Top 5 Most Commonly Asked Questions about Protein

Emily Stynes

ANutr, REGISTERED ASSOCIATED NUTRITIONIST, MSC DIETETICS STUDENT

Following my two recent articles on ‘Should I Use Protein Powders for My Health, Training and Performance?’ and ‘How to Optimise Your Protein Intake’, I have compiled the top 5 most commonly asked questions about protein in order to dispel any nutritional myths related to protein for your health and training.

Q1. What are the benefits of consuming protein for my health?

When we eat dietary protein, we digest and break it down into amino acids which are used to make new proteins in the body. These new proteins are used for a range of physiological functions. These include:

· Building of skeletal muscle alongside exercise which promotes healthy ageing (1) and healthy weight loss while increasing muscle mass and strength (2).

· Protein plays an important role in increasing immunity through the production of antibodies that help our bodies to fight against disease.

· Proteins form the building blocks of skin, hair and blood.

· Proteins play an important role in the production of hormones including insulin for blood glucose control and enzymes involved in our body’s metabolism.

· Protein can have appetite-suppressing effects due to its role in the production of various gut hormones (3). This is why when we consume adequate amounts of protein, we often feel fuller for longer due to its satiating effect which can prove to be beneficial for weight loss in some people.

Q2. Does the more protein I eat mean the more muscle that I will gain?

No, the more protein you eat does not mean the more muscle you will gain. The way protein works within our body is that there is a certain threshold to the amount of protein that is considered to be optimal for muscle protein synthesis (muscle building and repair) to occur.

Research has shown that consuming protein beyond the optimal recommended amount of 1.6g/kg/day for active individuals (working out 3-4 times per week) provides no further benefit in increasing muscle mass and strength (4).

So, this means that protein intakes beyond the optimal amount of protein for active individuals do not provide any further benefits for gaining more muscle.

Where does the excess protein I consume go then?

The excess protein that you consume does not necessarily go to waste if it is not used to build and repair muscle. The protein that we eat gets digested, absorbed and transported to the liver where it gets metabolised. In the liver, the protein is either used for protein synthesis or transported out to other tissues including our muscles for protein synthesis. The other two options outlined below include energy storage and passing out the body as a waste product.

Energy Storage

Any excess protein gets converted into other energy storage forms including glycogen, the storage form of glucose (a sugar used for energy in the body). If this energy is not used up through for example exercise, it gets converted to fat just as with excess carbohydrate intake.

Passed Out of the Body

Also, any other excess amino acids get metabolised and converted to ammonia and urea which are passed out of the body. The benefit of this is that high levels of ammonia can be toxic in the body, so the body gets rid of these excess amino acids to prevent the build-up of ammonia.

Q3. Is too much protein bad for you?

You may have heard that too much protein is bad for you as it can overload and put additional strain to your liver and kidneys, the two main organs that metabolise protein.

Research shows that consuming high amounts of protein has not been proven to be dangerous and there have been no adverse health problems reported to be associated with high protein intakes in recreationally-active people, athletes or general population groups (7). The exception to this evidence is that too much protein can be harmful for those with certain health conditions including those with liver and kidney damage (8)(9).

BUT, as with all foods and things in life, too much of anything can be harmful. It is more important to pay attention to the quality of protein in your diet if you are consuming relatively high amounts. For example, consuming salmon, eggs, pulses, beans, nuts, limiting your intake of red meat which has a high content of saturated fat and consuming protein alongside a range of high fibre vegetables, fruits and wholegrains.

Q4. If I eat high amounts of protein, will it make me “bulk out”?

Protein Intake and Training

As previously mentioned, it is the combination of consuming adequate amounts of protein alongside consistent weight and resistance training that will enable you to gain muscle mass and strength through enhancements in muscle protein synthesis (5). However, consuming high amounts of protein alone or a high amount of weight training alone will not result in increases to your muscle mass and strength.

Gender differences

For men, consuming an optimal level of protein (based on their activity levels) in combination with weight training will promote higher amounts of muscle growth than in women.

This is because us females have a different hormone profile to men. In particular, the hormone testosterone which plays a role in regulating muscle protein synthesis is lower in females than it is in males (6). This means that females do not have enough testosterone to gain the same amount of muscle mass and strength as men do.

Q5. Which is better animal or plant proteins?

It is often questioned as to which sources of protein (animal or plant) are better, particularly for those who are highly active, on the go and interested in incorporating protein powders into their diet.

Whether animal or plant protein sources are better than one another really comes down to two factors – their ability to stimulate muscle protein synthesis (MPS) (muscle building and repair) and from a sustainability perspective.

Animal Proteins & Muscle Protein Synthesis

The leucine content of protein which is an essential amino acid is particularly important for stimulating muscle protein synthesis. So, what we need to understand about the effectiveness of protein for MPS is the leucine content of differing animal and plant protein sources which are present in varying amounts.

· Whey protein is a rapidly digested form of protein with a high amount of the amino acid leucine (10).

· Casein is another form of animal protein that is slowly digested and it has a lower leucine content than whey protein (10).

In terms of which one of these animal proteins is “better”, research has consistently shown that the intake of whey protein stimulates a high level of MPS than casein due to its leucine content (11).  Eggs are also another animal source of protein with relatively adequate amounts of leucine (11).

Plant Proteins and Muscle Protein Synthesis

In terms of plant proteins, maize/corn has been found to be particularly high in leucine compared to whey and milk (10) followed by lentil, quinoa and peas.

Soy, rice, pea and hemp protein are all relatively low in leucine compared to whey protein. However, this does not mean that plant-based proteins are not as good for building muscle. In fact, plant-based proteins do have a complete profile of EAA’s, they just contain less of the EAA’s including leucine relative to animal proteins in most cases.

Knowing how to effectively incorporate a variety of plant-based proteins into your diet can ensure that you can effectively increase your muscle mass and strength. This includes tofu, tempeh, seitan, beans, pulses, grains and legumes. 

Animal Sources & Sustainability

Although animal sources of protein can be effective in building muscle mass and strength, they are at the bottom in terms of sustainability. This is due to their greenhouse gas emissions, impact on the supply of water and soil.  

In order of priority, this includes red meat such as (13)

·       Lamb

·       Pork

·       Beef

·       Milk

·       Eggs

·       Chicken

Plant Sources & Sustainability

In contrast, plant protein sources exhibit the lowest greenhouse gas emissions and they are at the top in terms of sustainability (18).

These include -

·       Soy  

·       Mycoprotein

·       Rice

·       Beans

·       Oats

·       Wheat

·       Potatoes

So, it’s also an important environmental and ethical decision as to whether to consume animal vs plant proteins. Plant proteins are considered a more sustainable and environmentally friendly source of protein. However, if you do enjoy eating animal sources of protein and they form an important part of your training, it can be helpful to reduce your consumption of them without having to completely eliminate them from your diet.

Take Home Message  

In summary, it is clear that understanding how and what type of protein to consume is key for muscle building and repair with resistance training. As to whether to consume animal or plant-protein sources, there are a number of factors that make this a personal lifestyle choice.

Make sure to keep an eye out on one of my upcoming blog posts about consuming a plant-based diet alongside your training.

Stay strong!

Emily

References

1.         Wolfe RR. The role of dietary protein in optimizing muscle mass, function and health outcomes in older individuals. Br J Nutr. 2012 Aug;108 Suppl 2:S88-93.

2.         Wolfe RR. The underappreciated role of muscle in health and disease1Ϫ3. :8.

3.         Effect of short- and long-term protein consumption on appetite and appetite-regulating gastrointestinal hormones, a systematic review and meta-analysis of randomized controlled trials | Elsevier Enhanced Reader [Internet]. [cited 2021 Aug 3]. Available from: https://reader.elsevier.com/reader/sd/pii/S0031938420304376?token=5C164415D143BF5D731F4A585DAF3574769667F5A0E7EC412A03E5F552FAF1A1BAEC9C6AA19FA739BEE86F07B595CF1C&originRegion=eu-west-1&originCreation=20210803143226

4.         Morton RW, Murphy KT, McKellar SR, Schoenfeld BJ, Henselmans M, Helms E, et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. Br J Sports Med. 2018 Mar;52(6):376–84.

5.         Trommelen J, Betz MW, van Loon LJC. The Muscle Protein Synthetic Response to Meal Ingestion Following Resistance-Type Exercise. Sports Med. 2019 Feb 1;49(2):185–97.

6.         Handelsman DJ, Hirschberg AL, Bermon S. Circulating Testosterone as the Hormonal Basis of Sex Differences in Athletic Performance. Endocr Rev. 2018 Jul 13;39(5):803–29.

7.         Jäger R, Kerksick CM, Campbell BI, Cribb PJ, Wells SD, Skwiat TM, et al. International Society of Sports Nutrition Position Stand: protein and exercise. J Int Soc Sports Nutr. 2017 Dec;14(1):20.

8.         Knight EL, Stampfer MJ, Hankinson SE, Spiegelman D, Curhan GC. The impact of protein intake on renal function decline in women with normal renal function or mild renal insufficiency. Ann Intern Med. 2003 Mar 18;138(6):460–7.

9.         Griffin JWD, Bradshaw PC. Effects of a high protein diet and liver disease in an in silico model of human ammonia metabolism. Theor Biol Med Model. 2019 Jul 31;16:11.

10.       Gorissen SHM, Crombag JJR, Senden JMG, Waterval WAH, Bierau J, Verdijk LB, et al. Protein content and amino acid composition of commercially available plant-based protein isolates. Amino Acids. 2018;50(12):1685–95.

11.       Witard OC, Wardle SL, Macnaughton LS, Hodgson AB, Tipton KD. Protein Considerations for Optimising Skeletal Muscle Mass in Healthy Young and Older Adults. Nutrients. 2016 Apr;8(4):181.

12.       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 Apr;85(4):1031–40.

13.       Macdiarmid JI, Kyle J, Horgan GW, Loe J, Fyfe C, Johnstone A, et al. Sustainable diets for the future: Can we contribute to reducing greenhouse gas emissions by eating a healthy diet? Am J Clin Nutr. 2012 Sep;96(3):632–9.