Health, Faith, Fitness, Backed by Evidence.

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weight training

Stop Getting Sick! Part 2: Training Approaches According To Research

Fitness/ Wellness

three pairs of assorted-color Rogue bumper plates
Everyone knows exercise is good for you, but does your training program help or hurt your immune system? (Image credit: cottonbro at Pexels)

Disclaimer: This post addresses general immune system health and fitness training. It does NOT address specifically COVID 19 pandemic prevention strategies, such topics are beyond the scope of this post. For information on COVID 19 preparedness and prevention, I suggest you go to CDC.gov.

Everyone knows that exercise is good for you. According to the Centers for Disease Control and Prevention (CDC, 2020a), adults should try to get the following amounts of exercise per week as the minimum standard:

  • 2 or more strength training sessions for the entire body each week PLUS
  • Moderate exercise such as brisk walking at least 30 minutes per day x at least 5 days per week each week, OR…
  • Vigorous exercise such as jogging/ running for at least a total of 1 hour and 15 minutes total per week, OR…
  • An even mix of moderate and vigorous exercise at least 2 days per week

While as many as 1 in 3 adults have no leisure exercise activity (CDC, 2020b), there are many of us accustomed to pushing ourselves beyond these recommendations. The CDC notes that additional health benefits can be recognized by exercising above the minimum guidelines. For those of us that push ourselves with heavy physical training, is there a point at which we jeopardize our immunity? If so, what is that point?

What training considerations should we implement so as to get the best exercise has to offer while minimizing our risk for compromised immunity? What does the evidence say? In the first part of this series, I explored research-backed nutritional factors that athletes and heavy exercisers can follow to improve their immune system competence and ability to resist respiratory infections. In this post, I will explore training considerations.

Moderate exercise enhances immune function

Research notes that exercise lasting less than 60 minutes at a time leads to numerous immune enhancing effects (Nieman & Wentz, 2019). Moderate to vigorous aerobic exercise limited to less than an hour:

  • Enhances virus and bacteria fighting activity of macrophage immune cells (which ingest and destroy infected cells, clean up debris, and notify other immune cells of invaders)
  • Enhances circulation of immunoglobulins (antibodies that bind and neutralize threats as well as make threats easier to destroy or expel)
  • Enhances circulation of anti-inflammatory immune cytokines
  • Enhances circulation of natural killer cells (which kill virus infected cells and tumor cells), neutrophils (which surround wounds/ damaged tissue to reduce risk of disease spread), cytotoxic T-cells (key fighters of virus infected cells and cancer cells), and B-cells (which activate T-cells and produce antibodies) (National Institute of Allergy and Infectious Diseases, 2014; Nieman & Wentz, 2019)
  • Moderate exercise REDUCES your risk of contracting upper respiratory tract infections by 40-50%!!!!!!!!!!!!! (Nieman & Wentz, 2019)

When aerobic exercise is kept to under an hour, stress hormones and inflammatory cytokines do not reach levels at which they negatively impact immune function (Nieman & Wentz, 2019).

Moderate to vigorous aerobic exercise boosts immune function WHEN KEPT under an hour in duration! (Image credit: Ben Maxwell at Pexels)

What is moderate resistance training?

Moderate resistance training:

  • Uses training loads at 60-80% of your 1 rep max
  • Multiple sets per exercise
  • 4 to 5 days a week (González-Badillo, Gorostiaga, Arellano, & Izquierdo, 2005)
  • Generally lasts under an hour
  • Is balanced with recovery, thereby preventing feelings of accumulated fatigue, significant pain, or significant delayed onset soreness
  • Allows for continued performance improvement (Grandou, Wallace, Impellizzeri, Allen, & Coutts, 2019; Nieman & Wentz, 2019) .

Training repetitions, sets, and rest periods vary widely. Individual response to such also varies widely. However, the above serves as a good guide for training within the moderate range. Staying within the moderate training range is one way to reduce the chances of over-training and non-functional overreach. The goal is to prevent overly large surges in stress hormones, reduced immune system function, and blunting of testosterone to cortisol ratios (Grandou et al., 2019).

What is “heavy training?”

Heavy training and heavy training loads of course are relative to SOME extent base on your fitness level. However, unless your entire life is devoted to training and recovery (such as professional athletes), most people that train to the extent described below will subject themselves to the risks associated with heavy training. In the research various examples are provided. Some of the examples of heavy training include:

  • Single events such as exercise exceeding 60 minutes, especially when reaching 90 minutes (1 and a half hours and beyond)
  • Competition events
  • Consecutive days of heavy training loads exceeding an hour, such as cycling or running 1-3 hours at your 50−70% V̇o2max (Peake, Neubauer, Walsh, & Simpson, 2017)
  • Consecutive days of interval training, such as 3 sets of 6-minute maximum-effort rowing two days in a row
  • Resistance training with high intensity (weights closer to 1 rep max), high frequency, and lacking exercise variety
  • Resistance training with insufficient recovery–detectable when symptoms of NON-FUNCTIONAL overreach occur, such as accumulated fatigue, pain, soreness, and possibly but not always, reductions in training performance (Grandou et al., 2019)

Pushing yourself to improve versus warning signs that you are crossing the line

Exercising at the above intensities quickly lead to states of overreaching in terms of the body’s recovery capabilities. Indeed, heaving training (as opposed to moderate training) has been shown to increase your risk of illness. When prolonged, heavy training loads can cause you to progress into states of over-training (Grandou et al., 2019; Peake et al., 2017). Over-training can take weeks or months for recovery (Grandou et al., 2019). While pushing yourself (or overreaching) to some extent can help boost performance, you know you have crossed the line when the following symptoms begin to manifest:

  • Persistent fatigue
  • Persistent muscle soreness
  • Declines in your training performance, such as reduced sprint, squat, bench, or other performance measures–this sign is not always present!
  • Changes in mood
  • Possibly worsened sleep–also not always present (Grandou et al., 2019; Peake et al., 2017).
Training close to your 1 rep max can quickly tax your recovery capabilities, boost stress hormones, and impede the immune system (Image credit: Victor Freitas at Pexels)

Heavy training negatively impacts your immune system

Researchers have observed that heavy training introduces a stress to the body’s recovery resources and immune system (Peake, Neubauer, Walsh, & Simpson, 2017). Intense exercise, by definition, acts as a significant physical stress (Walsh, 2018). Similar to psychological stress, intense physical stress activates hormones such as cortisol, epinephrine, and norepinephrine (Walsh, 2018). These hormones are essential for health and life, but when elevated at high levels over prolonged periods of time they can impede protective immune functions (McEwen, 2012).

Oxidative stress, post-training inflammation and muscle damage from heavy training require restorative processes that appear to shift immune resources away from virus monitoring and protection (Nieman & Wentz, 2019; Peake et al., 2017). These stresses on the immune system combine with other factors such as life stress, nutrition deficiencies, and sleep disruption to further impact our immune system function. Travel across time zones and environment extremes (such as winter time outdoors training) add additional challenges for some people (Walsh, 2018). Heavy training raises your risk of upper respiratory infection by 2 to 6 times the average population!!!!

Heavy training against the background of our lives

While it would be nice for many of us exercise fanatics to have lives that centered around our physical endeavors, the reality is that many of us juggle full time career demands and exercise serves as a recreational activity. Our perception of our life stressors can have significant impact on how such stressors impact us at a physiological level (McGonigal, 2015; Walsh, 2018). However, it is fair to say many of us have lost sleep at various times over work or life concerns.

Sleep is at times therefore less than optimal. Our work lives, even home lives at times, can contribute to our physical and mental stress burden. Keep this in mind if you still desire to train at the “heavy training” level. The truth is, for many of us, heavy training should be kept to short spurts during low risk times (if ever), with the majority of our training falling within the “moderate” range.

Additional research-backed immune-friendly training tips

The following tips are provided by the European Journal of Sport Science (Walsh, 2018) to assist athletes and exercisers in maintaining immune health while enjoying their physical training pursuits:

  • Adjust training volumes and training intensities so as to permit adequate recovery (auto-regulating your intensity according to your body’s recovery abilities)
  • Manage volume /intensity increases no greater than 5-10% each week
  • Frequent, shorter bouts of training are preferable to fewer, longer sessions of training
  • Recognize winter training as a particularly high risk time to perform heavy training sessions/ or loads
  • If training heavy, follow a heavy training session by several light or moderate training sessions
  • Consider a lighter, recovery week every 2nd or 3rd week of your training cycle
  • Allow for several weeks of active recovery after competition or season completion
  • Pursue recovery activities immediately post intense training sessions

Interestingly, many of these principles can be found in the popular 5-3-1 training protocol by Jim Wendler!! The basics of the program can be found here.

Summary

I will admit that I was skeptical in the past regarding moderate training. I felt heavy training would be the only training my body would respond too. I quickly altered the 5-3-1 program so as to continue my heavy weight training sessions. My sessions plus cardio would extend to an hour and a half to two hours at times on the weekend. However, I also got frustrated with the multiple respiratory illnesses I experienced each year (along with training set backs and minor injuries).

After diving into the research referenced above, and re-reading Jim Wendler’s works on the 5-3-1 program, I can see the value of “starting too light,” very gradually increasing the weights, having frequent deloads, and auto-regulating (where at times accessory exercises are skipped based on time or how your body feels, or resetting weights back by 10% or so if plateauing). In particular, staying FOR THE MOST PART in the 60-80% range of the 1 rep max will be an adjustment! Nonetheless, after reviewing the above, this seems to be the wisest way to train–limiting the heavy training to very short time frames when risk of illness is low.

Thanks for reading, I hope you enjoyed the post and learned something new! Feel free to leave a comment, sign up for my e-mail list, or share with friends! Sincerely, Donovan

Related Post

Healthy Lifestyle & Still Getting Sick? Nutrition Approaches

References

Centers for Disease Control and Prevention. (2020a). How much physical activity do adults need? Retrieved from https://www.cdc.gov/physicalactivity/basics/adults/index.htm

Centers for Disease Control and Prevention. (2020b). Percent of adults who who engage in no leisure-time physical activity. Retrieved from https://chronicdata.cdc.gov/Nutrition-Physical-Activity-and-Obesity/Percent-of-adults-who-who-engage-in-no-leisure-tim/6nef-e823

Grandou, C., Wallace, L., Impellizzeri, F. M., Allen, N. G., & Coutts, A. J. (2019). Overtraining in resistance exercise: An exploratory systematic review and methodological appraisal of the literature. Sports Medicine. Retrieved from file:///C:/Users/test/AppData/Local/Temp/Grandou2019_Article_OvertrainingInResistanceExerci.pdf

González-Badillo, J. J., Gorostiaga, E. M., Arellano, R., & Izquierdo, M. (2005). Moderate resistance training volume produces more favorable strength gains than high or low volumes during a short-term training cycle. Journal of Strength and Conditioning Research, 19(3), 689-697. doi: 10.1519/R-15574.1

McEwen, B. S. (2012). Protective and damaging effects of stress mediators. The New England Journal of Medicine, 338(1), 171-179. Retrieved from https://pdfs.semanticscholar.org/ee3c/1a87d21b1865abe72157226e38103b0d95cf.pdf

McGonigal, K. (2015). The upside of stress: Why stress is good for you, and how to get good at it. New York, NY: Penguin Random House

National Institute of Allergy and Infectious Diseases. (2014). Immune cells. Retrieved from https://www.niaid.nih.gov/research/immune-cells

Nieman, D. C. & Wentz, L. M. (2019). The compelling link between physical activity and the body’s defense system. Journal of Sport and Health Science, 8(3), 201-217. https://doi.org/10.1016/j.jshs.2018.09.009

Peake, J. M., Neubauer, O., Walsh, N. P., & Simpson R. J. (2017). Recovery of the immune system after exercise. Journal of Applied Physiology, 122(5), 1077-1087. https://doi.org/10.1152/japplphysiol.00622.2016

Walsh, N. P. (2018). Recommendations to maintain immune health in athletes. European Journal of Sport Science, 18(6), 820-831. https://doi.org/10.1080/17461391.2018.1449895

Discover the Healthiest Sources and Amounts of Protein! Current Research

Plant-based Diets, Entomophagy, and Evidence

What is the optimal amount of protein for health and performance? Cut through the hype, learn the truth according to current research (Image credit: Ashutosh Sonwani at Pexels)

Protein!!! It seems everyone is obsessed with “getting enough” protein nowadays. If you eat plant-based, the number one question you get is “where do you get your protein?” Athletes, and increasingly, non-athletes, slog down protein shakes–convinced that such is necessary for health and fitness goals.

Even in the plant-based world, icons for the plant-based movement frequently note “you can get all the protein you need eating plants.” Often, plant-based movement icons note that protein needs are exaggerated by marketers, etc. Yet many of them consume highly processed plant-based protein powders. With so many opinions and apparent contradictions, an evaluation of the current research can be helpful.

What does the research-based, current evidence actually say about protein needs–including for athletes? What daily amount is the right amount? Does it matter where you get your protein in terms of health outcomes? Are high-protein diets healthy? What does the evidence say?

Protein sources & Health: Animal, plant, does it matter?

Sources of protein–animal versus plants, does it matter? Eggs, yogurt, cheese, milk, chicken, fish…or legumes, beans, whole grains, nuts–as long as you stay away from evil fatty, red, or processed meats, does protein source really make a difference in your health according to research? Yes, it does matter–according to a growing body of high-quality research.

In research published in The European Journal of Epidemiology, 7786 participants of the “Rotterdam Study” in the Netherlands were analyzed for dietary patterns and mortality (death) rates. The meta-analysis (where multiple studies are combined and findings analyzed in totality) was conducted for a time span covering nearly 30 years (Zhang, Moumdjian, Gonzalez-Jaramillo, van der Schaft, Bramer, Ikram, & Voortman, 2020). A sub-analysis of the data collected evaluated the impact of protein source (animal versus plant) and all-cause mortality rates along with cardiovascular disease death rates.

As animal protein intake increases, so does mortality rate: Plant protein has the opposite effect

Researchers found that for every 5% increase in animal protein intake (as a percentage of total caloric intake), there was a measurable and significant increase in cardiovascular deaths and overall mortality rates. Those with the highest animal protein intake experienced a 12% higher mortality rate from all causes versus those with the lowest animal protein intake. Protein from meat and dairy strongly influenced the increase in cardiovascular mortality rates (Zhang et al., 2020). Protein from eggs and fish did not appear to impact mortality rates.

High protein intake from animal sources, such as meat and dairy, corresponded with increased deaths from all causes, particularly cardiovascular causes (Image credit: Andrey Niqi at Pexels)

Conversely, as protein intake from plant sources (legumes, nuts, vegetables) increased in percentage of total caloric intake, significant REDUCTIONS in mortality rates were noted. Every 3% increase in protein intake from specifically legumes, nuts, vegetables, and fruits (but not grains) resulted in 25% reductions in overall mortality rates during the study period (Zhang et al., 2020).

Bad news for keto enthusiasts: “Evil high-carb” legumes apparently protect you from premature death

Separately, the researchers also performed a meta-analysis on high quality, prospective cohort studies (studies where participants with similarities at the beginning of a study are followed over time to evaluate differences in outcomes and potential causes of such differences). This analysis included data from 350,452 participants and 11 studies, with time periods of the studies covering anywhere from 12 to 28 years. Once again, higher total protein intake, particularly intake from animal protein sources, was associated with higher rates of mortality with a 9% increase in deaths due to cardiovascular disease. The lower quartile of participants took 4.3% of their daily energy from animal protein, with the highest quartile consuming 20% of their daily energy from animal protein sources.

Those with the highest plant protein intake, on the other hand experienced a 7% reduction in all-cause mortality rates and a 14% reduction in cardiovascular death rates (Zhang et al., 2020). Researchers noted that the nature of amino acids found in animal products (branched-chain and aromatic amino acids) differ from those found in plants (which are low in branched-chain and aromatic amino acids). Amino acids in animal products appear to contribute to insulin resistance, obesity, and thereby, increased cardiovascular disease risk (Zhang et al., 2020).

Interestingly, fish, eggs, and grains were neutral, neither protective or particularly harmful (Zhang et al., 2020). This supports findings in the Blue Zones territories where the longest living, healthiest population groups ate scant meat. Frequently, these populations included only up to 3 eggs per week and small amounts of fish in their diets–plant nutrition being their dominant source of protein and caloric intake (Bluezones.com, 2020).

Protein amounts: How much do you need? It depends on your goals

According to the journal Food & Function published by the Royal Society of Chemistry, sedentary yet healthy adults need as little as 0.8 grams of protein per kilogram of body weight (Wu, 2016). In order to calculate your own protein needs if you are a sedentary (minimally active adult) and you live in the U.S., first divide your body weight in pounds by 2.2 to convert your body weight to kilograms.

185 lbs / 2.2 = 84 kgs (My body weight in kilograms)

So pretend I was not very physically active, at 185lbs (84kg), my daily protein requirements to maintain general healthy bodily functions would equate a mere 67 grams per day. Divided into 4 meals (snacks included as “meals”), I would only need 17 grams of protein per meal. This is easily achieved following a plant-based diet. Just 2 pieces of whole grain bread have 10 grams of protein! Add a handful of nuts or soup with beans and the target is easily achieve, no meat, no protein shakes, no dairy required. This applies to the nearly 1 in 4 adults in the U.S. (Americashealthrankings.org, 2020). For those desiring to maximize skeletal muscle tissue and minimize white fatty tissue, protein amounts of 1.4 grams/ kg are determined to be useful per research (Wu, 2016).

Health promoting proteins from beans, nuts, and legumes are useful in meeting daily protein goals (Image credit: Frans Van Heerden at Pexels)

As activity increases from mild to moderate to intense, protein needs increase to 1 gram / kg, then 1.3 grams/ kg, then 1.6 grams / kg respectively (Wu, 2016). Using my body weight again as an example, my protein needs with mild activity (such daily mild cardio training) would be 84 grams total, rising to 134 grams daily if I were to be very physically active (which I am). Divided into 4 meals, 33 grams of protein per meal is required for optimal health for a 185lb male. This too is achievable without supplements, powders, or meat, though selection of high protein plant foods (such as lentils, beans, whole grains, nuts, and high protein pasta) is necessary to achieve these numbers.

What if you are an athlete or weight train?

A frequently touted number for protein intake requirements for athletes is simplified to be approximately 1 gram of protein for every pound of body weight (if you live in the U.S.) or 1.8 grams of protein per kilogram (if you live pretty much anywhere else). Some plant-based enthusiasts argue that amount is excessive. Some weight training enthusiasts argue that amount is too low. What does the research say?

Guidelines for athletes who resistance (weight) train: Research suggests you may need less than you think

According to the “International Society of Sports Nutrition Position Stand,” the daily recommended amount of protein advised for building and maintaining muscle mass ranges from 1.4 grams/ kg – 2 grams / kg based on current research evidence (Jäger et al., 2017). Twenty to 40 grams of this total protein requirement needs to come from high quality protein (such as protein rich in leucine…a plant-based example being beans). This amount is somewhat less than 1 gram per pound of body weight. In order to calculate your own protein needs if you live in the U.S., first divide your body weight in pounds by 2.2 to convert your body weight to kilograms.

Next, multiply your weight x 1.4 grams to find the low range for your daily protein intake needs, or by 2 grams to find the upper range. According to the guidelines, this protein amount should be divided into multiple meals separated by 3 to 4 hours (Jäger et al., 2017). With my body weight of 185 lbs, my protein requirements to build and maintain muscle (paired with resistance training) would be as follows:

185 lbs / 2.2 = 84 kgs (My body weight in kilograms)

84 kgs x 1.4 grams protein / kg = 118 total grams of daily protein needed to maintain and build muscle according to research. Note, this is substantially less than 185 grams (1 gram per pound) suggested frequently by muscle magazines and other popular sources!!! Try the calculation yourself for your own body weight!!!

Protein requirements are increased for those that lift weights or engage in intense activity levels, but still lower than many believe (Image credit: Victor Freitas at Pexels)

Divided into 4 meals, this comes to about 30 grams per meal. This amount of protein is easily achieved following a plant-based diet without the use of protein powders. Whole grain pastas with beans and sauce on top, peanut butter sandwiches on whole grain bread with a lentil soup, etc are options that can help achieve an intake over 30 grams per meal. My plant-based, whole foods smoothie in the morning has nearly 50 grams of protein alone with no protein powders added.

At the upper end for muscle maintenance and building, 84 kgs x 2 grams protein/ kg = 168 total grams of daily protein required for my body weight of 185 lbs. This still amounts to less than the 1 gram per pound calculation touted by mainstream sources, but does result in requirements of 42 grams per 4 meals. Such an amount is doable, but a little more difficult to achieve when using strictly plant-based natural sources (excluding protein powder shakes). An option is to eat 5 meals per day instead of 4, bringing requirements down to 34 grams per meal. Another option is to incorporate protein powders, though they seem unnecessary at the lower ranges provided for building and maintaining muscle when resistance training.

Guidelines may be higher than you think if you are in a calorie deficit and want to keep muscle

During periods of calorie deficits (such as “dieting,” or “cutting”) the body enters a catabolic state where both muscle tissue and fat are lost. To reduce or avoid muscle loss during a period of low caloric intake, the International Society of Sports Nutrition recommends higher protein intakes. Recommendations for preserving muscle tissue during low calorie “cutting” phases equates 2.3 – 3.1 grams / kg / day.

Using my weight again as an example, at 185lbs (84 kgs), this would equal 193.2 grams of protein on the low end to 260 grams on the high end. Divided into five meals per day, approximately 40 grams to 52 grams would be required per meal. Doing this “naturally” without the use of protein shakes or lean animal protein sources while maintaining a caloric deficit would be admittedly difficult.

Chronic, very high protein intakes are not conducive to long term health

It MUST BE NOTED that such a high protein intake (over 2 grams/ kg) is NOT conducive to long term health according to current research (Wu, 2016). Chronically elevated protein intake levels (such as those frequently touted by mainstream popular magazines) are associated with digestive, kidney and vascular abnormalities (Kalantar-Zadeh, Kramer, & Fouque, 2020; Wu, 2016). While protein ingestion at rates over 2 grams/ kg may serve short term interests, they are recommended against for the long term (Wu, 2016). Such high intakes are generally unnecessary, even for highly active adults as noted in the research above.

Summary

What are your protein needs? If you are a generally healthy adult, just find your weight in kg and multiply the recommended protein amounts based on your activity levels and goals. According to the research cited above, the appropriate protein amount in grams appears to be as follows (based on personal activities and goals):

  • Your weight in kg x 0.8: If you are sedentary
  • Your weight in kg x 1.0: If you do mild/ light activity (activity levels can be determined by clicking here)
  • Your weight in kg x 1.4: If you do moderate activity and/ OR if you desire to improve your muscle to fat ratio (such as in fighting obesity)
  • Your weight in kg x 1.6: If you do intense activities including weight training/ resistance training (up to your weight in kg x 2.0)
  • Your weight in kg x 2.3 (up to 3.1): If you weight train/ resistance train and are in a “cutting” phase, such as during a temporary calorie deficit
  • No more than your weight in kg x 2.0 over the long term: to preserve long term kidney, digestive, and vascular health.

Further, based on research, the majority of your protein should come from plant-based sources if you are interested in long term health and prevention of premature mortality. For most people, protein powders are unnecessary though they may be convenient. Protein powders may come with their own risks, such as containing high levels contaminants and unknown long term health impacts (Harvard University, 2018). Protein intake requirements are dependent on your activity levels and goals, though frequently research-based intake requirements are lower than reported in popular magazines, books and websites.

Thanks for reading!!! I hope you found this article informative! Feel free to leave a comment, and/ or sign-up to receive email notice of new articles!!! Sincerely, Donovan

References

Americashealthrankings.org. (2020). Physical inactivity. Retrieved from https://www.americashealthrankings.org/explore/annual/measure/Sedentary/state/ALL

Bluezones.com. (2020). Food guidelines. Retrieved from https://www.bluezones.com/recipes/food-guidelines/

Harvard University. (2018). The hidden dangers of protein powders. Retrieved from https://www.health.harvard.edu/staying-healthy/the-hidden-dangers-of-protein-powders

Jäger, R., Kerksick, C. M., Campbell, B. I., Cribb, P. J., Wells, S. D., Skwiat, T. M., Purpura, M., Ziegenfuss, T. N., Ferrando, A. A., Arent, S. M., Smith-Ryan, A. E., Stout, J. R., Arciero, P. J., Ormsbee, M. J., Taylor, L. W., Wilborn, C. D., Kalman, D. S., Kreider, R. B., Willoughby, D. S., Hoffman, J. R., … Antonio, J. (2017). International Society of Sports Nutrition Position Stand: Protein and exercise. Journal of the International Society of Sports Nutrition, 14, 20. https://doi.org/10.1186/s12970-017-0177-8

Kalantar-Zadeh, K., Kramer, H. M., & Fouque, D. (2020). High protein diet is bad for kidney function. Nephrology Dialysis Transplantation, 35(1), 1-4. Retrieved from https://www.medscape.com/viewarticle/924423?nlid=134117_785&src=WNL_mdplsfeat_200225_mscpedit_nurs&uac=223310AV&spon=24&impID=2291225&faf=1

Wu, G. (2016). Dietary protein intake and human health. Food & function, 7(3), 1251-1265. https://doi.org/10.1039/C5FO01530H

Zhang, X., Moumdjian, A. C., Gonzalez-Jaramillo, V., van der Schaft, N., Bramer, W. M., Ikram, M. A., & Voortman, T. (2020). Dietary protein intake and all-cause and cause-specific mortality: results from the Rotterdam Study and a meta-analysis of prospective cohort studies. European journal of epidemiology, 10.1007/s10654-020-00607-6. Advance online publication. https://doi.org/10.1007/s10654-020-00607-6

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