How Fructose Turns ON Your ‘Fat Switch’

Recently by Joseph Mercola: Fat, Not Glucose, Is the Preferred Fuel for YourBody

Story at-a-glance

  • If you have ever struggled losing weight and keeping it off, you already know what a challenge that can be. In his new book, The Fat Switch, Dr. Richard Johnson overturns age old paradigms about diet and obesity by revealing how fructose turns your body into a fat-storage machine – not by way of excess calories but by turning on your u201Cfat switchu201D
  • He addresses the myth that large portions of food and too little exercise are responsible for weight gain
  • Hibernating animals regulate their body weight with distinct periods of gaining and losing fat and that has been an enormously useful adaption advantage. This appears to be regulated by a switch in the mitochondria that is turned on and off by a common food that no longer provides survival advantage to humans living in contemporary society
  • Contrary to the traditional view, which says that breakfast is the most important meal of the day, the reality is that breakfast may be one of the LEAST important meals, because skipping it may allow you to enter into a more efficient fat burning phase

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If you have ever struggled losing weight and keeping it off, you already know what a challenge that can be. Dr. Richard Johnson, chief of the Division of Renal Diseases and Hypertension at the University of Colorado has published hundreds of articles and two books on this topic: The Sugar Fix, and most recently, The Fat Switch, which presents a groundbreaking approach to preventing and reversing obesity.

According to Dr. Johnson, based on his decades of research:

u201CThose of us who are obese eat more because of a faulty u201Cswitchu201D and exercise less because of a low energy state. If you can learn how to control the specific u201Cswitchu201D located in the powerhouse of each of your cells — the mitochondria — you hold the key to fighting obesity.u201D

There are five basic truths that Dr. Johnson explains in detail in his new book that overturn current concepts:

  1. Large portions of food and too little exercise are NOT solely responsible for why you are gaining weight
  2. Metabolic Syndrome is A NORMAL CONDITION that animals undergo to store fat
  3. Uric acid is increased by specific foods and CAUSALLY CONTRIBUTES to  obesity and insulin resistance
  4. Fructose-containing sugars cause obesity not by calories but by turning on the fat switch
  5. Effective treatment of obesity requires turning off your fat switch and improving the function of your cells' mitochondria

I highly recommend picking up a copy of this book, which has been described as the u201CHoly Grailu201D for those struggling with their weight. Dietary sugar, and fructose in particular, is a significant u201Ctripper of your fat switch,u201D so understanding how sugars of all kinds affect your weight and health is imperative.

All Sugars are Not Created or Function Equally

As explained by Dr. Johnson, anytime we discuss sugar, we're talking about ALL forms of sugar, but some types are clearly more hazardous than others, in terms of their effect on your biochemistry:

u201CTable sugar is also known as sucrose, and sucrose contains one molecule of fructose and one molecule of glucose bound together. We call it a disaccharide. But one sucrose molecule actually has a fructose and a glucose molecule bound to it. Sucrose or table sugar is basically about 50 percent fructose. When you eat this sucrose, the sucrose gets metabolized in the intestines to free fructose and free glucose that you then absorb.

High-fructose corn syrup is the other major source of fructose.

High-fructose corn syrup consists of a mixture of fructose and glucose mixed freely together… (What I mean by free fructose is it's just fructose and glucose mixed together. They're not bound together.) There's a little bit more fructose than glucose. It's not exactly a 50-50 ratio, and the ratio can vary depending upon which food… [These are the two key ways that people are being exposed to fructose.

… I should mention that natural fruits also have fructose.

In my original book, The Sugar Fix, I was quite concerned about that, because it was another source of fructose. And we can show that fructose does a lot of bad things. But the good news is we've done subsequent studies, and we've been able to show that natural fruits, although there's some fructose there… there are so many wonderful things in natural fruits like vitamin C, antioxidants, resveratrol, flavonols, quercetin, and all these things that actually neutralize some of the effects of fructose. Because of that, natural fruits do not seem to carry the same degree of risk.u201D

That said, keep in mind that large amounts of fruits, as well as fruit juices and dried fruits will typically contain large doses of fructose, so use in moderation. Neither I nor Dr. Johnson recommend drinking fruit juice or eating dried fruits if you're struggling with your weight. Furthermore, although Dr. Johnson doesn't specifically mention them here, the term u201Csugaru201D also applies to other natural sources such as honey and agave syrup, for example, both of which are very high in fructose.

Surprise: Metabolic Syndrome May Not Be a Disease After All

Dr. Johnson's book, The Fat Switch, is not just another book about weight loss. No, in it he again reveals why I believe he deserves to be viewed as a true pioneer in this field.

u201CI've realized from my discussions with many people that there's more than one approach to try to figure out the cause of a disease,u201D he says. u201CMost of us as scientists have focused just on pure medical science like molecular biology, physiology, and genetics. These are incredibly important tools and have a critical role in helping us figure out diseases. But actually, there's a much bigger field to select from that can help us. For example, there is the field of comparative physiology… which means u2018study of animals in nature.'

… For example, most animals have learned how to become fat and how to become thin. They do it in a tightly regulated way… Hibernating mammals will double their weight and fat in the fall in preparation for winter… I realized that I can learn by reading the studies about these animals. As I read them, I had another insight, which had not been appreciated before: That these animals develop all the features of metabolic syndrome that we do. They get fat. They're visceral fat goes up. They get fatty liver. The triglycerides go up in their blood. They get insulin-resistant… It's a normal process.

It's not a disease. This is how animals store fat. It's part of the fat storage syndrome. I've actually proposed (and it's in press) that the metabolic syndrome really should be called the fat-storage condition, because it's just fat storage.u201D

The question, of course, is how do animals do it?

Through his earlier research, Dr. Johnson discovered the method that animals use to gain fat prior to times of food scarcity which turned out to be a powerful adaptive benefit. His research showed that fructose activates a key enzyme, fructokinase, which in turn activates another enzyme that causes cells to accumulate fat.

When this enzyme is blocked, fat cannot be stored in the cell. Interestingly, this is the exact same u201Cswitchu201D animals use to fatten up in the fall and to burn fat during the winter. Fructose is the dietary ingredient that turns on this u201Cswitch,u201D causing cells to accumulate fat, both in animals and in humans!

u201CThe enzyme that makes you fat is turned on in obese people,u201D Dr. Johnson explains, u201Cand the enzyme that makes you lean is turned off.u201D This is why the book is called The Fat Switch, because basically there is a switch that turns on and off. It looks to me like it's universal to all animals. This book is a story of that… [O]nce we realized that there was this switch, we asked, u201CWhy are people becoming obese?u201D Now we realized it was related to the sugar intake.

… The last part was connecting in with the evolutionary aspects. There's a very famous evolutionary biologist in London, in the Natural History Museum. His name is Peter Andrews. He trained with Richard Leakey. He's like a world expert on human evolution. It turned out that there were certain mutations that occurred in our past. For example, we don't make vitamin C. We also have higher uric acids than most other animals.

When we look at when these mutations occurred, we could see that they actually occurred during periods of human famine, and that these were probably mutations that allowed us to become fatter in response to fructose than other animals. We're much more sensitive to sugar than most animals, and it's because of these mutations.

Then I was able to work with a spectacular scientist who helped resurrect those extinct genes. We're able to basically prove that when we lost these genes, we became more sensitive to sugar… Then out of it comes the discovery that this pathway is probably important not just in obesity, but in a lot of other diseases like celiac disease, food allergies, and kidney disease.u201D

Why Breakfast May Not Be a Good Idea for Many

This clearly runs contrary to the traditional view, which says that breakfast is the most important meal of the day. The reality is that breakfast may be one of the LEAST important meals, because skipping it may allow you to enter into a more efficient fat burning phase.

Clearly, step number one, if you're struggling with your weight, is to reduce your sugar intake. Dr. Johnson suggests cutting it by one-half to one-third of your normal intake. I recommend keeping your total sugar/fructose intake below 25 grams a day, or as little as 15 grams a day if you have any health problems related to insulin resistance, such as high blood pressure, diabetes or heart disease. But you can further boost your fat loss efforts by incorporating the principles of intermittent fasting, and by exercising in a fasted state.

Intermittent fasting, when you stop eating for 14-18 hours, typically after dinner, has become increasingly popular in certain circles. It has been a strategy I have been personally using for the past several months to help me lower my waist size about two inches. In fact, at times I will fast for 20-22 hours.

The theory of intermittent fasting is based on the rationale that your body stores sugar as glycogen in your liver but only stores enough for 6-8 hours. So after this time, you have consumed your glycogen store, which forces your body to metabolize the fat stored in your body. It essentially replicates what our ancestors were exposed to in terms of food availability and, Dr. Johnson agrees, this form of intermittent fasting can indeed help you optimize your weight.

u201C… [I]f you want to burn fat, intermittent fasting is a pretty good way to do it. Normally when you fast, there's a short period of time where you're burning glycogen, which is the carbohydrates stored in your liver and other tissues but particularly in the liver.

While there's glycogen around, it's hard to burn fat, because your body will preferentially burn glycogen… [G]lycogen gets burned off fairly quickly, but it takes six to eight hours before it's really burned, or before it's completely removed. It takes a little bit longer in people who are obese.

If you eat a dinner early, for example, at 5:00 PM, then you decide not to eat afterwards until the morning, by two or three in the morning the glycogen is gone. Now your body burns fat. You are burning fat while you are sleeping.

It's a great move.  Whereas if you stay up until midnight and you're eating chips and things like this… you may never burn the glycogen at all. By the time you wake up in the morning, you still have glycogen in your liver. You've burned no fat.  Another thing that comes out of this… is that if you exercise in a fasting state, like in the morning, you will be burning fat.u201D

Another Bombshell: Under Certain Circumstances Your Body Can Convert Carbs to Fructose…

Dr. Johnson's research has revealed yet another major surprise: There are circumstances in which carbohydrates can be converted to fructose in your body even when there's no fructose in the carbs. The underlying mechanism for this is still unclear, but he believes that insulin resistance may be one of the conditions that allows for this odd conversion to occur.

u201CThe way I interpret this now, based upon the data we have, is that if you want to not gain weight, the most important thing is to reduce sugar/fructose intake from your diet. But if you're really overweight, the old low-carb diet may be a good way to go because it will reduce the fructose intake, but it will also reduce carbs that may be playing a role, under certain circumstances, in making fructose in the body,u201D Dr. Johnson says.

u201C… It looks like in normal, healthy, young people [carbs and/or glucose] is not being converted to fructose. But we do have some evidence that under certain conditions — one of them would be insulin resistance, or if you're overweight — you may be converting some of the carbs to fructose.u201D

In a previous interview, Dr. Johnson expounded on the links between fructose consumption and uric acid levels, and how your uric acid levels are a major predictor for obesity, diabetes, high blood pressure and fatty liver disease. It can also be used as a marker for fructose toxicity, and now he believes uric acid may be one of the key factors that determine whether your body will convert carbs to fructose.

 u201CWe actually believe that elevated uric acid turns on the enzyme that helps convert the carbs to fructose,u201D Dr. Johnson says. u201CMost people who are obese and insulin-resistant have high uric acid. We think that's the reason that they're converting the carbs to fructose.u201D

According to the latest research, the safest range of uric acid is between 3 and 5.5 milligrams per deciliter, and there appears to be a steady relationship between uric acid levels and blood pressure and cardiovascular risk, even down to the range of 3 to 4 mg/dl. Dr. Johnson suggests that the ideal uric acid level is probably around 4 mg/dl for men and 3.5 mg/dl for women.

All Calories are NOT Created Equal

Perhaps one of the most powerful details to emerge from Dr. Johnson's investigations is that the old adage u201Ca calorie is a calorieu201D is patently false. Furthermore, the idea that in order to lose weight all you have to do is expend more calories than you consume is also false…  The research clearly demonstrates that even if you control the number of calories you eat, if those calories come from fructose, you are at increased risk of developing metabolic syndrome, or prediabetes, which includes:

  • Insulin resistance
  • Fatty liver
  • High blood pressure
  • High triglycerides

Conventional thinking tells us that metabolic syndrome is the outcome of obesity, which is simply the result of eating too many calories and not exercising enough. The idea that this is incorrect continues to be met with great resistance. 

However, Dr. Johnson's research shows that a high fructose diet is the key to developing metabolic syndrome, and as soon as you throw fructose into the mix, u201Ccalories in versus calories outu201D is no longer a functional equation…

u201C[O]ne group [of animals] is getting a number of calories that an animal would normally eat, but it's high in fructose. Another group will get the same amount of food — exactly the same amount of food, but with a different carbohydrate, like glucose.

It's the fructose-fed rats that develop metabolic syndrome. Suddenly they get fatty liver. They get visceral fat. Their blood pressure goes up. Their triglycerides are high. They actually develop all these features, whereas the glucose-fed rats don't – and they're eating the same number of calories!

We even did a study two years ago that was even more remarkable. We took laboratory animals and we put them on a diet. We gave them 90 percent of what they normally eat, but one diet had 40 percent sugar. (Now remember, some kids are eating 30 percent of their diet as sugar right now)… The control rats were eating the same [amount of calories] in starch. What was amazing was that the sugar-fed animals developed fatty liver — like massive fatty liver — and even became diabetic. The control animals did not.

There's something special about fructose. It's not just a calorie. This led us to try to figure out why… It was a big challenge to figure out how fructose was causing diabetes and obesity through a mechanism that doesn't really require excessive calorie intake.u201D

Fructose Metabolizes Differently than Other Sugars

Fructose is a sugar, just like glucose. But when it's metabolized, it's actually very different from glucose, and this makes all the difference in the world in terms of weight and health.

While all cells use some energy in the process of metabolizing food, whether it's fat or sugar, fructose uses up so much energy that the cell becomes energy-depleted. As a result, the cell stops functioning normally and starts to develop an inflammatory response, also known as oxidative stress.

In a nutshell, a high-fructose diet causes chronic inflammation in your body, which glucose does not do.

u201CWe found that when the energy is depleted… the ATP levels fell (ATP is our energy source). The ATP that had been consumed broke down. Suddenly, a substance called uric acid formed. Uric acid is the substance that we know can cause gout, but it's been long associated with obesity… It wasn't really thought that the uric acid might have a role in obesity. This was a big challenge, because no one really wanted to believe that, but what we were able to show is that uric acid can actually stimulate fat accumulation in cells through this process of working on the mitochondria where the ATP is made,u201D Dr. Johnson explains.

Learn More…

I strongly recommend you listen to this interview in its entirety, or read through the transcript. In it, Dr. Johnson also discusses other recent research that backs up the theories discussed above.

I have written about the dangers of sugar for a long time, and of course, variables like exercise and calorie intake play a role in obesity, but I am fully convinced that if we can educate the public about the primary role fructose holds in creating obesity, we can actually reverse and eventually help to eliminate the obesity epidemic.

So please, keep learning, and keep sharing this information with your family and friends. I also highly recommend reading Dr. Johnson's new book – which by the way is published by, as it offers tremendous insight into what's really making you gain weight, and why it's so difficult to lose.

The obesity trend will not magically reverse itself — it will require each and every one of you to become educated, savvy consumers, and it will require that you bring back home cooking; using fresh, whole, organic foods.