#071 Do You Really Need 8 Glasses of Water Daily?

February 2nd, 2015 by

Do You Really Need 8 Glasses of Water Daily?

Your mother probably told you to drink 8 glasses of water each day. Many health “experts” also recommend getting at least 8 glasses (64 ounces or about 2 liters) of water each day.

Are you wondering if there’s actually any science backing up this advice?  Just how much water should we be drinking to lose weight and maintain optimal brain and heart function?

What the Science Tells Us about 8 Glasses of Water

You might be surprised to learn that there are actually no medical studies backing up the practice of drinking 8 glasses of water each day.  While there have been studies done on this subject, none of these studies to date have shown any significant benefit.

If there are no data supporting the medical need to drink 8 glasses of water each day then the question naturally arises, how much water should you drink?  The simple answer is, it depends.  In this article we will explore possible reasons why you may want to increase your water intake depending on your weight, brain, and heart goals.

How much water should you drink to stay hydrated?

It appears that the amount really depends on the individual person, where they live, and how active they are. Adults who live in an average climate and are moderately active can likely maintain their health drinking less than 8 glasses per day.  This doesn’t mean that you want to skimp on drinking your water however.

In contrast, those people who exercise frequently or live in very hot climates can lose up to 4 liters of fluid in just one hour of intense exercise on a hot day.  For these people, staying hydrated during a work out is critical for their health and to prevent a heat stroke.  These people could easily drink far more than 2 liters of water in a day.

Why is water so healthy?

Did you know that water makes up about 70% of your body?  Water helps to flush toxins from your bloodstream and cells, allowing your body to experience a daily “detox.”

Staying hydrated is also important for maintaining your energy, getting a good night’s sleep, and keeping your mood up.  If you want to appear young, water can also play an important role.  For example, if you are not drinking enough water, you may appear aged and can suffer from rough or cracked skin, bloating, or puffiness.

Can you really tell the difference between hunger and thirst?

Strangely, medical studies have shown us that we often cannot tell the difference between hunger and thirst. Unfortunately, most of us end up eating something when we really may just be thirsty.

Water helps us to feel full because it takes up a lot of volume in our stomachs.  Sometimes we may think we are hungry, and may even experience hunger pains, but in fact it may be that we are just experiencing mild dehydration.

When we don’t stay hydrated, we don’t feel the best that we could.  We tire easily, feel moody, get headaches, and we don’t function well overall. These uncomfortable feelings make us crave food because we are looking to food for more energy when all we really need is more water.

Water can help us to eat less at meal times as well. Try drinking 2 glasses of water right before you eat a meal and you may find you eat less since your stomach will feel partially full and you won’t be confusing thirst for hunger at all.

Why do water drinkers stay thin?

Have you ever noticed that people who carry a water bottle around with them seem to appear healthier and slimmer than most people?  What is the science behind water drinking and maintaining a healthy weight?

Besides not confusing hunger for thirst, the obvious answer is that if you are drinking a lot of water you probably are not drinking soda pop, fruit juice, or other sugary drinks.  This alone could cause significant weight loss.  I commonly see patients lose more than 20 pounds just by giving up all soda, fruit juice, sports drinks, and other sugary drinks.

Even diet soda may cause significant weight gain in many studies!  Studies show that even though you are not getting any “calories” from diet sodas, the aspartame in diet sodas is feeding your bad gut bacteria which, in turn, may cause weight gain.

Water also causes a significant calorie burn through the process of cold thermogenesis.  If you want to learn more about how to boost your metabolism through cold thermogenesis, I recently wrote an article on this subject (blog #68).

Studies have shown that by drinking 8 glasses (2 liters) of cold water, your body can be forced to burn an extra 400 calories!  Researchers report that most of this 400 calorie weight loss was due to the energy required by the body to heat the cold water up to body temperature.  If you do the math, drinking 2 liters per day of cold water, without increasing your food intake, would burn 42 extra pounds per year.

Since there is no risk in drinking more water for most people (see disclaimer at the bottom of this article), and you might even feel more energetic thereby increasing your work out routine, why not start drinking more water today?

Boost Cognition and Memory with Water

Could helping your child score well on the SAT or ACT college entrance tests be as simple as drinking more water?  Studies have consistently shown that children do better on tests when they are hydrated.  Even adults, based on medical studies, do better on cognition tests when they are well hydrated with water.

Other studies have shown that dehydration, or even relative mild dehydration like not drinking enough water during the day, can impair brain function.  Studies have even shown that fighter pilots don’t fly their planes as well if they are not drinking enough water.  Thus, if you want optimal brain and memory function learn to love water.

How much water should you drink to prevent heart disease?

If your goal is to prevent heart disease and never see a cardiologist, like me, then there are actually some data supporting how much water you should drink.

The Seventh Day Adventists are one of the healthiest groups of people in the world.  The Adventists have been extensively studied and have even been featured in the best selling health book, Blue Zones (affiliate link).

In this study, researchers closely followed 20,297 California Adventists for 6 years.  Interestingly, they found that those Adventists drinking 5 or more glasses of water each day were 54% less likely to die from heart disease!

Just how does water protect against a heart attack?  Could the benefit from water be because they drank water rather than soda pop, fruit juice, or other sugary drinks?  Likewise, could a high water intake be a manifestation of someone who is generally more health conscientious or someone who exercises a lot?

There are some studies that suggest that relative dehydration can cause you to have “thicker blood” or a higher blood viscosity.  If you are not drinking enough water then your blood particles are more likely to clump together and form clots.  These clots could lead to a heart attack or a stroke.  Regardless of how you can prevent a heart attack by drinking more water, it seems to me that drinking at least 5 glasses of water each day is a very healthy habit which we should adopt.

Dr. Day’s 6 Water Rules

To help you maintain a healthy weight and allow your brain and heart to function at its best, let my give you my six rules when it comes to drinking water.

1. Drink water instead of soda, fruit juice, or other sugary drinks

If you want to torpedo your health and your waist line, then drinking soda in either the high fructose corn syrup or diet varieties, juice, or other sugary drinks like sports drinks is a great strategy.  On the other hand, if you want to feel energized and maintain a healthy weight learn to love water.  If water isn’t yet your thing, try adding some fresh lemon or lime to your water.

2. If you are hungry between meals drink water first

Learn to notice the difference between your body’s true hunger signals, versus thirst signals. If you feel hungry between meals, try drinking something first. Wait 30 minutes. If you still feel hungry after 30 minutes, you probably are hungry and should eat something.

3. Drink water to boost your metabolism

To keep your body’s metabolism high, stay hydrated.  As discussed in this article, you can burn a significantly high amount of calories each day by drinking 2 liters of water.

4. Stay hydrated for optimal brain performance

Our brains require plenty of water to function optimally.  Stay hydrated to boost your cognition and memory.

5. Drink at least 5 glasses of water daily for your your heart

While 8 glasses of water (2 liters) has not been shown to make you “healthier,” there are data that drinking at least 5 glasses of water each day may protect your heart.  This may keep your blood viscosity low and prevent clots from forming.

6. Keep water with you throughout the day

As it is so easy for us to become dehydrated through the day, learn to carry a glass or stainless steel water bottle.  Having the water bottle with you is a great reminder to drink more.

How much water do you drink each day?  Do you carry a water bottle with you?


Please remember that if you suffer from heart failure, kidney failure, or other medical conditions you should discuss your optimal daily water intake first with your physician.

#068 How to Boost Metabolism: Cold Thermogenesis

January 26th, 2015 by

How to Boost Metabolism: Cold Thermogenesis

The world’s greatest swimmer, Michael Phelps, consumes 12,000 calories each day. Based on my calculations, he only burns 9,602 of these calories leaving him 2,398 extra calories each day that are simply unaccounted for.

Why doesn’t he gain any weight from overeating by the equivalent of more than 4 McDonald’s Big Macs each day (2,398 calories)?  Could these unaccounted for calories be due to cold thermogenesis? Just what is the science behind cold thermogenesis boosting metabolism and will this help me to lose or maintain a healthy weight?

Michael Phelps: The World’s Best Athlete

During the summer of 2008 the entire world was focussed on Michael Phelps at the Olympics in Beijing.  In just 8 short days he went on to win 8 gold medals and set many new world records, a feat never before accomplished at the Olympics.

With the 2012 London Olympics he has earned a total of 22 medals from three Olympics. He is arguably the greatest athlete who has ever lived.  In this inspirational video you can see him win each of these 8 memorable gold medals at the 2008 Beijing Olympics.

Michael Phelps: The World’s Biggest Eater?

While much has been written about Michael Phelps’ training schedule, one thing that is rarely mentioned is the 12,000 calories he eats each day.  Yes, he has a grueling daily work out, but no one can burn that many calories in a day long-term.  What is his secret to not gaining any weight?

As you know from my previous articles, I am a cardiologist who believes in science and I also look for the lessons that we can learn from medical outliers.  Here is my assessment of how Michael Phelps has boosted his metabolism to the point that he can eat 12,000 calories a day and yet not gain a single pound.

Michael is 6 feet 4 inches (193 cm) and weighs 194 pounds (88 kg).  According to the many published reports, he works out 6 hours a day from swimming, weight lifting, and running.  According to the Mayo Clinic, he would burn the following calories:

-A 200 pound (91 kg) man swimming vigorous laps burns 892 calories an hour.

-A 200 pound man weight lifting burns 455 calories an hour.

-A 200 pound man running very fast at 8 mph (17 kmh) burns 1,074 calories an hour.

-His basal metabolic rate or the amount of calories he burns at rest, according to the Haris-Benedict Equation, for an extremely active 200 pound man would be 3,602 calories per day.  This is an overestimate of the calories he burns as he only weighs 194 pounds and would actually burn less.

-Assuming he is burning an overly generous average of 1,000 calories an hour for 6 hours of working out plus his metab0lic rate of 3,602 calories daily (total of 9,602 calories) this leaves 2,398 calories that are completely unaccounted for.

Cold Thermogenesis and Michael Phelps

Could these unaccounted for 2,398 calories be due to cold thermogenesis? Lap swimmers usually swim at 75 degrees Fahrenheit (24 degrees Celsius). Body temperature on average is 98.6 degrees Fahrenheit or 38 degrees Celsius.

From a science perspective, heat loss is 20 times faster in water than air. The reason for this rapid heat loss from water is due to conductive heat loss. This also explains why people can suffer hypothermia in 41 degree Fahrenheit (5 degrees Celsius) water in just 10 minutes whereas you could spend hours outside at 41 degrees if you are dry.

Michael Phelps spends approximately 4 hours in the pool each day. In the cool lap pool he is losing a tremendous amount of body heat. This body heat needs to be replaced by boosting metabolism or burning more calories to stay warm. This term is called “thermogenesis” or the production of heat by the body. Thus, cold thermogenesis refers to the body’s attempt to keep the body warm in a cold environment by revving up metabolism or the burning of calories.

Brown Adipose Tissue or “Brown Fat”

You have probably seen many news articles recently about the role of brown adipose tissue or the so called “brown fat.” Brown fat is opposite the usual fat, or white fat, that we get from gaining weight.

Abundant brown fat can be found in newborns as well as animals that hibernate during the winter. For example, the polar bear has abundant brown fat which helps to keep the bear warm in the harsh arctic climate. As we age, most people lose their brown fat.

Brown fat has extensive blood vessels and burns a lot of calories to keep us warm and regulate our body temperature. Many researchers feel that if we could regain our brown fat that it just might help to reverse the obesity epidemic. Many drugs companies are even looking into creating pills that help people to develop more brown fat in order to boost metabolism and lose weight.

Interestingly, new studies have shown that people who spend a lot of time in cold environments can actually regain their brown fat that was lost as they grew older. Could the key to Michael Phelps’ incredible metabolism be that he has more brown fat than the rest of us?

How to Boost Metabolism with Cold Thermogenesis

Perhaps swimming 4 hours a day in a cold lap pool or a winter lake near your home is not your idea of a good time. The same is true for me. I have tried for years to enjoy swimming and I just can’t seem to make it work for me.

As you know, I live in Salt Lake City and love to exercise outdoors. Summer or winter you can find me on top of one of our local mountains.

I also keep my window open in the exercise room of our house where I keep my treadmill and bicycle desks. The fresh air energizes me, prevents sweating, and results in an increased energy burn. Even as I am writing this, I am in shorts on my bicycle desk with the window open. The outside air temperature right now is 20 degrees Fahrenheit or minus 7 degrees Celsius.

Even if you don’t enjoy exercising in the cold there are still ways you can enjoy the massive calorie burn that comes from cold thermogenesis. Let me give you the answer of how to boost metabolism in three simple steps with cold thermogenesis.

1. Exercise in a cool environment

Of course, exercising in a cool lap pool will boost your metabolism much more than cool air due to the much greater conductive heat loss properties of water. Regardless, even if it is cold in the morning when you get up for your run or walk at least you can tell yourself that the cool air is boosting your metabolism. While this is not an excuse to eat more, at least it can help you to maintain a healthy weight.

2. Turn the heat down in your home

Turning the heat down a few degrees in your home is a great way to save money on your energy bill and boost your metabolism. Indeed, a cooler home will require your body to burn more calories to keep you warm.

3. Drink 8 glasses of cold water daily

Eight glasses of water works out to about 64 ounces or almost 2 liters. While there is no scientific evidence that you must drink 8 glasses of water each day for optimal health, all this cold water does require your body to heat it to 98.6 degrees Fahrenheit or 38 degrees Celsius. This is also cold thermogenesis in action as calories must be burned to heat 2 liters of cold water to a much warmer body temperature.

According to this study, drinking 8 glasses or 2 liters of water burns 96 calories each day. If you do the math, drinking 2 liters of cold water each day without increasing your food intake would burn an extra 10 pounds each year.

The Downside of Cold Thermogenesis: Increased Hunger

By this point you may be thinking that cold thermogenesis is the key to boosting your metabolism and maintaining a healthy weight. While that may be the case, it comes at a significant price. The price is that cold thermogenesis dramatically increases hunger for most people.

I have found that if I am not careful, I tend to eat significantly more food after exercising in the cold.  Studies have also confirmed that cold thermogenesis can increase our appetite . What helps me is to realize this ahead of time so as to avoid mindless eating after exercising in the cold.

I realize that I am not burning as many calories per hour from cold thermogenesis as Michael Phelps as it is cold air rather than a cold lap pool for me. However, I love to start my morning work-outs with 1.5 liters of water. I will then go on to drink another liter or so of water over the rest of the day to keep myself hydrated and keep cold thermogenesis going.

If you can’t control the post-exercise hunger from cold thermogenesis then it could backfire on you and you may end up gaining weight in the process. Knowing how hungry you will be after a cold thermogenesis work out could help to prepare you to find ways to prevent mindless eating afterwards.

Sweating or Evaporative Cooling to Boost Metabolism

Perhaps the hunger that follows cold thermogenesis is too much for you. There is an alternative along the same principle and that is sweating or evaporative cooling to boost metabolism.

In this study, exercising in the heat causes much less hunger afterwards than exercising in the cold. Indeed, if the end result is weight loss and you don’t do well battling hunger then heat may be better for you than the cold. Remember, that if you are in a warm environment you will need much more water to stay hydrated. Does this get us back to cold thermogenesis again?

When it comes to how to boost metabolism it appears that either cold or heat could help you to accomplish this goal. The only difference is the level of hunger that you may experience afterwards.

Cold Thermogenesis Disclaimer

Cold thermogenesis or even exercising in the heat is definitely something that you should not try on your own at home. Likewise, drinking 2 liters of water each day could also be dangerous with some medical conditions like heart or kidney failure. If you are interested in exploring cold thermogenesis further, please work under the supervision of your physician.

Do you prefer exercising in the cold or the heat? How do you manage the hunger pains after exercising in the cold?