Carbohydrates and weight training: should you eat them before the training session?

Should you eat carbohydrates before or during your weight training session? This helps mostly if you train in a fasted state or for a long time, more than 45 minutes. For a short session after a meal, most trials find nothing. Adding sugar to your protein does not build more muscle, and the ketogenic diet keeps strength but costs a little lean mass. Here is what twenty-one studies measure.

Before or during the session: it depends on the session

A meta-analysis of 21 studies on 226 people compares carbohydrates taken right before or during the session to a placebo or water. On average, carbohydrates increase the total volume lifted (standardized mean difference of 0.61). The effect is clear for sessions lasting more than 45 minutes (1.02) and more modest after at least 8 hours of fasting (0.39). The more sets taken to muscular failure a session has, the more carbohydrates help; the dose itself changes nothing.

A 2022 systematic review qualifies this: in 13 out of 19 studies, more carbohydrates did not improve performance. The exceptions are comparisons with a group that remained fasted and sessions of more than 10 weight training sets per muscle group. Over several weeks of training, the amount of carbohydrates did not change progress in the majority of studies.

An example of a session where nothing moves: eight trained men performed squats at 85% of their maximum until exhaustion, with 0.3 g of carbohydrates per kilo before the session and after every second set, or a placebo. Sets, repetitions, total load: no difference.

Glycogen drops, strength holds

Weight training taps into glycogen, the muscle's sugar reserve. A 2003 review considers this drop large enough to hinder a high-volume session, and proposes carbohydrates before and during to limit it. A trial on eight trained men measures this: with 1 g of carbohydrates per kilo before and 0.5 g per kilo every 10 minutes, thigh glycogen went from 126.9 to 109.7 mmol/kg in about 39 minutes, compared to 121.4 to 88.3 under placebo. But strength, measured on a machine, did not differ between the two.

Breakfast: the effect is perhaps in the mind

A trial in 22 trained men used to eating breakfast compares three mornings: water alone, a breakfast with 1.5 g of maltodextrin per kilo, and a placebo of the same texture, thickened with xanthan gum and almost calorie-free. The participants believed both contained energy. Two hours later, at the squat, they performed 44 repetitions with carbohydrates, 43 with the placebo, and 38 with water. On the bench press, nothing significant.

A 2025 crossover trial in 16 trained individuals goes in the same direction: two hours before a mostly upper-body session, a liquid meal rich in carbohydrates (1.2 g per kilo), low in carbohydrates (0.3 g per kilo) or an almost calorie-free placebo gave the same number of repetitions. To compose a pre-session meal, the meal calculator details carbohydrates and proteins of what you eat.

Rinsing your mouth with sugar?

In endurance, some people rinse their mouths with a sugary drink without swallowing it. In bodybuilding, that does not work under normal conditions. In 15 trained men, a 6% carbohydrate rinse, caffeine rinse, or both changed neither the one-rep max nor the number of repetitions. In 12 men fasted for 8 hours, the maximum stayed at 101 kg in all three conditions. And in 36 trained men and women, the placebo and carbohydrates performed slightly better than water on the bench press (19.0 and 18.7 repetitions versus 17.7), with no difference between them.

The exception happens when the muscle is depleted. In 12 men exhausted by cycling effort the day before and in caloric deficit, carbohydrate rinsing between sets increased the volume lifted (9,354 kg vs. 8,525 kg), especially on the squat, on legs depleted by cycling (107 repetitions vs. 92).

After the session: sugar adds nothing to protein

Sugar is often added to one's shaker "for insulin". In 10 men, protein taken after the session with 0, 0.15, or 0.6 g of carbohydrates per kilo per hour yielded the same muscle protein synthesis for six hours, despite much higher insulin with carbohydrates. Before the session neither: in 22 young adults, essential amino acids and carbohydrates taken one hour before did not increase post-session protein synthesis, compared to training in a fasted state.

And without carbohydrates? The ketogenic diet

The ketogenic diet removes almost all carbohydrates. For strength, meta-analyses are reassuring: in trained individuals, it does not change the maximum squat (106 participants) or bench press (119 participants). A meta-analysis of 33 studies also finds no difference for muscle mass, power, or strength. In 31 trained men and women, one week at 5.4% carbohydrates caused weight loss without compromising strength or power.

For lean mass, it is less clear. A meta-analysis of 13 randomized trials on 244 people who do weight training finds, compared to a standard diet, 2.21 kg less fat, but also 1.26 kg less lean mass, which weight training does not compensate for. The meta-analysis of 33 studies finds the same trend, on a smaller scale (0.48 kg less lean mass and 1.31 kg less fat).

In summary

To see how many carbohydrates and proteins you actually eat around your training sessions, log your meals in the meal calculator.

Every figure in this article comes from a study you can open: the underlined mentions lead to the summary of the work it is taken from, written solely from the abstract. Most trials on the training session involve about ten to twenty trained men: women and beginners are poorly represented there. Informative content, which does not replace the advice of a healthcare professional: if you have diabetes or take medication, talk to your doctor before changing your carbohydrate intake.