Why is fluid important? Our bodies are made up of 50-70% water – it is found in every cell, tissue and organ. Our bodies need water to:
- transport nutrients in the blood
- help chemical reactions take place (eg: digesting food)
- replace fluid lost through sweating and breathing
- remove waste products through the urine.
Why is fluid important during exercise?During exercise, the body cools itself by sweating. This results in a loss of body fluid that can lead to dehydration if not replaced. Sweat production (fluid loss) differs for everyone and depends on factors such as age, genetics, clothing, body surface area, exercise intensity and the training environment – with increases in temperature, humidity and high-intensity exercise causing a higher rate of sweat loss, and therefore requiring a greater need for fluid replacement.
Dehydration and performance
Exercise performance can be impaired when an individual experiences even mild dehydration. The reason for this is reduced oxygen intake due to the cardiovascular system working harder to keep body temperature normal. This increase in heart rate and body temperature, with reduced oxygen intake, can make exercise feel more difficult (compared to training in a hydrated state) and mental fatigue can occur, bringing about lapses in skill level, concentration and decision-making.
But you can drink too much?
Drinking more fluid than required can also impair performance. A stomach full of fluid is certainly not comfortable when trying to exercise, and on a more serious note, over-hydration can dilute electrolytes in the blood causing serious side-effects such as headaches, disorientation and in very severe cases, coma or death. Please note this is quite rare and dehydration is a lot more common in exercising individuals.
How much fluid should I drink?
The amount of fluid you drink will depend on your individual needs. If you are a serious athlete, you should consult our GCP Fitness sports dietitian who can assist you with calculating your sweat losses and help you devise a hydration plan.
Before Exercise
It is important to start exercise in a hydrated state. An easy way to gauge this is to check the colour of your urine as per the image. If your urine is a light yellow colour, you are most likely hydrated. If your urine is darker, you’ll need to start sipping on fluids leading up to your exercise session. Between 200-400ml is a good start to help you commence exercise with an improved hydration status without feeling bloated from too much water.
During Exercise
“Drink to Thirst”, which means sipping on fluids as you feel is required. This will avoid multiple visits to the toilet and an upset stomach. Again, if you are a serious athlete, “drinking to thirst” may not be enough and a hydration plan may be needed.
After Exercise
The goal after exercise is to replace all lost fluids and electrolytes. One simple way to achieve this is to weigh yourself before and after exercise. If you weigh less after your session compared to before, multiply the difference by 125-150% and this is the amount of fluid you will need to drink over the next 4-6 hours to replace the fluids lost during exercise. In regards to electrolyte replacement, drinking fluids alongside slightly salty recovery snacks such as bread, milk or cereal, will help your body rehydrate more effectively. Another option is to drink a sports drink – especially if the session was over 90 minutes in length and/or in hot and humid conditions.
What are the best fluids to drink?
For short duration, lower intensity exercise, water is the best fluid option before, during and after exercise. If you’re exercising for over 90 minutes and/or in hot and humid conditions, sports drinks may be a better option due to their concentration of carbohydrates (for energy) and electrolytes (stimulating thirst and helping the body rehydrate more efficiently).
Two beverages that are not good to drink around exercise are alcohol and energy drinks. Alcohol is a diuretic (causing us to urinate), so drinking it before exercise will set you up for dehydration and prevent rehydration if consumed after exercise.
Energy drinks are another poor fluid choice due to their higher carbohydrate content, which can cause stomach discomfort during exercise. Also, while a small amount of caffeine via a coffee per se, may help you feel more alert and energised for exercise, a recent study found the caffeine from energy drinks results in more profound changes in heart rate and blood pressure, which could have serious consequences in regards to performance and health. This could be due to the other stimulants in energy drinks. (For more information on caffeine, check out our previous article titled “Caffeine and Performance”).
Take home message
While many athletes and fitness-lovers focus intently on training and nutrition, it is imperative that hydration is not forgotten as the consequences of dehydration can be quite serious. Sipping from a water bottle continuously throughout the day is one of the simplest and most effective ways to stay hydrated. Set alarms on your phone if need be to remind yourself, or drink a glass of water before every meal. Your body really will thank you for it!
If you have any questions, or would like to schedule an online consultation with our dietitian, feel free to contact Hannah at hannah@gcpfitness.com.
References available upon request.