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The Sweet Science



The important role that simple sugars can play in exercise energy.

Do you ever feel that low energy levels while training are hindering your ability to push yourself? Maybe you need a little sugar in your tank.

Adding a combination of carbohydrates (CHO) such as glucose/fructose to your preworkout regimen may be your best bet to promote an increase in sustained energy during exercise. History has shown that the proper use and timing of carbohydrates can extend time to fatigue in certain endurance sports, like running or cycling. Here’s what the science says.

Carbs As Fuel

In a new study published in the International Journal of Sport Nutrition and Exercise Metabolism, it was determined that “exogenous (external) CHO oxidation rates increased over time with continuous glucose consumption during exercise.” This cohesion of carbohydrates and oxygen results in longer spurts of sustained energy throughout your workout.

Since initial studies conducted back in 1984, we’ve known that carbohydrates help to improve prolonged athletic endurance. It has been suggested that “one of the primary proposed mechanisms for this improved performance is due to an enhanced maintenance of plasma glucose (prevention of hypoglycemia), which results in augmented exogenous CHO oxidation by the muscles during exercise.” Hypoglycemia occurs when an individual’s blood sugar is too low, making it difficult for the body to fuel itself with energy.

As usual, time has given researchers a broader understanding of just how reliable carbohydrates are when combined with sugars—in this new case, fructose, a simple sugar commonly found in fruits and vegetables. (It’s important to know that crystalline fructose is the preferred sugar form, as opposed to high-fructose corn syrup, but I will expand upon that later.)

In the aforementioned study, 23 healthy male cyclists underwent a series of trials at the Nestlé Research Center/Metabolic Unit to determine their carbohydrate oxidation rates. According to Nestlé’s mission, the center “explores ways in which human behaviour [sic] towards food influences dietary choices.”

Age, height, body mass, body mass index and peak oxygen consumption were all taken into account. Excluded from the trial were volunteers who identified as smokers, had allergies, had intestinal disorders, were unfit or injured, were on regular medication or did not follow the controlled dietary regimen.

Seven days before the trial commenced, volunteers “performed a continuous incremental cycling test on a cycle ergometer to exhaustion to determine peak oxygen consumption.” In regards to fueling, the subjects were only allowed water, and carbohydrates were kept to a minimum.

During the trial, it was found that in volunteers, exogenous CHO oxidation rates increased over time with continuous glucose consumption during exercise when compared with the pretrial surveys. Furthermore, peak exogenous CHO oxidation rates were reached at the end of 120 minutes of exercise—two hours to peak!

In addition, the study “has shown that increased exogenous CHO oxidation significantly correlated with improved endurance performance in a dose-dependent manner.” Subjects consumed 60 g of carbohydrates per hour, thereby enhancing their endurance performance. (The study concluded that 15–30 g of carbohydrates per hour was not nearly as sufficient in sustaining activity.)

What’s important when evaluating your energy needs is knowing your training/performance intensity and duration and the kind of carbohydrates you choose.

Know Your Sugars: Glucose vs. Fructose

In a separate study, published in the British Journal of Nutrition, when fructose and CHO were combined, trial subjects were found to have a 50% greater exogenous CHO oxidation during exercise as compared with glucose alone. Fructose seems to have a positive effect on the muscle’s ability to absorb carbohydrates, which, of course, allows for greater energy production and retention during prolonged exercise.

There is a difference between glucose and fructose. They are both simple sugars, but glucose is more specifically geared toward fueling cellular respiration, while fructose is commonly added to foods and drinks to improve taste.

Fructose has two common forms: crystalline fructose and fructose corn syrup. You’ve no doubt heard of high-fructose corn syrup and its potential to elevate triglyceride levels (lipids) in the blood. Crystalline fructose, on the other hand, is the more expensive form found available in crystallized form.

The two sugars are adequate sources of energy when consumed moderately, but too much of both are unhealthy. High levels of glucose (which is found in almost all carbohydrates, such as starch and table sugar) may be detrimental to diabetics without proper controls in place, while excess fructose levels can lead to complications like nonalcohol-related fatty liver disease and insulin resistance. So, we must find a happy medium.

Remember, fructose consumption outside of physical activity—say, watching TV in a sedentary position—can lead to a gain in body fat, and extreme, prolonged use of fructose can lead to obesity and other more life-threatening diseases like hyperlipidemia (highly elevated levels of all lipids or fats in the bloodstream).

Be Aware Of The Effects Of A High-Fructose Diet

In the April 2014 issue of the Journal of Nutritional Biochemistry, researchers evaluating the acute intake of a high-fructose diet in rats reported that it can lead to a drop in serum adiponectin concentrations: “Adiponectin, the most abundant adipokine secreted by adipose [fat] tissue, has been demonstrated to exert anti-inflammatory and anti-atherosclerotic effects,” according to the researchers.

In addition, the researchers concluded that “long-term consumption of highly concentrated liquid fructose led to visceral adiposity, elevated triglycerides, and hypothalamic [the portion of the brain that controls hunger] leptin resistance.” Leptin is a hormone that is produced by adipose tissue, which can inhibit food intakes and decrease body fat by altering the activity of the hypothalamus, which, among other things, controls the hunger response.

Use Only If You’re Active

Many of the studies I’ve mentioned were based on the use of crystalline fructose. Taken pre- or intraworkout, crystalline fructose or glucose plus carbohydrate should give you a boost in your endurance.

However, not everyone is best suited to follow the guidelines outlined in the human study. If you’re considering adding fructose to your diet and you are already overweight, obese, prediabetic or diabetic, fructose is not for you. If you are a healthy, active adult involved in a sport such as competitive cycling, you may opt for products containing crystalline fructose. To burn this fuel, you have to engage in intense activity.

When in doubt, contact your personal physician or a licensed nutritionist or dietitian to help you determine if fructose is cohesive to your diet.

About Mackie Shilstone
One of the top trainers in the world, Mackie Shilstone has worked with such sports superstars as Roy Jones Jr., Serena Williams and Bernard Hopkins. You can learn more about Mackie by visiting his website at

Link: Muscle&Body Magazine