Whey protein appears to be the ideal protein source for post-exercise recovery foods and to improve clinical outcomes in certain disease states. But is the hype consistent with the research? Robert Child, PhD, investigates
Much has been written about whey?s potential benefits for general health, athletes and its application for specific clinical conditions. Unfortunately much of the literature in the popular press either favours whey protein or heavily criticises its use. This article provides a brief but contemporary critique of the scientific evidence and explores biochemical mechanisms of whey protein action. Such information is important to optimise the potential benefits of whey protein in applications as a functional food in medicine and sport.
There is increasing scientific interest in whey—the fluid portion of milk obtained by coagulating and removing curd. A number of applications as a functional food to improve health have been described and these effects are not readily apparent when whey is simply considered as a source of protein.
Processing
Whey is a by-product of hard cheese manufacture and, though nutritious, has limited application as a food ingredient in this form. The dry matter in whey is about 55 per cent protein, which is of high biological value. In this unprocessed form whey also contains around 40 per cent lactose and is often referred to as sweet dairy whey.
Additional processing is usually desirable to reduce the lactose content, as many people are intolerant to this sugar. Heating and acid precipitation can be used to purify whey to provide whey protein isolates—a protein content above 90 per cent—but these treatments also denature some of the bioactive proteins so that their functional properties may be lost.1,2 Passing whey through a series of filters can produce whey isolates with a protein content of around 90 per cent, without the use of heat or strong acids.
This process is often referred to as cross-flow microfiltration and minimises damage to important protein molecules, which allows their functional properties to be retained. The lactose content of whey isolates can be reduced to 1?2 per cent, making them suitable for people with poor lactose tolerance. Specific protein fractions can be further purified using a combination of cross-flow microfiltration and ion exchange chromatography.
Whey Vs Other Proteins
Bovine whey is composed primarily of the proteins beta-lactoglobulin (50%), alpha-lactalbumin (20%), glycomacropeptide (20%) and bovine serum albumin (2?3%). These proteins act as excellent sources of cysteine and also have recognised functional effects as intact proteins.3 Despite the similarities in amino acid composition between whey, casein and soy (See Table 1), there are also some important differences. Whey has the highest content of branched-chain amino acids (BCAAs), especially leucine, as well as the most cysteine.
The digestion and absorption of whey and casein also differ, in that casein—unlike whey—coagulates in the stomach due to precipitation by stomach acids.4 Consequently, the gastric emptying time for casein is longer and there is a smaller rise in plasma amino acids relative to whey protein.
In 1997, French researcher Yves Boirie and colleagues introduced the terms ?fast? and ?slow? dietary proteins to describe these differences in whey and casein digestion. The higher concentration of plasma amino acids in the three-hour period following a whey meal results in higher rates of protein synthesis.5 After this period it is casein and not whey that results in higher rates of protein synthesis, a condition which is maintained for several hours. Anti-nutritional and estrogenic factors in soy may make this protein undesirable to some groups, especially male athletes; while the slow digestion of meats, fish and casein may limit their suitability when rapid absorption of amino acids is required.6,7
Exercise Demands
Intense physical activity increases oxidant formation and damage during exertion, which can result in further oxidative damage after exercise, because of muscle injury.8 Oxidant formation during exercise is also associated with muscle fatigue,9 oxidative damage to muscle proteins,10 lipids8 and the rupture of red blood cells.8 Also, prolonged and intense exercise has been shown to suppress the immune system, increasing susceptibility to infection.11
Whey protein could be a useful supplement for athletes because some of the reported functional effects could directly counteract some of the undesired effects of exercise. These include reduced oxidative damage, muscle fatigue, red blood cell lysis and the ability to increase cellular glutathione levels.12,13 The conditions that exist in the body after exercise also have many similarities with disease states, which can increase tissue breakdown, compromise antioxidant protection, suppress the immune system and even produce gut injury.8
The combination of increased protein damage and oxidation of leucine, isoleucine and valine (BCAAs) during exercise increases whole body protein requirements. The provision of amino acids after training (and in particular leucine) appears important for protein synthesis14,15 and to maintain muscle mass.16
There is clear scientific evidence that whey protein5,17,18 and in particular the BCAAs19,20,21 exert anabolic effects in muscle. Establishing pathways of action are important for any functional food; however, the most important end-point is whether the cellular changes translate to measurable benefits to body function.
To that end, Larry Lands and co-workers performed the first study on healthy males and females assessing the biochemical effects of whey supplementation and its effects on exercise performance in 1999.13 Twenty subjects were divided into two equal groups and supplemented with 20g/day of either whey protein or casein, over a period of three months. The authors found significant improvements in peak power and work output and indirect evidence for increased muscle mass. However, it was not clear if these changes arose from improved muscle strength and/or fatigue resistance; theoretically, whey supplementation could produce both of these effects.
In 2003, researchers investigated the effects of 70 days supplementation with either 40g/day whey protein isolate or 40g/day ovalbumin, in two groups of healthy males, each comprised of 12 subjects. Although the participants were not involved in a training programme, a 10 per cent improvement in muscle fatigue resistance was observed in the whey group, without changes strength or body mass.12
Studies specifically addressing the effects of whey protein supplementation on muscle mass and performance have generally reported positive findings. A 2001 study involved supplementation of two groups of 12 males with either whey or maltodextrin (both 1.2g/kg daily).22 Over the six-week supplementation period, the subjects also participated in a resistance training program. Whey supplementation during the training period produced significantly greater improvements in upper body strength measures, knee extension peak torque and lean tissue mass, relative to a maltodextrin placebo.22
In contrast, a recent study on whey supplementation in patients with HIV did not find gains in muscle mass or strength in sedentary subjects or those involved in training.24
Daily consumption of casein has been reported to produce greater gains in lean mass and greater reductions in weight and body fat loss relative to subjects consuming a whey hydrolysate.23 In this study, two groups of 14 overweight males participated in a resistance training study and consumed a hypocaloric protein-enriched diet for 12 weeks. The additional protein was provided by taking 1.5g/kg daily of either whey hydrolysate, or what the authors referred to as ?casein?. This was in fact a mixture of milk protein concentrate, calcium sodium caseinate, L-glutamine, whey protein concentrate, dried egg white, vitamin E, beta-carotene, selenium and additional minerals. This combination supplement produced greater gains relative to the whey hydrolysate for lean mass (4 kg vs 2 kg), total strength (59 per cent vs 29 per cent) and increased fat loss (-8 per cent vs -4 per cent).23 Although these findings are impressive, they reflect the effects of supplementing with a number of bioactive compounds (including whey and casein), rather than the effects of casein per se.
Despite the theoretical basis that whey protein can increase muscle growth more effectively than other protein sources, studies assessing long-term supplementation are not totally conclusive. Existing research has highlighted the importance of protein timing relative to exercise, to maximise protein synthesis and strength gains.25
It is possible that some conflicts regarding the ability of whey protein to increase muscle mass during training may have arisen from the failure to ensure that whey was taken immediately after exercise.
Maintain Muscle Mass
Whey protein appears to be the ideal protein source for incorporation into post-exercise recovery foods designed to return the body to its pre-exercise state as quickly as possible. Consumption of only 10g protein immediately after training can be effective at increasing muscle mass and strength.25
Whey would also appear suited to maintaining muscle mass, reducing muscle fatigue, minimising infection, improving gut health and even increasing antioxidant protection. The potential benefits of whey supplementation would be of importance to athletes and to improve clinical outcomes in disease states. Currently the most studied is HIV26,27 but beneficial effects have also been reported in patients with chronic hepatitis B.28
It must be stressed that the effects of any protein will be dependent upon its bioactive components. In whey these include alpha-lactalbumin, growth factors, bioavalable seleno-compounds and lactoferrin, the effects of which will reflect processing methods.1
References
1. Kinsella and Whitehead. Proteins in whey: chemical, physical, and functional properties. Adv Food Nutr Res 1989;33; 343-8.
2. Bounous and Gold. The biological activity of undenatured dietary whey proteins: role of glutathione. Clin Invest Med 1991;14:296-309.
3. Hambraeus, et al. Nitrogen and protein components of human milk. Acta Paediatr Scand 1978;67;561-5.
4. Miller, et al. Casein: a milk protein with diverse biologic consequences. Proc Soc Exper Biol Med 1990;195;143-159.
5. Boirie Y, et al. Slow and fast dietary proteins differentially modulate postprandial protein accretion. Proc Natl Acad Sci 1997;94;14930-5.
6. Grant. Anti-nutritional effects of soybean: a review. Prog Food Nutr Sci 1989;13;317-48.
7. Cassidy, et al. Biological effects of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. Am J Clin Nutr 1994;60;333-40.
8. Child R. Running and tissue damage. In Improving performance in middle and long distance running: A scientific approach to race preparation. Eds. Fallowfield and Wilkinson, John Wiley and Sons, Chichester, 1999. p122-39.
9. Reid. Muscle fatigue: mechanisms and regulation. In. Exercise and oxygen toxicity: a handbook. Eds. Sen, Packer and Hanninen, Elsevier Science, Amsterdam, Holland. 1999.
10. Saxton, et al. Indices of free-radical-mediated damage following maximum voluntary eccentric and concentric muscular work. Eur J Appl Physiol Occup Physiol 1994;68;189-93.
11. Bassit, et al. The effect of BCAA supplementation upon the immune response of triathletes. Med Sci Sports Exerc 2000;32;1214-9.
12. Child R, et al. Physiological and biochemical effects of whey protein and ovalbumin supplementation in healthy males. Med Sci Sports Exerc 2003;35,S270.
13. Lands, et al. Effect of supplementation with a cysteine donor on muscular performance. J Appl Physiol 1999;87;1381-5.
14. Layman. Role of leucine in protein metabolism during exercise and recovery. Can J Appl Physiol 2002;27;646-63.
15. Jefferson and Kimball. Translational control of protein synthesis: implications for understanding changes in skeletal muscle mass. Int J Sport Nutr Exerc Metab 2001;11;S143-9.
16. Phillips, et al. Resistance training reduces the acute exercise induced increase in muscle protein turnover. Am J Physiol 1999;276; E118-24.
17. Dangin et al. The rate of protein digestion affects protein gain differently during aging in humans. J Physiol. (in press).
18. Dangin, et al. The digestion rate of protein is an independent regulating factor of postprandial protein retention. Am J Physiol Endocrinol Metab 2001;280; E340-E348.
19. McLean, et al. Branched-chain amino acids augment metabolism while attenuating protein breakdown during exercise. Am J Physiol 1994;267,E1010-E1022.
20. Louard, et al. Overnight branched chain amino acid infusion causes sustained suppression of muscle proteolysis. Metabolism 1995;44:424-9.
21. Blomstrand, et al. BCAA intake affects protein metabolism in muscle after but not during exercise in humans. Am J Physiol Endocrinol Metab 2001;281:E365-E374.
22. Burke, et al. The effect of whey protein supplementation with and without creatine monohydrate combined with resistance training on lean tissue mass and muscle strength. Int J Sport Nutr Exerc Metab 2001;11;349-64.
23. Agin, et al. Effects of whey protein and resistance exercise on body cell mass, muscle strength and quality of life in women with HIV. AIDS 2001;15;2431-40.
24. Demling and De Santi. Effect of a hypocaloric diet, increased protein intake and resistance training on lean mass gains and fat mass loss in overweight police officers. Ann Nutr Metab 2000;44;21-9.
25. Esmarck, et al. Timing of postexercise protein intake is important for muscle hypertrophy with resistance training in elderly humans. J Physiol 2001;535;301-11.
26. Buchman. Glutamine for the gut: mystical properties or an ordinary amino acid. Curr Gastroenterol Rep 1999;1:417-23.
27. Micke, et al. Oral supplementation with whey proteins increases plasma glutathione levels of HIV infected patients. Eur J Clin Invest 2001;31;171-8.
28. Watanabe, et al. Nutritional therapy of chronic hepatitis by whey protein (non-heated). J Med 2000;31;283-302.
Robert Child BSc, MSc, PhD is CEO of Alimentarius Ltd., an independent consultancy, specialising in obtaining advertising approval for health claims for functional foods and nutraceuticals.
Respond: [email protected]
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