Many of us fasting through the month of Ramadan can attest to the annoying feeling of needing to get up to pee through the night and generally throughout the day.

Muslims observing the holy month refrain from eating from just before the sun rises until it sets, which means packing in all the hydration before fasting commences. That can leave us needing to run to the loo a lot more, of course.

But many Muslims will also notice frequent urinating through the fasting day too, despite not actually drinking anything.

So why do we need to pee so much? Surely what goes in has already come out by a certain point?

Well, just because you’re not drinking doesn’t mean the bladder’s job is done.

Dr Gareth Nye, an ambassador for the Society of Endocrinology, tells HuffPost: “So the bladder is actually the ‘waiting room’ of our urinary tract where urine is stored before we go to the toilet. To look at changes in urine output or how much we do/don’t wee, we need to take a step back and look at the kidneys.

“The kidneys are involved in filtering our blood. It takes toxins and waste products and keeps the useful products the body needs to keep. One of the main filtered products is water which can be let go or kept in different amounts based on our body’s needs.”

So, on average, water makes up about 60-70% of the human body, largely depending on your age. Our bodies lose water through our urine, sweat, faeces and breath, so we have to continually replace this by drinking and eating (around a third of the water we consume comes from our food). If we don’t do this, our bodies can become dehydrated.

But we’re dehydrated, which means less pee right? Not necessarily.

Dr Nye explains that the bladder still needs to flush to out toxins, even when you’re dehydrated, thus creating more urine.

You might even notice a different colour in your pee when you fast.

Dr Nye adds: “The first stage of dehydration is thirst, which kicks in when 2% of body weight is lost. The signals that tell our brain we are thirsty also act on the kidneys to send less water to your bladder, keeping the water within the body and darkening your urine. You do need to flush out the toxins and so your body still produces urine even if you are dehydrated.”

You might notice other changes too in your urine while fasting.

“The key thing is, our bodies can go quite a long time without drinking and show no change in our urine output. Regularly when we sleep we can go eight-10 hours without taking any fluid on board and when you do drink/eat your body will replenish. You may notice changes in concentration as you go through the day as the amount of available water drops.”

So when iftar comes round, don’t forget to drink up (though you will feel the effects of it later).