It’s always essential to ensure good hydration – even more so when you are regularly working out. It’s unlikely that anyone working out in the gym or classes should need anything more than water to re-hydrate, but read on to find out a little more about how much we really need to drink. Adequate hydration is crucial for good health, and critical to mental and physical performance. The human body is over two-thirds water weight, and whilst 2% dehydration will begin to affect our mental performance, 4% dehydration can affect aerobic performance by up to 25%. Water is involved in almost every metabolic reaction in the human body. It lubricates the eyes and joints, facilitates digestion, keeps the skin healthy and flushes out waste and toxins through the kidneys and sweat. Surveys have reported that less than 1% of people meet fluid intake recommendations, and 20% of GP visits are with symptoms such as tiredness and headaches, which can be caused by dehydration.
So how much should we be drinking? The NHS Eat Well Guide states that we should drink six to eight glasses of fluid daily, based upon original recommendations from the Food and Nutrition Board (1945) that we consume one ml of water per calorie consumed. The Institute of Medicine recommends 3.7 litres for men and 2.7 litres for women. However, a more accurate guideline is based upon an individual’s body weight. The Oxford Handbook of Nutrition and Dietetics (2012) recommends that we consume 35ml of fluid per kg body weight, but all of these recommendations are not taking account of the fluid consumed within our diet, from, for example, high water content fruit and vegetables, milk or soup. However, if your diet is not meeting the recommended 5 (to 10) portions of fruit and vegetables per day, your diet is less likely to be contributing much to your fluid requirements. For exercising individuals, the American College of Sports Medicine (ACSM) provides guidelines for re-hydration during and after exercise, as fluid requirements are higher for anyone engaged in regular activity. Although replacing weight lost through exercise at the rate of ‘a pint for every pound of weight lost’ is relatively well known, Evans et al. (2017) suggest that volume replacement during recovery should exceed that lost during exercise to allow for ongoing water loss, and that the addition of sodium, carbohydrates and protein to a rehydration solution is beneficial for fluid balance and maintenance, due to the effects on fluid distribution, extracellular osmolality and blood volume. In other words, less water is lost in urine formation when taken in the form of ‘liquid food’ or with food. For the average exerciser replenishing fluids during and after activity, water should usually be sufficient, but if sweating has been excessive or the exercise session longer than 90 minutes duration or particularly strenuous, an isotonic/electrolyte drink should be considered. However, after this period of time exercising in conjunction with not eating for a while beforehand, a meal of some sort is likely to be on the cards, which would provide the recommended carbohydrates, protein and electrolytes without them having to be present in hydration replenishment.
Can I drink too much? Hyponatremia is when there isn’t enough sodium compared to the water content in the blood. Sodium is essential for many essential bodily functions including nervous impulses, maintenance of fluid balance and maintenance of blood pressure. Hyponatremia is usually caused by excessive consumption of water without correcting electrolyte loss, often after endurance or strenuous exercise. A study published in the American Journal of Physiology (2002) and a further study in the Journal of the American Society of Nephrology (2008) demonstrated no significant health benefits of drinking the recommended 8 glasses of water daily. However, the kidneys do an excellent job of filtering and secreting excess water from the body, so surely it’s better to keep our organs and internal environment well watered for optimum health and performance, rather than accept sub-optimum existence or run the risk of ill health?
Best options for hydration – hypotonic, isotonic or hypertonic? Hypotonic drinks contain a lower level of solutes (sugars, mineral salts) than human blood. These types of drinks, such as water, are best for general on-going rehydration. Isotonic drinks contain 4 – 8% of solutes in solution, the same concentration as in blood (hence the prefix of iso-). The isotonic solution can enhance absorption across the intestinal and capillary membranes into the bloodstream, re-hydrating and replenishing mineral salts and sugars more quickly. Although not necessary for the average exerciser, these drinks can be useful after prolonged or very strenuous activity. Hypertonic drinks are those that contain more than 8% solutes, and include most carton fruit juices, which are usually 10% sugar, fizzy drinks and sports gels. These require digestion and are best for replenishing carbohydrates after sport or activity, rather than for rehydration purposes. However, you can use juices to make your own isotonic drink – just mix 50% fruit juice (containing 10g per 100ml sugar content) with 50% water, and you have diluted the sugar content down to 5%, creating your own isotonic drink.
Tips for meeting your fluid needs:
- Start the day with a drink of hot water rather than a caffeinated drink, which stimulates urine production and therefore fluid loss. Add a squeeze of fresh lemon/lime, or a drop of red grape juice or apple juice if you need a little flavour.
- Fill a 1.5 or 2 litre bottle and take keep it with you at work/home – drinking from this through the day gives you a measure of how much you’ve drunk, and having the bottle in front of you will remind you to drink regularly.
- Keep smaller water bottles in the car or in your gym kit bag, so you are never caught out without water to hand.
- Always take a filled water bottle to your exercise session (and drink it!).
- Sip fluids throughout the day – hydration is achieved more successfully in this way, rather than drinking a large amount quickly.
- Drink herbal or fruit teas through the day as these will hydrate you rather than act as diuretics like tea, coffee, hot chocolate and many energy drinks. A diuretic such as drinks containing caffeine stimulates urine production as a result of the caffeine prompting adrenaline release and the resulting increase in blood pressure. An increase in blood pressure is corrected by releasing more fluid from the blood via urine production, hence promoting the loss of fluid and electrolytes.
- Alcohol is also a diuretic as it switches off the release of anti-diuretic hormone from the posterior pituitary gland, so you need to drink more water whenever you consume alcohol.
- Consume foods with high water content such as fresh fruit (not dried) and vegetables.
Adequate hydration is achieved when the volume of urine produced matches fluid intake, or when the colour of urine is a pale straw colour – an easier way to monitor hydration levels!
Thanks for reading; all likes, shares and comments welcome. See you in the next one!
Guest post by: Sara Kirkham BSc. (Hons) Nutritional Medicine, MBANT, CNHC
For more advice on weight loss, sports nutrition or nutritional therapy for health call 07919 110440, email firstname.lastname@example.org or visit www.nutrition.org.uk