar to your morning routine, there are benefits to rehydrating quickly after training.

Replacing your lost weight is a great minimum, but re-hydrating up to 150% of your lost mass may account for the continued fluid loss after you stop exercising.

i.e. ~1.5 kg of fluid replacement for 1 kg of weight loss may counterbalance the continued fluid loss.

Otherwise, you may need to continue an elevated fluid intake post-workout or post-training. Your body temperature will remain elevated, as will fluid losses, even after you stop training.

Not all fluids are the same in this regard. It sounds counter-intuitive but milk is typically shown as the best rehydration fluid following exercise. Assuming you can tolerate lactose.

Water is the worst, with sports drinks (like powerade/gatorade) shown somewhere in the middle. This is likely related to the additional nutrition and electrolyte content.[26]

Of course, in the absence of a scale, urine colour after training is still a good gauge of dehydration. It would be hard use as a gauge during exercise, because urination/digestion is slowed to divert energy to working muscles.


Being well hydrated (the opposite of dehydrated) throughout the day is generally a good idea.

Ultimately people who stay adequately hydrated throughout the day are less likely to make poor food decisions. At least as the result of low energy, mood or decision fatigue.

They are less likely to deal with kidney/renal disease. Yet more likely to crush their training sessions.

What you generally see with people who are well hydrated is better overall food choices, which drives better energy balance adherence.

I’ve found this to be most prevalent for weight/fat loss purposes. However, even those seeking more muscle mass are more likely to stick with their eating routine when they are well hydrated.

We know dietary adherence is probably the most important consideration for whether or not a person sticks with any given diet.

You’ll stick with something if you feel better about the process. Staying hydrated it a surefire way to make yourself far more consistent in that aim.

People make the erroneous conclusion that if some water is good, more must be better. This is not the case, you need enough water.

If your pee is regularly perfectly clear and you have to go several times above that five-times-a-day, you’re probably over-hydrated.

This makes you at risk for electrolyte imbalances. In extreme cases (typically when paired with exercise) can lead to health problems, even death.

You probably want to drink a big glass of water first thing in the morning to restore hydration lost while you sleep.

Then work yourself up to about 5 large, off clear, slightly yellow urinations over the course of the day.

Not that you should only pee 5x a day, but approximately five of them should be that colour.

You don’t want to be super hydrated before bed — and thus have to disturb your sleep to pee. It might take a little while in the morning to work up to that colour too.

This is contrary to typical recommendations but it better reflects changes to your environment. In summer you’ll need more fluids than in winter. Bigger people need more fluids. Stuff like that listed above.

If you opt for the standard 8 glasses or 2 l of water a day, please consider at least tracking the colour of your urine for a week. To make sure this amount is appropriate for you. You may have to drink more or less.

If you’re consistently dark yellow or brown, please seek medical attention!

If you have questions, please leave a comment…