Lactose is a sugar found in milk. Is this type of carbohydrate a good source ion energy during exercise? This blog looks at the results of a recent study tat compared lactose with sucrose.
What is lactose?
Lactose is a sugar exclusively found in milk, which is comprised of a glucose and a galactose molecule (making it a disaccharide). It is found in dairy foods, and in the greatest amounts in milk, yoghurt, milk protein powders (e.g. whey, casein) and ice cream, with hard cheeses and butter having very little. It is also added to some foods such as baked goods or confectionary as a sweetener and to improve flavour, so it is present in the diet from both traditional and non-traditional sources.
How much do we eat?
Some individuals suffer gastrointestinal symptoms when they eat lactose, which is termed lactose intolerance, and is caused by an inability to digest lactose in the gut. Although this condition is common, most intolerant people can still eat 12-15g (the amount in a 250-300 ml cup of milk) without symptoms, and tolerant people can eat much larger amounts (>80g) without problems. Lactose is quite common in the Western diet, on average totalling ~12 g per day. However, athletes and recreationally active people may consume much more than this, as dairy products (such as milk, yoghurt and protein powders) are very popular aspects of the diets of athletes. There are no recommendations for lactose intake, nor is there any consideration of how it fits in to carbohydrate needs for athletes, and little is known about how it is metabolised in an exercise context.
Study
In a recent study we investigated whether lactose that is ingested during exercise can be oxidised quickly, effectively trying to answer the question of ‘can lactose be used as an energy source?’
11 participants cycled for 2.5 hours at a moderate intensity on three occasions. During exercise, they consumed beverages, containing either lactose, sucrose or water. We compared lactose to sucrose which is a disaccharide comprised of glucose and fructose and is known to be oxidised quickly during exercise. The participants consumed carbohydrates at a moderate rate of 48 grams per hour (or 0.8 grams per minute) which is in line with recommendations to take in 30-60g per hour for exercise of up to 2.5 hours. The carbohydrate conditions contained 120g of lactose or sucrose (roughly equivalent to 4-6 carbohydrate gels), which is amongst the largest amounts of lactose ever investigated.
We showed that the exogenous carbohydrate oxidation rates for lactose and sucrose were very similar (0.56 ± 0.19 g/min and 0.61 ± 0.10 g/min respectively) and were not significantly different. This demonstrates that lactose can be a quickly oxidizable fuel source during exercise (at least in these moderate amounts), similar to sucrose (glucose and fructose). Furthermore, the lactose beverage increased reliance on fat oxidation, and reduced oxidation of glycogen compared to sucrose, a favourable shift in metabolism that relates to glycogen sparing.
There were no differences in gastrointestinal symptoms between conditions on average, which shows that lactose can be consumed in large amounts by most lactose tolerant individuals. Although some participants did experience gastrointestinal problems with lactose, individuals should determine which carbohydrates and foods are appropriate for them to use around exercise, based on their preferences and responses. This is true for all carbohydrates, including fructose, considering the presence of fructose malabsorption in some individuals.
Summary and implications
Therefore, not only can lactose be used as a carbohydrate during exercise if desired, but dairy foods containing lactose can now be considered as part of a pre- or during exercise nutritional regimen for their carbohydrate content, as lactose is now known to be a readily oxidisable carbohydrate. Furthermore, even relatively large amounts of lactose do not cause gastrointestinal problems in most individuals, which can be a concern for athletes who need to minimise any GI problems around training.
References
Odell OJ, Wallis GA. The application of lactose in sports nutrition. International Dairy Journal. In press, 2020, p. 104970
Brisbois T, Marsden S, Anderson G, Sievenpiper J. Estimated Intakes and Sources of Total and Added Sugars in the Canadian Diet. Nutrients. 6(5):1899-912, 2014
Burke LM, Hawley JA, Wong SH, Jeukendrup AE. Carbohydrates for training and competition. Journal of Sports Science. 29 (Suppl 1):17-27, 2011
Odell OJ, Podlogar T, Wallis GA. Comparable Exogenous Carbohydrate Oxidation from Lactose or Sucrose during Exercise. Med Sci Sports Exerc. 52(12):2663-72, 2020
Putkonen L, Yao C, Gibson PR. Fructose malabsorption syndrome. Curr Opin Clin Nutr Metab Care. 16(4):473-7, 203
Wallis GA, Wittekind A. Is There a Specific Role for Sucrose in Sports and Exercise Performance? Int J Sport Nutr Exerc Metab. 23(571-583), 2013
