Why eight glasses of water?

Every thing you read nowadays particularly many of the new diet theories state that you must drink eight glasses of water a day. I’ve always been curious about this theory particularly in relation to weight reduction and weight control. So I decided to look into what the experts say on the subject.

Water is your body’s principal chemical component and makes up about 60% of your body weight. Water flushes toxins out of vital organs, carries nutrients to your cells and provides moisture for many tissues. Lack of water can lead to dehydration and even mild dehydration can drain your energy and make you tired. We lose water through our breath, perspiration, urine and bowel movements and for our bodies to function we need to replenish its water supply by consuming food and beverages that contain water.


Glass of water


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In 1945 it was published as part of dietary guidelines by the Food and Nutrition Board of the National Academy of Science that 2.5 litters of fluid should be ingested on a daily basis. No clinical study was ever cited in relation to this published guideline. It was then later put forward by the influential nutritionist Frederick J. Stare that humans would benefit from consuming six or so glasses of water a day. He was the first to recommend this.

So from then on the concept that normal healthy people should drink eight glasses of water a day became commonplace. This was based on those living in a temperate climate, those with a moderate lifestyle and those on a modern diet. Many medical practitioners began to claim that a lack of water was responsible for many preventable diseases. Recent studies have also stated that adequate hydration can keep kidney disease at bay and give our cognition a boost.

Studies have also stated that those who engage in long bouts of exercise need to increase their fluid intake to compensate for fluid loss to reduce the chance of developing hypernatremia which can be life threatening. For many people the body can require extra fluid intake in hot weather due to sweating. In winter a body may also require extra fluid due to heated indoor air as this can also cause your skin to lose moisture requiring extra fluid. Altitudes over 2,500 meters can result in rapid breathing, being at this altitude or over can cause some people to use up more fluid reserves and therefore require extra fluids.

Health conditions such as fever, vomiting or diarrhoea also depletes the body of fluids and in these cases it is important to also drink more fluids. For certain medical conditions such as bladder infections or urinary tract stones additional fluid intake is required (subject to medical recommendation). Some studies have shown that drinking lots of water can reduce the incidence of cancer of the bladder, colorectal cancer, urinary tract infections and urinary stones.

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Other health conditions such as heart failure, some kidney, liver and adrenal diseases may require that fluid intake is limited. And although rare it’s possible to drink too much water affecting your kidneys ability to excrete the excess water.

Around fifteen years ago the world was flooded with bottled water and many health conscious people turned to the commercially available (expensive) bottled water. That’s what the marketers wanted us to do. You only have to look at the available brands on the market to know that the promotion of ‘drinking 8 glasses of water a day’ has worked especially for the manufacturers of bottled water.

What you eat actually provides a significant proportion of the fluids you need. Our food on average provides 20% of our total daily water intake. Many fruit and vegetables such as tomatoes are 90% water by weight, and all the other beverages you drink contribute as well to your daily fluid intake. A survey found that the average diet does normally provide sufficient daily fluids; women usually take in about 2.8 litres of fluid a day and men take in about 3.4 litres. Generally if you drink enough fluid so that you don’t feel thirsty you will produce 1.5 litres or more of urine a day demonstrating for the average person that their fluid intake is adequate.

So how much extra water should you drink in a day?

It really depends on the individual but in my opinion if you don’t have any medical conditions that require you to limit your fluid intake I suggest those who are trying to control their weight try to:

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  • Drink a glass of water with each meal
  • Drink a glass of water between meals
  • Drink water before, during and after exercise

As we all know water is kilojoule free and inexpensive (or free) and can make you feel fuller so in a way it’s a dieter’s friend, that’s if you can make it your beverage of choice!

There is no easy formula except knowing your body’s needs for extra fluids. This will help you estimate how much extra water to drink daily. xxx CaroleL


Do you make sure you drink enough water? What creative ways do you have of keeping your fluids up?

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Check out your BMI if you don’t know it. It can be calculated at: www.health.nsw.gov.au 

If you would like me to cover any particular topic in this column please email me at [email protected] 

Anyone with a BMI over 25 and over the age of 60 should really look seriously at devising an eating plan that has reduced kilojoules. You need an uncomplicated plan that can also fit in with your lifestyle, and one that you can adapt if necessary for unavoidable social events.
Please note that Carole is not a physician, dietician or nutritionist. If a reader has any issues about their weight that are medically related then a professional opinion should always be obtained before embarking on any changes or restrictions to their diets.