Stevia in Sports Nutrition

Amidst the marathon journey of distilling the complexities of nutrition in endurance sports to the most actionable advice, our focus today sharpens on a seemingly innocuous ingredient with a potentially profound impact: Stevia. As a natural sweetener derived from the leaves of the Stevia rebaudiana plant, it offers the allure of guilt-free sweetness, free from calories. (Guilt-free, if you assign guilt to calories… which you shouldn’t.) This characteristic has propelled it into the limelight, especially among health-conscious circles. However, the terrain of endurance sports is fraught with unique nutritional demands, where the difference between triumph and tribulation on the side of the road can hinge on the details of an athlete’s fueling strategy and its chemical composition.

The question then arises: In the grueling world of endurance sports, does Stevia play the role of a friend or foe?

It's crucial to recognize that the challenges outlined here, associated with Stevia, are not exclusive to this natural sweetener alone. In fact, most nonnutritive sweeteners present in endurance beverages can lead to similar predicaments, creating a facade of energy intake without the substantive caloric support necessary for sustained performance. This is why I usually advocate against the inclusion of any artificial sweeteners in products intended for use during training and racing. The essence of endurance nutrition lies in the provision of real, substantive fuel to meet the body's demands, not in the illusion of sustenance without the caloric and carbohydrate backing.

From a biochemical standpoint, the body processes steviol glycosides differently than other carbohydrates. When ingested, steviol glycosides are not broken down into glucose in the digestive system, which means they do not provide calories or affect blood glucose levels in the same way as sucrose or other nutritive sweeteners. Instead, steviol glycosides are metabolized by bacteria in the large intestine into steviol, which is then absorbed into the bloodstream and eventually excreted in the urine, having provided next-to-zero energy to the consumer.

The Sweet Illusion: Stevia’s Impact on Perception and Performance

Within the realm of endurance sports—marathons, triathlons, ultrarunning—athletes embark on a taxing journey, pushing their bodies to the limits of endurance and performance. In this context, carbohydrates are not mere nutrients; they are the very lifeblood of sustained energy. When athletes sip on their sports beverages, each gulp is a calculated intake of fuel, meticulously planned to replenish the body and stave off the specters of fatigue and depletion.

Enter Stevia, with its seductive promise of sweetness without the caloric cost. At first glance, it seems like a panacea for athletes wary of excessive sugar intake. Yet, herein lies the paradox: the sweetness of Stevia may create a psychological mirage, leading athletes to believe they are ingesting more carbohydrates than they actually are. This misperception can skew fueling strategies, leaving athletes undernourished and under-fueled when they least can afford it.

Perhaps most dangerously, it’s in the earlier hours of an event where you can get away with consuming fewer carbohydrates, for the time being. And any artificially sweetened products may bait you into doing just that: under-consuming early. Given the gut limitations during endurance exercise, especially during dehydration or thermal stress, once you’re behind on carbs, you’re going to stay behind. You’ve left performance on the table.

The Carbohydrate Conundrum and Cramping Catastrophes

As the miles stretch on, the body’s cry for carbohydrates grows louder. These are the moments that test an athlete's preparation and endurance. However, if the body is deceived by the sweetness of Stevia, believing it to be a sign of ample carbohydrate consumption, the reality can be harsh and unforgiving. The shortfall in energy availability not only precipitates a decline in performance but also plays a notorious role in the dreaded phenomenon of muscle cramping. Though cramps aren’t the bane of every athlete's existence, they serve as a stark reminder of the body's intricate balance of electrolytes, energy availability, and work capacity - a balance easily disrupted in the absence of sufficient carbohydrate intake.

In the absence of adequate carbohydrates, the body, in its relentless quest for energy, turns to fat as an alternative fuel source. While fat is a more than capable energy reserve for its sheer amount, its utilization marks a shift in physiological efficiency. The metabolic machinery required to convert fat to fuel operates at a slower pace, demanding more oxygen and elevating the heart rate for a given workload. This shift not only diminishes performance but also amplifies the perception of effort, making each step feel laborious, each pedal stroke a monumental task.

This metabolic inefficiency will be worsened if someone is accustomed to consuming carbohydrate fuel in high quantities and then makes a switch in training or on race day, to a nonnutritive sweetener like Stevia.

The Hypoglycemia Fest: A Sweetener’s Subtle Havoc

The reliance on Stevia-sweetened beverages, with their low carbohydrate content, sets the stage for a physiological predicament. As athletes press on, their bodies' glycogen reserves dwindle, and the absence of incoming carbohydrates from their beverages leaves a void. The result is a perilous slide into hypoglycemia, a state where blood sugar levels plummet as muscles vacuum up all remaining blood glucose, bringing with it a cascade of symptoms—dizziness, weakness, confusion, and an overwhelming sense of fatigue. While neurogenic hypoglycemia doesn’t necessitate large drops in physical performance - read: you can actually perform very close to optimally with low blood sugar for a while - the most prominent effect is on your psychology and your willingness to suffer. Both of which you need as strong as ever during your hardest training sessions and races.

An example: imagine a marathoner, miles into a race, steadfastly relying on a Stevia-sweetened beverage as her primary source of hydration and fuel. Initially, the beverage's sweetness provides a comforting assurance of energy replenishment. However, as the miles tick by, her pace begins to falter; her muscles, once responsive and vigorous, now twitch with the early warnings of cramps. The psychological toll mounts as she realizes her energy stores are depleting far quicker than anticipated, her beverage providing none of the promised sustenance.

Desperately, her body shifts gears, tapping into fat reserves—a process far less efficient and far more demanding. Her heart pounds against her chest, each beat a reminder of the increasing effort required to maintain pace. The marathoner's thoughts grow foggy, her limbs heavy, as the first tendrils of hypoglycemia take hold. In this moment, the allure of Stevia's calorie-free sweetness reveals its true cost: a compromised performance and a battle not just against the clock, but against her own body, lacking the basic substrate for maximizing performance.

Navigating the Nutrition Maze: A Path Forward

For endurance athletes, the journey to optimal performance is paved with meticulous planning and an intimate understanding of their body's needs. The science of fueling for endurance is not just about avoiding the negative but proactively harnessing the positive—choosing beverages and fuel sources that provide the necessary carbohydrates, electrolytes, and hydration to sustain effort over hours of exertion. The focus should be on real, tangible energy sources that can be readily absorbed and utilized by the body, ensuring that the athlete can maintain pace, power, and endurance from start to finish.

The role of beverages, then, is not just to hydrate but to fuel—to provide a steady stream of energy that can sustain the athlete through the rigors of competition and training. Stevia's main problem is the lack of carbohydrate-based energy. That said, the potential side effects from Stevia absorption -- nausea, vomiting, GI distress -- are unlikely to be felt by most athletes as the amount of Stevia consumed during exercise is relatively small. For some folks, however, Stevia sensitivity is the real deal. If you know, you know. And, if you don’t know, you don’t want to know.

A Detailed Note on Fuel Consumption and Stevia Sweetness Interplay

You may have heard - endurance athletes need a specific mix of glucose to fructose, ideally in a ratio between 2:1 and 1:1 - to fuel their performance effectively. This requirement is crucial for optimal energy absorption and usage during long activities, especially when carb consumption rates exceed 60 grams per hour, but a mixed composition is almost always useful. If you’ve tried this composition, especially closer to 1:1 glucose:fructose, then you’ve also noticed that it is a rather sweet mix, even if the flavor intensity is kept low.

Ideally, for a less sweet taste, one might lean towards using only maltodextrin or HBCD, as these glucose sources are less sweet. However, this approach doesn't meet the necessary glucose:fructose ratio. To achieve this balance, it's essential to include a significant amount of fructose or primarily use sucrose, which naturally contains glucose and fructose in a near-perfect ratio for endurance needs. Both fructose and sucrose are moderately sweet and can be consumed in the needed concentrations without overwhelming sweetness.

The introduction of Stevia, while beneficial for reducing calorie content, complicates this delicate balance. Stevia's intense sweetness can make the overall drink mix much sweeter than desired. This is problematic because, to adhere to the glucose:fructose ratio without making the beverage overly sweet, the formulation relies on the natural sweetness of fructose and sucrose. Adding Stevia pushes the sweetness beyond the tolerable threshold, undermining the goal of creating a less sweet, yet energetically balanced, endurance beverage.


While Stevia and other nonnutritive sweeteners may offer advantages in certain dietary contexts, their role in the nutrition strategy of an endurance athlete should be carefully scrutinized. The addition of the necessary carbohydrates to the consumption strategy of the athlete is likely to over-sweeten the milieu, in the presence of stevia. The foundation of endurance nutrition is built on the provision of adequate energy—a task for which calorie-free sweeteners are ill-suited. The addition of anything extra to a mixture is also a recipe for increased gastrointestinal tract distress symptoms, which can be show-stopping during training and racing. As we chart our course through the world of sports nutrition, let us be guided by the principles of science, the lessons of experience, and the unwavering goal of supporting the performance and health of athletes at every level, rather than by sweetening up our beverages to suit flavor and sweetness preferences of humans at rest. If you’d like to sip on stevia-sweetened tea in the evening before bed as part of your healthy sleep hygiene routine, by all means. But I’d recommend minimizing it during training and racing.

Dr. Alex Harrison is the founder of Saturday, an app to assist endurance athletes with their fueling needs.