We have heard it all before about how important hydration is to so many aspects of life; health, body composition, performance, concentration. But for some reason it always seems to get neglected. Humans can survive weeks without food but cannot normally go without fluids for more than a few days.

The overall weight of the human body will be on average around 60% water (age & gender dependant). Yet we still underestimate the importance of hydration. In some ways it’s a similar scenario to sleep and recovery. We’ve all heard the dangers of a lack of sleep, yet we still stay up binge watching Netflix.

The purpose of this blog isn’t to scare people into glugging down 8 litres of water a day. It is to understand the basics of the importance of hydration on fat loss, general health and our brains abilities, and understand how we can make some quick improvements.

Water plays a vital role in a number of essential bodily functions. It is present in the process of most chemical reactions in the body, swallowing, lubricating joints, regulating body temperature, hormonal balance, helping the nervous system function and getting rid of waste products. And of course, we have all had a horrible headache before, then once we have some water it disappears.

If Adam Sandler has taught us anything from his movies, it’s the importance of high-quality H2O!


Sounds like a silly question. “Well it’s water, isn’t it?!”.

The main component in maintaining hydration levels is of course water. Water or fluid is also the craving we get when we are thirsty. But there are other components involved in maintaining a healthy hydration status. For example, we get on average around 20% of our fluid intake through food (depending on what food we eat). Many of the nutrients in our intake also have a significant effect on hydration status.

The main components involved are salt (sodium chloride and bicarbonate), potassium, magnesium and calcium. These solutes are what determine our osmolality, which is essentially the concentrations of these solutes in our intracellular and extracellular fluid.

Intracellular fluids are the fluids found inside our body’s cells, extracellular are the fluids found outside our body’s cells. We won’t get too into this detail, but the concentration levels of the solutes mentioned, or osmolality, is also a very important part of our hydration status. Too much or too little of them can also lead to dehydration of some kind.

Therefore, hydration isn’t just about drinking lots of water, it’s also about getting the appropriate amount of these nutrients. This has a vital role to play in the function of the skeletal system, and the moving of fluids and nutrients into and out of cells.


The human body is defined as mildly dehydrated when there is 1% or greater loss of body mass due to fluid loss. Therefore, for a 90kg person, they would be considered dehydrated if they lost 0.9kg of body weight, during exercise for example.

This may sound like quite a lot, particularly if you were trying to lose 0.9kg of fat! But research has shown that the human body can lose this 1% of mass after just 13 hours of consuming no fluids. Research has also shown that we can lose up to 2% in just 24 hours. I imagine at one point or another we have got to the end of the day and realised we have barely eaten and not even had a drink.

That 2% body mass loss from lack of fluids can have some pretty negative effects. Headaches and symptoms of fatigue begin, cognitive function is impaired, so we struggle to perform day to day tasks and concentrate on work. Physical performance begins to reduce too, which we will discuss further.

The long-term consequences of chronic dehydration have also been researched. Maintaining good hydration levels has been shown to reduce the incidence of kidney stones, coronary heart disease, asthma and hypertension. Although more research is required on the long-term effects of dehydration, particularly on certain cancers. It can also be tough to measure long term fluid intake, but the warning signs are there.


The biggest effect we see from lack of hydration is in physical performance. The 2% drop in body mass we discussed earlier has been shown to reduce endurance performance, increase fatigue, decrease motivation and an increased perceived effort. On top of this, during exercise, just drinking when you are thirsty is not enough to stay adequately hydrated. That is why it is important to keep sipping away at fluids throughout the day prior to exercise, but also continue to drink during intense exercise, regardless of whether you feel thirsty or not. This is most relevant when it comes to training in warmer climates of course, and environments where we lose more fluids through sweat and heavy breathing.

Our cognitive performance is also compromised through dehydration. This is possibly the area that affects our day to day living most. Mild dehydration (2-3% loss) can disrupt our mood, decrease concentration, alertness and short-term memory function, particularly in the young and elderly.


As previously mentioned, fluid has a vital role to play in many bodily functions. Did you know that having low fluid levels can even increase your chance of constipation? It is a common treatment to be recommended to those suffering. However, increasing fluid levels only helps this scenario if you are dehydrated.

There is a broad association between chronic dehydration and an increased level of the hormone angiotensin II. An increase of this hormone is linked to many chronic diseases, such as obesity, diabetes, cancer and cardiovascular disease.

Our kidney function also becomes impaired through lack of hydration. The kidney is a key component in removing waste from the body, and regulates the bodies water balance. Adequate fluid is vital for the kidney to perform its task of filtering waste from the bloodstream and excreting it from the body.

Next up, the heart. The way in which the heart may be affected by dehydration is through a decrease in blood volume. Blood volume may be lowered by a loss of body water, normally seen through exercise or lack of fluid ingestion. This, along with moving from laying down to upright, can lead to an increased heart rate and a drop in blood pressure. Fluid intake can help to alleviate this pretty quickly.

Dehydration can also have an effect on our mental health too. The main mechanism for this is the direct link to the stress hormone (cortisol), where it has been shown that even mild dehydration can increase levels in the body. The indirect repercussions of this can be just as harmful, however. This increased feeling of stress can lead to making poor decisions when it comes to nutrition, lower our motivation to exercise and eat well, and make us feel more tired in general.


This is something we regularly stress to clients when they start working with GWD Performance, and it is possibly the point that gets met with the most scepticism. How can consuming more water help with fat loss?

A 2014 study was conducted on overweight females. The participants were instructed to continue their food and fluid intake as normal, but to drink an extra 1.5L of water per day; 0.5L 30 minutes before breakfast, lunch and dinner.

Despite the increase in fluid intake, at the end of the 8-week study on average there was a significant reduction in body mass, body fat percentages, BMI, and there was also a reported suppression of appetite.

Another 2003 study looked at the effect of having water with a meal compared to various different beverages, including milk, juice and sugar sweetened beverages. Having the various beverages increased total energy intake by anything between 5 and 25% compared to having just water.

There are other mechanisms by which staying hydrated can help with fat loss and body composition levels. The study discussed above showed that consuming more water prior to eating can help to suppress appetite and help prevent overeating.

For someone that tends to consume calories from fluids (fizzy drinks, juice etc.), consuming more water can prevent you from doing just that. The more water you consume, the less thirst you will feel for these calorific drinks, and therefore can naturally reduce daily calorie intake, all by just making a slight change to a habit.

As discussed previously, our kidneys are vital to us removing waste from the body. Adequate hydration is very important in keeping our kidneys working effectively. The simple process of urinating is a removal of waste, and of course water intake has a huge role to play in that, too. This, combined with all of the general health benefits of staying hydrated, are going to keep the body optimal for exercise and energy levels. The more we feel motivated and energetic, the more we are going to want to train and stay active. That raised activity level can help to create a more effective energy balance for fat loss.

The healthier you are, the more your body and mind is prepared to stay active, positive and motivated.


This is a tough one because every persons fluid intake will be unique to them. But there have been a few changes to recommendations over the years, mainly due to poor guidelines previously.

US guidelines, for example, were based on the average amount of fluid intake of the population and did not take into account whether that population were dehydrated or not! We always say as a general rule of thumb, on an average day, females should consume at least 2.5L of water per day and males at least 3L per day.

If we take weight into it, I would recommend consuming 20ml per pound of body weight. So therefore, if you weigh 150lb (around 68kg), then you should be drinking 20mlx150, which equals 3L per day. This may work out a little more than our general numbers above but is a little more accurate based on a persons weight.

However, there are so many factors involved in hydration levels. Activity levels can be a factor, how much we sweat, air and body temperature, what type of foods are consumed, the list goes on.

With all the technology out there these days, the best way to self-measure hydration levels is the good old-fashioned way; urine colour! You can get colour charts to do a daily check to make sure you are hydrated, it’s not the prettiest way but it’s great instant feedback to make changes quickly if you need to.


  1. Always have a water bottle with you. It’s so easy to not drink when you don’t have one available all the time.
  2. Try the water bottles with time markers on. They may look a bit gimmicky, but it gives you a target to aim for all the time.
  3. Keep chipping away at your daily target. Don’t rely on glugging down 1L at a time, keep sipping throughout the day.
  4. Start your day with a glass of water and get ahead of your target from the off. Sip down 500ml when you wake up, it may also help to wake you up (especially if it’s cold).
  5. Have a glass of water 30 minutes before your main meals, it may help to suppress appetite.
  6. If you’re exercising, take that into account and try to get more fluids in BEFORE you exercise, rather than trying to play catch-up after.
  7. Add some flavour. Squeeze a citrus fruit into your bottle or add some berries to add a bit of taste. Even a little bit of squash is fine if it means you drink more.
  8. Don’t forget your electrolytes. We mentioned it in the blog, these are vital to keeping hydrated too.
  9. Keep checking your urine! If it ain’t clear, it ain’t right.
  10. Caffeinated drinks and alcoholic drinks can have a slight diuretic effect. If you’re drinking them, make sure you have a glass of water along with them.
  11. Try and drink most of your fluids before the evening. Nobody wants to be getting out of bed 5 times a night!


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