It is well known that taking carbohydrates before and during endurance exercise helps to increase both speed and endurance. It is not as well known that taking carbohydrates before and during resistance training for strength can increase intensity and duration of workouts. A review of 21 randomized controlled studies that included 226 young adults (ages 20-30, 95 percent men and five percent women) found that taking carbohydrates before or during lifting weights increased training volume, and caused higher peak blood lactic acid and sugar levels (Sports Med, Nov 2022;52(11):2691-2712). These are indirect measures of the intensity of workouts.
The athletes in the studies had been lifting weights from two months to more than five years and the studies did not separate the athletes by how long they have been lifting weights. This review found that taking carbohydrates during resistance exercises:
• was more effective in training sessions lasting more than 45 minutes and containing at least 8–10 sets
• did not prolong or improve workouts in sessions lasting less than 45 minutes
• was beneficial only when the athletes did not eat any food for several hours before each workout
• was most effective in sessions in which the athletes took such intense workouts that they went into failure or close to failure
• was not effective in workouts in which the athletes lifted only up to less than 85 percent of the maximum weight that they could lift
• was not effective when they took less than 0.3 to 2.5 grams of carbohydrate per kilogram of body weight
The carbohydrate dose is a matter of personal preference, because the amount of weight lifted and endurance increased as long as the lifter took at least 0.3 grams of carbohydrates per kilogram of body weight.
Taking Extra Carbohydrates Does Not Increase Performance In Average Lifters
Eating extra carbohydrates increases weightlifting performance and muscle size and strength only when people train close to their limits (Nutrients, Feb 2022;14(4):856). The average lifter does not do this. To gain maximum size and strength, a lifter has to cause extensive damage to the Z-lines of muscle fibers that lead to increased muscle size and strength (J of Appl Physiol, Oct 18, 2018;126(1):30–43).
Weight Lifting May Help to Control Diabetes and Excess Weight Better than Aerobic Exercise
People should not take in extra refined carbohydrates (sugar-added foods and those made from flour) when they are diabetic or trying to lose weight. Sugar and refined carbohydrates promote weight gain (BMJ, Sept 27, 2023;382:e073939) and high blood sugar levels and diabetes (The Am J of Clin Nutr, May 2004;79(5):774-779). Indeed, diabetics may be able to gain better control of their diabetes by lifting weights than by performing aerobic exercises such as running or cycling (Diabetologia, Oct 2023;66(10):1897-1907). When they lifted weights, they lost more fat and gained more muscle.
Why You Need Carbohydrates During Intense Exercise
Competitive weightlifters spend hours lifting weights, but they still follow the rules of “stressing and recovering”. On one day, they take very intense workouts that damage a specific muscle group and then on the next day, they go easy on that muscle group and take intense workouts stressing a different muscle group. The more intensely you can stress a muscle group without causing an injury, the stronger you become.
When you lift weights, your muscles use carbohydrates, fats and proteins as sources of energy. They need oxygen to convert food to energy. The limiting factor for how intensely you can exercise is the time it takes to move oxygen from your bloodstream into your muscles. Since the sugars from carbohydrates take less oxygen than fats and proteins to produce energy, sugar becomes the primary fuel from food to power your muscles. You have only a limited amount of sugar stored in your body, mostly in your liver and muscles. When you start to run low on sugar stored in your muscles and liver, you need more oxygen. If you are already working at your maximum, you have to slow down.
Lactic Acid Measures Intensity of Exercise
You can measure the intensity of a resistance workout by the weight that you can lift, but you can also measure intensity of a workout indirectly by seeing how high blood lactic acid levels rise during a workout. When you exercise as hard as you can, you use primarily carbohydrates for energy because carbohydrates require less oxygen than fats and proteins do. When you can’t keep up with your needs for oxygen, you start to accumulate large amounts of lactic acid in your muscles and bloodstream. The harder you exercise, the higher your blood lactic acid levels rise, so blood lactic acid levels are an indirect measure of how intensely you are exercising.
Protein Ingestion and Muscle Size and Strength
Taking extra protein to increase muscle size and strength is very controversial. Older data showed some benefits of extra protein, while most recent studies showed little or no benefit. Certainly healthy elderly men gained no extra strength or muscle mass by taking extra protein after each exercise session for three months (The Am J of Clin Nutr, Feb 2009;89(2):608-616). Furthermore, human and mice studies show that consuming over 22 percent of dietary calories from protein can lead to increased activation of immune cells that play a role in forming arterial plaques that increase heart attack risk. Specifically, the amino acid, leucine, is associated with increased plaque formation (Nat Metab, Feb 19, 2024;6:359–377).
My Recommendations
When you plan to exercise near your maximum intensity for endurance or resistance for 45 minutes or more, you need an adequate store of carbohydrates. Eat a full meal three hours before your exercise bout or competition, or take a sugared drink before your workout or race. Almost all sugared drinks contain 10 grams of sugar per 100cc, because that is the concentration of sugar in drinks that tastes best. If your competition or intense workout takes more than 45 minutes, you may consider taking a sugared drink 30 to 45 minutes after you are into your race or intense workout. If your workout or race lasts longer than two hours, you should try to eat some food. This is very important, especially in hot weather. If your workout or race takes more than three hours, you should include some salted foods.
