by James Barnum
by Paulnoblesjr on March 21, 2013
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In recent years, while the rest of the world continued to live in fear of fat, the fitness community totally embraced it. Carbohydrates became the target of our frustrations; we blamed them for making us fat, compromising our immune function, keeping us inflamed, and generally ruining our lives. We’ve learned our lesson now and carbs have had their reputation restored. It’s really about time, considering the role that carbohydrates play in the performance of nearly every sport.
NOTE: This article discusses a lot of theory regarding physiology. It’s important to understand that because an interpretation of the way things work on a micro level may not always be accurate as research evolves, and it may not make that much of a difference in the great scheme of things. Still, if you’re already doing everything right and you’re looking for a way to tweak things to get an extra few percent-worth of muscle growth, fat loss, or performance, this is the article for you.
Which Carb Sources are Best?
Without a doubt, one of the hardest things to tell someone that’s seeking improved performance and body composition is that fruit should not make up the bulk of the carbohydrates in your diet. Hold on though – I am in NO WAY implying you shouldn’t eat fruit. It’s just not the easiest, most efficient way to fuel your body. One last tme; FRUIT IS GOOD. EAT PLENTY OF IT!
What’s wrong with using fruit as a performance carb then? First of all, from the top down, there is usually quite a bit of fiber and water in fruit. It’s just not very energy-dense, so you need to eat a lot of it – far more than is feasible for most people – for it to replenish muscle glycogen quickly. That’s really your primary concern.
Second, as the nomenclature implies, most fruits are chock-full of fructose, as well as sucrose (which is just a compound of glucose bonded to fructose) as well as glucose. As far as performance is concerned, fructose and sucrose leave a bit to be desired. Fructose is not bad in moderation; it’s just an inefficient carbohydrate. After fructose has been digested, it’s absorbed into the bloodstream and merrily sent on its way to the liver. However, while glucose sort of passes through and heads out to be utilized by other tissues by way of glycolysis, fructose metabolizes through its own unique pathway (fructolysis). It kind of hangs around and turns into pyruvate, then into glucose which is used to replenish liver glycogen storage. These stores are accessed to create glucose for other tissues during times of low blood sugar and stress, when plasma concentrations of glucocorticoids (like cortisol) are high. As far as performance goes, it’s nowhere near as fast as simply storing glucose as readily-available glycogen within skeletal muscle.
The second issue here is that once liver glycogen is full, the rest of the fructose you ingest is promptly metabolized into triglycerides; consuming more than 50-75g a day (200-300 calories) is a surefire way to store body fat. This is especially true for women, who typically express a lower capacity to oxidize carbohydrate during intense exercise than men (although they do burn more fat).
The caveat here? Well, to store any body fat at all, you have to be in a calorie surplus! If you train hard 5-6x a week, your liver will hardly have an opportunity to fully replenish glycogen stores.
As valuable source of vitamins, minerals and fiber, fruits have definitely got their place in a balanced approach to nutrition. Furthermore, you’d have to eat a lot of fruit every day to reach that kind of fructose intake. As I mentioned in the first paragraph of this section, you’d also have to eat a lot (and I mean a lot) of fruit to satisfy your carbohydrate/calorie requirements after training; it’s just not optimal (or in some cases, feasible) to rely upon fruit as an energy source. Thankfully, there are other natural sources of carbohydrate available that are positively brimming with glucose as well as important micronutrients.