- 1. Whey protein overview
- 1.1. What is Whey Protein and Where does it Come From?
- 1.2. Production of Whey Protein
- 1.3. What Types of Whey Protein are There?
- 1.4. How does Whey Protein Work and What Are The Benefits?
- 1.5. Assessing the Quality of Whey vs. Other Protein Sources
- 1.6. Who Can Benefit from Using Whey Protein Supplements?
- 1.7. Do Any Foods Contain Whey Protein?
- 1.8. Does Whey Protein Have any Side Effects?
- 1.9. How and When Should I Use a Whey Protein Supplement?
- 1.10. How Much Whey Protein Should I Use?
- 2. Choosing the Right Whey Protein Supplement
- 2.1. Pros and Cons of Whey Protein Concentrate (WPC)
- 2.2. Pros and Cons of Whey Protein Isolate (WPI)
- 2.3. Pros and Cons of Whey Protein Blends
- 3. Whey Protein - Common Questions Answered
- What whey protein is and where it comes from.
- Who can benefit from using whey protein supplements.
- How to choose the right whey protein supplement.
- How much whey protein should you take, and when is the best time.
What is Whey Protein?
Whey protein is the term used to describe a group of milk proteins that are isolated from whey, which is the left over product of milk after it is coagulated during the cheese making process. Most people think that whey protein is just the typical amino acids we know about but contains a lot of other molecules.
For example, the mixture of proteins usually contains about 65% beta-lactoglobulin, 25% alpha-lactalbumin, 8% bovine serum albumin, and small amount immunoglobulins, lactose, and fat.
How is Whey Protein Made?
Whey protein can be manufactured directly from milk or even cheese, however almost all major brands of whey protein are made directly from milk.
First the whey is separated from the milk using straining methods. This results in a liquid whey product. Then the first step in the actually manufacturing process of whey is to pasteurize it using HTST pasteurization. HTST stands for High Temperature/Short Time.
Essentially, the product is heated to a required minimum temperature of 161°F for 15 seconds. Milk is pasteurized to kill any pathogenic bacteria that may be present.
Next is to isolate the proteins from the whey liquid. This can be achieved by ion exchange or mechanical filtering.
Ion exchange often requires the use of acids (e.g. hydrochloric acid) or bases (e.g. sodium hydroxide), this may cause some denaturation of the proteins.
While the chemical based nature of ion exchange is cheaper and often times more amino acids are captured, a draw back to the ion exchange method is that you may also lose some of the other important compounds in the whey product, such as lactoferrin and many of the immunoglobulins.
The mechanical filtering, often known as cross-filtering is a physical process that often results in a better product. However, it can be expensive and more laborious.
The kind and size of filter you use and the number of times you filter it are key in what type of whey you produce. The finer the filter and the more times you filter it results in a purer product. With each filtering step you reduce the amount of lactose, fat, ash, and other small impurities in the protein product.
The kind of filter and the number of times it is filtered is the primary difference in the production of the different types of whey protein (isolate and concentrate primarily).
Types of Whey Protein
There are three main types of commercially available whey protein: whey protein isolate, whey protein concentrate, and whey protein hydrolysates.
Whey Protein Isolate
Whey protein isolate is considered the purest form of whey protein available. It contains between 90-95% whey protein, very little fat (0.5-1.0%), and very little lactose (0.5-1.0%). This makes whey protein isolate a good protein source for people who have lactose intolerance or issues digesting lactose.
One of the things to note about whey protein isolate is that it often lacks a lot of the other beneficial components of whey, including immunoglobulins and other small molecules that have beneficial health properties. So, choosing whey protein isolate may be missing some of the magic.
Whey Protein Concentrate
Whey protein concentrate is lower in protein as it typically ranges from 25-89% with most commercially available concentrates containing about 80%. Whey protein concentrate often has about 4-8% lactose, fat, and other minerals.
This is the type of whey often seen in protein bars and other food products.
Whey Protein Hydrolysates
Whey protein hydrolysates (also known as hydrolyzed whey) is whey protein that has been enzymatically treated to break down long proteins in to shorter proteins. This process makes the whey protein more easily absorbed by the body and often reduces the potential for allergic responses and gut issues. As such, it is often included in infant formulas and sports and medical nutrition products.
Benefits of Whey Protein
Whey protein (WP) supplementation has recently gained popularity amongst athletes as it is reported to improve athletic performance. WP is a popular dietary protein supplement intended to provide improved muscle strength and body composition due to a greater compliment of essential amino acids and branched chain amino acids and to result in greater biological value1-4.
Additionally, WP supplementation has shown to reduce oxidative stress through increasing endogenous glutathione production and improve compromised gut health associated with intense exercise5-8.
While the majority of the research and topics covered in this post are WP supplementation specific,I want to remind everyone that whole foods sources of whey protein may be superior in terms of nutrient synergy than WP supplementation.
Increase Strength and LBM
Most athletic events are reliant upon force production of muscles, with greater ability to produce force associated with improved performance. As force is equal to mass x acceleration (F=M*A), increasing the muscle mass is the most common way athletes aim to increase force production.
Skeletal muscle hypertrophy requires proper resistance training and nutritional status in which muscle protein synthesis (MPS) exceeds muscle protein breakdown (MPB).
One of the major concepts in the literature surrounding skeletal muscle hypertrophy is the idea of net protein balance (NPB). NPB is defined as MPS minus MPB (NPB = MPS – MPB). Thus, if MPS is greater than MBP, skeletal muscle hypertrophy will occur9.
One of the critical factors influencing MPS and MBP is the availability of amino acids10,11. WP supplementation is a source of high biological value amino acids and has been purported to increase muscle mass and strength.
There is an extensive body of research surrounding the efficacy of WP supplementation in increasing strength and muscle mass. The results of the research are not entirely unequivocal; however, a significant amount of evidence suggests that WP increases both strength and muscle mass12-15.
Additionally, researchers have recently shown that the constituents of whey protein upregulate the cell signaling pathways, specifically mTOR, responsible for muscle protein synthesis and muscle hypertrophy16.
Whey Protein and Glutathione
Oxidative stress refers to an imbalance between antioxidant defense systems and production of reactive oxygen species (ROS)17. Oxygen consumption during heavy exercise can increase up to 100 times normal resting levels, thus increasing the production of free radicals and resulting in oxidative stress.
Although the data is not unequivocal, evidence exists showing increased free radical production and cellular damage following heavy exercise18.
Athletes are at a higher risk of elevated oxidative stress than their non-athletes counterparts due to the increased pro-oxidative process they expose themselves to19. The increased levels of ROS produced during heavy exercise must be reduced by the body’s endogenous antioxidant system in order to maintain oxidative balance.
Glutathione, the most abundant and important antioxidant, is a tripeptide synthesized from the amino acids L-cysteine, L-glutamic acid, and glycine20. It is the most important redox couple and plays crucial roles in antioxidant defense, nutrient metabolism, and the regulation of pathways essential for whole body homeostasis21.
Additionally, glutathione serves as a regulatory compound in the activation of the circulation agents of the immune system, lymphocytes22.
It is apparent that glutathione is a critical compound in maintaining health and glutathione deficiency and has been linked to numerous pathological conditions including, cancer, neurodegenerative disorders, cystic fibrosis, HIV and aging23. Glutathione is of particular interest in the athletic population as the concentration of glutathione varies considerably as a result of nutritional limitation, exercise, and oxidative stress.
The intense physical demands of athletics places athletes’ bodies under high levels of physiological stress. Glutathione plays a critical role in maintaining normal redox status during exercise24,25. Furthermore, exhaustive exercise has been shown to reduce glutathione status24,25,26.
Thus indicating the need for bolstered levels of glutathione in athletes. Researchers have shown that the amino acid cysteine is the rate-limiting factor in glutathione synthesis27,28. Therefore, the inclusion of cysteine rich protein sources may prove efficacious in increasing glutathione re-synthesis rates by providing ample amounts of cysteine to the amino acid pool.
Supplementation with free cysteine is not advised however as it spontaneously oxidized and has shown to be toxic29. Dietary sources of cysteine present as cystine (two cysteines linked by a disulfide bond) are more stable than free cysteine and properly digested. WP supplements, including WP isolate and WP concentrate are protein sources rich in cysteine and deliver cysteine to the cells via normal metabolic pathways30,31.
By providing abundant cysteine, WP supplementation allows cells to replenish and synthesize glutathione without adverse effects31 (Thus, WP supplementation may serve to bolster the endogenous production of glutathione and improve oxidative stress in athletes).
The use of WP supplementation to mitigate a training-induced decline in blood glutathione levels has been studied extensively. Researchers have shown that WP supplement is beneficial in maintaining normal physiological levels of glutathione in athletic and non-athletic populations in response to exercise32-34.
Furthermore, researchers have shown that WP improves the athlete’s ability to deal with acute oxidative stress and WP may serve as a safe and effective alternative source of antioxidants for prevention of athletic injuries and sickness caused by excessive reactive oxygen species (ROS)35.
The research regarding WP supplements and glutathione status supports the use of WP in athletics to improve health status in athletes by augmenting the endogenous antioxidant system.
Whey Protein and Immune Function
Strenuous exercise and heavy training regimens are associated with depressed immune cell function36-40. Furthermore, inadequate or inappropriate nutrition can compound the negative influence of heavy exertion on immunocompetence. Suppression of the immune predisposes the individual to an increased risk of infection.
Athletes increase both the volume and intensity of their training at certain stages of the season which may result in a state of overreaching or overtraining. Recent evidence has emerged indicating that immune function is indeed sensitive to increases in training volume and intensity.
Although the research has not shown that athletes are clinically immunocompromised during these periods of depressed immune function, it may be sufficient to increase the risk of contracting common infections.
As the components of the immune system are highly dependent on amino acids, endogenous and dietary amino acids can impact the state of the immune system.
In comparison to other protein sources, research shows that whey proteins are unique in their ability to promote strong immunity through several beneficial compounds including: glutamine, α-lactalbumin and β-lactoglobulin, and minor fractions such as serum proteins, lactoferrin, as well as a series of immunoglobulins41-43.
Whey Protein and Gut Health
Intense physical exercise leads to reduced splanchic blood flow, hypoperfusion of the gut, and increased intestinal temperatures4. Reduced intestinal blood flow and high intestinal temperatures during intense exercise can lead to intestinal barrier dysfunction through increased permeability of the tight junctions5,8.
The increased permeability of the intestinal wall leads to invasion of Gram-negative intestinal bacteria and/or their toxic constituents (endotoxins) into the blood circulation45-47. Endotoxins are highly toxic lipopolysaccharides (LPS) of the outer cell wall of Gram-negative bacteria. LPS are a major trigger in vivo for the host immune response via induction of the cytokine network45. (Jeukendrup, et al., 2000).
This process, endotoxemia, can result in increased susceptibility to infectious and autoimmune diseases, due to absorption of pathogens/toxins into tissue and blood stream48.
The field of intestinal permeability is relatively new and long-term prospective studies have yet to clearly identify the potential hazards of chronic, low-grade levels of intestinal permeability.
However, recent research has established a link between intestinal permeability and a host of autoimmune diseases including Chron’s disease, Hashimoto’s Thyroditis, lupus erythmatosis, psoriasis, and rheumatoid arthritis49-53. Additionally, intestinal permeability has been associated with mental illness including schizophrenia and depression54,55.
As previously mentioned, tight junctions constitute the major component of gut barrier function and acts as physical and functional barrier against the paracellular penetration of macromolecules from the lumen56,57. Therefore, the regulation of tight junction permeability is critical in maintaining gut integrity and reducing the exposure of the body to endotoxins.
The amino acid glutamine is critical in maintaining the integrity of these tight junctions56. Glutamine, the most abundant amino acid in the blood, is considered a “conditionally essential” amino acid56. Under normal conditions glutamine is produced in sufficient quantities in the body to maintain the normal physiological functions.
However, under stressful situations, such as exercise, endogenous production of glutamine insufficient and the body must rely on exogenous sources of glutamine to meet its requirements.
Glutamine supplementation has been shown to improve gut permeability through restoration of tight junction integrity caused by a variety of physiological stressors through multiple molecular mechanisms58-60. Additionally, glutamine supplementation has proven effective in reducing exercise induced intestinal permeability61.
WP is a rich source of glutamine and researchers have shown that WP supplementation is capable of reducing intestinal permeability62,63. Therefore, WP may be beneficial in reducing exercise induced intestinal permeability and the risk of endotoxemia and autoimmune disorders.
Whey protein is an excellent source of a wide range of amino acids and additional nutrients that are beneficial to health. Whey protein has been shown to increase lean body mass in conjunction with resistance training, bolster glutathione status, have immunomodulatory effects and improve gut health.
A healthy, well balanced diet may be enhanced with whey protein through either whole food sources or occasional whey protein supplements.
How and When to Use Whey Protein
There are no real hard rules about how and when to use whey protein as it is essentially a food product, just like cheese or yogurt. However, there are a few smart ways to use it!
Whey protein is often used post workout as it is quickly digested and has been shown to augments muscle protein synthesis and reduce muscle protein breakdown after training. The typical range for consuming whey protein after training is between 20-40 grams.
You can get an effect at lower doses but it does not appear to maximize the effect and much more than 40 grams results in a lower return on investment. You can consume your post workout whey by itself mixed in water or you can mix it with milk. You can combine it with frozen fruit for a smoothie or add it to any other food in increase the protein content of your post workout meal.
Whey protein can also be used for a protein source at a meal or an on the go snack. For example, mixing whey protein with your oatmeal in the morning can increase the protein content of your breakfast or you can take it to work and drink it as a snack.
Whey Protein Side Effects
Whey protein can have a range of minor gastrointestinal side effects, including constipation, gas, and bloating. Some people who have allergies to milk may experience an allergic reaction and should consult a doctor prior to taking whey protein or if they experience allergy symptoms after consuming it.
Foods That Contain Whey Protein
Dairy foods such as milk, cheese, butter, and yogurt contain whey protein. (Fun fact, the liquid at the top of your yogurt is whey, so don’t thrown your gains down the garbage!).
Whey protein is also used industrially in food products as it is a highly versatile ingredient. It is often used as an emulsifier in baked products, ice cream mixes, and dressings. It is used to improve solubility of infant formula, frozen desserts, and even soups and sauces.
Typically the amount of whey found in these products is not going to help you build muscle but it is most certainly in there!
Other Protein Sources (not whey)
Soy Protein is a protein source derived from soy plants/soy beans. Soy protein is well documented in its ability to provide amino acids to the amino acid pool and is considered a “fast” digesting protein. Additionally, soy protein has been shown to enhance muscle protein synthesis over placebo.
Unfortunately soy appears to be an inferior protein source when compared to whey. For example, ingesting 30 g of either whey or soy protein resulted in equivalent p70S6K phosphorylation (a molecule involved in muscle protein synthesis at 2 hours post exercise, however, unlike whey, soy protein failed to promote prolonged phosphorylation of p70S6K to 4 hours post-exercise ref).
In another study, there was a 14.54% greater thermic effect for the whey protein than soy, indicating it may be more beneficial for weight loss. In that same study the average peak in oxygen uptake was 29.94% for whey protein and 23.98% for soy protein, respectively Soy appears to be faster digesting, but may be inferior for muscle protein synthesis.
Milk protein consists of whey and casein protein. Casein is often considered the “other” protein. Much like whey protein, casein is a rich source of amino acids and provides a biological complete amino acid profile.
Casein is digested slower than whey, and as a result provides a longer time frame of amino acid infusion into the blood stream. This has led to the hypothesis that casein may be superior for muscle gain by providing a longer infusion of amino acids and that it is especially helpful when taken at night before bed.
While there are substantial claims about the superiority of casein, they don’t stand up to scientific scrutiny. What we really should hang our hat on is that casein is probably a better nighttime choice than whey, but whey is probably better post workout.
From a weight loss perspective casein may have a slight edge on whey protein, albeit indirectly. One potential benefit of casein over whey is the “fullness” effect of casein. As it is slower digesting it often results in a longer period of post-prandial (after eating) satiety. This may help reduce overall caloric intake and benefit weight loss to a greater degree than whey.
Whey Protein vs. Other Protein Sources
The two most popular indications of determining a protein sources overall quality/efficacy are the biological value (BV) and protein digestibility corrected amino acid score (PDCAAS). The BV of a protein source refers to a practical measurement that assesses the degree to which an animal is able to utilize that protein. It is computed by analysis of nitrogen retention in an animal after ingesting the intended protein source to be tested.
The PDCAAS is a number between 0 And 1 that evaluates protein quality based on its amino acid contents in relation to human’s requirements for them. Essentially, the higher the BV and PDCAAS of a protein the more efficiently it is utilized by the respective animal (yes, humans are animals too). Below is a chart that summarizes the BV and PDCAAS of a variety of common protein sources for humans:
|Whey Concentrate and Isolate||104 to 159||1.00|
Best Whey Protein Powders
1. Muscle & Strength
100% Whey Protein
Total Fat: 0g
Total Carbohydrate: 4g
Total Protein: 25g
2. Optimum Nutrition
100% Whey Gold Standard
Total Fat: 1.5g
Total Carbohydrate: 3g
Total Protein: 23g
Total Fat: 2.5g
Total Carbohydrate: 4g
Total Protein: 30g
Total Fat: 2.5g
Total Carbohydrate: 9g
Total Protein: 30g
5. BPI Sports
Total Fat: 2g
Total Carbohydrate: 3g
Total Protein: 24g
Total Fat: 1g
Total Carbohydrate: 5g
Total Protein: 25g
Combat 100% Whey
Total Fat: 2.5g
Total Carbohydrate: 4g
Total Protein: 25g
Total Fat: 2g
Total Carbohydrate: 3g
Total Protein: 24g
Total Fat: 6g
Total Carbohydrate: 14g
Total Protein: 22g
How much whey protein should I use?
There is no real guideline for how much you should use. That being said there are a few things to consider. There appears to be good reason to aim for 20-30 grams of whey protein after a workout to improve the post workout muscle growth response. Some individuals may need more or less to optimize that but there isn’t a hard and fast number. This often depends on the type of protein as the leucine content of it will determine that muscle growth response.
In the context of “daily” intake, it would be wise to use whey as a supplement and not base your entirely daily intake on it. 1-2 servings of whey per day would be a general guideline to follow.
I’m lactose intolerant, can I still use a whey protein supplement?
People have varying degrees of stomach and intestinal reactions to whey protein. Typically, whey protein isolate has the lowest amount of lactose and presents the lower probability of an individual having any gastric distress surrounding it. If you are unable to find a whey protein that is suitable for your current lactase insufficiency then rice protein may be the next best alternative for you.
I’m allergic to milk, is a whey protein supplement safe for me?
Each person’s type of allergy to milk and the level of “allergic response” to milk differ. If you are allergic to the milk proteins than you might be able to consume hydrolyzed whey or a very pure whey protein isolate as many of the allergenic compounds have been removed.
If you are lactose intolerant the whey protein isolate is often virtually void of lactose and presents no issue for a lot of people. It is wise to consult your doctor and try small doses of the whey protein isolate or hydrolyzed whey and see how your body responds.
Is it true that whey protein is bad for the kidneys?
In otherwise healthy individuals with no history of kidney disease and normal kidney function there is no scientific evidence to date that whey protein has any measureable negative effect on your kidneys.
Is it true that whey protein is bad for my bones?
This is a good question! One of the common arguments I hear against high-protein diets, specifically those high in animal protein, is that they are detrimental for bone health. Let’s take a look and see what the science actually has to say on the topic.
Did you know that high-protein diets increase calcium absorption in the digestive tract and that a large body of evidence is surfacing that supports the hypothesis that the increased intestinal calcium absorption due to high protein diets may actually increase bone health.
Additionally, in a recent paper by one of the leading protein and bone health investigators the authors stated, “Recent epidemiological, isotopic and meta-analysis studies suggest that dietary protein works synergistically with calcium to improve calcium retention and bone metabolism.
The recommendation to intentionally restrict dietary protein to improve bone health is unwarranted, and potentially even dangerous to those individuals who consume inadequate protein”64.
From my opinion, I think the issue of high-protein diets having a negative impact on bone health is due to an increase in the net acid load of the body has been put to rest. High-protein diets are not only safe for bone health, they may in-fact be highly beneficial, especially in older individuals and those at high risk for osteoporosis.
So that was my long-winded way of saying, whey might actually help your bones!
Can I combine whey protein supplements with my other powdered supplements like creatine, glutamine, etc?
Absolutely!!! You can mix creatine in with your whey protein but glutamine might be a bit of overkill since whey already has a substantial amount of glutamine in it. Powdered greens make an excellent addition to it as well for a little extra micronutrition.
Does it matter what liquid I use to mix my whey protein with?
Yes and no. The liquid changes the composition and texture of your drink. Water often makes it very thin while mix makes it thicker and gives more mouth feel.
From an absorption standpoint you can make some arguments that consuming it with milk or another carbohydrate and sodium may increase the rate of uptake but that is not likely to make a large or even noticeable difference in the overall amount of protein absorbed and its effect on muscle protein synthesis.
Doesn’t cooking/baking with denature the protein?
Yes, cooking or baking can denature the protein. However, that has virtually no effect on the muscle building capacity of the protein as that lies in the amino acids themselves. The denaturing process may reduce some of the bioactivity of the other components of whey but it is not something to spend too much time worrying about it.
Are there any dangers with taking whey protein?
There are some dangers to taking whey protein. The first one is allergic responses to milk based proteins. Some people have allergies to milk proteins and they can have allergic reactions to whey.
There is also some danger in taking whey protein derived from a nonreputable source or from a company with poor quality control. Just like any other food product, if it is handled and manufactured poorly there can be some dangers. However, the potential dangers are so miniscule that they are massively outweighed by the potential benefits for most people.
Is whey protein safe for teens?
Based on the current scientific evidence (and there are an obscene amount of studies using whey protein in humans), there is no evidence to suggest it is harmful for teens. In fact, it may actually be beneficial for teenagers as a lot of the components of whey will help their growing bodies!
Do women have to use different whey protein to men?
There are no real reasons why women should use protein differently from men. As women often weigh less than men they can have lower total daily protein requirements which means they may need a little bit less whey protein but there is no special requirements for women in terms of how and when to take it!
Since whey protein isolate has the highest amount of protein should I take only that?
Whey protein isolate does indeed have the highest “purity” and the highest amount of protein per serving which makes it a great choice for building muscle.
However, whey protein isolate also filters out some of the other important bioactive compounds such as alpha lactalbumin, beta lactalbumin, immunoglobulins, glycomacropeptides, and lactoferrin, just to name a few. So it may be a really good idea to get both types in your supplementation routine.
- Burke, D. G., Chilibeck, P., Davison, K., & Candow, D. (2001). The effect of whey protein supplementation with and without creatine monohydrate combine with resistance training on lean tissue mass and muscle strength. International Journal of Sport Nutrition and Exercise Metabolism, 11, 349-364.
- Coburn, J. W., Housh, D., Malek, M., Beck, T., Cramer, J., Johnson, G., et al. (2006). Effects of leucine and whey protein supplementation during eight weeks of unilateral resistance training. Journal of Strength and Conditioning Research, 20 (2), 284-291.
- Frestedt, J. L., Zenk, J., Kuskowski, M., Ward, L., & Bastian, E. (2008). A whey-protein supplement increases fat loss and spares lean muscle in obese subjects: A randomized human clinical study . Nutrition & Metabolism , 5 (8), 1-7.
- Willoughby, D. S., Stout, J., & Wilborn, C. (2007). Effects of resistance training and protein plus amino acid supplementation on muscle anabolism, mass, and strength. Amino Acids , 32 (4), 467-477.
- Lambert, G. P. (2009). Stress-induced gastrointestinal barrier dysfunction and its inflammatory effects. Journal of Animal Science , 87 (E. Supplement), E101-E108.
- Low, P. L., Rutherfurd, K., Gill, H., & Cross, M. (2003). Effect of dietary whey protein concentrate on primary and secondary antibody responses in immunized BALB/c mice . International Immunopharmacology , 3 (3), 393-401.
- Micke, P., Beeh, K., Schlaak, J., & Buhl, R. (2001). Oral supplementation with whey proteins increases plasma glutathione levels of HIV-infected patients. European Journal of Clinical Investigation , 31 (2), 171-178.
- Pals, K. L., Chang, R., Ryan, A., & Gisolfi, C. (1997). Effect of running intensity on intesttinal permeability. Journal of Applied Physiology , 82, 571-576.
- Hulmi, J. J., Lockwood, C., & Stout, J. (2010). Effect of protein/essential amino acids and resistance training on skeletal muscle hypertrophy: A case for whey protein . Nutrition & Metabolism , 7 (51).
- Dickinson, J. M., & Rasmussen, B. (2011). Essential amino acid sensing, signaling, and transport in the regulation of human muscle protein metabolism. Current Opinion in Clinical Nutrition & Metabolic Care , 14 (1), 83-88.
- Li, J. B., & Jefferson, L. (1978). Influence of amino acid availability on protein turnover in perfused skeletal muscle .Biochimica et Biophysica Acta , 544 (2), 351-359.
- Esmarck, B., Andersen, J., Olsen, S., Richter, E., Mizuno, M., & Kjaer, M. (2001). 18. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. Journal of Physiology , 535, 301-311.
- Cribb, P. J., Williams, A., Carey, M., & Hayes, A. (2006). The effect of whey isolate and resistance training on strength, body composition, and plasma glutamine. International Journal of Sports Nutrition and Exercise Metabolism, 16 (5), 494-509.
- Buckley, J. D., Thomson, R., Coates, A., Howe, P., DeNichilo, M., & Rowney, M. (2010). Supplementation with a whey protein hydrolysate enhances recovery of muscle force-generating capacity following eccentric exercise . Journal of Science in Medicine and Sport, 13, 178-181.
- Tipton, K. D., Elliot, T., Cree, M., Wolf, S., Sanford, A., & Wolf, R. (2004). Ingestions of casein and whey proteins result in muscle anabolism after resistance exercise. Medicine and Science in Sports and Exercise, 36, 2073-2081.
- Hulmi, J. J., Tannerstedt, J., Selanne, H., Kainulainen, H., Kovanen, V., & Mero, A. (2009). Resistance exercise with whey protein ingestion affects mTOR signaling pathway and myostatin in men. Journal of Applied Physiology, 106, 1720-1729.
- Sachdev, S., & Davies, K. (2008). Production, detection, and adaptive responses to free radicals during exercise. Free Radical Biology & Medicine, 44 (2), 215-223.
- Adams, A. K., & Best, T. (2002). The role of antioxidant in exercise and disease prevention. The Physician and Sports Medicine, 30 (5), 2002.
- Lowery, L. (2001). Antioxidants supplements and exercise. In J. Antonio, & J. Stout (Eds.), Sport Supplements (pp. 260-278). Philidelphia, PA: Lippincott, Williams and Wilkins.
- Thomas, J. A. (1999). Oxidative stress and oxidant defense. In M. Shils, J. Olson, M. Shike, & A. Ross (Eds.), Modern Nutrition in Health and Disease (pp. 751-782). Baltimore, MD: Lippincott Williams & Wilkins.
- Wu, G., Fang, Y., Yan, S., Lupton, J., & Turner, N. (2004). Glutathione metabolism and its implications for health.Journal of Nutrition, 134, 489-492.
- Droge, W. (1996). Modulation of the immune response by cysteine and cysteine derivatives. Italian Society for Parenteral and Enteral Nutrition, 14, 1-4.
- Townsend, D. M., Tew, K., & Tapiero, H. (2003). The importance of glutathione in human disease. Biomedicine & Pharmacotherapy, 57, 145-155.
- Li, J. J., & Fu, R. (1992). Responses of glutahtione system and antioxidant enzymes to exhaustive exercise and hydroperoxide. Journal of Applied Physiology, 72 (2), 549-554.
- Kerksick, C., & Willoughby, D. (2005). The antioxidant role of glutathione and n-acetyl-cysteine supplements and exercise-induced oxidative stress. Journal of the International Society of Sports Nutrition, 2 (2), 38-44.
- Gohil, K., Viguie, C., Stanley, W., Brooks, G., & Packer, L. (1988). Blood glutathione oxidation during human exercise. Journal of Applied Physiology, 64 (1), 115-119.
- Lyons, J., Rauh-Pfeiffer, A., Yu, Y., Lu, X., Zurakowski, D., Tompkins, R., et al. (2000). Glood glutathione synthesis rates in health adults receiving a sulfur amino acid-free diet. Proceedings of the National Academy of Sciences of the United States of America, 97 (10), 5071-5076.
- Rathbun, W. B., & Murray, D. (1991). Age-related cysteine uptake as rate-limiting in glutathione synthesis and glutathione half-life in the cultured human lens. Experimental Eye Research, 53 (2), 205-212.
- Meister, A. (1984). New aspects of glutathione biochemisty and transport selective alterations of glutathione metabolism. Nutrition Reviews, 42, 397-410.
- Chitapanarux, T., Tienboon, P., Pojchamarnwiputh, S., & Leelarungrayub, D. (2009). Open-labeled pilot study of cysteine-rich whey protein isolate supplementation for nonalchoic steatohepatitis patients. Hepatology , 24, 1045-1050.
- Sindayikengera, S., & Xia, W. (2006). Nutritional evaluation of caseins and whey proteins and their hydrolysates from Protamex. Journal of Zhejian University Science B , 7 (2), 90-98.
- Mariotti, F., Simbelie, K., Makarious-Lahham, L., Huneau, J., Laplaize, B., Tome, D., et al. (2004). Acute ingestion of dietary proteins improves post-exercise liver glutathione in rats in a dose-dependent relationship with their cysteine content. Journal of Nutrition , 134, 128-131.
- Middleton, N., Jelen, P., & Bell, G. (2004). Whole blood and mononuclear cell glutathione response to dietary whey protein supplementation and trained male subjects. International Journal of Food Science Nutrition , 55 (2), 131-141.
- Vatani, D. S., & Golzar, F. (2012). Changes in antioxidant status and cardiovascular risk factors of overweight young men after six weeks supplementation of whey protein isolate and resistance training. Appetite , 59, 673-678.
- Xu, R., Liu, N., Xu, X., & Kong, B. (2011). Antioxidative effects of whey protein on peroxide-induced cytotoxicity.Journal of Dairy Science , 94 (8), 3739-3746.
- Gleeson, M. (2007). Immune function in sport and exercise. Journal of Applied Physiology , 103, 693-699.
- Gleeson, M., McDonald, W., Cripps, A., Pyne, D., Clancy, R., & Fricker, P. (1995). The effect on immunity of long-term intensive training in elite swimmers . Clinical & Experimental Immunology , 102 (1), 210-216.
- Baj, Z., Kantorski, J., Majewska, E., Zeman, K., Pokoca, L., Fornalczyk, E., et al. (1994). Immunological status of competitive cyclists before and after the training season. International Journal of Sports Medicine , 15 (6), 319-324.
- Bury, T., Marechal, R., Mahieu, P., & Pirnay, F. (1998). Immunological status of competitive football players during the training season. International Journal of Sports Medicine , 19 (5), 364-368.
- Shepard, R. J., Rhind, S., & Shek, P. (1994). Exercise and the immune system. Natural killer cells, interleukins and related responses. Sports Medicine , 18 (5), 340-369.
- Cribb, P. J. (2005). U.S. whey proteins in sports nutrition. U.S. Dairy Export Council.
- Cribbs, P. J. (2004). Whey proteins and immunity. U.S. Dairy Export Council.
- Walzem, R. M., Dillard, C., & German, J. (2002). Whey components: millennia of evoluation create functionalities for mammalian nutrition: What we know and what we may be overlooking. Critical Reviews in Food Science and Nutrition , 42 (4), 353-375.
- Qarnar, M. I., & Read, A. (1987). Effects of exercise on mesenteric blood flow in man. Gut , 28, 583-587.
- Jeukendrup, A. E., Vet-Joop, K., Sturk, A., Stegen, J., Senden, J., Saris, W., et al. (2000). Relationship between gastro-intestinal complaints and endotoxaemia, cytokine release and the acute-phase reaction during and after a long-distance triathlon in highly trained men. Clinical Science , 98, 47-55.
- Lambert, G. P. (2008). Intestinal barrier dysfunction, endotoxemiz, and gastrointestinal symptons: the ‘canart in the coal mine’ during exercise-heat stress? Medicine and Sport Science , 53, 61-73.
- Van Deventer, S. J., & Gouma, D. (1994). Bacterial translocation and endotoxin transmigration in intestinal ischaemia and reperfusion. Current Opinions in Anaesthiology , 7, 126-130.
- Lamprecht, M., Bogner, S., Schippinger, G., Steinbauer, K., Fankhauser, F., Hallstroem, S., et al. (2012). Probiotic supplementation affects markers of intestinal barrier, oxidation, and inflammation in trained men; a randomized, double-blinded, placebo-controlled trial . Journal of the International Society of Sports Nutrition , 9 (45), 1-13.
- Sasso, F. C., Carbonara, O., Torella, R., Mezzogiomo, A., Esposito, V., deMagistris, L., et al. (2004). Ultrastructural changes in enterocytes in subjects with Hashimoto’s thyroiditis . Gut , 53 (12), 1878-1880.
- Caradonna, L., Amati, L., Magrone, T., Pellegrino, N., Jirillo, E., & Cacavvo, D. (2000). Invited review: Enteric bacteria, lipopolysaccharides and related cytokines in inflammatory bowel disease: biological and clinical significance .Journal of the International Endotoxin Innate Immunity , 6 (3), 205-214 .
- Apperloo-Renkema, H. Z., Bootsma, H., Mulder, B., Kallenberg, C., & van der Waajj, D. (1994). Host-microflora interaction in systemic lupus erythematosus (SLE): colonization resistance of the indigenous bacteria of the intestinal tract. . Epidemiiology and Infection , 112 (2), 367-373.
- Hamilton, I., Fairris, G., Rothwell, J., Cunliffe, W., Dixon, M., & Axon, A. (1985). Small intestinal permeability in dermatological disease. QJM , 56, 559-567.
- Smith, M. D., Gibson, R., & Brooks, P. (1985). Abnormal bowel permeability in ankylosing spondylitis and rheumatoid arthritis. The Journal of Rheumatology , 12 (2), 299-305.
- Wood, N. C., Hamilton, I., Axon, A., Khan, S., Quirke, P., Mindham, R., et al. (1987). Abnormal intestinal permeability. An aetiological factor in chronic psychiatric disorders? . The British Journal of Psychiatry , 150, 853-856.
- Maes, M., Kubera, M., & Leunis, J. (2008). The gut-brain barrier in major depression: Intestinal mucosal dysfunction with an increased translocation of LPS from gram negative enterobacteria (leaky gut) plays a role in the inflammatory pathophysiology of depression. Neuroendocrinology Letters , 29 (1), 117-124.
- Rao, R. K., & Samak, G. (2012). Role of glutamine in protection of intestinal epithelial tight junctions. Journal of epithelial biology and pharmacology , 5, 47-54.
- Mitic, L. L., & Anderson, I. (1998). Molecular architecture of tight junctions. Annual Review of Physiology , 60, 121-142.
- Wilmore, D. W., Smith, R., O’Dwyer, S., Jacobs, D., Ziegler, T., & Wang, X. (1988). The gut: A central organ after surgical stress. Surgery , 104, 917-923.
- Peng, X., Yan, H., You, Z., Wang, P., & Wang, S. (2004). Effects of enteral supplementation with glutamine granules on intesinal mucosal barrier function in severe burned patients. Burns , 30, 135-139.
- Kozar, R. A., Schultz, S., Bick, R., Poindexter, B., DeSoignie, R., & Moore, F. (2004). Enteral glutamine not but alanine maintains small bowel barrier function after ischemia/reperfusion injury in rates. Shock , 21, 433-437.
- Hoffman, J. R., Ratamess, N., Kang, J., Rashti, S., KElly, N., Gonzalez, M., et al. (2010). Examination of the efficacy of acute L-alanyl-L- glutamine ingestion during hydration stress in endurance exercise . Journal of the International Society of Sports Nutrition , 7 (8).
- Kotler, B. M., Kerstetter, J., & Insogna, K. (2013). Claudins, dietary milk proteins, and intestinal barrier regulation.Nutrition Reviews , 71 (1), 60-65.
- Benjamin, J., Makharia, G., Ahuja, V., Rajan, K. D., Kalaivani, M., Gupta, S. D., et al. (2012). Glutamine and whey protein improve intestinal permeability and morphology in patients with Chron’s disease: A randomized controlled trial. Digestive Diseases and Sciences, 57 (4), 1000-1012.
- Kerstetter, J., Kenny, A., Insogna, K. Dietary protein and skeletal health: a review of recent human research. (2011). Current Opinions in Lipidology. 22(1), 16-20.