There is a lot of conflicting information surrounding post-exercise nutrition: anabolic window, blood sugar levels, insulin spiking, and eating post-workout carbs (1). Many articles or bodybuilders will tell you that you must eat protein with simple carbohydrates like maltodextrin or glucose directly after your workout so that you do not miss out on the anabolic window and squander your muscular gains (2). This idea is based on the hypothesis that insulin promotes protein synthesis, and therefore maximizing insulin will maximally increase muscle mass. However, scientific research does not fully support this claim (3).
Insulin is an anabolic hormone produced by the pancreas which stimulates the uptake of amino acids and protein synthesis in muscle cells (4). Diabetic patients with high insulin levels have increased muscle mass while patients with low insulin have muscle atrophy. Also, patients with type 2 diabetes have a relatively poor insulin sensitivity and insulin resistance, which results in lower muscle mass and quality (4). Individuals with insulin deficiency can be in a protein catabolic state with loss of muscle mass that can only be reversed by insulin therapy (1). When patients are given insulin infusions, they see an immediate increase in muscle protein synthesis and a decrease in muscle breakdown. However, this only occurs in the presence of adequate amino acids and blood flow (1).
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There have been many studies showing that insulin stimulates protein synthesis, yet there are very few clinical trials showing that elevated insulin levels actually lead to building muscle (3).
To answer the question whether to consume protein or carbohydrates after strength training, a study comparing the effectiveness of protein-only and carbohydrate-only post workout supplements concluded that protein stimulated more muscle protein synthesis as compared with the intake of carbohydrate only (5). The consumption of carbohydrates after weight training did in fact increase glucose levels and insulin saturation, but it did not trigger as much muscle growth as the protein only group (6).
To determine whether it is more beneficial to consume protein or protein with carbohydrates, a randomized controlled trial found that post workout consumption of carbohydrates with protein did not synergistically or additively improve muscle growth (7). This study had two groups of men perform single leg knee extensions. Group 1 ingested 25 grams of protein and Group 2 ingerst 25 grams of protein and 50 grams of the carbohydrate maltodextrin. Both groups demonstrated muscle protein synthesis and inhibition of muscle protein breakdown. However there was no difference between the groups (7). Another study found that a post exercise protein supplement stimulated more abdominal fat loss and lean muscle growth than a post workout supplement with protein and carbohydrates (8).
In a study comparing a low glycemic milk-based supplement and a high glycemic soy-based supplement found that non-fat milk promoted more muscle protein accretion than soy beverage (9). This demonstrates that a higher glycemic index associated with blood glucose levels was not positively associated with muscle gains (6).
Lastly, scientists tested protein, protein with carbohydrates, and protein with leucine to determine which would stimulate the most muscle growth and determined that coingestion of protein and leucine optimizes whole body protein balance compared with the intake of carbohydrate (5). They reasoned that leucine improved bioavailability of the whey protein, resulting in a lower protein oxidation rate. Leucine also increases skeletal muscle Insulin-like Growth Factor 1 (IGF-1) concentration in resistance-trained men (10).
Although carbohydrates might not necessarily increase your muscular growth, there are other reasons for including carbohydrates in your post workout nutrition. Carbohydrates can help muscle glycogen restoration, especially when there is a short turn around between workouts (11). Also leucine needs the presence of some insulin to help stimulate protein synthesis. Creatine and carnitine can also be more effective after insulin binds to muscle receptors.
Based on the available clinical data, there is no evidence that the addition of carbohydrates to a protein supplement will acutely increase muscle protein synthesis or muscle growth to a greater extent than protein alone.
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So if you think the insulin spike from a sugary carb-filled pastry after an intense workout is maximizing your muscle growth, you should rethink that decision, since a high quality protein powder like BBCOM’s Signature Whey are all you really need for maximal muscle growth, especially if you are focused on a weight loss or fat loss cycle.
References:
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https://eje.bioscientifica.com/view/journals/eje/181/6/EJE-19-0514.xml#bib1
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https://pubmed.ncbi.nlm.nih.gov/15562251/
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