Wednesday, June 8, 2011

What the Fruc(tose)?!?

Fructose, simply put - fruit sugar.  We've all heard about it; good (few and far between), bad (most common), and otherwise (the controversy).  The most common 'bad guy' is not just plain old fructose but its evil counterpart - high fructose corn syrup (HFCS).  This stuff has been linked to hypertension, obesity, diabetes, insulin resistance, elevated blood lipids, atherosclerosis, non-alcoholic fatty liver disease, kidney stones, gout, and metabolic syndrome. 

Before we break into all the in's and out's of the "F" word (fructose), here's a look at some not so sweet sugar stats.  We (Americans) consume on average 38 teaspoons of sugar every day - that adds up to 130 pounds of the stuff each year; 36% percent of it comes from energy drinks, soda, and sports drinks.

Now, back to fructose and HFCS.  What is it and is one really worse than the other?  First, some basics:
Fructose is a 'simple sugar' (monosaccharide), just like glucose and galactose.  All three have roughly 15 calories per teaspoon.  It's a combination of these 'simple sugars' that make up the other
-oses (sucrose or table sugar is a combination of fructose + glucose).  Unlike glucose, which serves as the body's main fuel source and is readily used for energy, fructose is not so easily metabolized.  Let's get 'sciencey' for a minute.  Glucose, the body's preferred fuel source, uses insulin as a shuttle to get into cells where it is used for energy.  Insulin controls the amount of glucose in the blood at any one time.  Unfortunately, fructose requires a little more work.  It isn't regulated by insulin nor is it shuttled into cells for use.  Fructose is carried from the small intestine to the liver via a special carrier protein called GLUT-2.  The liver metabolizes fructose into a variety of different things including glycogen, triglycerides, LDL cholesterol and uric acid.  It is this special processing that results in fructose's negative health effects.

Now onto the controversy - for every study or ad telling us that HFCS is bad there's another one sending the opposite message.  What's the deal?  Now that we see how fructose is metabolized, (this applies to ALL fructose -  from fruit, from soda, and from HFCS and other sweeteners), is HFCS really any worse than plain old fructose, table sugar, honey, agave, etc.?  Consider this - HFCS and table sugar have nearly the same amount of fructose.  Table sugar (sucrose) is 50% glucose and 50% fructose.  There are two types of HFCS; one of which is 55% fructose and 42% glucose (used in beverages) and one that's 42% fructose and 53% glucose (used in cereals, yogurt, etc.).  Compare that with honey - 50% fructose and 50% glucose, agave - 56-92% fructose depending on the brand, and an apple - 70% fructose.  Even the 'innocent' strawberry is about 52% fructose...  Does that help clear up the 'limit fruit' recommendation...?  Fruit's redeeming factors are that, comparatively speaking, it's low in calories, has some fiber, vitamins and minerals unlike the 'hard' sugars.  Whether it's fructose, sucrose, dextrose, maltose, xylose, invert sugar, molasses, fruit , fruit juice concentrate, maltodextrin, turbinado sugar, malt syrup, brown rice syrup, agave nectar, maple syrup, HFCS and yes, even straight-up fruit, it's all going to the liver and the net result will be the same.

There really is no definitive answer as to which is the worst.  As I like to say "Sugar is as sugar does."  And what does 'sugar do' - not a whole heck of a lot of anything good.

So, what the fruc(tose)?!?  Let's make it a 'sugar-free summer'!



  1. Thanks for the heads up on that! Robb Wolf likens fructose to your crazy aunt who appears innocent enough, but messes up a perfectly good party by being weird and destructive. I suspect the liver has other things to do than to have to obsessively deal with fructose. Thirty-six teaspoons of sugar are excessive. We do better on a lot less and we can even use our protein and fat calories for energy as well.

  2. It is sad that people put HFCS and fruit into the same category. Any source of fructose other then the natural fruit is troublesome.

    There are things I like about the paleo diet, however the fruit limiting belief is silly, IMO.

    100 grams of banana has almost 5 grams of fructose. While a can of soda contains around 12 grams of fructose. I believe I've seen numbers of around 3 cans of soda a day for the average male teen. The body is fully capable of dealing with normal levels fructose, but the 36 grams of soda each day + the fructose coming in during most other meals of the day is the issue. Imagine the fructose content of a Burger King meal with the large soda and amount of ketchup on the fries and burger, the bun has HFCS too.

    From what I understand, the net result is not the same. The amount is a difference.

  3. I don't think you intend to do this, but it seems as if you are somewhat anti-fruit. What do you mean by "limit fruit?" How many servings a day do you recommend?

    If fruit is my biggest source of fructose during the day is that a bad thing?

  4. Susan,
    There seems to be something to limiting fruit in favor of more starchy, lower fructose carbs like sweet potatoes, yams, roots and tubers, winter squash etc. If you eat paleo and are trying to lean out or are looking to optimize performance, recovery, health and longevity switching out fruit for more favorable carbs might be a smart move.

  5. limiting fruit as it is sugar is sensible. But eliminating the pleasure of in season fresh picked fruit is punitive and silly. I do, however appreciate what you say, Amy, that to achieve a weight loss goal, it's wise to lay off for a time.


  6. Amy,

    Thoughts on the difference between unbound fructose in HFCS (and subsequent production of reactive carbonyls) vs. bound fructose molecules naturally occurring in whole food?

  7. Doesn't Cordain say eat all the fruit you want, unless you're obese?

  8. First off awesome article Amy.

    From the reading I have been doing most studies show that if you are going to eat sugars (such as fruit or what ever your vice) the optimal time to do it would be after a workout when you system is at a low and needs the insulin boost to get things going. Generally speaking anything within 30 min of a workout shouldn't even count because the chaos that is taking place in your body. I'm not saying go kill yourself in the gym just so you can justify eating a tub of your favorite ice cream just be conscious of what you are putting in and when. All in all sugar does have its side affects but like Watts said it really isn't the quality of the sugars that are affecting people today it's the quantity. If you want to truly live at your maximum potential listen to Amy and don't look back. After a couple weeks even days for some people you'll start to feel the difference.

  9. Love this article because it speaks the truth. I hear the argument countless times from people around me that because it's "fruit" or "natural" sugar in fruits that it's okay to eat as much as you want. Sugar is sugar and I'll choose to get my nutrients and minerals from vegetables any day rather than from fruits.

  10. Numerically, it is the sum of the calories that matters. We tend to eat more good tasting stuff, and fruit generally tastes great. Cut carb to loose weight. If your weight is ok, eat what ever you like. If your weight changes, adjust your eating.

    Addition to food is more of an issue.

  11. Hi Amy,
    I have a question for you regarding fruit. I have a friend (she is not diabetic) but has experienced low blood sugar in the past. she recently went paleo and is experiencing crashes more than ever (although this seems counterintuitive to me). do you have any idea what could be happening? do you think she needs more carbs? in the past she has always relied on fruit and fruit juice to lift her crash, but im assuming that is not the best option and could maybe just set her up for another crash??? she is not active and pretty overweight . . . any insight would be greatly appreciated!!

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