Has Fructose Been Framed?

fruit chasing man in dark alley

Fructose: The New F Word

We used to be told that fructose (aka “fruit sugar”) was the ideal sweetener for people with diabetes because it doesn’t cause blood sugar spikes. However, in recent years its reputation has tanked, as some experts have decided that fructose is the silently sinister sister of the sugar family, single-handedly responsible for obesity, diabetes, heart disease, fatty liver disease, gout, cancer, and worldwide destruction. Perhaps most famously, UCSF pediatric oncologist Dr. Robert Lustig delivered a lecture about the perils of fructose in which he blamed fructose for the childhood obesity epidemic and dubbed it a poison.

But wait just a gosh-darned minute…Mother Nature wouldn’t hide a poison inside an apple, would She?

Just a few weeks ago, yet another fructose study1)Luo S et al PNAS | May 19, 2015 | vol. 112 | no. 20 | 6509–6514made headlines, including this New York Times article and a nicely balanced report in ScienceNews claiming that fructose may make it harder to control appetite and food cravings than glucose, paving the way to overeating and obesity.

Many of us had finally come to understand that excess refined carbohydrate intake, not saturated fat, is endangering our health, and some of us started cutting back on sugar and flour to protect ourselves. These changes aren’t easy—baked goods, pasta, ice cream and candy are cheap, convenient, and delicious! I personally would love to be told that I can safely eat all sugars except for fructose, and I bet I’m not alone. So what’s going on here?

It turns out that fructose is a fascinating and complicated topic, so what started out as a single blog post became a four-part series (my condolences in advance). Those of you already familiar with my pro-meat, pro-saturated fat, pro-cholesterol, anti-carbohydrate, plant-foods-are-not-to-be-trusted nutritional philosophy might guess fructose would be an easy target for me, but to my own surprise, the more I dug into the science, the more I found myself defending the the fruity little guy. Fructose is no health food, but it’s no poison either. Well, no more poisonous than any other sugar has the potential to be, anyway. Come with me to discover what fructose is, how it compares to other sugars, and how much you can safely consume. No time for details? Feel free to skip to the summary points.

I’ve broken up the fructose fun into five articles to aid digestion:

  1. FRUCTOSE METABOLISM VS GLUCOSE METABOLISM. Today’s article reveals fun facts about fructose and how it behaves in your body compared to other sugars. If you had as much trouble following Dr. Lustig’s chemistry lesson as I did, read on to understand what the real differences are between fructose and glucose processing.
  2. DOES FRUCTOSE MAKE YOU HUNGRIER? In article two, Fructose Raises Appetite… for Better Science, we look under the hood of the new study that claims fructose can cause overeating to see if we should be concerned.
  3. FRUCTOSE AND YOUR HEALTH. In article three, Is Fructose Bad for You? A Summary of the Research, I review and summarize for you the latest research about fructose and diabetes, obesity, fatty liver, gout, heart disease and cancer.
  4. FRUCTOSE MALABSORPTION. In article four, Is Fructose Malabsorption Causing Your IBS? we look at how to find out if fructose is the culprit of your IBS symptoms, and if so, how you can minimize fructose in your diet.
  5. FRUCTOSE IN THE REAL WORLD. In the fifth article, How to Diagnose, Prevent, and Treat Insulin Resistance, we finally look at real foods! We examine your favorite sweeteners, fruits, vegetables, grains and legumes to see how they measure up. I’ll share with you my dietary recommendations, provide a downloadable PDF with medical tests for insulin resistance that you can discuss with your health care provider, and include an infographic with helpful tips to guide you in your dietary decisions.

And away we go!

First, a bit of context.  Where does fructose stand in relation to its natural simple sugar sisters?

Simple Sugars, Short and Sweet

Glucose: aka blood sugar. A 6-carbon monosaccharide (single sugar ring) used by all plants and animals as their primary energy source, and therefore critically important to life. Glucose is not very sweet—less than half as sweet as fructose– which is why glucose isn’t used as a sweetener. All plants contain some pure glucose, and some plants also contain glucose linked together in long chains in the form of starch (amylose), which is not sweet at all. Dextrose is simply the name given to the glucose extracted from plant starch.

Fructose: aka fruit sugar. A 6-carbon monosaccharide (single sugar ring) used by plants to sweeten their fruits and make them more appealing to animals. Fructose is the sweetest of all the natural sugars and is found in its free form primarily in sweet fruits and vegetables. In humans, fructose is used by only a few cell types in the body for energy (notably sperm cells), but the body can make fructose from glucose where necessary.

Sucrose: aka table sugar, white sugar, cane sugar, beet sugar, or just plain old sugar. Sucrose is a disaccharide (double sugar ring) used by plants to transport and store energy. Each sucrose molecule consists of one glucose molecule bonded to one fructose molecule. We break this bond easily during digestion to free up glucose and fructose for absorption:

There are a few other simple natural sugars I’m not describing here for the sake of brevity: lactose and galactose (from milk), maltose (see article four), and trehalose (from mushrooms). All of them turn into glucose in our bodies. Even unnatural sugars such as high fructose corn syrup, brown rice syrup and agave syrup all turn into glucose and/or fructose in our bodies. [There’ll be more details about these sweeteners in article four.]

Since all of the sugars we eat ultimately break down into glucose, fructose, or some combination of the twofrom here on we will focus on the differences between fructose and glucose.

The arguments in the fructose vs glucose war center around differences in how fructose and glucose are handled by the liver, so we unfortunately have to review some biochemistry. I’ll make this as painless as possible. Pretty pictures are included. Sit back, have yourself a nice baked potato, and we’ll get started.

GLUCOSE METABOLISM

You can think of your baked potato as a lovely lump of glucose. Baked potatoes are full of a starch called amylose, which is just long chains of glucose molecules. Your intestinal enzymes rapidly digest potato starch into pure glucose and your intestinal cells absorb it completely, causing your blood glucose (blood sugar) to spike. Fast on its heels, insulin rushes into your bloodstream to direct glucose traffic and bring your blood sugar back down.

Your liver is the first organ to see the blood glucose wave, and soaks up about 1/3 of the glucose for processing.2)Moore MC et al 2012 Adv Nutr 3: 286–294 The remaining 2/3 of the glucose circulates throughout your body to feed your cells. The absorption of glucose by liver cells does NOT require insulin.3)Rojas JM and Schwartz MW 2014 Diabetes Obes Metab 16 suppl 1:33-40, but insulin is required to keep the glucose inside liver cells.

Insulin is not simply a blood sugar regulator; it is a powerful growth hormone.

Once glucose is locked inside a liver cell, the cell can do a variety of things with it, depending on the circumstances. Remember that you have an insulin spike travelling with your glucose. Insulin is not simply a blood sugar regulator; it is a powerful growth hormone. Insulin sets the stage in the body for growth, and one of the ways it does this is by telling your liver: “build, grow and store!” If insulin is present, it will crank up the activity of a series of enzymes in the liver cell needed to process all the glucose rushing in.

The first liver cell enzyme turned on by insulin is glucokinase, which immediately slaps a phosphate onto glucose, trapping glucose inside the cell so it can’t leak back into the bloodstream.4)Massa ML et al 2011 IUBMB Life 63(1):1-6 The phosphate comes from a molecule called ATP (adenosine TRI-phosphate), our body’s chief energy storage molecule. After ATP sacrifices one of its phosphates to glucose, it is then called ADP (adenosine DI-phosphate). When your insulin level is low, as it should be between meals, glucokinase will turn off so that the liver can release glucose back into the bloodstream to keep your blood sugar from dropping.

Which pathway glucose takes once it’s captured by a liver cell depends on MANY things, including levels of insulin, ATP, and a variety of other molecules that help the liver cell know what its needs are at any given moment. These molecules control glucose processing by turning enzymes on and off. The master regulator enzyme on the glucose conveyor belt is called PFK-1. One of the things that turns PFK-1 on is insulin, and one of the things that turns it off is ATP. When PFK-1 is turned on, glucose will be sent to the chopping block to be cut in half for further processing.

Wow, that was a lot to take in…you’ve earned a cute baby animal photo break. Awww, isn’t she adorable? Ok, back to glucose!

Under the influence of insulin, your liver can do any of following things with the new glucose load, depending on your body’s needs at the time:5)Lehninger’s Principles of Biochemistry; Nelson and Cox (eds), 5th edition published by WH Freeman and Co, NYC 2008

BURN IT or FERMENT IT for energy (ATP). If liver cells need energy to conduct their cellular business, glucose will be chopped in half in preparation for burning in the mitochondria (your cellular furnace). Mitochondria require oxygen to turn glucose fragments into ATP; this process is called aerobic glycolysis. If there’s not enough oxygen around to burn it, glucose will be fermented instead, producing lactic acid (anaerobic glycolysis). The liver can release lactic acid into the bloodstream to be burned by working muscle or other oxygen-starved cells for energy.

TRANSFORM IT into 5-carbon building blocks (ribulose-5-phosphate) plus powerful helper molecules (NADPH) required to build components of new or growing cells, such as proteins, RNA, and DNA. This “build and grow” route is called the “pentose phosphate pathway.”

STORE IT as glycogen or fat. In a process called glycogenesis, the liver strings glucose molecules into long chains of animal starch called glycogen, which is stored in the liver. If the liver’s glycogen tank is already full, glucose can be turned into fat instead (lipogenesis). The healthy liver doesn’t store much fat; it prefers to ship it out to other cells by releasing it into the bloodstream as triglycerides.

Glucose can be burned, stored, or used to build new cellular components

(If your browser is not displaying this image, view it here.)

So, as you can see, glucose is a versatile little dude whose destiny depends on sophisticated signals between food, hormones, the liver, and the rest of the body. How is fructose different? Have a nice big swig of agave syrup (mostly fructose, as you’ll see in article four) and we’ll get started.

Differences between Glucose and Fructose Metabolism

Difference #1: The intestine does not absorb fructose as well as it absorbs glucose. There’ll be more details about fructose absorption issues in articles two and three, but for now suffice it to say that pure fructose is difficult for most of us to absorb completely.

Difference #2: The liver absorbs a LOT more fructose than glucose. Since you don’t need fructose to feed your cells, there’s no need to keep any of it in circulation, so your liver removes as much of it as it possibly can, like a big sponge. 6)Laughlin MR 2014 Nutrients 6:3117-3129

Difference #3: Glucose triggers insulin release, but fructose doesn’t.7)Mayes PA 1993 Am J Clin Nutr 58(suppl)754S-765S Insulin plays a major role in turning key enzymes on or off, so without an insulin spike, the enzyme environment within the liver cell may be very different, and therefore the processing pathways available to fructose bits may be very different. (The important truth is that all foods that contain fructose also contain glucose, and some fructose gets converted into glucose, so when you consume fructose there usually WILL be some insulin around, but just for now, let’s stick with pure fructose for now to highlight the metabolic differences).

Difference #4: The first two steps in fructose processing are completely separate from glucose processing, unregulated, and irreversible. Once inside the liver cell, ATP tags fructose with a phosphate no matter what, trapping it inside the cell. The enzyme responsible for this step is fructokinase, which is turned on by fructose, and doesn’t listen to insulin. Next, an enzyme called aldolase B unceremoniously chops fructose in half. These first two steps completely bypass PFK-1, the master enzyme that controls glucose processing, so regardless of what your body needs or wants at the moment, fructose will be broken down, because, unlike glucose, fructose molecules can’t be stored, and can’t be released back into the bloodstream. The liver cell has no choice but to break down every molecule of fructose it receives.

Similarities between glucose and fructose metabolism

Which pathway fructose and glucose take is determined by your body’s needs at that moment and by the amount of fructose and glucose you eat.

Glucose and fructose travel separate roads for just the first few steps of processing. However, as soon as fructose gets chopped in half, it turns into the very same 3-carbon molecule that glucose forms when glucose is chopped in half (glyceraldehyde-3-phosphate, or G3P for short). All G3P molecules, whether they come from fructose or glucose, get funneled into a single common pathway. From that point on, you can’t tell the difference between them; fructose bits can turn into ATP, lactic acid, building blocks, glycogen, or fat, just like glucose bits can, because the bits are identical. Fructose pieces can even turn into glucose! Which pathway fructose and glucose take is determined by your body’s needs at that moment and by the amount of fructose and glucose you eat.8)Sun SZ and Empie MW 2012 Nutrition & Metabolism 9:89.

illustration simplifying the basic components of glucose and fructose metabolism in the liver

This illustration highlights the key differences between glucose and fructose metabolism in the liver. Fructose follows its own unidirectional, unregulated pathway until it is cleaved into Glyceraldehyde-3-Phosphate (G3P), which is identical to G3P from glucose. At that point, the G3P from fructose enters the glucose metabolic pathway and can become lactic acid, ATP, or fat, or can cycle back through the glucose pathway to enter the Pentose Phosphate Pathway, become glycogen, or re-enter the bloodstream as glucose. (If your browser is not displaying this image, view it here.)

Phew, you are doing great. Reward yourself with this furry-headed creature! Awww.

Fructophobic Claims

The gist of the fructophobes’ argument is that fructose is dangerous because it bypasses the usual checks and balances that control glucose (namely insulin and PFK-1), heads straight to the liver, and turns instantly into fat, slashing and burning precious ATP (energy molecules) along the way, leaving piles of toxic waste (uric acid) in its wake.9)Sievenpiper JL et al 2014 Curr Opin Lipidol 25:8–19

Uric acid? What’s that? Under normal circumstances, whenever ATP donates a phosphate to fructose or glucose, the ADP leftover is recycled back into ATP. However, the liver absorbs only a portion of the glucose you consume, whereas it absorbs almost all of the fructose you consume. If too many fructose molecules flood the liver, they could theoretically use up too much ATP too fast, and ADP leftovers could overwhelm the recycling machinery. If ADP can’t be recycled, cells can turn it into a waste product called uric acid and send it out via the bloodstream to the kidneys for removal from the body. High levels of uric acid in the blood can trigger gout in some people. For more information about gout see article three of this series, and also my post Got Gout But Love Meat?

SCARY CLAIM #1: Fructose is Fast Fat

Those in the fructose-phobia camp would say that the liver turns all the fructose we eat instantly into fat, and that the fat either pours into the bloodstream (raising bad cholesterol and triglyceride levels and increasing risk for heart disease) or getting trapped in the liver, causing fatty liver disease.

As you now know, fructose can turn into anything that glucose can. There’s no evidence in humans that a realistic amount of fructose under ordinary circumstances causes an increase in fat production by the liver compared to glucose.10)Sievenpiper JL et al 2014 Curr Opin Lipidol 25:8–19

In fact, a review of studies that used radioactive tracers to stalk fructose as it traveled through people’s bodies found that less than 1% of the fructose consumed by the research subjects ended up as fat! 11)Sun SZ and Empie MW 2012 Nutrition & Metabolism 2012, 9:89 A decent amount of the fructose, as much as 54%, actually turned into glucose! Why did so little of the fructose turn into fat? Fructose doesn’t trigger insulin spikes, and you need insulin to turn on fat-building pathways. Insulin is a growth hormone that tells the liver to grow and store; when insulin levels are low, fat-building pathways are turned off. This is how low-carbohydrate diets work.

SCARY CLAIM #2: Fructose drains cells of ATP, our precious energy molecules

There is no evidence that ATP depletion occurs in humans except when fructose is injected directly into someone’s veins (don’t try this at home…).12)Abdelmalek MF et al 2012 Hepatology 56(3):952-96013)Cortez-Pinto H et al 1999 JAMA 282(17):1659-166414)Nair S et al 2003 Am J Gastroenterol 98(2):466-470

SCARY CLAIM #3: Fructose raises uric acid levels, which can cause gout.

While there are human studies showing that fructose can raise uric acid levels more than glucose can, all of these studies used extremely high doses of fructose (approximately 215 grams)—this is roughly the amount of fructose in 2-1/2 liters of Mountain Dew or grape juice (don’t try this at home either). In addition, people in these studies were given these mega-doses of fructose on top of their usual diet, increasing their daily calorie intake by about 1/3. Therefore it is impossible to say whether it was the extreme fructose exposure or simply the excess calories that caused uric acid levels to rise in these cases. Human studies of fructose under normal calorie conditions found no increase in uric acid production.15)Wang DD et al 2012 J. Nutr. 142: 916–923, Angelopolous TJ et al 2015 J Clin Hypertens 17:87-94

SUMMARY OF KEY POINTS

  • All of the sugars and starches in our diet, whether natural or artificial, ultimately break down into glucose, fructose, or a combination of the two.
  • Glucose from sweets and starches spike in the bloodstream, triggering an insulin spike. Fructose spikes in the liver, and does not directly trigger an insulin response.
  • Insulin is a powerful hormone that puts your liver in growth and storage mode.
  • The first phase of glucose processing is very tightly controlled because glucose must obey both insulin and the regulatory enzyme PFK-1, whereas fructose bypasses these important checks and balances.
  • The remaining phases of glucose and fructose processing merge and become identical. Therefore both glucose and fructose can turn into ATP (energy), lactic acid (energy), glycogen (storage), ribulose-5-phosphate (building blocks for new/growing cells), or fat, depending on the body’s needs.
  • Very little of the fructose we eat turns into fat in the absence of glucose/insulin.
  • There is no evidence that fructose drains cells of ATP unless you inject it into your veins.
  • Fructose only raises uric acid levels in the blood at high doses under high calorie conditions.

CONCLUSIONS:

Yes, fructose is handled differently by the body than glucose in a variety of ways. It is absorbed less well by the intestines, absorbed in far greater amounts by the liver, and the first two steps of its processing in the liver are unregulated, meaning that fructose gets broken down by the liver no matter what. However, there is no reason to believe that these metabolic differences make ordinary amounts of fructose any worse than ordinary amounts of glucose when it comes to ATP reserves, fat production, or uric acid levels. Fructose byproducts are identical to glucose byproducts and can turn into all of the same things that glucose can. Fructose is primarily just another source of glucose in the diet.

If fructose were an actual poison, Mother Nature would not have installed receptors in our intestines designed specifically to welcome fructose into our bodies.

 

How do I know fructose is not a poison? The body has a variety of sugar receptor molecules that help simple sugars enter cells. One of them, called GLUT-5, is specific for fructose alone16)Douard V and Ferraris RP 2008 Am J Physiol Endocrinol Metab 295(2):E227-E237.We also turn a good deal of the fructose we eat into glucose, a molecule critical to life. We do not require fructose (or any sugar) to live or be healthy, but fructose can certainly be used as a source of nourishment, and in my book, that means it’s not a poison. Yes, too much fructose, like too much of anything, can be potentially harmful, but that doesn’t make it poisonous. If you drink too much water, your sodium levels will drop, you will have a seizure, and you could die. But water is clearly not a poison. In the case of fructose, as in the case of water, the dose makes the poison. How much fructose can you safely eat? it all depends on who you are…find out more in article four!

BOTTOM LINE: I don’t believe that the fact that fructose is handled differently than glucose by the body makes fructose any worse than glucose when it comes to the health of our cells. As you’ll see in the rest of the series (if you’re still alive after having slogged through this basic science article), fructose is not the nutritional super-villain it’s been made out to be. What is the dietary scourge of our time? Sugar. Excessive sugar of any type, including fructose, but perhaps glucose worst of all. If you don’t believe me, stay tuned for more!

There you have it. Did that make sense? Are you any more or less afraid of fructose than you were before? Please share your thoughts and questions below so we can continue to learn from one another.

In article two, Fructose Raises Appetite…for Better Science, we answer the following questions:

Is the new study about fructose and appetite worth your attention? How good are scientific studies of fructose in general? Can we count on them to give us useful information about what we should eat to be healthy?

Sign up below if you’d like to have future articles delivered to your inbox.

Sign up to be notified of my latest posts!

Signup now and receive an email once I publish new content.

I will never give away, trade or sell your name or email address. You can unsubscribe at any time.

Tagged with:
Has Fructose Been Framed? Find out what fructose is ACTUALLY doing to you.

References   [ + ]

Tagged with:
  • Puwdytat

    Fructose isn’t easy to digest, which is why many people end up with SIBO after ingesting it. The fact that fructose has been processed and concentrated into high gruxtose corn syrup, which is a massive overload for our bodies…its like pourinf sugar in your gas tank….we can’t digest it, so we end up with massive bacterial and yeast ivergrowths in our small intestines…where it is not supposed to be….and then a host of other diseases develops.

    • Dear Puwdytat

      Right you are! We digest glucose completely, but most of us don’t absorb fructose very well, and there’ll be more details about this in article two. In article four we’ll see that high fructose corn syrup is no worse than regular sugar (sucrose) for our health, even though one is natural and the other isn’t.

  • JohnH

    Thanks for this new article series Dr. Ede.
    I’ve restricted my fruit consumption to low-fructose fruits in lower quantities to what I ate previously so I am looking forward to finding out if I may be able to revise this.

    • Hi John

      As we’ll discuss in article four, some of us are luckier than others when it comes to fructose processing, so depending on the reasons why you decided to limit fructose in the first place, you may or may not be able to ease up on your restrictions. Thanks for reading!

  • RIchard Feinman

    Great article. We made some of the same points in our review (Feinman RD, Fine EJ: Perspective on Fructose. Nutr Metab (Lond) 2013, 9). We also made the point that insofar as fructokinase reduces ATP (transiently), it indirectly does regulate PFK-1 increasing processing of glucose. Also, the product of fructokinase F-1-P tells the liver to pick up more glucose from the blood. In other words, the liver expects glucose to come in with any ingested fructose which is how we normally eat — humans almost always take in more glucose than fructose. I think that this is why, as you point out, taking in pure fructose is what is bad — by regulating PFK-1 and glucokinase in the direction of taking in more glucose, this may be disruptive to the control of blood glucose.

    • Dear Dr. Feinman

      I’m honored that you read this post and took the time to share your thoughts! I am glad to be learning more from you, particularly about the complex regulation of PFK-1. I find it intriguing that fructose metabolism enhances glucose metabolism, just as I was surprised to learn that glucose ingestion facilitates fructose absorption in the intestine. As you say, we always eat fructose with glucose, so it makes sense that our bodies process them synergistically. I wish I had encountered your excellent review article sooner, as its scope and clarity would have saved me countless hours of frustration in my quest to understand this complicated topic. I look forward to drawing from your review to improve the information in the remaining posts, especially the next one, which focuses on fructose research methodology. I am delighted to see that it is an open access article, so I will post links to it within this series so that people seeking a more sophisticated and thorough understanding of fructose metabolism can benefit from it. Readers, here is a link to Dr. Feinman’s work: http://www.nutritionandmetabolism.com/content/10/1/45

    • George

      So we are likely correct in wanting HFCS banned and replaced with sugar to restore the glucose/fructose relationship in many those bad foods we drink and eat.

      • Hi George
        There’ll be more information about HFCS in article four of this series, but the surprising truth is that there is no difference between HFCS and plain old sugar.

        • Ike_Kiefer

          That’s a sweeping statement. Since the typical ratio of fructose to glucose in HFCS is 55:41 (versus 50:50 for sucrose), and since these are in monosaccharide form (vice disaccharide), I would be very surprised if it were true.

  • Marijke

    According to Dr Natasha Campbell McBride, people with a damaged gut wall lack the enzymes to digest disacharides. As all higher sugars are broken down via disacharides, and they are too big to pass the gut wall into the blood, the disacharides end up in the large intestine where they are fermented, causing trouble.

    So sugars and starches have other ways to harm some bodies.

    • Hi Marijke
      As we’ll see in article three, fructose, which is a monosaccharide, doesn’t need to be digested down into anything smaller–it is already as small as possible, but yes, as you rightly point out, many people have difficulty absorbing fructose, so it ends up in the colon, where bacteria ferment it.

  • Elizabeth Bowler

    Excellent, as always Dr. Ede. Fructose seems to be the new cholesterol re being unfairly demonized.

  • paleopete

    I am really glad to see someone is writing such an indepth series on fructose metabolism…..In our OFM program we actually utilize fructose as a “strategic” carbohydrate for fueling fat-adapted athletes because as you are so elegantly explaining here the pathway is very different than in an athlete being fueled by glucose.

    • Hello PaleoPete

      Glad you like the post–thanks for reading! I haven’t studied the effects of fructose on athletes, but imagine there could be some advantages, since a higher percentage of fructose enters the liver than glucose does and could therefore replenish glycogen stores more efficiently than glucose.

      • paleopete

        Yes, what we are doing at Vespa with our OFM program (OFM=Optimized Fat Metabolism) is literally ahead of the science (even Jeff Volek is saying this)….you are correct about this. but more so how fructose converted into fatty acids can then be readily converted into ketones and glucose in a fat-adapted athlete to meet demand……interestingly enough we have found both alcohol and fructose to be great dietary substrates for certain athletes in moderate amounts. We see these fascinating post exercise surges in ketones and glucose in athletes….the ketone surge is actually very moderate in most while the glucose surge can be surprisingly high yet transient because this glucose is shunted to the muscles and stored as glycogen (Jeff just submitted a paper on this). But here is the deal…..these athletes are seeing this even when exercising in a fasted state!

        Don’t know how much you follow Jeff but the pubs which will be emerging from the FASTER study are going to create a paradigm shift in sports physiology because the data from FASTER for the Low Carb Cohort (LCD) literally is not considered possible. I worked with most of these guys….more interesting times ahead.

        • That is fascinating! I look forward to learning more about this topic! Thank you~

  • Esmée La Fleur

    I react terribly to whole fresh fruit. It makes me hungry and incredibly irritable. A mere 1/2 cup of berries can do this to me. I will be hungry for the entire rest of the day no matter what I eat, and I turn into a total bitch. Fruit does not do my body good.

    • Hello, Esmee

      I’m so sorry to hear this! We are all so different when it comes to food tolerances, no? Some of us are so much luckier than others. Even I, with my boatload of food sensitivities, can tolerate small amounts of most berries, and I’d be sad if I couldn’t 🙁 But it’s good to know ourselves well and listen to our bodies. So many people suffer from food intolerances without being aware of it, living with lots of symptoms and/or taking medications to try to feel better, not realizing that changing their diet could bring them tremendous relief.

  • Thanks for the very balanced perspective! It seems like the main food problems these days are fructose, transfats and, still, saturated fats. However, I would really love an article about the problems of our very skewed omega 6 to omega 3 intake due to seeds, soybeans, and peanuts, and their oils.From what I’ve read, our over-consumption of these fats, especially as refined oils, is problem number one, even when it comes to our sugar-eating habits. My own sugar cravings completely disappeared when I stopped eating nuts and seeds, and using the oils (including going to restaurants), ate more fish, and only used butter for my fat. It’s also delicious!

    Omega 6’s are converted into our inflammatory hormones when they are in excess, and inflammation may be the basis for all disease, as I understand it, so this is truly a serious problem. Yet, all the attention is on sugar and transfats, which are found in these unstable plant fats (also, when fed to animals, it ends up their fat as well as in ours).

    • Hello, Joan

      Yes, I agree, that the nature of the fats we eat is an extremely important topic. I have written about omega-3’s and 6’s, as well as saturated fat, on my fats page: http://www.diagnosisdiet.com/food/fats/ , and the information I have on that page supports your understanding 100%. I am also planning to write a post specifically about the role of fats in mental health in the near future. Thanks for the input!

  • Laura James

    Dr Ede, Will you say something about the efficacy of taking digestive enzymes when ingesting fructose containing foods? I have no idea if I have fructose malabsorption problems, yeast, sibo or histamine intolerance or some combination. Been studying and experimenting for years to come up with my best diet for preventing and healing and health.
    I’ve reduced sugars and carbs to a lower level but don’t try to avoid all together. I started taking both digestive enzymes and proteolytic enzymes and have seen some results. Mainly better feeling digestion and less histamine intolerance symptoms.

    As you know many of the Paleo template and low carb diets rely on a lot high histamine foods. I think that’s what got me into trouble on those regimens. Don’t get me started on Ray Peat. I was sick for a year after doing his milk/orange juice/slow-cooked meat/gelatin diet. Lots of histamines there.

    I’ve just been thinking that moderation plus keeping fructose/glucose/omega 6/and histamines low is the best path. But it’s a hard diet to do long term. It feels like the digestive and proteolytic enzymes help keep symptoms under control.

    • Dear Laura

      I have not studied digestive enzymes myself, but I will do my best to be helpful given what I have studied already. If the problem were strictly fructose malabsorption, digestive enzymes would be unlikely to help. Fructose doesn’t need to be digested down into anything smaller–it is already as small as it can be–it just needs to be absorbed before it reaches your colon, where bacteria will ferment it, leading to the potential for uncomfortable symptoms. There’ll be more about fructose malabsorption later in this series, as well. People with severe cases do need to avoid all fructose in order to feel better, but there are, as you point out, many causes of IBS-type symptoms, not just fructose malabsorption. I share your pain, as I struggled at first with ketogenic diets until I discovered my sensitivity to biogenic amines such as histamine. The most efficient strategy I know of to identify culprits is to remove all foods except for fresh/frozen meat/seafood/poultry and see if your symptoms go away (they often will), and then add back one food group at a time. If you have not already seen them, the following posts may be useful as well:

      http://www.diagnosisdiet.com/common-constipation-culprits/
      http://www.diagnosisdiet.com/histamine-intolerance/

      • Laura James

        Thanks for the info about fructose. The experiment goes on…

  • paleopete

    I am really glad to see someone is writing such an indepth series on fructose metabolism…..In our OFM program we actually utilize fructose as a “strategic” carbohydrate for fueling fat-adapted athletes because as you are so elegantly explaining here the pathway is very different than in an athlete being fueled by glucose.

  • Sweet summary! (the cutesy animal pics made me hungry though)

    Re: the gout thing, it’s not because of increased production of uric acid which is what everyone touts, but failure to utilise/excrete – which is something the rollercoaster of fructose/glucose/ketones can interfere with.

    • Dear Ash

      Your comment about the animal pics is hilarious:) There will be more information about gout and fructose in article three, but for now suffice it to say that you are correct–there’s a lot more to gout than elevated uric acid levels!