Study: Should You Combine Protein With Carbs?

Geschatte leestijd: 8 minuten Do you need to combine proteins with carbohydrates after a workout for more muscle mass? Here we try to answer this question based on all relevant research.

Combining Proteins with Carbohydrates?

This is a question that can be answered in many ways. For example, you can look at the absorption of both under the influence of each other. Do the amino acids from the proteins, for example, get better absorbed by the muscles if mixed with carbohydrates? Do the muscles take up more glycogen from carbohydrates when you take them with proteins? You can also look at the different effects on insulin and infer from there what the effect on muscle mass will be. We will examine these under the microscope, but mainly focus on studies that have actually looked at the effect on muscle mass.

Proteins, Carbohydrates, and Muscle Mass

Proteins and carbohydrates after a workout can both contribute to muscle growth. We have dedicated many articles to the effect of both on muscle mass. As an introduction, I will give a very brief summary here. However, the reality is much more complex and depends on many factors such as hormonal factors, energy status throughout the day, amount of experience with strength training, the nature of this training, etc.

Carbohydrates and Muscle Mass

Carbohydrates can contribute to muscle mass in various ways. A few of the most important ones are:

• Supplier of energy as a quick source of glucose
• Following this, the enhancing effect on insulin

Carbohydrates are a quick source of glucose, an important fuel, if not the most important. Some researchers argue that lactic acid is even more efficient, but glucose is also needed for that (unlike lactic acid, which cannot be obtained from normal food). Carbohydrates are short or long chains consisting of different sugars, or saccharides. These can contain glucose themselves (such as the long chains in starch) or can easily be converted into glucose by the body (such as fructose). Whether your body builds tissue (such as muscle and fat mass) or breaks it down largely depends on the amount of glucose in your blood. Also known as your blood sugar, this is an important signal for the body. This signal is given by insulin. When there is enough glucose in the blood, the pancreas will release insulin. Insulin travels in the blood and tells fat cells and muscle cells that there is available glucose. Fat cells can convert glucose into fatty acids for long-term storage. So-called ‘fast sugars’ cause a rapid increase in blood sugar and thus lead to a higher peak in insulin. The muscles can store glucose as glycogen as a quick source of energy. Moreover, insulin ensures that available amino acids in the blood are absorbed by the muscles for so-called protein synthesis. This involves the production of proteins in the muscles, the main form of muscle growth (through training/nutrition).

Proteins and Muscle Mass

Then, of course, amino acids must be available. These come from the protein you get from food and possibly from supplements. We have also written a lot about the different types of protein, the amino acids in them, and their effect on muscle growth. Often, extra value is attached to essential amino acids and Branched Chain Amino Acids (BCAAs). Essential amino acids cannot be produced by the body itself and can only be obtained from food. The BCAAs, especially leucine, play a special role in muscle growth. In practice, however, proteins are needed that contain many or all of the different amino acids. Anything that your body has to convert from (‘non-essential’) amino acids for other processes can detract from the amino acids available for muscle growth. The maximum absorption of some amino acids also depends on the availability of other amino acids.

Combining Proteins and Carbohydrates for Muscle Growth?

Both can contribute to muscle growth, in general, but also specifically in a sports drink or shake after a workout. Proteins are preferred for this purpose in practice, which is supported by research. The theory that combining both after training will result in more muscle growth is, simply put, as follows: Proteins provide the amino acids for protein synthesis, carbohydrates ensure that these are better absorbed by increasing insulin. The questions that researchers then try to answer include:

1. What levels of insulin are needed for optimal absorption of amino acids from proteins?
2. What effect does protein itself have on insulin?
3. Does the combination of carbohydrates and proteins lead to more muscle growth?

Time to dive into the research!

“Insulin needed for amino acid absorption”

The researchers at Northern Illinois University suggest that the combination is advisable.

An ideal supplement following resistance exercise should contain whey protein that provides at least 3 g of leucine per serving. A combination of a fast-acting carbohydrate source such as maltodextrin or glucose should be consumed with the protein source, as leucine cannot modulate protein synthesis as effectively without the presence of insulin. Such a supplement post-workout would be most effective in increasing muscle protein synthesis, resulting in greater muscle hypertrophy and strength

That seems clear. The leucine in the proteins would lead to less effective protein synthesis in the absence of insulin. But who says there is no insulin present when you do not consume carbohydrates in your post-workout shake? The studies on which the researchers base themselves used cell cultures in a petri dish [2,3]. Under those conditions (‘in vitro’), it is possible to look at the effect of amino acids when there is no insulin at all. This circumstance does not necessarily have to be representative of reality ‘in vivo’.

“Always enough insulin for amino acid absorption”

Even when you wake up in the morning and have not eaten yet, there are low levels of insulin in your blood (~5 mU/L). Even at these low levels, amino acids in proteins can be used for protein synthesis. This was shown in a 2008 study by the University of Nottingham [4]. Even when the researchers increased these low levels thirty times, protein synthesis remained the same. That is comparable to insulin levels after a meal with fast sugars. In both situations, enough amino acids were present in the blood. So, indeed, insulin is needed to allow proteins to contribute to muscle growth. However, the mentioned study shows that under normal circumstances, there is already enough insulin. People training for muscle growth also normally do not train on an empty stomach. In practice, you will not quickly train with such low insulin levels.

Proteins themselves also increase insulin

The mistake can also be made to think that only carbohydrates lead to an insulin response. Proteins do this too. Two studies from 2010 showed that intake of proteins can double or even triple the insulin level on an empty stomach [5,6]. That is still not as much as the response after a meal with carbohydrates. However, we have seen that such high levels do not improve the absorption of the proteins. So, I mention it more to emphasize that proteins themselves also raise insulin, but actually, that is irrelevant if insulin does not need to rise further.

Combining Carbohydrates with Proteins to Limit Muscle Breakdown?

Irrelevant for protein synthesis, perhaps not for muscle growth. That may sound contradictory, but it is not. Muscle growth, maintenance, or loss is the result of the continuous production but also breakdown of proteins in the muscles. This result is also called the net protein balance. When you produce more than you break down, your muscles will grow. Limiting the breakdown of these muscle proteins is therefore just as important as stimulating the production. Here, too, insulin, or rather the lack thereof, plays an important role. At low levels (and the release of other hormones such as glucagon), fat cells and muscle cells will be instructed to make glucose through breakdown. This breakdown is often welcome when it comes to fats, but not when it comes to muscle mass. Research has indeed shown that ingesting 100g of fast sugars after a workout can increase muscle growth by specifically limiting breakdown [7]. However, research from 2011 also showed that protein is also capable of inhibiting this breakdown without combining with carbohydrates [8]. Adding 50 grams of maltodextrin to 25 grams of whey protein also did not improve the net protein balance compared to whey alone.

Protein Source More Important than (Source of) Carbohydrates

Then there are two more studies that compared the effects of milk on muscle growth with those of soy milk. Both sources contain carbohydrates in addition to protein (lactose and maltodextrin, respectively). The amount of carbohydrates was the same. However, maltodextrin has a higher glycemic index than lactose. This means that it causes a faster increase in blood sugar and thus a higher insulin peak. However, it was the milk that led to higher protein synthesis and more dry mass [9,10].

Conclusion: Enough Protein is Enough

If you take enough proteins after a workout, that is sufficient for the optimal effect of the proteins on muscle growth. Adding carbohydrates does not seem to have added value. Except for the aforementioned 2011 study [8], there are two other studies that tested this in young adults [11,12]. It should be noted, however, that no ‘normal’ proteins were used. In 2007, researchers at Maastricht University found that adding carbohydrates to protein hydrolysate had no added value [11]. Research from McMaster University compared the effect of essential amino acids alone or with carbohydrates [12]. Here too, they saw no increased effect by adding carbohydrates to the mix. The researchers saw similar results in 2013 with older men when ‘slow’ casein protein was used [13]. The similarity between these studies is that all worked with 20-25 grams of high-quality protein or amino acids with sufficient leucine. The conclusion is that you do not need carbohydrates to make your protein shake work optimally. The proteins alone can have just as great an effect as the combination with carbohydrates and a greater effect than carbohydrates alone. So, does it make no sense at all to take carbohydrates in your protein shake after training? Maybe. However, you take these for the effect of the carbohydrates themselves and not to increase the effect of the proteins. For example, to more easily meet your daily carbohydrate needs.

References

1. Protein timing and its effects on muscular hypertrophy and strength in individuals engaged in weight-training. Stark M, Lukaszuk J, Prawitz A, Salacinski A J Int Soc Sports Nutr. 2012 Dec 14; 9(1):54.
2. Amino acids mediate mTOR/raptor signaling through activation of class 3 phosphatidylinositol 3OH-kinase. Nobukuni T, Joaquin M, Roccio M, Dann SG, Kim SY, Gulati P, Byfield MP, Backer JM, Natt F, Bos JL, Zwartkruis FJ, Thomas G. Proc Natl Acad Sci U S A. 2005 Oct 4; 102(40):14238-43.
3.  hVps34 is a nutrient-regulated lipid kinase required for activation of p70 S6 kinase. Byfield MP, Murray JT, Backer JM J Biol Chem. 2005 Sep 23; 280(38):33076-82.
4. Disassociation between the effects of amino acids and insulin on signaling, ubiquitin ligases, and protein turnover in human muscle. Greenhaff PL, Karagounis LG, Peirce N, Simpson EJ, Hazell M, Layfield R, Wackerhage H, Smith K, Atherton P, Selby A, Rennie MJ Am J Physiol Endocrinol Metab. 2008 Sep; 295(3):E595-604.
5. Effect of premeal consumption of whey protein and its hydrolysate on food intake and postmeal glycemia and insulin responses in young adults. Akhavan T, Luhovyy BL, Brown PH, Cho CE, Anderson GH Am J Clin Nutr. 2010 Apr; 91(4):966-75.
6. Comparison of different sources and degrees of hydrolysis of dietary protein: effect on plasma amino acids, dipeptides, and insulin responses in human subjects. Morifuji M, Ishizaka M, Baba S, Fukuda K, Matsumoto H, Koga J, Kanegae M, Higuchi M J Agric Food Chem. 2010 Aug 11; 58(15):8788-97.
7. Effect of carbohydrate intake on net muscle protein synthesis during recovery from resistance exercise. Børsheim E, Cree MG, Tipton KD, Elliott TA, Aarsland A, Wolfe RR J Appl Physiol (1985). 2004 Feb; 96(2):674-8.
8. Carbohydrate does not augment exercise-induced protein accretion versus protein alone. Staples AW, Burd NA, West DW, Currie KD, Atherton PJ, Moore DR, Rennie MJ, Macdonald MJ, Baker SK, Phillips SM Med Sci Sports Exerc. 2011 Jul; 43(7):1154-61.
9. Consumption of fluid skim milk promotes greater muscle protein accretion after resistance exercise than does consumption of an isonitrogenous and isoenergetic soy-protein beverage. Wilkinson SB, Tarnopolsky MA, Macdonald MJ, Macdonald JR, Armstrong D, Phillips SM Am J Clin Nutr. 2007 Apr; 85(4):1031-40.
10. Consumption of fat-free fluid milk after resistance exercise promotes greater lean mass accretion than does consumption of soy or carbohydrate in young, novice, male weightlifters. Hartman JW, Tang JE, Wilkinson SB, Tarnopolsky MA, Lawrence RL, Fullerton AV, Phillips SM Am J Clin Nutr. 2007 Aug; 86(2):373-81.
11. Coingestion of carbohydrate with protein does not further augment postexercise muscle protein synthesis. Koopman R, Beelen M, Stellingwerff T, Pennings B, Saris WH, Kies AK, Kuipers H, van Loon LJ Am J Physiol Endocrinol Metab. 2007 Sep; 293(3):E833-42.
12. Addition of carbohydrate or alanine to an essential amino acid mixture does not enhance human skeletal muscle protein anabolism. Glynn EL, Fry CS, Timmerman KL, Drummond MJ, Volpi E, Rasmussen BB J Nutr. 2013 Mar; 143(3):307-14.
13. Carbohydrate co-ingestion with protein does not further augment post-prandial muscle protein accretion in older men. Hamer HM, Wall BT, Kiskini A, de Lange A, Groen BB, Bakker JA, Gijsen AP, Verdijk LB, van Loon LJ Nutr Metab (Lond). 2013 Jan 25; 10(1):15.