Putting It All Together.
Every time you eat, your body's systems act like an internal combustion engine, converting chemical energy from food into fuel for all bodily functions. We make over a thousand food-related decisions annually – up to eighteen hundred if you factor in snacks. This is where DuelFuel comes in, helping you make smart nutritional choices to support your individual lifestyle. Understanding how your body uses fuel is key to making those decisions.
Let's start with your digestive system...
From Mouth to Muscles...and Beyond.
Your digestive system breaks down food for absorption. This involves mechanical digestion (chewing) and chemical digestion in the stomach and intestines[1]. This entire breakdown process is called catabolism[2].
The fats (lipids), proteins, and carbohydrates in your food must be digested before absorption. Mechanical digestion breaks down these macronutrients into smaller particles for efficient chemical digestion. Chemical digestion further breaks down molecular structures with digestive enzymes, making them absorbable into the bloodstream.
After leaving the stomach as a liquid called chyme[3], food moves to the small intestine. Here, muscles mix food with digestive juices from the pancreas, liver, and intestine. The small intestine walls absorb water and digested nutrients into the bloodstream. This final absorption continues in the large intestine.
Digested nutrients enter the bloodstream primarily as glucose (from carbohydrates), amino acids (from protein), and fatty acids (from lipids)[4].Your blood then carries these to the liver, which stores, processes, and distributes them to the rest of the body as needed[5].
Your Workout Energy Source.
After digestion, nutrients enter your bloodstream as glucose, amino acids, and fatty acids. Glucose is your body's most important energy source.
Since glucose is key for energy[6], your body stores it as glycogen for later use. Glycogen is primarily stored in your muscles and liver[7]. When you're active, your muscles convert glycogen into adenosine triphosphate (ATP), your body's direct energy currency[8]. DuelFuel provides the easily accessible carbohydrates needed to efficiently top up these crucial glycogen stores, ensuring your body is always primed and ready for optimal performance.
ATP - Your Body's Energy Currency.
ATP is your body's direct 'energy currency', continuously needed for everything from lifting weights to thinking. It fuels metabolism and life-sustaining biochemical reactions. Your body uses three energy systems to produce ATP[9]:
- ATP-PC System: For short, intense movements (<10 seconds). This anaerobic system uses stored ATP and phosphocreatine (PC) for immediate energy.
- Lactic Acid System: (Anaerobic Glycolysis) Fuels high-intensity activity for a few minutes using muscle glycogen. Lactic acid buildup contributes to fatigue and the 'burn'.
- Aerobic System: This provides most of your body's ATP. It produces energy from glucose and fatty acids with oxygen, involving glycolysis, the Krebs cycle, and mitochondria. It's slower but sustains energy for longer activities (> few minutes) and general bodily functions like tissue repair and digestion.
The three energy systems are always active, but their primary role shifts based on the type, intensity, and duration of your physical activity[10].
Carbohydrates: Essential for Performance.
Carbohydrates are crucial for exercise performance[12]. Active muscles constantly need ATP, fuelled by glucose from your bloodstream and stored glycogen. DuelFuel provides readily available carbohydrates, crucial for topping up these vital energy stores before, during, and after intense activity.
During intense exercise, muscle ATP production can increase a thousand fold[14]. At intensities above ~60% maximal oxygen consumption (VO2max)*,blood glucose and muscle glycogen become the primary fuels to sustain activity[15].
*VO2max is your maximum oxygen utilization during exercise, indicating aerobic capacity[16].
The importance of carbohydrates for performance has been understood for over a century[17]. Early research linked glucose levels to fatigue in marathon running[18], showing that pre-marathon carb intake prevented weakness[19]. This link was solidified in the 1960s by Scandinavian research, confirming muscle glycogen's major impact on endurance[20, 21, 22, 23].
Today, it's widely accepted that adequate carbohydrates before, during, and after exercise improve performance and recovery[24, 25]. Starting exercise with topped-up glycogen stores significantly enhances performance, and replenishing these stores is vital for recovery and maintaining capacity for future sessions[26, 27].
Exercise Done. Recovery Time.
That aching sensation after exercise? That's often muscle protein breakdown (MPB)[28], where intense activity causes micro-tears in your muscles that need repair[29, 30].
Muscle Protein Synthesis (MPS)
Muscles repair through muscle protein synthesis (MPS)[31, 32,33], a process where protein repairs exercise-induced muscle damage. It counteracts MPB. MPS is enhanced by consuming protein post-exercise, as digested amino acids replenish those lost.
How Much Protein After Exercise?
Studies suggest that in the region of twenty grams of protein post-exercise is ideal for optimal MPS[34, 35, 36, 37]. This is a good target for recovery. DuelFuel products are formulated to deliver optimal protein doses, ensuring your muscles get the building blocks they need when it matters most.
When to Eat Protein After Exercise?
While research is ongoing, some studies indicate that consuming protein sooner after exercise may lead to a higher rate of MPS[38, 39].
A Word About Leucine.
Protein with leucine is considered even better for muscle recovery[40]. Leucine is one of nine 'essential' amino acids (your body can't produce it, so you get it from food). It's crucial because it stimulates a signalling pathway that initiates muscle protein creation, directly supporting recovery. High-quality protein sources found in DuelFuel provide these essential amino acids, including the critical leucine, to help kick-off the muscle building process.
Studies suggest targeting 0.7g - 3g of leucine per 20g of protein for optimised MPS[41].
References.
1. Patricia JJ, Dhamoon AS. Physiology, Digestion. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2025 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK544242/
2. Gurina TS, Mohiuddin SS. Biochemistry, Protein Catabolism. [Updated 2022 Dec 11]. https://www.ncbi.nlm.nih.gov/books/NBK556047/
3. Moxon TE, Nimmegeers P, Telen D, Fryer PJ, Van Impe J, Bakalis S. Effect of chyme viscosity and nutrient feedback mechanism on gastric emptying. Chem Eng Sci. 2017 Nov 2;171:318-330. doi: 10.1016/j.ces.2017.05.048. PMID: 29104301; PMCID: PMC5569601. https://pmc.ncbi.nlm.nih.gov/articles/PMC5569601/
4. Andrea T. Da Poian, Tatiana El-Bacha, & Mauricio R. M. P. Luz. Nutrient Utilization in Humans: Metabolism Pathways 2010.
5. National Institute of Diabetes and Digestive and Kidney Disease. Your Digestive system and how it works. 2021.
6. Victòria Ceperuelo-Mallafré, Miriam Ejarque, Carolina Serena, Xavier Duran, Marta Montori-Grau, Miguel Angel Rodríguez, Oscar Yanes, Catalina
Núñez-Roa, Kelly Roche, Prasanth Puthanveetil, Lourdes Garrido-Sánchez, Enrique Saez, Francisco J. Tinahones, Pablo M. Garcia-Roves, Anna M Gómez-Foix, Alan R. Saltiel, Joan Vendrell, Sonia Fernández-Veledo, Adipose tissue glycogen accumulation is associated with obesity-linked inflammation in humans, Molecular Metabolism, Volume 5, Issue 1, 2016, Pages 5-18, ISSN 2212-8778, https://doi.org/10.1016/j.molmet.2015.10.001.
7. Alberts B, Johnson A, Lewis J, et al. Molecular Biology of the Cell. 4th edition. New York: Garland Science; 2002. www.ncbi.nlm.nih.gov/books/NBK21054/
8. Julien S. Baker, Marie Clare McCormick,and Robert A. Robergs. Interaction among Skeletal Muscle Metabolic Energy Systems during Intense exercise. Journal of Nutrition & Metabolism 2010.
9. Julien S. Baker, Marie Clare McCormick,and Robert A. Robergs Interaction among Skeletal Muscle Metabolic Energy Systems during Intense Exercise. Journal of Nutrition & Metabolism 2010.
10. Ludwig DS, Hu FB, Tappy L, Brand-Miller J. Dietary carbohydrates: role of quality and quantity in chronic disease. BMJ. 2018 Jun 13;361:k2340. doi: 10.1136/bmj.k2340. PMID: 29898880; PMCID: PMC5996878. https://pmc.ncbi.nlm.nih.gov/articles/PMC5996878/
11. Murray B, Rosenbloom C. Fundamentals of glycogen metabolism for coaches and athletes. Nutr Rev. 2018 Apr 1;76(4):243-259. doi: 10.1093/nutrit/nuy001. PMID: 29444266; PMCID: PMC6019055. https://pmc.ncbi.nlm.nih.gov/articles/PMC6019055/
12. D.G. Allen, G.D. Lamb & H. Westerblad Skeletal Muscle Fatigue: Cellular Mechanisms School of Medical Sciences and Bosch Institute, University of Sydney, Sydney, New South Wales, and Department of Zoology, La Trobe University, Melbourne, Victoria, Australia; Department of Physiology and Pharmacology, Karolinska
Institutet, Stockholm, Sweden
13. Meyer RA, Wiseman RW.. The metabolic systems: control of ATP synthesis in skeletal muscle. In: Farrell PA, Joyner MJ, Caiozzo VJ, ed. ACSM’s Advanced Exercise Physiology. 2nd ed.Philadelphia, PA: Wolters Kluwer; 2012:363–378.
14. Jensen TE, Richter EA. Regulation of glucose and glycogen metabolism during and after exercise. The Journal of Physiology (London). 2012;590:1069–1076.
15. Volek, Jeff S.; Duncan, Noel D., Mazzzetti, Scott A et al Performance and muscle fiber adaptations to creatine supplementation and heavy resistance
training. Medicine & Science in Sports & Exercise 31(8):p 1147-1156, August 1999. https://journals.lww.com/acsm-msse/fulltext/1999/08000/performance_and_muscle_fiber_adaptations_to.11.aspx
16. August Krogh, Johannes Lindhard; The Relative Value of Fat and Carbohydrate as Sources of Muscular Energy. Biochem J 1 July 1920; 14 (3-4): 290–363. https://doi.org/10.1042/bj0140290
17. Levine Sa., Gordon B., Derick C., Some Changes in the Chemical Constituents of the Blood Following a Marathon Race. JAMA. 1924;82(22):1778–1779.
https://jamanetwork.com/journals/jama/article-abstract/240244
18. Gordon B, Kohn LA, Levine SA et al. , Sugar content of the blood in runners following a marathon race—especial reference to the prevention of
hypoglycemia. Journal of the American Medical Association 1925;83:508–509.
19. Bergstrom J., Hultman, E.Muscle Glycogen Synthesis after Exercise : an Enhancing Factor localized to the Muscle Cells in Man. Nature 210,
309–310 (1966). https://doi.org/10.1038/210309a0
20. Bergström, J., Hermansen, L., Hultman, E. and Saltin, B. (1967), Diet, Muscle Glycogen and Physical Performance. Acta Physiologica Scandinavica,
71: 140-150. https://doi.org/10.1111/j.1748-1716.1967.tb03720.x.
21. Hermansen L, Hultman E, Saltin B.. Muscle glycogen during prolonged severe exercise. Acta Physiol Scand. 1967;71:129–139.
22. Hultman E, Bergström J. Muscle glycogen synthesis in relation to diet studied in normal subjects. Acta Med Scand. 1967 Jul;182(1):109-17. https://onlinelibrary.wiley.com/doi/10.1111/j.0954-6820.1967.tb11504.x
23. Hawley JA, Leckey JJ. Carbohydrate Dependence During Prolonged, Intense Endurance Exercise. Sports Med. 2015 Nov;45 Suppl 1(Suppl 1):S5-12. https://link.springer.com/article/10.1007/s40279-015-0400-1
24. Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise 48(3):p 543-568, March 2016. https://journals.lww.com/acsm-msse/fulltext/2016/03000/nutrition_and_athletic_performance.25.aspx
25. Nutrition and Athletic Performance. Medicine & Science in Sports & Exercise 48(3):p 543-568, March 2016. https://journals.lww.com/acsm-msse/fulltext/2016/03000/nutrition_and_athletic_performance.25.aspx
26. Burke LM, van Loon LJ, Hawley JA.. Post-exercise muscle glycogen resynthesis in humans. J Appl Physiol. 2017;122:1055–1067. https://journals.physiology.org/doi/full/10.1152/japplphysiol.00860.2016
27. Tipton, K.D., Hamilton, D.L. & Gallagher, I.J. Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans. Sports
Med 48 (Suppl 1), 53–64 (2018). https://doi.org/10.1007/s40279-017-0845-5
28. Proske U, Morgan DL. Muscle damage from eccentric exercise: mechanism, mechanical signs, adaptation and clinical applications. J Physiol. 2001 Dec
1;537(Pt 2):333-45 https://physoc.onlinelibrary.wiley.com/doi/10.1111/j.1469-7793.2001.00333.x
29. Tipton, K.D., Hamilton, D.L. & Gallagher, I.J. Assessing the Role of Muscle Protein Breakdown in Response to Nutrition and Exercise in Humans. Sports Med 48 (Suppl 1), 53–64 (2018). https://doi.org/10.1007/s40279-017-0845-5
30. Chris McGlory, Michaela C. Devries, and Stuart M. Phillips, Skeletal muscle and resistance exercise training; the role of protein synthesis in recovery and remodeling Journal of Applied Physiology, 6th March 2017 https://journals.physiology.org/doi/full/10.1152/japplphysiol.00613.2016
31. Atherton PJ, Smith K. Muscle protein synthesis in response to nutrition and exercise. J Physiol. 2012 Mar 1;590(5):1049-57. https://journals.physiology.org/doi/full/10.1152/japplphysiol.00613.2016
32. Witard OC, Bannock L, Tipton KD. Making Sense of Muscle Protein Synthesis: A Focus on Muscle Growth During Resistance Training. Int J Sport
Nutr Exerc Metab. 2022 Jan 1;32(1):49-61. https://journals.humankinetics.com/view/journals/ijsnem/32/1/article-p49.xml
33. Schoenfeld, B.J., Aragon, A.A. How much protein can the body use in a single meal for muscle-building? Implications for daily protein distribution. J
Int Soc Sports Nutr 15, 10 (2018). https://jissn.biomedcentral.com/articles/10.1186/s12970-018-0215-1
34. Witard OC, Jackman SR, Breen L, Smith K, Selby A, Tipton KD. Myofibrillar muscle protein synthesis rates subsequent to a meal in response to
increasing doses of whey protein at rest and after resistance exercise. Am J Clin Nutr. 2014 Jan;99(1):86-95. https://www.sciencedirect.com/science/article/pii/S0002916523049213?via%3Dihub
35. Phillips SM. The science of muscle hypertrophy: making dietary protein count. Proceedings of the Nutrition Society. 2011;70(1):100-103. https://www.cambridge.org/core/journals/proceedings-of-the-nutrition-society/article/science-of-muscle-hypertrophy-making-dietary-protein-count/F0E5C7D9AA3C5385287C806EE504E18E
36. Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., … Antonio, J. (2017). International Society of Sports
Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14(1). https://doi.org/10.1186/s12970-017-0177-8
37. Aragon, A.A., Schoenfeld, B.J. Nutrient timing revisited: is there a post-exercise anabolic window?. J Int Soc Sports Nutr 10, 5 (2013). https://jissn.biomedcentral.com/articles/10.1186/1550-2783-10-5#citeas
38. Levenhagen DK, Gresham JD, Carlson MG, Maron DJ, Borel MJ, Flakoll PJ. Postexercise nutrient intake timing in humans is critical to recovery of leg glucose and protein homeostasis. Am J Physiol Endocrinol Metab. 2001;280(6):E982-93 https://journals.physiology.org/doi/full/10.1152/ajpendo.2001.280.6.E982
39. [40] Tyler A Churchward-Venne, Leigh Breen, Danielle M Di Donato, Amy J Hector, Cameron J Mitchell, Daniel R Moore, Trent
Stellingwerff, Denis Breuille, Elizabeth A Offord, Steven K Baker. Leucine supplementation of a low-protein mixed macronutrient beverage
enhances myofibrillar protein synthesis in young men: a double-blind, randomized trial. The American Journal of Clinical Nutrition, Volume 99, Issue
2, February 2014, Pages 276-286 https://www.sciencedirect.com/science/article/pii/S0002916523049444?via%3Dihub
40. Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., … Antonio, J. (2017). International Society of Sports
Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 14(1). https://doi.org/10.1186/s12970-017-0177-8
