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  Last updated:6/11/2021


Glucose and fat can both power muscle cell contraction. At modest levels of exertion, equal Calories come from each. As exertion increases, this ratio shifts towards carbohydrates as the dominant energy source. And at your VO2max (edge of being completelyanaerobic), only glucose can be utilized by muscle cells. For normal daily activity, there is enough glucose (stored in the liver and muscles as glycogen) to supplement our almost limitless fat stores and keep us going for the entire day, but with intense exercise, we will run out of liver and muscle glycogen in less than 70 minutes.

If you are healthy, on a normal diet, you won't need any additional Calories for a ride of two hours or less before you bonk and your performance deteriorates. For longer rides you will need snacks to supply carbohydrate Calories. Cycling doesn't require special sports drinks or power bars to supply these Calories, and even elite athletes can get the majority of these needed Calories from ordinary foods.

If you are planning a ride of more than 2 hours, a reasonable target for carbohydrate replacement (food/energy drink/energy bars) is 1 gram of CHO per kg body weight per hour or approximately 60 grams of carbohydrate (200 to 300 Calories). As a rule of thumb, the higher the planned intensity of the ride (closer to your VO2max), the more you should lean towards simple sugars (glucose, sucrose) in your snacks, while on slower, more endurance oriented rides, snacks with complex carbohydrates and a higher fat content offer more options.

Carbohydrate supplements will protect glycogen stores during exercise, slowing the rate they are being used by the exercising muscles, but will not replace them once they are depleted. If you are planning to use supplements for your ride, begin them as you get on the bike - don't wait until you are beginning to bonk.

Sport drinks are among the most commonly used energy supplements. They provide the fluid that limits dehydration as they protect glycogen energy stores. Most contain electrolytes as well, but it's questionable if those are beneficial aside from minimizing the rare risk of hyponatremia when ingesting large volumes of fluid in high heat and humidity conditions.


The Calories/minute of oral carbohydrate your digestive system can deliver to exercising muscles is limited by the rate at which they can be absorbed from the small intestine into the bloodstream.

There are two separate and independent monosaccharide transport mechanisms in the small intestine - one for glucose and another for fructose. Both can be saturated (maxed out) at high sugar concentrations which sets an upper limit for the rate of absorption for each sugar. But saturating one does not limit the other. This provides a workaround to maximize carbohydrate absorption rates. A pure glucose drink is limited to a maximum absorption of 1 gram of carbohydrate per minute, but a glucose/fructose combination can deliver a bit more than 1.7 grams of carbohydrate a minute into the blood stream.

If either the sugar concentration (fructose, glucose, complex carbohydrates) of a sports drink or drinking large amounts delivers more monosaccharide than the small intestine can absorb, the excess sugar passes into the colon where it is metabolized by resident bacteria. The resulting gas (one of the metabolic breakdown products) can then lead to cramping and bloating.

This study used MRI technology to evaluate the protection of liver and muscle glycogen stores during prolonged endurance-type exercise (3 hours at 50% of peak power output) compared sucrose (table sugar, a disachharide of glucose and fructose with an inherent ratio of 1:1) with the monosaccharide glucose . Both were delivered at 1.7 g/min or 102 g/h.

They found:

However sucrose did have several advantages: The bottom line - table sugar (sucrose) has an edge as the carbohydrate of choice for home made sports drinks.

What is the maximum sugar concentration for concentration for an "ideal" drink? A meta analysis (summary of multiple studies) demonstrated a wide range of 3 to 10%. The study mentioned above used drinks of 108 g of carbohydrate in 750 ml of water with a final concentration of 14% - and reported minimal side effects. If you'd like to try higher concentrations, your only risk from pushing the limits on concentration are palatability and short term GI side effects.

Although it has been suggested that the addition of protein to a mixture of glucose and fructose could increase the rate of CHO absorption - during exercise as well as in recovery drinks, a a 2014 review of 26 studies concluded: "When carbohydrate is delivered at optimal rates during or after endurance exercise, protein supplements appear to have no direct endurance performance enhancing effect." However protein might be considered to enhance flavor or by those who cannot tolerate the sweetness of high, maximum carbohydrate drinks.

An unexpected benefit of carbohydrate supplements is minimizing the inflammatory effect of intense exercise as documented in this study comparing water alone to either a carbohydrate drink or fructose containing fruit/fruit juices. Sports drink manufacturers have responded to this criticism by adding multiple "natural" ingredients. But as well critiqued in this blog they have their own set of potential side effects.


The American Academy of Pediatrics (position paper) has identified risks of over stimulation (for caffeine containing drinks) and obesity (from the extra carbohydrate Calories) when they are used OUTSIDE of exercising. This is especially a hazard for adolescents and preteens.

Over stimulation - jitteryness, rapid heart rate - is a particular risk with caffeine containing "energy drinks" such as Red Bull and Monster. There is no evidence to support these energy drinks improving performance compared to a calorie equivalent low level caffeine/glucose drink while exposing you to the risks of an immediate increase in blood pressure in addition to the rare occurence of cardiac rhythm irregularities and sudden death. If you would like more information, this interview from provides additional insight into their negative cardiovascular effects.

The sugar content of sports drinks is another risk, especially if you are drinking more carbohydrate Calories than are being expended on the bike.

Weight gain/obesity has been mentioned. It's a simple math. Calories in greater than Calories expended = weight gain.

These is evidence that excess sugar can increase body wide inflammation reflected by inflammatory blood markers such as C-reactive protein. Chronic inflammation will injure normal tissues, and when monitored over time, groups with elevated C-reactive protein levels have been shown to have higher rates of diabetes, cardiovascular disease, and cancer.

Of more concern is the increasing evidence that an increase in colon cancer in younger patients correlates with decades of over use of sugar-sweetened beverages.

The type of carbohydrate in the sports drink may be a different problem. Fructose is metabolized to glucose before it can be used for muscle contraction. Above a specific threshold level fructose affects insulin/carbohydrate metabolism. This may be why diabetes (as well as glucose intolerance or pre-diabetes) which is more common now than 50 years ago, tracks directly with the increasing use of fructose (corn syrup) derived sweeteners after WWII. This study suggests that fructose specifically activates a liver enzyme which then causes a) resistance in the liver to the effects of insulin as well as b) increasing the production of additional glucose from the liver cells - a positive feedback loop. And a prediabetic state.

As a GI specialist in liver disease, I regularly saw patients with metabolic syndrome - the clinical triad of a) glucose intolerance, b) fat accumulation in the liver, and c) high blood pressure. For those interested in more detail, I've pulled together some background as well as a diet that made sense to me. It also qualified as a healthy diet approach for all of us. Here's the link.)

What is the take away for me? I limit my total drink carbohydrate Calories to those being used for a ride, and then only if the ride is at a moderate-to-high intensity lasting for more than hour. Otherwise, it's best to hydrate with water.

Finally, there has been speculation that the acids and sugars in sport drinks explain the increasing incidence of cavities (caries) in athletes. One study from England suggested that although sports drinks might be more damaging than colas, lemon tea was even more so. The most recent review articleI could find, from 2005, identified only a single study supporting the idea that sports drinks might be a dental risk for athletes. The article noted that the real culprit might be poor saliva formation, aggravated by dehydration and mouth breathing. Here is the perspective of my son, a practicing dentist - with a few thoughts on prevention.

Possible solutions if this is a worry for you:

  1. Focus on drinking duing a ride. Dehydration reduces saliva production. Water is key to keeping the mouth moist (counteracting the cyclist's tendency to mouth breath) and restoring a more normal pH.
  2. Add a sugar free flavoring to the water. Palatability eliminates a barrier to regular drinking. Any flavoring will do. Flavored waters (many are commercially available) will work too. But after 2 hours a cyclist may start to run out of carbs.


Commercial sports drinks are widely available, but pricey. If you are only interested in the Caloric supplement component, there are have several options to save a few dollars.

A few ideas:

  1. Bars and gels - drink plenty of water (the only comparative advantage to a drink). Save a few dollars by using a high carbohydrate cookie such as Oreos, or peanut bars.
  2. A link to natural smoothie recipes.
  3. Make your own water bottle mixture with table sugar (sucrose) which has a natural 1:1 glucose/fructose ratio.
  4. From

  5. Complex carbohydrates. For a little extra oomph, or for those looking for a less sweet alternative, complex carbohydrates will provide carbohydrate Calories in a drink that is not overly sweet tasting. Purchase a complex carbohydrate in a health food store and mix with the flavor of your choice or use it to supplement a current favorite drink. Maltodextrin is a corn starch molecule which has been broken down into glucose polymers (chains of glucose molecules). When added to water or other drinks, it increases the energy content without the disadvantage of an overly sweet taste and a highly concentrated solution which may delay gastric emptying.

    A 16 ounce water bottle (480 cc) of a 7% sugar solution at 4 Cal per gram of carbohydrate will contain about 136 Calories. If you add 1/2 cup of Carboplex (a commercial maltodextrin) you will add another 220 Calories almost tripling the energy density (concentration) of your drink with minimal chances of nausea or other side effects.


There have been some encouraging studies on the use of glycerol to minimize the negative impact of dehydration on performance. For those interested in a commercial product, try the internutria website.

Lactic acid has always been considered a by-product of metabolism , and something to be eliminated from the muscles as quickly as possible. Yet a recent study looked at lactate as a possible energy source and demonstrated that it is actually metabolized more quickly than glucose. We may see more drinks with lactate as a fuel source coming soon.

Except under conditions of extreme heat/humidity, or undertaking a long (4 or 5 hour) high level event such as a marathon.electrolytes (particularly sodium chloride or salt) do not need to be replaced along with fluids. If you feel you will need additional electrolytes, these homemade electrolyte gummies are an option. They will definitely cover all your electrolyte needs when used with a carbohydrate based sports drink. One batch (4 tbs Gatorade electrolyte powder) per hour should be enough to avoid severe electrolyte imbalance.