Do you need to consume a large amount of carbohydrates after training to better increase muscle mass (increase muscle protein synthesis)?

Carbon water is not only an important energy substance for our body, but also a source of food that makes us happy (addicted). The high blood sugar index of late night snacks on our social media strongly illustrates this. For fitness enthusiasts, simply saying "to gain muscle" can perfectly rationalize the behavior of consuming a lot of carbohydrates (especially after training).

Before delving deeper into the discussion, it is necessary to introduce a few concepts related to myoprotein synthesis.

Leucine can activate the Akt/mTOR pathway, which is an upstream molecule that not only inhibits protein breakdown but also initiates downstream mTOR. MTOR (mammalian rapamycin target cells) is the master switch of protein synthesis, responsible for regulating the growth of proteins in the body. Insulin, as an important hormone that promotes synthetic metabolism, plays a crucial role in the synthesis of substances in the body. After consuming carbohydrates and other nutrients, it can induce the secretion and elevation of insulin in the body, thereby initiating a series of cellular level synthesis activities for energy substances. So for muscle enhancement, both leucine as a nutrient and insulin as a signaling molecule play important roles. Of course, there are not only these two pathways for muscle synthesis, but we will gradually introduce the others in the future.

Some people believe that consuming carbohydrates after exercise can maximize muscle gain [2], and the main reason for this is

1. Insulin and leucine have a synergistic effect on protein synthesis

2. Adding carbohydrates to protein supplement products can increase lean weight more than eating protein alone

Do these two criteria hold water? Let's look at them separately.

First sentence: Insulin and leucine have a synergistic effect on protein synthesis

Can taking leucine alone stimulate muscle protein synthesis? The answer is yes (provided that the nutrients are abundant). Experiments have shown that the insulin levels in the body of the subjects who fasted overnight (12 hours) were very low (but not zero, about~5 mlU/L). At this time, giving the subjects amino acids containing leucine showed an increase in protein synthesis levels. It indicates that protein synthesis can completely occur at low insulin levels.

Someone may have said, would an increase in insulin levels at this time have a better effect on muscle growth? Experiments have also investigated this issue [4]. The experimenters used experimental methods to increase the serum insulin levels of the subjects to more than 30 times the fasting level (at least 150ml U/L, which is already 1-3 hours after meals) and tested the protein synthesis level at this time. The results showed that higher insulin levels did not further improve the protein synthesis level. Although theoretically, an increase in amino acid delivery levels does require insulin to enhance muscle protein synthesis, extremely low levels of insulin can meet the requirements.

In addition, leucine itself has the ability to stimulate insulin secretion. Taking protein foods on an empty stomach can increase circulating insulin levels to 2-3 times that of an empty stomach, which has been confirmed by many experiments.

Therefore, it is indeed true that insulin has a synergistic effect on leucine, but this synergistic effect does not require high levels of insulin.

Since increasing insulin does not increase muscle protein synthesis in the body, can insulin reduce the rate of protein breakdown? There is experimental evidence to show that consuming around 100g of carbohydrates after training can reduce protein breakdown rate. However, is this reduction irreplaceable? Not really. Eating a protein based diet after exercise can also induce transient hyperinsulinemia (i.e., a short-term increase in serum insulin levels after meals), which is sufficient to inhibit protein breakdown after training.

Second sentence: Adding carbohydrates to protein supplement products can increase lean weight more than eating protein alone

The controversy surrounding this statement lies in the fact that as of now, there is no strong comparative analysis to demonstrate that the impact of consuming protein+carbohydrates alone on lean body weight is superior to that of pure protein. However, there was an experiment [6] that investigated the effect of beverages from different protein sources (milk vs. soy) on muscle synthesis levels. Although these two foods contain protein, they also contain a certain proportion of carbohydrates. The difference is that soy beverages contain maltodextrin (high GI), while the milk group contains lactose (low GI). The experimental results showed that low GI beverages (milk) produced the highest lean weight gain level and muscle protein synthesis rate, which was also higher in the milk group. And we all know that low GI foods have a weaker effect on inducing insulin secretion in the short term than high GI foods. This at least indicates that the glycemic index (the ability to induce insulin secretion) is not positively correlated with muscle growth.

Currently, existing studies on the combination of carbohydrates and proteins versus individual proteins for muscle protein synthesis have shown that [7, 8, 9], the combination of carbohydrates and proteins has no cumulative or synergistic effect on muscle protein synthesis and anti degradation. But it does not mean that insulin cannot increase protein synthesis (but additional experimental conditions are required), but at least based on current research, physiological insulin increase induced solely by carbohydrate intake does not have a synergistic effect on muscle protein synthesis.

After saying so much, the conclusion is that if you are a natural fitness enthusiast who relies solely on diet and training to gain muscle growth, then consuming a diet or exercise supplement rich in leucine is enough to increase muscle protein synthesis levels. In addition, carbohydrates are not entirely useless. Both this and this article mention the important role of carbohydrates in prolonging training time and reducing training fatigue (glycogen recovery does not equate to muscle protein synthesis). Different nutrients play different roles in training and recovery, and understanding their respective roles is essential to better serve our training goals.

Reference materials:

1、THE MECHANISMS OF MUSCLE HYPERTROPHY AND THEIR APPLICATION TO RESISTANCE TRAINING，BRAD J. SCHOENFELD，Global Fitness Services, Scarsdale, New York

2、Stark M, Lukaszuk J, Prawitz A, Salacinski A: Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training. J Int Soc Sports Nutr. 2012, 9 (1): 54-10.1186/1550-2783-9-54.

3、Nobukuni T, Joaquin M, Roccio M, Dann SG, Kim SY, Gulati P, Byfield MP, Backer JM, Natt F, Bos JL, Zwartkruis FJ, Thomas G: Amino acids mediate mTOR/raptor signaling through activation of class 3 phosphatidylinositol 3OH-kinase. Proc Natl Acad Sci USA. 2005, 102: 14238-14243. 10.1073/pnas.0506925102.

4、Greenhaff PL, Karagounis LG, Peirce N, Simpson EJ, Hazell M, Layfield R, Wackerhage H, Smith K, Atherton P, Selby A, Rennie MJ: Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle. Am J Physiol Endocrinol Metab. 2008, 295 (3): E595-604. 10.1152/ajpendo.90411.2008.

5、Børsheim E, Cree MG, Tipton KD, Elliott TA, Aarsland A, Wolfe RR: Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise. J Appl Physiol. 2004, 96 (2): 674-678.

6、Wilkinson SB, Tarnopolsky MA, Macdonald MJ, Macdonald JR, Armstrong D, Phillips SM: Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Am J Clin Nutr. 2007, 85 (4): 1031-1040.

7、Staples AW, Burd NA, West DW, Currie KD, Atherton PJ, Moore DR, Rennie MJ, Macdonald MJ, Baker SK, Phillips SM: Carbohydrate does not augment exercise-induced protein accretion versus protein alone. Med Sci Sports Exerc. 2011, 43 (7): 1154-1161.

8、Koopman R, Beelen M, Stellingwerff T, Pennings B, Saris WH, Kies AK, Kuipers H, Van Loon LJ: Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis. Am J Physiol Endocrinol Metab. 2007, 293 (3): E833-842. 10.1152/ajpendo.00135.2007.

9、Glynn EL, Fry CS, Timmerman KL, Drummond MJ, Volpi E, Rasmussen BB: Addition of carbohydrate or alanine to an essential amino acid mixture does not enhance human skeletal muscle protein anabolism. J Nutr. 2013, 143 (3): 307-314.

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