Does protein cause an insulin spike & does this build muscle?

Protein – You can’t deny it’s a hot topic right now and even the big brands are jumping on board to meet demand. Protein bars, protein cereal, protein bread, protein powders – these items are flying off the shelf. What’s so magical about protein? We’ve written about protein before in the context of pre/post workout, plant based protein and homemade protein snacks. There are two aspects to the question above in the title: protein intake and skeletal muscle mass. But what is the role of skeletal muscle mass for strength but also for human health? This blog aims to dive into protein for muscle protein synthesis, the role of skeletal muscle mass as well as the hot question in the title: does protein cause an insulin spike? 

Would you like to learn more about sports nutrition? Check out our Sports Nutrition to Fuel Performance specialised short course. 

Does protein cause an insulin spike? 

Let’s put that question aside for the moment and look first at skeletal muscle mass and the role it plays in health and performance. 

Muscle Mass

When it comes to human health, muscle plays a few key roles; muscle is where most of our glucose is stored as glycogen so there’s a benefit here in offsetting obesity/diabetes for example. But in addition to this, we need muscle for our independence as we age etc. Muscle tissue is also very metabolically active meaning the more muscle mass you have, the better for your metabolism and caloric needs. Moving into performance, more muscle mass allows you to jump higher, sprint faster, run longer etc.


While we can survive without consuming carbohydrates or fat, protein is different in that it is an essential macronutrient. So setting aside the fitness association, protein is a macronutrient we need to survive and thrive, albeit the amount required is quite small. This is also why most foods, even fruits and vegetables, contain some amount of protein. The benefits of protein stem beyond just muscle building; dietary proteins represent key nutrients for bone health and thereby function in the prevention of osteoporosis, protein is vital to build and repair body tissue and fight viral and bacterial infection and so plays a role in immunity, protein is used in the production of hormones and as a building block for bones, muscles, cartilage, skin, and blood.

So how do you increase muscle mass?

There are two ways to increase muscle mass; weight bearing/resistance training or taking some sort of endocrinological boost like testosterone. Consuming heroic amounts of protein on its own will not necessarily build muscle but it can certainly support the process. 

The amount of muscle you have is regulated by how many proteins you synthesize and how many you breakdown as part of that muscle tissue. This is called muscle protein synthesis (MPS) and muscle protein breakdown (MPB). In general, we’re always turning over muscle – synthesizing and breaking it down. If we’re gaining muscle we’re synthesizing more than we are breaking it down and if we’re losing it, we breakdown a lot of amino acids to use as fuel for the body. How rapid is this turnover? Nutrient-driven increases in MPS are of finite duration (∼1.5 h), switching off thereafter despite sustained amino acid availability and intramuscular anabolic signalling (source).

There’s obviously inter-individual differences to consider but muscle as a whole is relatively slower turnover relative to other organs like the liver and/or brain. 

Protein amount recommendation

Protein source, protein spacing, protein timing, distribution – all of these have an acute effect on this process. For example there’s certain amino acids that are more anabolic like leucine. There’s also the muscle full effect consideration; If you flood your cells with protein, at some point this increase in muscle protein synthesis falls off meaning we can’t just flood our body with protein and expect a more is better approach. 

Two practical takeaways: 

  • You need to spread protein over the day with moderate doses separated by 3 hours + seem to have the best effect.
  • The range of protein intake recommended at this time for muscle gain is 1.6-2.2g per kg of bodyweight. 

Dietary Protein vs Supplemental protein

What does the evidence actually tell us when it comes from what’s better? The truth is that the general population eat enough protein from a regular whole food diet to meet their DRI (dietary requirements intake) needs. Aside from whole food versus supplements, it’s more about total intake throughout the day and less about the source. Post exercise rise in hormones

As a general, when you exercise you create certain endocrinological changes in the body

Hypertrophy with resistance training is the result of accumulated periods of positive muscle protein balance meaning a higher rate of muscle protein synthesis (MPS) vs breakdown. Nutritional and contractile variables influence changes in MPS and hypertrophy. For example, the type of protein consumed after resistance exercise can determine the acute amplitude of MPS and lean mass gains. Different exercise programs can result in differential responses of MPS after resistance exercise (source). 

Physical activity has a beneficial effect on insulin sensitivity in normal as well as insulin resistant populations. A cell that is full of energy is an insulin resistant cell. An empty, “starving” cell is an insulin sensitive cell. Any exercise that burns glycogen and leaves your muscles empty and gaping for more will necessarily increase insulin sensitivity. 

Role of Insulin

Insulin is a peptide hormone, produced by beta cells of the pancreas, and is central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, skeletal muscles, and fat tissue to absorb glucose from the blood. In the liver and skeletal muscles, glucose is stored as glycogen, and in fat cells it is stored as triglycerides. Improving insulin sensitivity and reducing fasting insulin levels have major ramifications for your health, longevity, and resistance to disease (source).  

Does protein cause an insulin spike? 

So does protein cause an insulin spike? Short answer – yes.

Nillson et al. (2018) showed that there was a correlation of insulin responses after meals with consumption of amino acids and protein. The strongest correlations were shown for leucine, valine, lysine, and isoleucine. Milk powder and whey were shown to have substantially lower blood glucose increases. 

Is that insulin spike a bad thing? Not necessarily. Insulin isn’t bad in and of itsel and insulin spikes are a normal part of eating. Plus, there’s other things too; Protein triggers glucagon, a hormone that works along with the hormone insulin to control blood sugar levels. 

Context matters – while you might want to track this spike for specific reasons like say when on a keto diet and trying to get into ketosis, the relative spike in insulin isn’t worth shouting about. Beyond the keto diet, factors like age, BMI, lifestyle, muscle mass, training regime etc all matter.  For example, supplementation with whey proteins improved fasting lipids and insulin levels in overweight and obese individuals.

Does the insulin spike build muscle? 

Exercise triggers complex processes through which cells sense and respond to mechanical stimuli by converting them to biochemical signals that elicit specific cellular responses. There’s also physico-chemical (i.e. endocrine, auto/paracrine) sensory mechanisms (Glass, 2010; West et al. 2010). Subsequent activation of receptor and non-receptor mediated intramuscular signalling modulates cellular apparatus regulating both short-term control of protein turnover and gene expression (mRNA/miRNA) and long term changes in cellular metabolic capacity. Insulin is required in this process (source).

Without insulin, we’d have a hell of a time trying to build muscle or move glycogen into muscle stores. Why? Insulin is responsible for muscle growth and the storage of muscle glycogen. 

Insulin is an anabolic hormone i.e. a growth promoting agent. It is primarily known to help lower blood glucose. However, it also has some key roles with regards muscle gain; insulin is required to build muscle and it also inhibits the breakdown of muscle, it actively transports certain amino acids directly into the muscle cells and helps the storage of glucose in muscle cells, thereby improving performance, recovery, and the size of your muscles. Insulin also stimulates protein synthesis (and therefore muscle growth) by directing ribosomes to make more protein

What’s the catch?

It’s indiscriminately anabolic and doesn’t care whether it helps with the building of muscle or the accumulation of fat. Its primary job is to maintain safe and steady blood glucose levels. 

From another angle, weight training has actually been shown to help with insulin resistance; Low muscle strength and obesity have been shown to be associated with higher incidence of insulin resistance in type 2 diabetes. Resistance exercise to increase muscle strength and mass has been found to increase insulin sensitivity in type 2 diabetes as well as healthy adults (source). 

There is obviously a relationship between protein consumption and its potential on impacting muscle synthesis. So if as a general public, we’re hitting our protein needs, what are the conditions necessary for this to occur in the first place? 

This is probably one of the most hard hitting points. Truth is that at minimum, 75% of change in muscle you get is from the weight lifting. The extra benefit of higher versus lower protein intake is actually quite minimal. Lifting weights makes you more sensitive to amino acids. If you were to just sit there and eat and eat protein, those amino acids wouldn’t necessarily get shunted into the muscle. Resistance training alone has been shown to promote a twofold increase in protein synthesis following exercise. So first we need resistance training. However, getting a successful adaptation, i.e. altered muscle physiology and improved performance, varies exquisitely according to the activities imposed (e.g. force, duration, etc.) as well as by an individual’s genetic makeup, which designates his or her ‘responder status’ (Source, citing Timmons, 2011). 


Short summary: Does protein cause insulin spike? Yes. Does this insulin spike build muscle? Yes. But of course there’s always more to the story, some of which we touched on. There’s other considerations here that we haven’t had time to get into – for example trying to maintain muscle mass on a caloric deficit. And then looking at people doing different types of training – conditioning versus resistance – AND even sports (triathlon versus bodybuilding). Or athletes in combat sports who need to make weight and can’t risk gaining too much muscle mass. Or endurance athletes who although they need muscle and strength & conditioning as beneficial to their sport, still need to stay lean. 


Would you like to learn more about sports nutrition? Check out our Sports Nutrition to Fuel Performance course


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