Intro: Sugar is a hotly debated topic in nutrition. On one hand, it’s often blamed for weight gain and chronic diseases; on the other, runners rely on sugar (carbohydrates) as a crucial fuel for training and races. So, what’s the truth about sugar for runners?
This article examines how sugar impacts health and performance, drawing on current research rather than anecdotes. We’ll explore the links between excess sugar and metabolic diseases, how sugar affects hormones like insulin and leptin, differences between types of sugar (glucose vs fructose), and the role of sugar in energy, recovery, and performance.
Finally, we’ll provide practical tips on minimizing harmful sugars while still fueling your runs effectively. (Spoiler: it’s about finding the right balance.)
Sugar, Health, and Metabolic Risks
Eating too much sugar has well-documented impacts on health. When we regularly consume excess sugar (especially in sweetened drinks, desserts, and processed foods), it can lead to metabolic syndrome – a cluster of conditions including high blood pressure, elevated blood sugar, unhealthy cholesterol levels, and increased abdominal fat health.harvard.edu. This syndrome is associated with chronic inflammation and significantly raises the risk of cardiovascular disease and type 2 diabetes health.harvard.edu.
In fact, being overweight from consuming more calories than you burn (often aided by sugary foods) increases the likelihood of heart disease, certain cancers, and type 2 diabetesnhs.uk.
Research shows that high sugar diets can harm the body in ways that go beyond just extra calories. For example, large amounts of fructose (a component of table sugar and high-fructose corn syrup) are processed in the liver and can lead to fat buildup in the liver, unfavorable blood lipid levels, insulin resistance, and elevated uric acid pmc.ncbi.nlm.nih.gov.
These changes are linked to non-alcoholic fatty liver disease, an increased risk of heart disease, and impaired blood-sugar control pmc.ncbi.nlm.nih.gov. Epidemiological studies have found that consuming a lot of added sugars is associated with a higher prevalence of fatty liver, insulin resistance, heart disease, and type 2 diabetes – sometimes even when total calorie intake isn’t excessive pmc.ncbi.nlm.nih.gov.
In other words, sugar may contribute to metabolic diseases through specific biochemical pathways, not just by causing weight gain.
That said, it’s important to note that most of the damage from sugar comes from excess consumption. If you regularly take in more sugar (and calories) than your body needs, you’ll likely gain weight and strain your metabolic health.
One expert review concluded that while excess sugar can indeed promote weight gain and eventually type 2 diabetes through overeating, sugar has no unique “diabetogenic” (diabetes-causing) effect at normal physiological intake levels mysportscience.com.
In other words, sugar itself isn’t a poison – but a high-sugar diet makes it easy to overconsume calories and slowly erode your health. This is especially relevant for runners: even if you’re active, a consistently sugary diet can push you into calorie surplus and fat gain if you’re not careful. Over time, conditions like insulin resistance or fatty liver can develop and ultimately impair your athletic performance and overall well-being.
Public health guidelines reflect these risks. The World Health Organization (WHO) recommends capping “free sugars” (added sugars plus sugars in honey, syrups, and juices) at less than 10% of your daily calorie intake, and says reducing to 5% (around 25 grams, or 6 teaspoons) per day would provide additional health benefits who.int.
For context, 10% of calories is roughly 50 grams (12 teaspoons) of sugar on a 2,000-calorie diet. Currently, many people far exceed these limits – for instance, adults in the UK get about 16–17% of their calories from free sugars on average who.int, well above the 5% goal. It’s easy to see how: a single can of soda can contain around 40 g of sugar (10 teaspoons), overshooting the recommended daily amount in one go who.int.
For runners, the key takeaway is that while you might “burn off” some extra sugar, the long-term health risks of a high-sugar diet (weight gain, metabolic disease, etc.) still apply.
Sugar’s Effect on Hormones: Insulin and Leptin
Sugar doesn’t just add calories – it also triggers hormonal responses that can influence your appetite, energy storage, and metabolism. Two key hormones to understand are insulin and leptin.
Insulin is a hormone released by the pancreas when blood sugar levels rise (for example, after you eat a meal or a sugary snack). Insulin’s job is to help cells take up glucose (sugar) from the bloodstream to use for energy or store for later. Consuming sugar causes a spike in blood glucose, which in turn causes an increase in insulin. In the short term, this is a normal response – especially for athletes, since muscles readily absorb glucose to replenish glycogen.
However, problems arise when insulin spikes are chronic and excessive due to constant high sugar intake without corresponding physical activity. Over time, cells can become less responsive to insulin, a condition known as insulin resistance. When insulin resistance develops, the body has to produce more and more insulin to control blood sugar, and blood glucose stays elevated longer than it should mysportscience.com.
Insulin resistance is a precursor to type 2 diabetes and is often part of the metabolic syndrome that can sap your athletic performance (causing fatigue, slower recovery, etc., in advanced stages).
It’s important to note that regular exercise improves insulin sensitivity. Endurance athletes, even those who consume a lot of sugary sports drinks and gels during training, are typically more insulin-sensitive than the average person mysportscience.commysportscience.com. Their muscles efficiently use glucose, and their blood sugar and insulin levels return to normal more quickly.
In fact, studies find no evidence that sugar intake itself causes insulin resistance in healthy, active individuals mysportscience.com. The main driver is overall energy balance: consistently eating more calories (including from sugar) than you burn can lead to insulin resistance over time, whereas consuming sugar during or after workouts is usually offset by the body’s heightened demand for fuel.
The bottom line on insulin: if you maintain a healthy weight and active lifestyle, moderate sugar won’t suddenly “give you diabetes,” but a continual overload of sugar without exercise can push your body toward insulin problems. Runners should still be vigilant – training hard doesn’t grant a license to gorge on sweets with no consequences.
Leptin is another hormone that plays a crucial role. Leptin is produced by fat cells and helps regulate appetite by signaling to your brain when you’ve had enough to eat (it’s often called a “satiety hormone”).
When you’ve eaten and your fat stores are adequate, leptin levels rise, telling your brain to reduce appetite. However, diets high in sugar, especially fructose, can interfere with this system.
Research suggests that fructose does not stimulate leptin production the way glucose does pmc.ncbi.nlm.nih.gov. In simple terms, consuming a lot of fructose-rich sugar (like sugary drinks, candies, or desserts made with high-fructose corn syrup) might not trigger the normal “I’m full” signals, leading you to eat more than you otherwise would. Over time, consistently high sugar intake can contribute to leptin resistance, a state where the brain stops responding properly to leptin’s message.
When leptin resistance occurs, you don’t get the normal sense of fullness, and this can result in overeating and weight gain. In fact, scientists have observed that obesity and type 2 diabetes often involve both insulin resistance and leptin resistance in the brain, which together drive a vicious cycle of increased appetite, excess calorie intake, and further metabolic disruption mdpi.commdpi.com.
For runners, the effects of sugar on these hormones have practical implications. If you’re indulging in a lot of sugary foods outside of training, you might be blunting your body’s natural appetite regulation. Ever notice how easy it is to polish off a big dessert even when you’ve already had a full meal? Foods high in added sugars bypass some of the normal satiety signals, partly due to the leptin effect. This doesn’t mean you can never enjoy sweets – but it’s a reminder to be mindful.
Over-relying on sugar for snacks or drinks can lead to consuming excess calories without feeling as satisfied, which over time can negate the calorie burn from your runs and even lead to weight gain. By keeping most of your diet centered on whole, nutrient-rich foods (which do trigger fullness signals effectively) and using sugary products strategically (like during long runs or immediately after workouts), you can avoid hormonal imbalances that undermine your training.
Glucose vs. Fructose: Why the Type of Sugar Matters
Not all sugars are created equal. The two most common simple sugars in our diet are glucose and fructose – and they affect the body differently. Understanding their differences is important for runners making smart fueling choices.
Glucose is the body’s preferred energy source. When you eat starchy foods or table sugar (which is half glucose), the glucose enters your bloodstream and can be used by nearly every cell in your body. Muscles, in particular, love glucose – during exercise, your muscles burn glucose for energy, and after exercise they soak it up to refill glycogen stores. Eating glucose-rich foods causes blood sugar to rise, prompting an insulin response so that cells can absorb the sugar. If you consume more glucose than your immediate energy needs, some of it will be stored as glycogen in the liver and muscles, and excess beyond that can be converted to fat. But in an active runner, moderate amounts of glucose are readily burned. In terms of appetite, glucose tends to trigger insulin and leptin, which help signal satiety after a meal.
Fructose, on the other hand, is metabolized almost entirely in the liver. Common table sugar (sucrose) is 50% fructose, and high-fructose corn syrup (found in many sports drinks, sweets, and processed foods) contains roughly 55% fructose. Unlike glucose, fructose doesn’t raise blood sugar sharply in the short term, so it causes little immediate insulin release. That might sound good, but there’s a catch: the liver converts fructose into other substances, including fat if you consume too much. Excess fructose can overload the liver, leading to increased fat synthesis in the liver and bloodstream (triglycerides) pmc.ncbi.nlm.nih.gov. Over time, a high-fructose diet is linked to non-alcoholic fatty liver disease and higher levels of triglycerides, which are risk factors for heart disease pmc.ncbi.nlm.nih.gov. Another downside is that fructose doesn’t stimulate leptin and satiety signals as effectively as glucose pmc.ncbi.nlm.nih.gov. This is why drinking a big glass of fruit juice or a sugary soda (both high in fructose) might not curb your hunger the way eating a whole piece of fruit or a starchy snack would – the liquid fructose slides right in without telling your brain you’ve consumed hundreds of calories.
In practical terms, what does this mean for runners? It means that the source of your sugar and the context in which you consume it matter. Natural sugars found in whole fruits, vegetables, and milk come packaged with fiber, water, and nutrients. These natural sources of fructose and glucose are digested more slowly and do not cause the same metabolic havoc as free sugars. (The WHO notes there’s no evidence of adverse effects from sugars naturally present in whole fruits, veg, or milk who.int.) So, an apple’s 10-15 grams of sugar is far different from 10-15 grams of sugar in a gel or cookie – the apple’s fiber will fill you up and moderate the blood sugar rise, whereas the added sugars in a gel hit quickly and lack micronutrients.
On the flip side, added sugars (the sugar in your sports drink, energy bar, or candy) are absorbed fast. For running performance, fast absorption can be a good thing – during a marathon, you want that quick blood sugar spike to feed your muscles. But when you’re sedentary or it’s outside of exercise, those added sugars can be a bad thing by spiking blood glucose or dumping excess fructose on your liver. The key is timing and quantity.
To summarize: glucose mainly fuels muscles and triggers satiety hormones, whereas fructose primarily burdens the liver and doesn’t send “I’m full” signals effectively. Most sugary foods and drinks contain a mix of both (sucrose or various syrups), so it’s wise to limit those in everyday diet. But strategic use of fast sugars around exercise can boost performance – which brings us to the next point.
Sugar as Fuel: Impact on Energy, Performance, and Recovery
Carbohydrates are the primary fuel for endurance exercise, and that includes simple sugars. For runners, especially those doing long or intense workouts, consuming sugar at the right times can significantly improve performance and recovery. The body can burn glucose for immediate energy, delaying fatigue when running, and can quickly store sugar as glycogen in muscle and liver for later use. Here’s how sugar intake can benefit your running when used appropriately:
- Immediate Energy During Exercise: During moderate to high-intensity exercise, your muscles draw heavily on glycogen and blood glucose. If you run long enough (over about 60–90 minutes), those fuel stores begin to deplete. Ingesting simple carbs (sugars) during exercise – for example, sipping a sports drink or taking an energy gel – provides a rapid source of glucose to keep blood sugar levels stable. This prevents the dreaded “bonk” (when blood glucose plummets) and allows you to keep performing. Studies have shown that consuming a mix of glucose and fructose together during endurance exercise can increase the total amount of carbohydrate your body can use and improve endurance performance compared to consuming glucose alone pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov. This is why many sports drinks and gels use a combination of sugars: glucose for quick absorption and fructose to maximize uptake via a separate pathway in the gut, effectively delivering more energy to the body. In fact, endurance athletes who consumed glucose+fructose were able to exercise longer and with less gastrointestinal distress than those who took only glucose pmc.ncbi.nlm.nih.gov pmc.ncbi.nlm.nih.gov.
- Enhanced Recovery After Exercise: Right after a hard run or workout, your muscles are primed to replenish glycogen. Insulin sensitivity is high and enzymes that store glycogen are very active. Consuming some fast-digesting carbs (like sugars) soon after exercise helps speed up glycogen restoration. Research indicates that adding fructose to post-exercise carbs can accelerate the refill of liver glycogen in particularpmc.ncbi.nlm.nih.gov. Replenishing liver glycogen is important for recovery, especially if you have another training session the next day. Many recovery drinks or post-run snacks (chocolate milk, for example) leverage sugar for this reason – it’s a quick way to reload energy stores. Pairing carbs with some protein is even better, as protein helps muscle repair while carbs refuel; but the carbs (sugars) are what drive the rapid glycogen recovery. In short, a bit of sugar after your run can help you bounce back faster for your next run.
- Maintaining Performance in Long Events: In marathon or ultramarathon scenarios, the ability to take in carbohydrates during the event is often the difference between a strong finish and crawling to the end. The digestive system can only absorb so much glucose per hour (around 60 grams per hour via one pathway), but it can absorb additional fructose via another pathway (around 30 grams per hour). By combining the two, athletes can oxidize up to ~90 grams of carb per hour pmc.ncbi.nlm.nih.gov, supplying more energy to working muscles. This strategy has been a game-changer in sports nutrition – it’s why you’ll see runners taking sports gels, chomping on chews, or drinking electrolyte mixes that contain sugars. It’s a well-researched performance benefit, not just a marketing gimmick.
While sugar around workouts is beneficial, using sugar as a performance tool is different from having a high-sugar diet overall. Runners should distinguish between strategic fueling and casual snacking. If you down a sports drink during a half-marathon, that sugar is going straight to work powering your muscles. But if you sip the same drink while sitting at your desk in the office, that sugar is far more likely to end up stored as fat or contributing to insulin spikes and crashes. Also note that some athletes can rely more on their fat stores for energy (through training or a lower-carb approach), but even the best fat-adapted runners will benefit from some carbohydrate intake when pushing at higher intensities. The goal is not to demonize sugar or ban it entirely – it’s to use it wisely: enough to fuel performance, but not so much that it undermines your health.
Practical Tips for Runners to Manage Sugar Intake
Achieving the right balance with sugar will help you stay healthy and perform your best. Here are some practical, research-backed strategies for runners to minimize harmful sugar intake while still getting the fuel you need:
- Emphasize Whole Food Carbohydrates Day-to-Day: Make unrefined carbs like whole grains, legumes, fruits, and vegetables the main sources of carbohydrate in your daily diet. These foods contain naturally occurring sugars and starches along with fiber, vitamins, and minerals. They provide longer-lasting energy and promote satiety. For example, oatmeal with fruit for breakfast or sweet potatoes with dinner are better daily choices than sugary cereals or desserts. Naturally occurring sugars in whole foods are not a major concern – health authorities like WHO note there’s no evidence of harm from sugars in whole fruits, veg, or milk who.int. By centering your diet on whole foods, you automatically curb “free sugars” and reduce your risk of metabolic issues.
- Time Your Use of Added Sugars: Use quick sugars intentionally around your workouts, when your body can put them to work. If you have a long run or intense training session, consuming a sugary sports drink, gel, or snack during or immediately after exercise can boost performance and recovery. However, try to limit sugary foods and drinks during the rest of the day when you’re not active. For instance, water or electrolyte drinks without added sugar can hydrate you during easy runs or throughout the day, instead of sugary sports beverages. Save the gummies and energy bars for training, not casual nibbling.
- Beware of “Hidden” Sugars in Foods: A lot of the sugar we eat isn’t from obvious sweets. It’s hidden in processed foods marketed as healthy. Check ingredient lists and nutrition labels for foods like flavored yogurts, cereals, protein bars, sauces, and sports products. Ingredients such as cane sugar, corn syrup, brown rice syrup, dextrose, maltose, fruit juice concentrate, and anything ending in “-ose” are forms of added sugar nhs.uk. Even savory products like ketchup or salad dressing can be surprisingly high in sugar – for example, a single tablespoon of ketchup can have about 4g of sugar who.int. Remember that ingredients are listed in order of quantity; if some form of sugar appears near the top of the list, the product is likely high in added sugars nhs.uk nhs.uk. Being label-savvy helps you choose options with little or no added sugars.
- Understand Nutrition Labels: When reading nutrition facts, look at the line for “Carbohydrates (of which sugars)” to gauge how much sugar is in a serving. In the UK, foods with over 22.5g of total sugars per 100g are considered high in sugar, while 5g or less per 100g is lownhs.uk. Note that “total sugars” includes natural sugars too, so also cross-check the ingredients for added sugars. Some products tout “no added sugar” – which is good – but they may still contain natural sugars (like those in fruit puree) that count as free sugar. For example, a smoothie made with only fruit still packs a lot of (natural) sugar and can spike your blood sugar similarly to a soda. Use front-of-package traffic-light labels (if available) as a quick guide: if the sugar indicator is red, it’s high in sugar; green means low nhs.uknhs.uk.
- Moderate Your Sweet Snacks and Desserts: You don’t have to completely eliminate treats – that’s a recipe for misery and cravings. Instead, practice moderation and choose smarter sweets. If you crave something sweet, consider having a piece of whole fruit or a handful of berries first. The fiber and water in fruit will fill you up more than a cookie, and you’ll satisfy some of the sweet craving with far less sugar (plus getting nutrients). If you do indulge in dessert or a sugary snack, keep the portion reasonable and try to have it after a balanced meal rather than on an empty stomach – the other components of the meal (fiber, protein, fat) will slow down sugar absorption and mitigate blood sugar spikes. And on days you aren’t training intensely, be extra mindful about those indulgences. Runners might burn a few hundred extra calories, but it’s easy to eat a few hundred extra from sweets if you’re not paying attention.
- Stay Hydrated with Low-Sugar Fluids: Many sports drinks and recovery beverages contain a lot of sugar. While these can be useful during prolonged exercise, you don’t need sugary drinks throughout the day or during short workouts. Quench daily thirst with water, herbal tea, or electrolyte tablets that have little to no sugar. Save the carbohydrate-containing drinks for the times you genuinely need the fuel (long runs, races, very intense or long training sessions). Similarly, be cautious with “energy” drinks, as they not only contain sugar but often caffeine and other stimulants – they’re not ideal for routine hydration.
By implementing these strategies, you can significantly reduce unnecessary sugar in your diet without sacrificing your ability to fuel your runs. Many elite and recreational runners thrive on diets that are rich in whole foods and relatively low in added sugars, yet still take in carbs strategically for training – it’s a winning formula for both health and performance.
Conclusion
Finding the balance is key. For runners and fitness enthusiasts, sugar is neither a magical performance elixir nor a toxic poison to be entirely banned. It’s a tool – one that can boost energy and recovery when used at the right times, but can also undermine your health if overused. The truth about sugar for runners lies in moderation and timing. Anchoring your everyday diet in vegetables, fruits, lean proteins, and whole grains will keep your added sugar intake low and provide steady energy. In turn, strategically incorporating fast-digesting sugars around your workouts (and staying within recommended limits) will help you train harder and recover faster without the downsides of chronically high sugar consumption.
Remember that even as an athlete, you’re not immune to the health impacts of excess sugar. Metabolic diseases like type 2 diabetes, heart disease, and fatty liver can affect anyone given enough cumulative dietary strain – and they will certainly hamper your running in the long run. The encouraging news is that by staying active, being thoughtful about your diet, and heeding guidelines (such as keeping free sugars under about 5–10% of your calories who.int), you can enjoy the best of both worlds: the fuel for high performance and the foundation for long-term health.
In essence, use sugar as a servant to your running, not as a master of your diet. Enjoy it in sensible amounts when it counts, but don’t let it take over your meals and snacks. By following the research-backed advice above – from understanding the types of sugar and their effects, to reading labels and timing your fuel – you’ll empower yourself to run strong today and safeguard your health for the years ahead. Here’s to wise choices and many happy miles!
Sources:
- NHS – Sugar: the factsnhs.uknhs.uk
- Harvard Health – Excess sugar and metabolic syndromehealth.harvard.edu
- Stanhope KL, et al. – Sugar consumption and metabolic disease (Critical Reviews in Clin. Lab. Sci)pmc.ncbi.nlm.nih.govpmc.ncbi.nlm.nih.gov
- WHO – Guideline on free sugar intake (2015)who.intwho.int
- Jeukendrup A. – “Is sugar bad for athletes?” (mysportscience, 2023)mysportscience.commysportscience.com
- Van Loon LJ, et al. – Journal of Physiology (2019) on glucose/fructose for endurancepmc.ncbi.nlm.nih.govpmc.ncbi.nlm.nih.gov
- NHS – Tips for reading nutrition labels (added sugars)nhs.uknhs.uk
- MDPI – Diabetology (2023) on sugar, leptin and insulin resistancemdpi.com