What "sugar" means in practice
Table sugar is sucrose: one glucose molecule plus one fructose molecule. When digested, it becomes glucose (which enters the bloodstream quickly) and fructose (metabolized mainly by the liver). The glycemic index of sucrose is 65, lower than white rice (72) or the common potato (78). Sugar is not metabolically unique: it is a carbohydrate like any other.
For athletes: timing makes the difference
Fast-absorbing sugar (pure glucose, maltodextrin, sucrose) has a specific role in sport: it replenishes glycogen more quickly after training and provides energy during exercise. The maltodextrin in sports gels and the sucrose in isotonic drinks exist exactly for that.
Jeukendrup, "Carbohydrate and Exercise Performance: The Role of Multiple Transportable Carbohydrates", Current Opinion in Clinical Nutrition & Metabolic Care, 2010
The real problem: ultra-processed food and calorie excess
The harm of sugar in the context of general health does not come from sugar itself, but from calorie excess and the high palatability of the ultra-processed products that contain it. Sugar-sweetened beverages are the only food that large systematic reviews consistently associate with weight gain: the liquid form does not trigger the same satiety mechanisms as solid food.
Fructose: the specific caution
Excess fructose (above 25 to 50 g per day outside the sports context) can be converted into triglycerides via de novo lipogenesis. This matters for sedentary people on a hypercaloric diet, not for athletes who train 8 to 15 h per week with glycogen stores constantly depleted.
Artificial sweeteners: what we know
Recent reviews (WHO, 2023) do not recommend long-term use for weight control in non-diabetics, given the lack of evidence of real benefit and possible effects on the gut microbiota. For athletes controlling calories, they can be a useful tool with caveats. There is no evidence of harm at usual doses.
In high-performance sport, glucose stopped being something to avoid and became data to monitor. Between 2020 and 2022, the continuous glucose monitor (CGM) popularized by Supersapiens became a craze in the endurance peloton, with cyclists tracking blood glucose in real time to calibrate when to eat. Chris Froome, seven-time Grand Tour winner, joined the company as a technical advisor and investor in September 2021, after being one of the first to train with the Abbott Libre Sense sensor on his arm.
The technology created so much perceived advantage that the UCI banned it in competition. In March 2023, American Kristen Faulkner crossed the line in third at the Strade Bianche Donne after a solo attack and was disqualified days later because the glucose sensor was visible on her arm during the race and on the podium, which breaks rule 1.3.006bis. The federation cited the risk of formulaic racing and inequality between athletes who can or cannot pay for the equipment, and third place went to Cecilie Uttrup Ludwig. The episode shows the size of the practical interest in reading glucose during effort.
The capacity to absorb carbohydrate during exercise keeps being pushed upward. A study by Podlogar and colleagues (European Journal of Applied Physiology, 2022) measured a peak exogenous carbohydrate oxidation of 1.60 g per minute while ingesting 120 g per hour of maltodextrin plus fructose, against 1.36 g per minute at 90 g per hour, about 18 percent more. This reinforces the logic of the two intestinal transporters: at high rates, the glucose plus fructose mixture beats glucose alone, which saturates around 60 g per hour and tends to cause gastrointestinal distress above that.
The takeaway
Outside training, excess sugar is a problem of context: sweetened drinks, ultra-processed food, liquid calories that escape satiety. Inside training, it is a performance tool so serious that the UCI bans glucose monitors in racing, and disqualified Kristen Faulkner for wearing one on her arm during the 2023 Strade Bianche. The same molecule that becomes the villain in a sedentary person's diet sustains elite cyclists absorbing up to 120 g of carbohydrate per hour with a mixture of maltodextrin and fructose. How much and when to adjust this in your routine is a conversation for a dietitian, but the central lesson is ready to take with you: on the couch, sugar is calorie excess disguised as pleasure; on the track or on the bike, it is the fuel that separates those who finish strong from those who hit the wall.
