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    The Evils of Fructose

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    The Evils of Fructose
    by Cassandra Forsythe, PhD(c), CSCS, CISSN
    Next Page | Pages 1 2

    Are you looking for that nutritional edge to get your body composition to the next level?

    Have you been eating your "five-a-day" like a good boy should, but just can't shake that last bit of icing off your jelly belly?

    Well, take close note: if you reduce the fructose in your diet, you will lose that stubborn body fat!

    Fructose Metabolism 101, the simplified version

    Fructose is a type of simple sugar (a carbohydrate in its simplest form) that is much different than its sister sugar, namely glucose. When you eat fructose, it's absorbed more slowly in the intestine, and its absorption is slightly limited.

    Some people—like those with diabetes, see fructose as a superior simple sugar because it doesn't get used as quickly or as efficiently. What they don't realize, is that fructose is normally consumed at the same time as glucose, which speeds up the absorptive process.

    Once fructose passes through the intestine, it's quickly taken to the liver for processing. Here, it has two fates: it's either turned into glucose and then stored as liver glycogen; or it's used for energy by liver cells.

    Unlike glucose, fructose can only be metabolized in the liver, whereas glucose can be passed to other body tissues, like your muscles.

    Why fructose is a problem for dieters:

    If you have a lot of fructose in your diet, it only has one place to go: your liver. If your liver glycogen levels are full, which is the case all times of the day except before you eat breakfast, then that fructose is turned into fat!

    Since your liver doesn't want to store this new fat, it ships it to other parts of your body; places you don't want it, like your abdomen or lower back.

    Do you now see why too much fructose in your diet can be one of the biggest reasons you can't shrink those last few fat cells?

    How do I avoid eating fructose?

    When people hear the word fructose, they usually think fruit. Ready for a shocker? Fruit is actually not the major source of fructose in your diet!

    Yes, it does have fructose, but only certain fruits are high in it, while others are relatively low. Not all fruits are bad for your body composition; vegetables are the same way.

    The major contributors of fructose in your diet, in descending order, are as follows:

    • High Fructose Corn Syrup (HFCS)
    • Table Sugar, which is a 50:50 combination of glucose and fructose
    • Brown Sugar
    • Maple Sugar
    • Cane Sugar
    • Molasses
    • Honey
    • Concentrated Fruit Juice
    • Fruits
    • Vegetables

    Avoid the top eight in this list at all costs!
    green apples

    Read labels carefully, because HFCS is hiding in almost every food you eat nowadays. And, just because honey is natural, doesn't mean you should use it in abundance.

    How do we really know fructose makes your fat?

    You must have been living under a rock if you haven't already heard about HFCS being related to every common human disease we face today, such as diabetes, heart disease, obesity and cancer.

    This relationship was first discovered in lab experiments with rodents. (1) When a high fructose diet (about 50-60% of total energy intake) is given to rats, they present symptoms of the Metabolic Syndrome, which is the precursor to full-blown diabetes and heart disease.

    These animals develop high blood pressure, endothelial dysfunction, weight gain, increased abdominal fat, hyper-triglyceridemia, and insulin resistance. The weight and fat gain is thought to be due to leptin resistance; rats that eat a high fructose diet long-term have higher leptin levels than rats that don't eat a lot of this simple sugar.

    Researchers then concluded that in humans, it's the fructose and not glucose that begins the cascade of Metabolic Syndrome risk markers (2); and this seems to be initiated by insulin resistance. Men forced to eat experimental high fructose diets develop insulin resistance within a week (3), compared to no insulin abnormalities in people given a high starch diet.

    Sucrose, also known as "table sugar" (glucose and fructose combination), is even worse: people given a 28% sucrose diet for 10 weeks not only develop insulin resistance, but also gain weight and have increased blood pressure!

    In another study, when overweight women were put on a "no-restriction" diet high in either sucrose, fat, or starch, only the high starch diet group lost weight and body fat. (4)

    Today, most Americans are eating about 70-100 grams of fructose per day, and we're getting fatter by the minute. In bright contrast to today's world, this nation consumed just 15 to 40 grams of fruit & veggie-derived fructose in the 19th century, when we weren't even close to being this chubby. (5)

    Why does fructose cause fat-gain?

    Fructose and fructose-containing foods will usually make your meals taste better, so you end up eating much more than necessary. They also fail to make you feel satisfied after you eat them, due to inadequate stimulation of leptin and ghrelin, the two satiety hormones. (6)

    There is also evidence that fructose slows your metabolism: kids who drink sodas and fruit juices (both are rich in HFCS and fructose) are fatter than those who don't drink them, but who eat the same amount of calories. (7)

    So, what kinds of fruits and vegetables can I eat and not get fat?

    Although fruit does contain some fructose, it's not the only sugar that it contains. Fruit is beneficial for you because it's the best natural source of antioxidants that help you fight free-radicals, a major cause of aging and muscle damage. It's also an important source of fiber.

    Your best bet is to choose fruits that are low in fructose, and only eat the higher fructose fruits in the morning, when your liver glycogen levels are low. At this time, your liver can use or store the fructose without converting it to fat.

    The following fruits are highest in fructose (per typical serving size)*. They contain more than 4 grams of fructose per serving.

    Stay away from these outside of an occasional breakfast:

    • apple
    • banana
    • cherries (1 Cup)
    • grapes (1 Cup)
    • mango
    • melon (2 wedges)
    • orange
    • pear
    • pineapple (2 rings)
    • watermelon (1 large slice)

    These fruits are lowest in fructose; they contain less than 4 grams of fructose per serving.

    You can eat these with less restriction:

    • apricot
    • avocado (1/3 medium; yes, it's a fruit)
    • blackberries (1/2 cup)
    • figs
    • grapefruit (1/2 medium)
    • papaya
    • peach
    • plum
    • raspberries (1/2 cup)
    • strawberries (1/2 cup)
    • tomato (yes, also a fruit)

    *Note, these values were calculated by adding all of the fructose plus half of the sucrose per typical serving size (i.e., a typical apple weighs 120 grams).

    Vegetables are much lower in fructose than fruits. The highest fructose-containing vegetables are corn and sweet potatoes, and they only have roughly 1.2 grams of fructose per serving. If you're really trying to keep this sugar low, also avoid white potatoes and green peas.

    Bottom Line:

    Fructose may be one of the reasons your body is not dropping the stubborn body fat you've been fighting for weeks, or even months. Before you start avoiding the produce section of the grocery store, start scanning the labels of some of your most frequently consumed foods.

    Does your salad dressing contain HFCS? Do you douse your morning eggs with HFCS-laden ketchup? Or maybe you're known to eat "all-natural" products made with honey?

    Once you've eliminated these major fructose-suspects, turn to your fruit intake. Don't eliminate it completely because some fruit will aid your overall health and studliness by fighting free-radical-induced aging and muscle damage. Just choose fruits lower in fructose.

    Apples may keep the doctor away, but with their high fructose content, they'll keep your six-pack just as out of sight.

    About the author:

    Cassandra Forsythe is a Ph.D. candidate at the University of Connecticut studying exercise science and nutrition. She received her M.S. in Human Nutrition and Metabolism and her B.S. in Nutrition and Food Science from the University of Alberta in Edmonton, Canada. She is certified as a Strength and Conditioning Specialist (CSCS) from the National Strength and Conditioning Association (NSCA), and is a Certified Sports Nutritionist (CISSN) through the International Society of Sports Nutrition (ISSN).
    lab rat

    At UConn, Cassandra studies under Jeff Volek, PhD, RD researching the effects of low-carbohydrate ketogenic diets and resistance exercise on risk factors for heart disease, diabetes and body composition. She works as a nutritional educator and weight-loss coach and is the author of two popular books for women: "The New Rules of Lifting for Women", co-authored with Lou Schuler and Alwyn Cosgrove, and "Women's Health Perfect Body Diet". In August 2008, she will begin her dietetic internship to become a Registered Dietitian and will complete her PhD in January 2009. She can be reached at her website.


    1. Segal MS, Gollub E, Johnson RJ (2007) Is the fructose index more relevant with regards to cardiovascular disease than the glycemic index? Eur J Nutr 46:406-417

    2. Elliott SS, Keim NL, Stern JS, Teff K, Havel PJ (2002) Fructose, weight gain, and the insulin resistance syndrome. Am J Clin Nutr 76:911–922

    3. Beck-Nielsen H, Pedersen O, Lindskov HO (1980) Impaired cellular insulin binding and insulin sensitivity induced by high-fructose feeding in normal subjects. Am J Clin Nutr 33:273–278

    4. Raben A, Vasilaras TH, Moller AC, Astrup A (2002) Sucrose compared with artificial sweeteners: different effects on ad libitum food intake and body weight after 10 wk of supplementation in overweight subjects. Am J Clin Nutr 76:721–729

    5. Raben A, Macdonald I, Astrup A (1997) Replacement of dietary fat by sucrose or starch: effects on 14 d ad libitum energy intake, energy expenditure and body weight in formerly obese and never-obese subjects. Int J Obes Relat Metab Disord 21:846–859

    6. Teff KL, Elliott SS, Tschop M, Kieffer TJ, Rader D, Heiman M, Townsend RR, Keim NL, D'Alessio D, Havel PJ (2004) Dietary fructose reduces circulating insulin and leptin, attenuates postprandial suppression of ghrelin, and increases triglycerides in women. J Clin Endocrinol Metab 89:2963–2972

    7. Dennison BA, Rockwell HL, Baker SL (1997) Excess fruit juice consumption by preschool-aged children is associated with short stature and obesity. Pediatrics 99:15–22

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  2. Back To Top    #2
    well what do you think?

    Wouldnt that make regular table sugar inferior to buying glucose? I think it was big ben who said had mentioned regular sugar will do in a thread about PWO nutrition


  3. Back To Top    #3
    Mecca V.I.P. tim290280's Avatar
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    Jul 2006
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    Yeh it is definitely all that fruit that is bad for us.

    Yes HFCS and table sugar are not that great. But steering away from processed foods should limit their intake anyway so it shouldn't be an issue.

    Next point is that KM and I have already had this discussion and I recently bumped his thread on this. My basic conclusion was that while fructose is not a great sugar source, the actual content you would take in from fruit is tiny. You would have to be eating fruit all day from the most fructose heavy fruits to take in enough to be worried about. The problem comes from HFCS which is a popular additive (mainly in America where they have subsidised the arse out of the corn industry instead of making real sugar). So eat fruit, just don't eat processed junk.

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  4. Back To Top    #4
    Quote Originally Posted by MrChewiebitums View Post
    well what do you think?

    Wouldnt that make regular table sugar inferior to buying glucose? I think it was big ben who said had mentioned regular sugar will do in a thread about PWO nutrition
    Well regular sugar will do. For the record i think that white sugar sucks and i was probably answering the question in context to the thread or a goal.

    you accept this article for what it inferrs you would be making a mistake. I hate the idea that fruit makes you fat. How often do you see a vegetarian that eats fruit all day that is obese? Sucrose is composed of glucose and fructose monomers. Fructose is EASILY converted to glucose in the liver.By her logic someone who ate fruit all day would have low blood sugar b/c their liver would be hogging all the glucose converted from fructose right? They would be experiencing glycogenolysis and lipolysis frequently b/c fructose is insufficient at supplying the blood stream with glycogen. So if someone ate fruit all day the way she tells it they would have low blood sugar b/c fructose does not supply the blood stream with glycogen and be fat b/c to much fructose gets stored as fat?

    This article trying to say that if your muscles required glucose and you supplied sucrose from fruit that of the glucose and fructose monomers supplied that zero fructose is going to enter the blood stream after glucose conversion. I disagree and my reasoning is all the above I just typed.

    This woman needs to be ashamed of herself for the way she is trying to discourage people form eating fruit.

    Even if the liver did store all that fructose as glycogen the bodies ATP requirements would cause glycogenolysis unless the person was over eating. In that case the point is invalid b/c overeating of any type will cause glycogen and fat to be stored.

    She notes a study that compares eating a complex carbohydrate diet to eating simple sugars, fructose. And she thought she was making this amazing discovery that a diet high in simple sugars like fructose caused higher insulin resistance and higher blood sugar levels. Add 60% of any kind of simple sugar to a diet and tell me the person will not have the same problems they had with fructose in the study she cited. If this is the case then why don't all fruitarians have diabetes? The people in the studies were most likely eating to many calories or at maintenance for body weight in general for their energy requirements. And the ones eating 60% of to many calories as simple sugars developed health problems, is this really a surprise? Wouldn't this happen with any sugar in that same situation. And for the record it does not even say that they ate only fruit which i am assuming they did not, but that is what she is inferring.


  5. Back To Top    #5
    Mecca V.I.P. tim290280's Avatar
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    Jul 2006
    Western Australia
    ^^ Isn't the problem the storage of fructose as it waits to be converted? My memory is vague.

    I agree that seeing a problem with fruit is just rubbish. I have met fat vegetarians and vegans, but they weren't big on fruit.

    Funny story, we were buying groceries yesterday and the fat check out chick asked as what this bag of fruit was (nectarines). The wife and I both commented that she looked like someone who wouldn't have eaten much fruit, ever.


  6. Back To Top    #6
    thx for the replies


  7. Back To Top    #7
    what about lactose? how is it in relation to replenishment of glycogen


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