Is Sugar Bad for Athletes? An Evidence-Based Analysis for Performance Optimization

Sugar has become one of the most controversial topics in nutrition. Headlines warn that sugar is a “silent killer” linked to obesity, diabetes, and cardiovascular disease. Yet sports nutrition products proudly advertise their high sugar content as essential for athletic performance. For professional athletes navigating these contradictory messages, the question becomes critical: Is sugar bad for athletes?

The answer is more nuanced than a simple yes or no. The effects of sugar depend heavily on context—particularly energy balance, physical activity levels, training status, and timing of intake (Moore & Fielding, 2016). This article examines the scientific evidence to help you understand when sugar supports your performance and when it may undermine your health.

Understanding Sugar: What Athletes Need to Know

Sugar is a carbohydrate—a molecule made of carbon, hydrogen, and oxygen (Jeukendrup & Gleeson, 2018). While various sugars exist in our diet, glucose is the primary fuel your muscles use during exercise. Understanding the different types helps clarify why not all sugars behave identically in your body.

Types of Sugars in Athletic Nutrition

Important note: Not all sugars are “fast” and not all complex carbohydrates are “slow.” Maltodextrins and some starches are absorbed as quickly as pure glucose, making them equally rapid fuel sources for performance (Jeukendrup & Gleeson, 2018).

How Sugar Powers Athletic Performance

From Food to Fuel: The Simple Explanation

When you eat carbohydrates, your body breaks them down into glucose (Jeukendrup & Gleeson, 2018). This glucose goes through a process called glycolysis, which produces energy molecules called ATP—the fuel that powers your muscle contractions.

During this process, glucose is converted to a substance called pyruvate. This pyruvate then enters another energy-producing system called the TCA cycle (or Krebs cycle), which squeezes out even more energy. Eventually, all the carbon from the original glucose molecule leaves your body as carbon dioxide when you breathe out (Jeukendrup & Gleeson, 2018).

What Happens During High-Intensity Exercise

During intense training or competition, your muscles produce pyruvate faster than your body can process it through the TCA cycle. To prevent a traffic jam that would shut down energy production (and cause you to fatigue), your body converts the excess pyruvate into lactic acid (Jeukendrup & Gleeson, 2018).

Myth buster: Contrary to what many commentators say, lactic acid doesn’t cause fatigue—it actually prevents it by keeping your energy production running. The lactic acid breaks apart into lactate and hydrogen ions. It’s the buildup of hydrogen ions that may cause that burning sensation in your muscles during hard efforts (Jeukendrup & Gleeson, 2018).

Your Body’s Energy Systems

Glucose and its stored form (glycogen) are the most important fuels for athletic performance in most sports (Jeukendrup & Gleeson, 2018). Even very short explosive events and ultra-long events (24+ hours) still require carbohydrates during training preparation.

Why “Fat Burns in the Flame of Carbohydrate”

This old saying is scientifically accurate. Research shows that your body burns fat less efficiently when carbohydrate stores are low (Jeukendrup & Gleeson, 2018). Carbohydrates play two critical roles: they provide direct fuel AND they help your body’s entire metabolism function properly.

For performance, glucose is extremely important. While you can also eat longer chains of glucose (like maltodextrin or certain starches), these get broken down into glucose anyway—so ultimately, it’s sugar (glucose) that powers most of your athletic performance.

The Health Concerns: What the Evidence Shows

What Health Organizations Recommend

The World Health Organization recommends that adults and children keep free sugar intake below 10% of total daily calories (about 50 grams or 12 teaspoons per day), with even more health benefits at less than 5% (25 grams or 6 teaspoons). The Dietary Guidelines for Americans and UK guidelines have similar recommendations.

Why these limits? Because research clearly shows excessive sugar intake is linked to health problems in the general population.

What Studies Show About Sugar and Health

A large study following over 11,000 American adults found that people consuming about 20% of their calories from added sugars had a 38% higher risk of dying from cardiovascular disease compared to those consuming only 8% (Yang et al., 2014).

Another study tracked 198,285 people in the UK for seven years, during which 3,166 died (Anderson et al., 2020). Higher sugar intake and sugar-sweetened beverage consumption were both associated with increased risk of death from any cause.

Summary of Health Effects

Key point: Sugar itself doesn’t directly cause diabetes (Lean & Te Morenga, 2016). However, eating too much sugar can lead to weight gain, and excess weight can lead to diabetes.

The Critical Question: What Does “Excessive” Mean for Athletes?

This is where general population guidelines don’t apply well to athletes. Context is everything.

Comparing Two Scenarios

Sedentary person: Burns 2,000 calories per day. Eats 100 grams of sugar (400 calories) = 20% of daily intake. This is clearly excessive.

Elite endurance athlete: Burns 5,000 calories per day, including a 3-hour training session that uses 500 grams of carbohydrate. Eats 100 grams of sugar = only 8% of daily intake. Even eating 300 grams of sugar during that 3-hour workout may only be 24% of daily calories, but it directly replaces what was burned during exercise.

The Real Measure: Carbohydrate Balance

A better way to think about “excessive” is whether you’re in positive carbohydrate balance—meaning you consume more carbohydrate calories than you burn over 24 hours (Moore & Fielding, 2016).

When you’re in positive carbohydrate balance, your body converts the excess into fat, which raises triglycerides in your blood—a risk factor for heart disease (Moore & Fielding, 2016).

Athletes often maintain neutral or negative carbohydrate balance despite eating large amounts of sugar, simply because they’re burning it all (and sometimes more) during training.

Debunking Common Misconceptions About Sugar for Athletes

Myth: Blood Sugar “Spikes” Are Dangerous for Athletes

When you eat, your blood glucose naturally rises—this is normal physiology, not a health problem. These temporary changes are completely different from chronically high blood glucose levels.

What happens during exercise: When you consume carbohydrates during a workout, your blood glucose and insulin barely rise—and during very intense exercise, insulin may actually decrease even as you’re drinking a sports drink.

Athletes who regularly consume sugar during training actually have better insulin sensitivity than the general population, not worse, despite frequently having glucose and insulin fluctuations.

One comprehensive review concluded: “Excess sugar can promote weight gain, thus type II diabetes mellitus through extra calories, but has no unique diabetogenic effect at physiological levels” (Lean & Te Morenga, 2016). In simple terms: sugar doesn’t directly cause insulin resistance; excess calories and weight gain do.

Myth: Sugar Causes Fatty Liver in Athletes

Excess sugar can be converted to fat and stored in the liver, contributing to fatty liver disease. However, this happens primarily from consuming too many total calories, not specifically from sugar (Moore & Fielding, 2016).

Fatty liver develops when you consistently eat more energy than you burn—something that rarely happens in athletes who train regularly.

Sugar Intake in Energy Balance: The Game-Changer for Athletes

The most important question: Does sugar cause health problems when you’re in energy balance (calories in = calories out)?

A thorough scientific review concluded that while sugar clearly links to health problems in overfeeding studies and in people who overeat, there is no convincing evidence that sugar causes health problems when people maintain energy balance (Moore & Fielding, 2016).

The Endurance Athlete Paradox

If sugar directly caused insulin resistance and metabolic problems, then endurance cyclists and triathletes—who consume the most sugar—should have the worst metabolic health. But the opposite is true: endurance athletes have far better insulin sensitivity than the general population, despite consuming more sugar through sports drinks, gels, and energy bars.

Studies also show that health markers improve during weight loss even when people consume relatively high amounts of sugar, suggesting that excess calories—not sugar specifically—are the real problem (Moore & Fielding, 2016).

Important clarification: This doesn’t mean you can eat unlimited sugar as long as you maintain your weight. Whole grains improve health markers more than refined grains (Malin et al., 2018), showing that while sugar may not harm you in energy balance, better food choices still provide superior benefits.

The Exercise Factor: What Most Studies Miss

Almost every study examining sugar’s health effects fails to adequately measure or control for physical activity—a huge oversight, since exercise dramatically changes how your body handles glucose.

Exercise improves insulin sensitivity both immediately (effects lasting up to 48 hours after a single workout) and long-term (training adaptations). Most nutrition research doesn’t account for this, which is why general population findings don’t apply well to athletes.

What Actually Determines Sugar’s Effect on Your Health

For the general population:

• Energy balance (calories in vs. out)
• Physical activity level
• Training status (trained vs. untrained)
• Current weight status
• Existing insulin resistance

Specifically for athletes:

• How many calories you burn during exercise
• How much carbohydrate you burn (depends on intensity)
• How long you train
• When you consume sugar relative to training

High Sugar Intake During Competition: Do the Math

Sports nutrition guidelines recommend 90 grams of carbohydrate per hour during prolonged exercise, with some athletes consuming up to 120 g/h. Is this “excessive”?

Breaking Down the Numbers

Scenario: You consume 90 g/h for 4 hours = 360 grams total

At first glance: General population upper limit is 50 grams daily, so 360 grams seems like 7 times too much.

The reality:

• Your metabolism during exercise increases 10-fold or more (Jeukendrup & Gleeson, 2018)
• Your body uses 70-80% of ingested carbohydrate immediately as fuel (Jeukendrup, 2004)
• Of 90 g/h consumed, 63-72 grams are burned right away (Jeukendrup, 2004)
• A moderately trained athlete burns 100-120 g/h of carbohydrate during exercise (Jeukendrup & Gleeson, 2018)
• A highly trained athlete may burn 250 g/h (Jeukendrup & Gleeson, 2018)

The outcome: Those 360 grams you consumed don’t even replace the 400-480 grams you burned during 4 hours of exercise. You’re still in negative carbohydrate balance, with depleted glycogen stores that need refilling after you finish.

Carbohydrate Intake vs. Use During Exercise

Essentially, all the sugar you consume during and immediately after exercise either fuels your workout or replaces depleted glycogen stores. The 360 grams that seemed excessive is actually less than what you burned during that same period.

Natural vs. Added Sugars: Does It Matter for Athletes?

Chemically, glucose from an apple is identical to glucose from table sugar. Your body cannot tell the difference between glucose sources.

What IS different is the food matrix—what else comes with the sugar and how that affects absorption.

Comparing Food Sources

Whole fruits contain fiber, vitamins, minerals, and beneficial plant compounds (polyphenols). The structure of the whole fruit slows down sugar absorption. Ultra-processed foods with added sugar typically lack fiber and nutrients, allowing very rapid absorption—which is exactly what you want in sports nutrition products designed for quick fuel delivery, but not ideal for daily eating.

The supposed health benefits of “natural” sugars like honey, agave, and maple syrup are often overstated. While they contain trace amounts of minerals, you’d need to eat unreasonable quantities to get meaningful nutrition. Their advantage over refined sugar is minimal.

Practical Guidelines for Athletes

When Sugar-Rich Sports Nutrition Makes Sense

Use sports nutrition products with sugar when:

• Training or competing for more than 75 minutes (Jeukendrup, 2004)
• Training quality matters for your adaptation goals
• You need rapid recovery (less than 8 hours until next session)
• You’re in a period of very high training load

How to use them:

• Follow sports nutrition guidelines when performance is critical
• Consume 30-90 g/h during prolonged exercise (varies by duration and intensity) (Jeukendrup, 2004)
• Use 90-120 g/h for ultra-endurance events lasting over 3 hours, if you can tolerate it (Jeukendrup, 2004)
• Choose fast-absorbing sugars during exercise: glucose, sucrose, or maltodextrin (Jeukendrup & Gleeson, 2018)
• Right after hard training, consume 1-1.2 g/kg body weight of carbohydrate for rapid glycogen replenishment (Jeukendrup & Gleeson, 2018)

Daily Nutrition Outside Training Windows

General approach:

• Follow standard healthy eating guidelines most of the time
• Emphasize whole foods rich in nutrients
• Minimize highly processed foods that contain mostly sugar and fat
• Choose fiber-rich carbohydrate sources when you have 24+ hours to recover
• Include plenty of fruits and vegetables for micronutrients and health-promoting compounds

Strategic Recovery Nutrition

The Bottom Line: Context Is Everything

Population-wide recommendations for limiting sugar serve an important public health purpose—they address the reality of overconsumption and sedentary lifestyles in modern society. However, these one-size-fits-all guidelines cannot account for individual differences in energy expenditure, physical activity, training status, and timing of intake (Moore & Fielding, 2016).

For professional athletes, sugar’s role depends entirely on context:

Sugar benefits athletic performance when:

• Consumed during prolonged exercise to maintain energy availability (Jeukendrup, 2004)
• Used immediately after exercise for rapid recovery (Jeukendrup & Gleeson, 2018)
• Total intake stays within or below daily energy expenditure
• You’re training regularly with high carbohydrate utilization

Minimize sugar intake when:

• You’re outside training and recovery windows
• It displaces nutrient-dense whole foods in your daily diet
• Your energy intake consistently exceeds expenditure
• Training load is low or during off-season periods

The scientific evidence is clear: there is no convincing research showing sugar causes negative health effects in athletes who maintain energy balance and train consistently (Moore & Fielding, 2016). The recommendation is not to consume gels and sports drinks all day long. Rather, strategically use sugar when performance matters, while building your daily nutrition around whole, minimally processed foods.

The most important takeaway: Be physically active and use your carbohydrate reserves regularly. Your body’s remarkable ability to handle sugar intake depends largely on how well you utilize it through consistent training and competition.

 

Frequently Asked Questions

Does sugar cause diabetes in athletes? No, sugar does not directly cause diabetes (Lean & Te Morenga, 2016). Diabetes develops as a result of insulin resistance, which typically comes from long-term excess calorie intake and weight gain—not from sugar specifically.

Is sugar during exercise the same as sugar from junk food? Chemically, glucose is glucose regardless of source. However, the context matters enormously. Sugar during exercise immediately fuels your performance and doesn’t create excess. Sugar from junk food consumed while inactive provides empty calories without the other nutrients your body needs.

How much sugar is safe for athletes daily? There’s no single answer because it depends on your energy expenditure, training volume, and timing. An athlete burning 5,000 calories daily can safely consume far more sugar than someone burning 2,000 calories—especially when that sugar is consumed during and after training.

Do blood sugar spikes from sports drinks harm athletes? No. The temporary rise in blood glucose after consuming carbohydrates during meals or training is normal physiology and completely different from chronically elevated blood glucose, which causes health problems. Athletes who regularly consume sugar during training actually have better insulin sensitivity than the general population (Moore & Fielding, 2016).

Should athletes avoid sugar completely? No. Sugar (glucose) is your muscles’ primary fuel during most types of exercise (Jeukendrup & Gleeson, 2018). Strategic sugar intake during exercise and recovery supports performance and adaptation. The key is timing and context—use sugar when it serves performance, minimize it when it doesn’t.

 

References

Anderson, J. J., Gray, S. R., Welsh, P., Mackay, D. F., Celis-Morales, C. A., Lyall, D. M., Forbes, J., Sattar, N., Gill, J. M. R., & Pell, J. P. (2020). The associations of sugar-sweetened, artificially sweetened and naturally sweet juices with all-cause mortality in 198,285 UK Biobank participants: A prospective cohort study. BMC Medicine, 18(1), 97. https://doi.org/10.1186/s12916-020-01554-5


Jeukendrup, A. E. (2004). Carbohydrate intake during exercise and performance. Nutrition, 20(7-8), 669-677. https://doi.org/10.1016/j.nut.2004.04.017


Jeukendrup, A. E., & Gleeson, M. (2018). Sport nutrition (3rd ed.). Human Kinetics.


Lean, M. E. J., & Te Morenga, L. (2016). Sugar and type 2 diabetes. British Medical Bulletin, 120(1), 43-53. https://doi.org/10.1093/bmb/ldw037


Malin, S. K., Kullman, E. L., Scelsi, A. R., Haus, J. M., Filion, J., Pagadala, M. R., Godin, J. P., Kochhar, S., Ross, A. B., & Kirwan, J. P. (2018). A whole-grain diet reduces peripheral insulin resistance and improves glucose kinetics in obese adults: A randomized-controlled trial. Metabolism, 82, 111-117. https://doi.org/10.1016/j.metabol.2017.12.011


Moore, J. B., & Fielding, B. A. (2016). Sugar and metabolic health: Is there still a debate? Current Opinion in Clinical Nutrition and Metabolic Care, 19(4), 303-309. https://doi.org/10.1097/MCO.0000000000000289


Yang, Q., Zhang, Z., Gregg, E. W., Flanders, W. D., Merritt, R., & Hu, F. B. (2014). Added sugar intake and cardiovascular diseases mortality among US adults. JAMA Internal Medicine, 174(4), 516-524. https://doi.org/10.1001/jamainternmed.2013.13563