Friend or foe; the role of sugar in athletic health

Sugar is often labelled and seen as negative for our health. Many headlines on social media, newspapers and websites claim that sugar causes cancer, obesity or cardiovascular disease. However, sugar is often recommended for athletes to consume around or during exercise. Carbohydrate gels, drinks and powders are on the market and sold based on the premise of fuelling sports performance due to their sugar content. It can be confusing for athletes who want to fuel their performance but also maintain and improve their health, as these two sides of the coins contradict each other. In this article, I will explain the contexts where sugar may be a detriment to our health, and where it may be beneficial. When it comes to science, in particular nutrition and sport science, context is key to understanding negative and positive impacts of foods, supplements or training protocols. 

Sugar is the simple version of carbohydrates, which are the main energy source for our body, with 50-60% of our calories coming from this macronutrient. Sugars are generally sweet and added sugars can be labelled as different names on food labels such as sugar, fructose, syrup, dextrose, glucose and more. Some sugars can also be found naturally such as fructose in fruit and lactose in milk and other diary products. The World Health Organisation (WHO, 2003) recommends an intake of no more than 10% of total calories to come from free sugars. So, if you were consuming 2000 calories per day, no more than 200 calories should be from free sugars, which would equal 50g/day, or 12 tsp (as carbohydrates have 4kcal per gram). Free sugars can be defined as all sugars added to foods and drinks, but also sugars that occur naturally in honey, syrup and fruit juices. 

There is a large body of evidence that excessive sugar intake is negative for our health, and has been implicated in obesity, metabolic disorders, diabetes, cancer and depression (Gillespie et al., 2023). Excessive intake depends on the context, as an excess for an inactive diabetic will look different to a professional endurance athlete. Along with this, sugar is not necessarily the main culprit here, but what a high sugar intake comes with. Often, a high sugar intake means there is less room for nutritious foods for our health, and as highly processed sugary foods often do not contain the likes of protein or fibre, which can aid in appetite regulation (making us fuller for longer), there is a chance of overconsumption of calories in general. 

Recommendations for carbohydrate intake for athletes varies, but generally for endurance athletes that perform in multiple hour events, intakes up to 90-120g carbohydrates/hour are used. A large amount, if not all, of these carbohydrates will be in the form of sugar, to be easily assimilated, digested and used as fuel. During exercise, 70-80% of carbohydrates ingested are immediately used to fuel the exercise bout (Jeukendrup, 2004), so let’s look at an example. An ultra-endurance runner who has a 4 hour long run, consuming carbohydrates at a rate of 90g/hr during this bout, would equate to 360g carbohydrates, all coming from sugar, which is much, much higher than the recommendation for the general population. However, 70-80% of these carbohydrates (250-290g) will be used directly for fuel. Along with this, carbohydrate use during exercise in a moderately trained athletes ranges from 100-120g/hour, but in highly trained individuals this could reach up to 250g/hour. So even with an intake of 90g/hour, this would not match the sugar use during exercise and the athlete would still need to utilise their carbohydrates reserves in their muscles. So 360g sugar over a 4-hour exercise bout does not seem that excessive considering it will be used for fuel.

When performance is crucial, athletes should adhere to sports nutrition requirements; otherwise, they should generally follow regular dietary guidelines. When exercise quality matters, fuelling with carbohydrates and sugar is a smart choice. When fast recovery is required afterwards (for example, if a hard training session or another round of competition is scheduled for a few hours later), use sugars to rapidly restore glycogen. Athletes can also use alternative carbohydrate sources to replace glycogen if they have more time (>24 hours), and eat nutritious, nutrient-dense foods throughout the day and limit highly processed foods, which frequently just have sugar and fat as their main constituents.

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Gillespie, K.M., Kemps, E., White, M.J. and Bartlett, S.E., 2023. The Impact of Free Sugar on Human Health—A Narrative Review. Nutrients15(4), p.889.

Jeukendrup, AE. Carbohydrate intake during exercise and performance, Nutrition, Volume 20, Issues 7–8, 669-677, 2004.

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