I’m frequently asked to explain why fruits and fruit juices are not included in my nutrition program. The answer has to do with a little-understood simple sugar found in fruit: fructose. Fructose came into favor years ago because of its stabilizing effect on blood sugar. Unlike other simple sugars, it trig-gers neither a surge of insulin nor a corre-sponding drop in blood sugar an hour or so after eating it. That’s the good news. But there’s more to the fructose story.Anyone trying to maximize muscle gain and maximize fat loss should avoid fruit and foods to which fructose has been added. Here’s why:Fructose is readily converted to body fat. Because of fructose’s molecular struc-ture, the liver readily converts it into a long-chain triglyceride (a fat). Put another way, fructose is metabolized as a fat in your body. Therefore, a majority of the fruit you eat can ultimately end up as body fat on your physique. You’ll notice an incredible difference when you eliminate fruits and juices from your diet. Incidentally, fructose may turn out to be one of the reasons we’re becoming a na-tion of fatties. This simple sugar is found not only in fruit, but also in processed foods in the form of high-fructose corn syrup, the chief sweetener in sodas. Get this: Consumption of soda has been linked to the rise in obesity rates in our country.
And, paralleling the rise in obesity is a ten-fold increase in the consumption of fructose.Fructose can cause your body to ab-sorb extra fat from meals.If you wash a cheeseburger and French fries down with a soda, or drink orange juice with your breakfast, your body could be sopping up excess fat. In a recent study, volunteers drank milkshakes flavored with either fructose, glucose, aspartame, or no sweetener at all with meals. The amount of fat absorbed from the fructose and glucose-sweetened shakes was 38 to 60 percent higher than that absorbed from the artificially sweetened or unsweetened shakes. These findings are further evi-dence that fructose has a fat-forming ef-fect on the body. (1) Fructose does not efficiently restock muscle glycogen. After you work out, your body moves from an energy-using mode (catabolism) to an energy storage and rebuilding mode (anabolism). During the transition, di-etary carbohydrate is broken down into glucose and fructose to be used for “gly-cogenesis,” the manufacture of glycogen to restock the muscles and liver.Fructose is used primarily to restore liver glycogen; it’s really not a good re-supplier of muscle glycogen. Glucose, on the other hand, bypasses the liver and is carried by the bloodstream straight to the muscles you just worked, where the glycogen-making process begins. Any muscle emptied of glycogen due to exer-cise is first on the list to get its quota of glucose .
Clearly, one of the keys to effectively restoring glycogen is the type of carbo-hydrate you eat. Natural, starchy carbo-hydrates such as potatoes, yams, whole grains, corn, and legumes do a better job at this than simple sugars do. Research has shown that a diet high in starchy car-bohydrates can restock more glycogen in the muscles 48 hours after exercise than simple sugars can .(2) If you eat simple sugars like fructose, you’re not going to be able to store as much glycogen had you consumed natu-ral, starchy carbohydrates. What implica-tions does this have for you as an athlete or bodybuilder?First, you won’t be able to train as hard or as long during your next workout, because you haven’t stored as much gly-cogen. Nor will you be able to recover from your workouts as efficiently. Plus, the simple sugars are likely to spill over into fat stores, with just a fraction con-verted to glycogen. By contrast, eating ample amounts of starchy carbohydrates will extend your endurance and effective-ly re-supply your muscles with glycogen for better recovery. You’ll stay leaner too, since starchy carbs are fully utilized for energy production and glycogen syn-thesis .Second, you’ll notice less of a “pump” while working out, also due to low gly-cogen stores in the muscle.
The “pump” describes an exercised muscle heavily engorged with blood. If you can’t get a good pump, it’s difficult to get the full benefits of “fascial stretching.” This is my system of stretching between exercise sets. It stretches the fascia tissue sur-rounding the muscle so that it has more room to grow. The best time to stretch is when the muscle is fully pumped, because the pump helps stretches the fascia too. With low glycogen levels in the muscle, you can’t stretch to the maximum. This limits your growth potential. Fructose can lead to insulin resis-tance.Studies have demonstrated that diets high in simple sugars (particularly su-crose) lead to a condition known as insu-lin resistance . Sucrose and other simple sugars trigger a rapid spike in glucose, and the pancreas responds by pumping out more insulin into the bloodstream to handle the sugar. Over time, insulin lev-els in your blood remain higher than they should be. Eventually, cells ignore – or become resistant to – insulin. Because of insulin resistance, insulin can’t open the cell. Glucose is locked out, and it clutters up the bloodstream.
These adverse meta-bolic events can lead to type 2 diabetes. Insulin resistance is also associated with excess blood levels of triglycerides, and low levels of heart-protective HDL cho-lesterol, conditions that set the stage for heart disease. (3) Fructose is “hidden” in many body-building foods.Many sports and bodybuilding supple-ments are sweetened with fructose – a dis-covery I made when surveying the ingre-dients of nutrition bars several years ago. I found that 25 out of 26 bars had fructose as a first or second ingredient. High-fructose corn syrup and fruit juice are frequently used as ingredients in sup-plements because they are inexpensive sweeteners. But buyer beware: They can hamper your bodybuilding efforts, so read the labels.Look instead for supplements sweet-ened with rice dextrin, which is found in our bars. Rice dextrin is a short chain glu-cose polymer made from rice. It gives you the quick energy you want from a sports bar, but without fat-forming fructose.The Final Word on Fruit and Fruc-toseI’m not knocking fruit. True, it’s high in vitamins, minerals, and fiber — but so are natural, complex carbohydrates. If you want to get leaner and more muscular — and build your recuperative powers by re-stocking glycogen more efficiently — avoid fruit. Choose starchy and fibrous carbohydrates instead.
1. Wollard, K. 1999. Did you know? Newsday, May 4, p. C05.
2. Costill DL, et. al. 1981. The role of dietary carbohydrates in muscle glyco-gen resynthesis after strenuous running. American Journal of Clinical Nutrition, 34: 1831-1836 .
3 . Storlien, L .H ., et al . 2000 . Diet com-position and insulin action in animal mod-els. British Journal of Nutrition 83: S85-S90 .