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Research Review:
Water and weight loss


Glug glug glug… ahhh.

Sorry, I was just finishing off a glass of dihydrogen monoxide.

Where did I get it? From a top-secret lab – okay, not so much… actually from my tap.

I’m sure many of you have caught on that dihydrogen monoxide is H2O, or good old water. And according to media reports, it might be the next big weight-loss supplement.

Grab a drink and let’s talk.


What water does

Pretty much everybody has heard that their body is over 60% water. Thus, if you weigh 150 lb (68 kg) then 90 lb (41 kg) if you is water.

Why don’t you hear a lot of sloshing when you walk around with all that water? Well, even though water is in your blood and other bodily fluids that are liquidy, a lot of that body water is in your cells or attached to molecules like proteins and carbohydrates (1).

Water does seven main things in our bodies

  • transporting;
  • dissolving;
  • cleaning;
  • reacting;
  • padding; and
  • regulating temperature.


Even though water isn’t coursing through your veins and arteries the way it runs through a river, it does transport things to and from the cells of your body, such as:

  • nutrients and oxygen that are important for the cell to grow and repair itself
  • important messages from hormones
  • cell waste products, like carbon dioxide


As a toddler, perhaps you discovered a key function of water when you dropped mama’s sugar bowl, full of sugar, into the toilet bowl. (Or maybe that’s just my kid.)

Yep, you discovered that water is a solvent and it dissolves sugar as well as most things. Water is a nearly universal solvent.

The one thing water can’t dissolve are lipids (fats, oils, waxes, etc.) but your clever body can surround water-insoluble molecules with proteins so they can be transported in water.


Every time you wash your hands or take a shower, you take advantage of water’s function as a cleaner. While there’s no soap inside your body (unless you swear, perhaps), water flushes important filtering organs like the kidneys and liver that remove toxins from our bodies.


Water is an important molecule of most of the body’s chemical reactions, but in some cases it has to be broken down, or hydrolyzed, during some chemical reactions. When sugar (sucrose) is digested into fructose and glucose, water is also a part of the reaction and is hydrolyzed.


Water is the major ingredient in body fluids that — even though icky — are very important to moisten and lubricate our bodies.

Even when we breathe, we need water-based lubrication, called surfactant. Otherwise each breath would feel like we’ve collapsed a lung. (One of the major challenges for premature babies is that they haven’t yet developed lung surfactant.) Joints and the digestive tract also need water-based lubrication to work properly.


You probably don’t think of water as padding or a shock absorber, but that is exactly what it does for your joints.

Your joints contain sacs filled mostly with water. When you jump, punch, fall or even move, these sacs prevent the two ends of the joint from smashing into one another. Between the vertebrae of your spine, water makes up the filling of your vertebral discs that allow you to bend, twist and jump without agony – just ask someone with degenerative back disease how important it is to have water in your discs.


Going for a run up a hill during a July noon in Texas makes you appreciate water. You’ve probably already figured out that sweating buckets helps regulate your temperature.

Yet water does more than just make up sweat. Water in blood vessels at the surface of your skin can help get rid of heat from your body, kinda like how a radiator works. Cooling fluid (blood) goes from the engine (major organs, heart, liver, lungs, kidneys, etc.) to the radiator (skin) where heat can be dissipated.

Research question

Clearly (get it?), water is important stuff. But can it help us lose weight? That’s the question we address this week.

Dennis EA, Dengo AL, Comber DL, Flack KD, Savla J, Davy KP, Davy BM. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity (Silver Spring). 2010 Feb;18(2):300-7.


In this study, the researchers recruited men and women between the ages of 55 and 75 years old that were overweight or obese (BMI between 25-40 kg/m2).

Researchers excluded recent yo-yo dieters. That meant the participants’ weight had to be the same, within 2 kg (about 5 pounds) for the last year or longer. Participants were also excluded if they had:

  • a history of depression
  • diabetes
  • uncontrolled high blood pressure
  • heart, lung or kidney disease
  • a history of eating disorders


Before the study started, everybody had to come into the lab twice: once to eat as much food as they wanted, and once to drink 500 mL of water and then eat as much as they wanted.

Researchers wanted to see whether people would eat less if they drank water before a meal. 12 weeks later, at the end of the study, the participants did the water-drinking test again.

Caloric intake

After the initial lab visits, researchers put all the participants on a diet that permitted 1200 kcal/day for women and 1500 kcal for men. Since the average male participant was around 90 kg, 167 cm tall, and 62 years of age this seems a bit restrictive.

What do I mean? Well, let’s look more at basal energy expenditure. This is the amount of energy that your body needs to be alive, and fuels things like breathing, your heart’s beating, and your cells absorbing nutrients.

How to calculate basal energy expenditure


66.5 + (13.75 x kg) + (5.003 x cm) – (6.775 x age)

Thus: 66.5 + (13.75 x 90 kg) + (5.003 x 167 cm) – (6.775 x 62 years)

=1709 kcal/day (or 209 kcal/day more than they were eating in the study)


655.1 + (9.563 x kg) + (1.850 x cm) – (4.676 x age)

=1531 kcal/day (or 331 kcal/day more than they were eating in the study)

Source: Harris J, Benedict F. A biometric study of basal metabolism in man. Washington D.C. Carnegie Institute of Washington. 1919.

Looks like the caloric allotment in the study fell a bit short.

Remember, these are calories needed to live if people are comatose — doing absolutely nothing but staying alive… no going for a walk, no standing washing dishes, not even getting up to go to the washroom. Just basic physiological functions are included here.

Water for weight loss

Everybody was on the same diet, but half the participants had the secret pre-meal supplement – 500 mL water.

Before each of their three meals, the water group drank 500 mL of water and then they could eat. There was no other difference between groups for the 12 weeks of the study.


Eating fewer calories than you need causes weight loss; mostly fat but some lean body mass too.

Over the 3 months the water group dropped 4.4% body fat (from 39.9% to 36.5%) and 5.4 kg total fat while the nonwater group only dropped 1.1% body fat (from 41.0% to 38.9%) and 3.3 kg of total fat.

And remember the gluttony testing — you know, the one where the participants ate as much as they wanted with or without drinking 500 ml before eating — well, if they drank water before a meal, they ate less (about 50 kcal less), but only before the study started; after the 12 week diet, drinking water didn’t affect how much calories the participants ate.

One explanation is that everybody was eating less per meal without drinking water (541 kcal before and 506 kcal after the 12 weeks). Or there may be a certain amount of calories the body requires and it can’t be fooled by being filled with water.


Drinking water (500 mL or about 16 oz) before three meals a day while on a diet increases fat loss in overweight and obese individuals.

Doh! Haven’t we’ve heard this before? Yes and no.

Yes, nearly every diet plan or nutritionist will tell you to drink more water to help you lose weight and no, because this is the first scientific study that randomly assigned participants to comparison groups to see if water helps with weight loss and if so, how much more weight would be lost.

Why water helps with weight loss may be obvious. Not only does water make you feel fuller, so you eat less, drinking water also replaces energy-containing drinks like juice, soda pop, and vitamin water. People on average drink over 400 kcal/day in North America. Water may even increase metabolism.

A few years back, a study found that if you drank 500 mL of water, your body would use 24% more calories for 60 minutes after drinking water. The researchers figured that this was because of changes in osmolarity caused by drinking water and that your body has to expend energy to bring everything back in balance (2).

Bottom line

Drinking two cups of water before a meal will keep you hydrated, fuller, and may even boost your metabolism for an hour. And all you need to do is turn on your tap. Talk about convenience.

Before you go off to your favorite vitamin shop to try the latest weight-loss supplement, try drinking two cups (500 mL) before you sit down for a meal.

Oh, and make sure you’re near a toilet.

Eat, move, and live… better.©

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Click here to view the information sources referenced in this article.