CARBOHYDRATES - fuelling exercise
What are carbohydrates?
Carbohydrates are molecules built of carbon (carbo), hydrogen, and water (hydrate).
What are examples of carbohydrates?
Carbohydrate-rich foods include grains, potatoes, pasta and rice.
What is the function of carbohydrates for energy production?
Carbohydrates are the predominant fuel during high-intensity exercise and when stored as glycogen (carbohydrates stored in muscle and liver) can provide more than 32 calories per minute of energy. Despite fat having more than double the calories of carbohydrates, “burning fat”/ oxidising fat as a main fuel is insufficient for high intensity exercise as carbohydrates (via glucose oxidation) produce 4 to 5 times more energy during high-intensity exercise than fat does.
Are there sex-differences for the use of carbs for exercise?
Tarnopolsky and colleagues (Tarnopolsky LJ, MacDougall JD, Atkinson SA, Tarnopolsky MA, Sutton JR. Gender differences in substrate for endurance exercise. J Appl Physiol (1985). Jan 1990;68(1):302-8. doi:10.1152/jappl.1990.68.1.302) found that women, during endurance exercise, use 25% less glycogen than men (who also use a lot more proteins), due to women’s higher intramuscular triglyceride (fat stored in muscle) stores, facilitating a higher rate of fat mobilisation and use as fuel during exercise.
What defines “high intensity” exercise?
Intensities greater than 60% of maximal oxygen consumption.
How much carbohydrate should I eat a day?
Dietary guidelines suggest an intake of at least 130g a day for both children and adults as this is the minimum amount necessary to fuel the brain with glucose (the main source of fuel for the brain). Carbohydrate intakes of competitive lifters and throwers tend to be around 3 to 5g /kg of body weight, whilst weightlifters tend to be around 4 to 7g per kg of body weight (Slater G, Phillips SM. Nutrition guidelines for strength sports: sprinting, weightlifting, throwing events, and bodybuilding. J Sports Sci. 2011;29 (Suppl:S67-77.doi:10.1080/02640414.2011.574722). I personally, recommend on training days for clients to have a minimum of 3g per kg of body weight.
(Remember, you need fibre as well in your diet to optimise health so please educate yourself on fibre intake).
Can carbohydrates aid in muscle growth?
Carbohydrates, post-exercise, is anti-catabolism which opposes catabolism (catabolism harms your gains). Carbohydrates have a protein sparring effect, so when consumed your body reduces the rate of break down of muscle or other proteins for fuel. Catabolism is killer of gains! However, saying this, Muscle Protein Synthesis (muscle building) has 4x the effects of Muscle Protein Breakdown (your body is in a continuous cycle of muscle breakdown which is why we need sufficient protein and exercise to prevent/ reduce muscle loss/ atrophy) when exercise occurs. If you train with low glycogen, your body turns protein into sugar to be oxidised as fuel for exercise. Your muscles are the largest store of protein! Where there might be an issue is if you have two exercise sessions in less than 6 hours.
Not taking carbohydrates directly after exercise will not prevent you making gains but will harm gains if you do two exercise bouts in close succession of each other (Hulmi JJ, Laakso M, Mero AA, Häkkinen K, Ahtiainen JP, Peltonen H. The effects of whey protein with or without carbohydrates on resistance training adaptations. J Int Soc Sports 209. Nutr. 2015;12:48, doi:10.1186/12970-015-0109-4)!
Each muscle, as well as the liver, has a pool of glycogen. Every time you exercise some of that pool of glycogen is used to a point where there’s not enough glycogen in the liver to turn into glucose to fuel the brain sufficiently. This drop in blood glucose is called hypoglycaemia and is the reason why you stop exercise and this can cause dizziness. In order to replenish these stores to a point where “normal” levels of glycogen can be stored and blood glucose levels can be balanced (homeostasis can occur), the body needs about 6-8 hours. Consuming 1.2g per kg of body weight of carbohydrates per hour for at least 4 hours should be enough carbohydrates to sufficiently refuel glycogen stores for a second bout of exercise (PMID: 24482590 International Society of Sports Nutrition Symposium, June 18-19, 2005, Las Vegas NV, USA - Macronutrient Utilization During Exercise: Implications For Performance And Supplementation).
How I can help you?
Personal Training and Online Coaching for all levels of fitness with accurate calorie targets and nutritional advice which will be realistic around your goals, evidence based and health prioritised.
Performance Nutrition for working professionals that incorporates nutrition around your life style, aiding in better sleep, reduced stress, increased concentration and, of course, increased performance.
Performance Nutrition for the athlete who is trying to increase their performance physically, cognitively, prepare for competition, fuel for competition or simply to make weight.
I use evidenced based practice. There are no guesses.