As a dietitian I am often asked questions regarding water and fluid intake generally e.g. how much should I drink? Does tea and coffee count? And what about carbonated beverages? Where do they fit in?
Interestingly, guidelines around the world are different. The American Institute of Medicine gives guidelines suggesting women need approximately 2.5 litres per day of fluid and men need just under 3 litres. The UK government suggests 6 – 8 glasses per day for women and men, or 1.2L – 1.6L. Both institutions base their guidelines on the science of not becoming dehydrated as fluid is needed to keep our bodies functioning properly. We all get some of our fluids from foods that we consume, about 20%, think yogurt, custard, and sauces.
So how much fluid should I drink every day?
We are all somewhat different and what we need is determined by 3 things.
How much we eat.
If you eat a lot of food then you need more fluid to support the metabolic processes associated with a high intake. If you eat less, you can drink less, but you still require a minimum of the recommended 6 glasses or 1.2L of fluid in the day. You may have noticed becoming particularly thirsty after a large meal if you did not meet your fluid requirements before, during or immediately after the meal. You might also notice this if the meal was particularly salty.
What the weather is like
If you have been on a hot holiday you will recall how much thirstier you are than normal. This is because your body is working hard to keep you cool. As your body heats up due to the sun, your body initiates sweating to bring water to the surface of your skin to help cool you down. The sweat evaporates off the surface of your skin so you need to replenish the fluid you have lost. Hence we drink more when on a hot holiday. Even the humidity of a country can affect how much we drink as a high water content in the air can make it more difficult for our sweat to evaporate, you also notice this in the sauna, where you become exceedingly thirsty as your body struggles to cope with the heat.
How much activity we do
In a similar way to being on a hot summer holiday, being more active than usual involves burning up more calories than normal. This process creates heat internally which needs to be gotten rid of – we sweat, losing fluid from the surface of our skin, which of course needs to be replenished.
So now what should we drink?
Consider the options: water, tea, coffee, milk, juices, and carbonated beverages can contribute to our daily intake of fluids.
The Harvard School of Public Health has helpfully put these drinks into a list in just the above order. Ideally, drink about half of your fluid requirements as plain and simple water to take you to a healthy hydration status. Tea and coffee come next on the list with interesting evidence coming out regularly around the health benefits of these delicious drinks. Lower fat milks are an excellent way of getting fluid and other nutrition with a suggestion of one to two servings per day (250ml – 500ml) helping to meet your calcium needs. No more than one small glass (150ml) of juice per day is a good idea, particularly if weight management is topping your priority list. Lastly we have the carbonated beverages which although some may imbibe and consider delicious should really be drunk as a treat. The reality is that these fizzy drinks (diet and ordinary) are not contributing anything to your healthy diet and in fact may be doing some harm. It is possible that fizzy drinks may stimulate high sugar cravings encouraging us to seek out sugary and high carbohydrate foods.
Am I properly hydrated?
There is a simple test for this. Check the colour of your pee the next time you go to the loo. A straw like colour is good news but if your pee is coming in a darker shade of yellow you need to drink more.