Fitness professionals working with enthusiastic resistance-training clients inevitably face questions about protein supplementation.
Protein supplements are some of the most common and most popular nutritional products on the market today (Pasiakos, Lieberman & McLellan 2014). But with all this abundance, it’s easy to get lost in the colorfully stocked shelves and become confused about which types to buy, when to use them and how much to take.
This article will point fitness professionals to practical answers and applications based on what we know from current scientific evidence. Guiding clients toward evidence-based literature and referring them to licensed dietary pros you trust—rather than recommending or prescribing specific supplements—is the smart approach when wading into these waters. Before getting started, review your scope of practice in this area, and know your boundaries in order to protect yourself.
The Basics of Protein
Human proteins contain 20 naturally occurring amino acids divided into two subclasses: nine “essential” amino acids that must come from food because the body can’t synthesize them, and 11 “nonessentials” that the body can synthesize. Amino acids form the building blocks of many components in the body, including muscle protein, which is developed via the process of muscle protein synthesis (MPS). To build or maintain skeletal muscle mass, humans must eat enough protein to provide adequate amino acids to support metabolic processes like MPS (Layman et al. 2015; Phillips 2004).
Not All Protein Is Created Equal
Dietary protein is either “complete” or “incomplete.” Complete proteins have all the essential amino acids needed for MPS, so it’s fine to consume these proteins by themselves. They typically come from animal and dairy sources.
Several vegetable-based proteins are classified as incomplete, meaning they lack some essential amino acids and must be complemented with a second protein source to supply the ones that are missing. Getting all the essential amino acids needed for optimal MPS is called mutual supplementation (Onoja & Obizoba 2009). With a basic understanding of what protein is and why it’s important, let’s shift our focus to protein supplements.
Whey: From Concentrate to Isolate . . . What’s the Difference?
Protein supplements run the gamut from dairy-derived protein, like whey and casein, to vegetable-based proteins, such as soy and quinoa. Whey protein is a popular supplement these days, so we’ll start there before moving on to vegetable proteins.
Milk has two key proteins: whey (~20%) and casein (~80%). Whey is a complete protein that’s typically classified as either an isolate or a concentrate. Whey protein concentrate is more similar to the original milk protein form. Because whey protein concentrate has some lactose in the powder, it may cause gastric issues in those who are lactose intolerant.
Lactose-intolerant people are better off using a whey protein isolate (WPI) because in this form the protein has been separated from the fat, cholesterol and lactose, so the end product is a purer protein (Hoffman & Falvo 2004). You may see the term “hydrolyzed” on a protein supplement label. This means the protein has been broken into its component amino acids. There is no literature investigating whether hydrolyzed whey protein isolate is any more effective than its nonhydrolyzed counterparts.
Casein: The “Nighttime Protein”
Casein digests more slowly than other proteins, so it’s often recommended as the protein to take before bedtime or other long periods of not eating. Casein raises blood levels of leucine concentrations, which are detected about 40 minutes after ingestion and last for approximately 7 hours. With whey protein, in contrast, higher concentrations are seen after about 20 minutes and last for just 3–4 hours (Dangin et al. 2001). This makes casein look like the logical protein supplement for a person who won’t be able to eat again for a long time, but Bohe and colleagues (2001) challenged this idea. Their findings demonstrated that having a slow-digesting protein was not more beneficial before a prolonged fast.
Casein contains some lactose, so lactose-intolerant clients should be informed.
Vegetarian Protein Options
Popular vegetarian or vegan protein options include soy, quinoa, pea, rice, amaranth and hemp. The primary challenge is that soy, quinoa and amaranth are the only vegetable sources of complete protein. That’s why blended plant proteins are commonly the best options when supplementing with plant protein powders.
For example, a protein powder combining bean and rice proteins would satisfy all essential amino acid requirements and make a complete protein through mutual supplementation. A secondary consideration with vegetable proteins is assessing their amino acid levels to determine the right dosages needed per meal.
Leucine: The King of Amino Acids
Leucine is often called the “king of amino acids” because it is the essential-amino-acid “engine” that drives MPS, while the other 19 amino acids are the “fuel.” It has been well established that a meal must have a minimum amount of leucine to generate a meaningful rise in MPS (Layman et al. 2015).
This is where protein choice really comes into focus. For instance, a whey protein isolate usually has about 10.8% leucine, while soy protein has significantly less, typically around 6.2% (Phillips, Tang & Moore 2009). This can have a substantial impact on the quantity of protein you must consume during a meal.
For example, to get the MPS from 30 grams of WPI, you’d need to eat 55 g
of soy protein. The minimum quantity needed to stimulate MPS is known as the leucine threshold, and this rises with age (Katsanos et al. 2006). Given the higher caloric intake needed to elicit the MPS response, plant-based proteins may not be the optimal choice for clients concerned with weight management. Also, protein intake must increase as people age, since older adults need higher doses of leucine (Katsanos et al. 2006).
Take-Home Guidelines on Protein
One of the first questions some clients ask is whether too much protein is bad for you. The research indicates that high-protein diets should not cause any harm to healthy people (Layman et al. 2015).
The next and perhaps chief factor to consider is how many grams of protein a client needs per day. Though this number varies by age and activity level, a recent meta-analysis published in the British Journal of Sports Medicine recommends a targeted protein dosage of up to 1.6 g per kilogram of body weight per day for healthy resistance-training women and men (Morton et al. 2017). That’s double the current Recommended Dietary Allowance. Another interesting finding by Morton and colleagues is that there is no difference in protein recommendations between sexes, though the researchers acknowledge that more research is needed on female resistance-training enthusiasts.
As for protein intake timing, Morton et al. conclude that it plays, at most, a minor role in determining resistance-exercise-induced gains in muscle. Morton et al. also share a telling message for fitness professionals and their clients: Resistance exercise training alone is the most important and potent stimulus for developing optimal gains in muscle mass and strength. Thus, clients may not need supplements if they are eating enough protein through whole foods and putting in the appropriate time and effort with their training.
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