fructose vs. glucose

Parent Cafe
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<p>idad, this one if for you!</p>

<p>Dr. Lustig seems to be saying that it is fructose that is toxic – he implies that glucose…well, I’m not really sure. He gives the example of all the rice - containing no fructose - that is eaten in Japan with no obesity problems.</p>

<p>I’m not saying folks should go crazy with glucose, but doesn’t he pretty much say stay away from only fructose – fruit juice, fruit, sweets and anything with added sugar, like bread?</p>

<p>I mean, it <em>is</em> hard to find fat people in Japan – and they do eat a lot of rice – many people three times a day, for breakfast, lunch and dinner. But rice has glucose, which is used by all the body’s cells - not fructose.</p>

<p>The words for ice cream, desert, donut, cookie, cake, chocolate are all English. The Japanese like sweets, but the portion sizes are much smaller than in the U.S., and they are are considered a special treat, not a daily event. </p>

<p>And fruit, far more beloved than sweets - is so expensive that most people consume only a very small amount with tea - and not every day. Yeah, a lot of the thinness is genetic, but still.</p>

<p>If anyone can explain this without using too much biochemistry, I’d really like to understand. I don’t mind long answers, but too technical and I’m afraid it will go right over my head.</p>

<p>I’m especially interested in the implications for weight loss and diabetes.</p>

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<p>I thought that glucose was the simple sugar that our body turns ALL our nutrients onto! It is what stimulates insulin production and storage of what is not burned off, I think.
I am sure you could google fructose, sucrose, krebs cycle to learn about this.
I, too, am curious why fructose is so bad in Dr Lustig’s eyes!! Perhaps it is because it is the simplest therefore most glycemic form of sugar that we consume…</p>

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<p>fructose is sugar derived from fruit or so i’ve heard.</p>

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<p>Table sugar (or cane sugar or honey or maple syrup) is 50% glucose and 50% fructose. Glucose and fructose are metabolized completely differently in the body. Glucose is metabolized by virtually every cell in the body. It is a primary fuel. It also triggers an insulin response which tells the body to store fat and just burn glucose until blood sugar levels return to normal.</p>

<p>Fructose is not metabolized anywhere in the body except in the liver, which has limited capacity to process a load of fructose. A small amount, like eating one orange, is not a problem. But, drink 12 ounces of orange juice and the abilty of the liver to process the huge intake of fructose is swamped. The liver converts it directly into fat (triglycerides that go into the blood stream and eventually into fat cells) and fat that causes fatty liver disease in a process that is essentially the same as the liver metabolizing alcohol. Fructose also triggers no insulin response and the various feedback loops that go with an insulin spike.</p>

<p>The other very big problem is that fructose metabolism in the liver is thought to be a primary trigger for insulin resistance. Once someone is insulin resistant, they make too much insulin too often in response to eating carbohydrates (glucose, grains, etc.) which makes their bodies store fat. Obesity and type II diabetes are essentially caused by insulin resistance. This insulin resistance may be the connection between fructose consumption and the inabilty to handle carbohydrates in general. Lustig thinks that it may be that carbohydrates in general may not be the problem IF it weren’t for the excessive fructose consumption and associated insulin resistance. We don’t know because the fructose consumption is so high.</p>

<p>His first step in his pediatric obesity clinic is to get kids to stop drinking sugar. No soda, no juice, no sports drinks, no sweetened milk.</p>

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<p>BTW, rice would be instantly converted into glucose in the stomach, just like wheat, bread, cereal, pasta, and most carbohydrates. How much glucose each of us can handle depends on our metabolism, the amount of energy we burn exercising, and the degree of insulin resistance. A healthy person with a skinny, high-reving metabolism, who runs marathons, and isn’t insulin resistant might well fall apart without a lot of carbohydrates/glucose fuel. However, someone who is insulin resistant is going to trigger excessive insulin levels all day long by eating carbohydrates and keep their body in a perpetual state of storing more and more fat. That in turn forces them to eat more (because so much fuel is being diverted into fat storage). It’s also going to force them to exercise less because they are literally starving (even while getting fat).</p>

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<p>Here’s something I didn’t know. Juice (from frozen concentrate) wasn’t invented until the end of WWII and didn’t become commercially available until the 1950s. Drinking sugar in large quantiies is, apparently, a fairly recent development.</p>

<p><a href=“http://www.history.com/shows/modern-marvels/videos/inventions-of-war-orange-juice#inventions-of-war-orange-juice[/url]”>http://www.history.com/shows/modern-marvels/videos/inventions-of-war-orange-juice#inventions-of-war-orange-juice&lt;/a&gt;&lt;/p&gt;

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<p>The part I do not understand is how FRUCTOSE causes insulin resistance. Is it more of a trigger than sucrose or glucose? If so, WHY? Seems counter-intuitive, given that glucose is what raises the insulin.
Is it because the fatty liver (from fructose) keeps the insulin pump on at all times??
Also, can excessive sucrose, glucose, complex carbs also lead to fatty liver?</p>

<p>So, does Lustig have an alternative to the glycemic index, ranking foods by their fructose content- aka the “frycemic” index? I assume that whole raw fruit is less frycemic because of all the fiber, as opposed to the liquified fruit in juice?</p>

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<p>The fundamental difference is that only 20% of the glucose gets processed by the liver. 80% gets burned by all of the other cells in the body. Fructose is ONLY metabolized by the liver, so 100% of the fructose you consume hits the liver.</p>

<p>Both glucose and fructose can be metabolized to fat by the liver, but it’s only a negligible percentage of glucose calories. Different story with fructose. 30% of fructose calories are converted to fat by the liver. Fructose is literally a high-fat diet. Some of the fat is triglycerides that go into the blood stream and eventually into storage in fat cells. Some is converted to free fatty acids that go into muscle cells. Lustig says that the elevated levels of these free fatty acids is the biochemistry link to insulin resistance. There is an additional form of fat that stays in the liver and causes liver insulin resistance.</p>

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<p>Yes. He recommends eating fiber with your carbs because the fiber slows the digestion and, therefore, reduces the spike of fructose. Plus, you can only eat one, maybe two oranges where you might be drinking the fructose of six oranges in a glass of juice. The fructose load is much much higher than you could ever get eating raw fruit. It’s a matter of dose.</p>

<p>An old six ounce bottle of Coke is one thing. A 20 ounce bottle of Coke is a different story.</p>

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<p>So this is why those energy gels like GU and Hammer Gel are mostly maltodextrin, which metabolizes into glucose and not fructose. Hmm.</p>

<p>What actual foods are quickly metabolized into glucose and not fructose?</p>

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<p>Glucose is probably the most abundant monosaccaride. Many natural polysaccharides are polymers made of multiple glucose units linked together by so called glycosidic bonds(starch, glycogen, cellulose, etc.). The longer the polymer, the longer it takes for the digestive system to break it down into individual units that then get absorbed and processed by the body (in cellulose, the glucose units are bound together in such a way that it takes too much energy to break them down, so the digestive system takes a pass). Maltodextrin is partially hydrolized (digested) starch, so it provide glucose in much easier digestable form.
(Of course, this is a greatly simplified description of carbohydrate chemistry).</p>

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<p>Let me rephrase the question: suppose I’m bicycling along and I want some quick-energy food. Gel is great stuff and hits like a bag of hammers, but let’s say I have another forty miles to go and I want to eat food. What should I eat that will quickly provide me with glucose in the bloodstream but won’t clog my body up with (hypothetically) useless fructose?</p>

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<p>Good question, CF. What I was trying to say that the folks who make GU probably have done some research to find the “perfect” quick source of glucose. </p>

<p>The answer probably depends on how much time you have between your meal and the next leg of your ride. Anything starchy will provide plenty of glucose, but it will take some time for the body to process it. Lactose, which is found in milk, is a disaccharide of glucose and galactose, and it gets digested much faster than starch, but with milk you will be also getting some protein which will linger in your stomach for a while.</p>

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<p>The fructose will also metabolize into glycogen in the liver, so – if you are glycogen depleated on a long ride, there will be no problem consuming fructose. The problem is not endurance athletes drinking sports drinks; it’s fat kids drinking sports drinks.</p>

<p>Starches (like potatoes, rice, etc.) and simple carbs (white bread, pasta, etc.) break down into glucose fairly quickly. Basically, any high glycemic food. It it spikes insulin, it’s probably putting a lot of glucose in the bloodstream (and vice versa).</p>

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One of the feedback loops that interesteddad is referring to is appetite suppression. The one good thing about an insulin spike is that your appetite shuts off (if the loop is working properly).</p>

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<p>What about maltitol? Is it good or bad for the body?</p>

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<p>That’s a two-edged sword, though. One of the strongest “hunger” triggers is blood glucose/insulin levels falling at a rapid rate. Thus, all things considered, trying to level things out and avoiding the big spikes is probably preferable from a fat loss standpoint.</p>

<p>This is a perfect example of how broken metabolism/insulin resistance can get you caught in a bad feedback loop. Eat carbs, the body releases way too much insulin to try to get a response. The extra jolt of insulin shoves a bunch of calories into stored fat, so you have less fuel to burn. Then, the insulin falls and you get get hammered with hunger triggers. Eat more carbs and start the cycle over. This explains why insulin resistant people typically lose more weight on low carb diets and non-insulin resistant people see unspectacular results. Insulin resistant people need the low carb approach to break the viscious cycle and lower their overall levels of insulin throughout the day.</p>

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<p>Usually the idea is to eat something and get right back on the bike. Sounds like you’re saying a sandwich would be a good idea, if I still had an afternoon of riding, because it would stick with me. But for quick energy, something sweet because even if it has fructose, it has glucose as well. And this is in fact my experience.</p>

<p>Chocolate milk, loaded as you say with lactose, is a popular energy food with touring cyclists. </p>

<p>I’m just trying to figure out how this glucose/fructose story fits in with my favorite activity, taking long bike rides day after day. A low carb diet, I’m afraid, would be a disaster, but trying to cut back on fructose is more possible.</p>

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<p>Cardinal:</p>

<p>You are burning so much fuel on a long-distance bike ride that I can’t imagine eating carbs (glucose or fructose) is going to be a problem. The bigger risk for extreme endurance athletes may be the difficulty in maintaining muscle mass in the face of such high calorie burn rates. I’m guessing that eating sufficient protein day in and day out is really important.</p>

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<p>i-dad, as I read it, I think CF is mostly concerned with getting stomach problems from eating food that is not converted into energy quickly.</p>