Have you ever wondered if there’s a natural way to lower your high blood pressure, guard against Alzheimer's, lose weight, and feel better? Well as it turns out there is. Michael Greger, M.D. FACLM, founder of NutritionFacts.org, and author of the instant New York Times bestseller “How Not to Die” celebrates evidence-based nutrition to add years to our life and life to our years.

Boosting Our Metabolism

Today we explore the health effects of speeding up our metabolism.

This episode features audio from How to Get the Weight Loss Benefits of Ephedra Without the Risks, The Effect of Drinking Water on Adrenal Hormones, and What Is the Safest Metabolism Booster?. Visit the video pages for all sources and doctor’s notes related to this podcast.


There has been a lot of research lately on the best, and safest, way to boost our metabolism. And, here is a sample of what we found. 

In our first story, we look at how our adrenalin system plays a role in regulating our metabolism and our weight.

Thermogenic drugs like DNP can cause people to overheat to death; they can increase resting metabolic rates by 300 percent or more. A more physiological spread would range about 10 times less, from a 30 percent slower metabolism in people with an underactive thyroid to a 30 percent higher metabolism when the part of our nervous system that controls our fight-or-flight response is activated. In response to a fright or acute stress, special nerves release a chemical called noradrenaline to ready us for confrontation. You experience that by your skin getting paler, cold, and clammy as blood is diverted to your more vital organs. Your mouth can get dry as your digestive system is put on hold. Your heart starts to beat faster. What you don’t feel is the extra fat being burned to liberate energy for the fight. That why people started taking ephedra for weight loss.

Ephedra is an evergreen shrub used for thousands of years in China to treat asthma, because it causes that same release of noradrenaline that offers relief to asthmatics by dilating their airways. In the United States, it was appropriated for use as a metabolic stimulant––shown to result in about two pounds of weight loss a month in 19 placebo-controlled trials. By the late 1990s, millions of Americans were taking it. The problem is that it had all the other noradrenaline effects like increasing heart rate and blood pressure; and so, chronic use resulted in strokes, heart arrhythmias, and death. The FDA warned the public of the risks in 1994, but it wasn’t banned until a decade later after a Major League pitcher dropped dead.

In the current Wild West of dietary supplement regulation, a supplement can be marketed without any safety data at all, and the manufacturer is under no obligation to disclose adverse effects that may arise. No surprise, then, that online venders assured absolute safety: “No negative side effects,” “100 percent safe for long-term use.” The president of Metabolife International, a leading seller of ephedra, assured the FDA that the company had never received a single “notice from a consumer that any serious adverse health event has occurred….” In reality, they received 13,000 health complaints, including reports of serious injuries, hospitalizations, and deaths.

If only there was a way to get the benefits of ephedra without the risks. There is, but to understand it, first you have to grasp a remarkable biological phenomenon known as the diving reflex.

Imagine yourself walking across a frozen lake and suddenly falling through the ice, plunging into the icy depths. It’s hard to think of a greater instant fight-or-flight shock than that. Indeed, noradrenaline would be released, causing the blood vessels in your arms and legs to constrict to bring blood back to your core. You can imagine how fast your heart might start racing, but that would actually be counterproductive because you’d use up your oxygen faster. Remarkably, what happens instead is your heart rate actually slows down. That’s the diving reflex, first described in the 1700s. Air-breathing animals are born with this automatic safety feature to help keep us from drowning.

In medicine, we can exploit this physiological quirk with what’s called a “cold face test.” To test to see if a comatose patient has intact neural pathways, you can apply cold compresses to their face to see if their heart immediately starts slowing down. Or more dramatically, it can be used to treat people who flip into an abnormally rapid heartbeat. Remember that episode of ER where Carter dunked the guy’s face into a tray of ice water? (It was on TV when I was in medical school, and a group of us would gather around and count how many times they violated “universal precautions.”)

Okay, but what does this have to do with weight loss? The problem with noradrenaline-releasing drugs like ephedra is the accompanying rise in heart rate and blood pressure. What the diving reflex shows is that it’s possible to experience selective noradrenaline effects, raising the possibility that there may be a way to get the metabolic boost without risking stroking out. Unbelievably, this intricate physiological feat may be accomplished by the simplest of acts—instead of drowning in water, simply drinking it. Wait, what? You can boost your metabolism drinking water? Buckle your safety belts; you are in for a wild ride.

In our next story, we discover the effect of drinking water on adrenal hormones. Drink a few cups of water, and within three minutes the level of the adrenal gland hormone noradrenaline in your bloodstream can shoot up 60 percent. Have people drink two cups of water with electrodes stuck in their legs, and within 20 minutes you can document about a 40 percent increase in bursts of fight-or-flight nerve activity. Chug two or three cups of water, and blood flow squeezes down in your calves and arms, clamping down nearly in half as arteries to your limbs and skin constrict to divert blood to your core. That’s why, for example, drinking water can be such a safe, simple, effective way to prevent yourself from fainting (known medically as syncope).

Fainting is the sudden, brief loss of consciousness caused by diminished blood flow to your brain. About one in five people experience this at least once, and about one in ten may have repeated episodes, causing millions of emergency room visits and hospitalizations every year. Though fainting can be caused by heart problems, it is most often triggered by prolonged standing (because blood pools in our legs) or strong emotions, which can cause your blood pressure to bottom out.

About 1 in 25 people have what’s called blood-injury-injection phobia, where getting a needle stick, for example, can cause you to faint. More than 150,000 people experience fainting or near-fainting spells each year when they donate blood.  All you have to do to help prevent yourself from getting woozy, though, is just chug two cups of water five minutes before getting stuck. The secret isn’t in bolstering your overall blood volume. Drinking two cups of water—even a whole quart—and your blood volume doesn’t change more than 1 or 2 percent. It’s due rather to the shift in the distribution of blood toward your center caused by the noradrenaline-induced peripheral artery constriction.

Water drinking stimulates as much noradrenaline release as drinking a couple of cups of coffee or smoking a couple of unfiltered cigarettes. If the simple act of drinking water causes such a profound fight-or-flight reaction, why doesn’t it cause our heart to pound and shoot our blood pressure through the roof? It’s like the diving reflex I talked about in the last video. When we drink water, our body simultaneously sends signals to our heart to slow it down, to “still your beating heart.” You can try it at home: measure your heart rate before and after drinking two cups of water. Within 10 minutes your heart rate should slow by about four beats per minute, and by 15 minutes you should be down six or seven beats.

One of the ways scientists figured this out is by studying heart transplant patients. When you move a heart from one person to another, you have to sever all the attached nerves. Amazingly, some of the nerves grow back. But still, give healed heart transplant patients two glasses of water, and their blood pressure goes up as much as 29 points. The body is unable to sufficiently quell the effect of that burst of noradrenaline. Some people have a condition known as autonomic failure, in which blood pressure regulation nerves don’t work properly, and their pressures can dangerously skyrocket over 100 points after chugging two cups of water. That’s how powerful an effect the simple act of drinking a glass of water can be, and the only reason that doesn’t happen to all of us is that we have an even more powerful counter-response to keep our heart in check. It reminds me of the poor woman who had a stroke after taking the ice bucket challenge, due to an insufficient diving reflex to tamp down all that extra noradrenaline release.

The remarkable water effect can be useful for people suffering from milder forms of autonomic failure such as orthostatic hypotension, which is when people get dizzy standing up suddenly. Drinking some water before getting out of bed in the morning can be a big help. But, what about that metabolic boost? With so much noradrenaline being released, with your adrenal gland hormones in overdrive, might drinking a few glasses of water cause you to burn more body fat? Could tap water be like a safe form of ephedra—all the weight loss, but with a nice slowing of your heart rate instead? Researchers decided to put it to the test, which we’ll explore next.

Finally today, drink two cups of water and you can get a surge of the adrenal hormone noradrenaline in your bloodstream, as if you just smoked a few cigarettes or downed a few cups of coffee.


Given the 60 percent surge in the adrenal hormone noradrenaline within minutes of just drinking two cups of plain water, might one get the weight-loss benefits of noradrenaline-releasing drugs, like ephedra, without the risks? You don’t know until you put it to the test. Published in the Journal of the Endocrine Society, the results were described as “uniquely spectacular.” Drinking two cups of water increased the metabolic rate of men and women by 30 percent. The increase started within 10 minutes and reached a maximum within an hour. In the 90 minutes after drinking a single tall glass of water, the study subjects burned about an extra 25 calories. Do that four times throughout the day and you could wipe out 100 extra calories— more than ephedra! You’d trim off more calories drinking water than taking weight loss doses of the banned substance, ephedrine—the active component of ephedra—three times a day. And we’re just talking about plain, cheap, safe, and legal tap water!

Using the 10-Calorie Rule I explained previously, unless we somehow compensated by eating more or moving less, drinking that much water could make us lose 10 pounds over time. “In essence,” concluded one research team, “water drinking provides negative calories.”

A similar effect was found in overweight and obese children. Drinking about two cups of water led to a 25 percent increase in metabolic rate within 24 minutes, lasting at least 66 minutes until the experiment ended. So, just getting the recommended daily “adequate intake” of water—about 7 cups a day for children ages 4 through 8, and for ages 9 through 13, 8 cups a day for girls and 10 cups for boys—may offer more than just hydration benefits.

Not all research teams were able to replicate these findings, though. Others only found about a 10 to 20 percent increase, a 5 percent increase, or effectively none at all––pouring cold water, one might say, on the whole concept. What we care about, though, is weight loss. The proof is in the pudding. Let’s test the waters, shall we?

Some researchers suggest, “The increase in metabolic rate with water drinking could be systematically applied in the prevention of weight gain.” Talk about a safe, simple, side-effect-free solution—in fact free, in every sense. Drug companies may spend billions getting a new drug to market; surely, a little could be spared to test something that, at the very least, couldn’t hurt. That’s the problem, though. Water is a “cost-free intervention.”

There are observational studies suggesting those who drink, for example, four or more cups of water a day appear to lose more weight, independent of confounding factors such as less soda or more exercise. But you don’t really know until you put it to the test.

And finally, in 2013, “Effect of ‘Water Induced Thermogenesis’ on Body Weight, Body Mass Index and Body Composition of Overweight Subjects.” Fifty overweight “girls” (actually women, ages 18 through 23) were asked to drink two cups of water, three times a day, a half hour before meals, over and above their regular water intake, without otherwise changing their diets or physical activity. And, they lost an average of three pounds in eight weeks. What happened to those in the control group? There was no control group, a fatal flaw for any weight loss study due to the “Hawthorne effect,” where just knowing you’re being watched and weighed may subtly affect people’s behavior. Of course, we’re just talking about water; so, with no downsides one might as well give it a try. But I’d feel more confident if there were some randomized, controlled trials to really put it to the test. Thankfully, there are!

Oh, I hate it when the title ruins the suspense. Overweight and obese men and women randomized to two cups of water before each meal lost nearly five pounds more body fat in 12 weeks than those in the control group. Both groups were put on the same calorie-restricted diet, but the one with the added water lost weight 44 percent faster. A similar randomized controlled trial found that about 1 in 4 in the water group lost more than 5 percent of their body weight compared to only 1 in 20 in the control group.

The average weight loss difference was only about three pounds, but those who claimed to have actually complied with the three-times-a-day instructions lost about eight more pounds compared to those only did the extra water once a day or less. This is comparable to commercial weight loss programs like Weight Watchers, and all they did was drink some extra water.

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