WHEY PROTEIN ISOLATE

Key conclusions

• An acute exercise stimulus, especially resistance training, and protein intake stimulate muscle protein synthesis, and their action is synergistic when protein is consumed before or after resistance training. The authors note at the same time that the anabolic effect of exercise lasts at least 24 hours after training, though it weakens over time.
• The position statement indicated that for building muscle mass and maintaining it in most physically active people, a total daily protein intake at the level of 1.4 to 2.0 g/kg of body weights sufficient, while in periods of energy deficit in people training for strength, 2.3 to 3.1 g/kg of body weight dailymay be needed in order to maximise maintenance of lean body mass. The authors also mention data suggesting that intake above 3.0 g/kg of body weight daily may favour improvement in body composition in people training for strength.
• The authors report that the general recommendation for a single serving for maximising muscle protein synthesis is around 0,25 g/kg masy ciała or 0.25 g/kg of body weight or 20 to 40 g,depending on, among others, age and the nature of the exertion. Such a serving should deliver around 700 to 3000 mg of leucine and be spread evenly every 3 to 4 hours throughout the day.
• The position statement emphasised that quickly digested proteins containing a high proportion of exogenous amino acids and an adequate amount of leucine most effectively stimulate muscle protein synthesis. The authors also note that the type and quality of protein influence bioavailability after intake.
• The authors describe that whey protein shows an advantage over some other protein sources in the acute stimulation of muscle protein synthesis. In the cited data, whey protein stimulated muscle protein synthesis more strongly than soy protein and casein, and 25 g of whey given in a single dose intensified muscle protein synthesis and anabolic signalling more than the same total amount of protein given in 10 servings of 2.5 g..
• The position statement also cited the results of pooled analyses, according to which protein supplementation combined with resistance training was linked with an increase in lower-limb strength of 13,5 kg (95% confidence interval: 6.4 to 20.7 kg) and a mean increase in lean body mass of 0,69 kg (95% confidence interval: 0.47 to 0.91 kg) compared with placebo.
• The authors also report that whey proteins, including hydrolysates and isolates, are among the best-researched protein sources for use before and after resistance training, among others on account of their higher content of exogenous amino acids and leucine, good solubility and favourable digestion kinetics. The position statement also noted that a larger proportion of exogenous amino acids from whey proteins reaches the peripheral tissues than in the case of some other sources, such as soy.

Key conclusions

• The position statement stated that a protein supplement usually delivers 20 to 50 g of protein in a single serving, and the protein source can be, among others, whey, casein, milk, egg or soy. The authors also note that some such products may contain additional ingredients, which aren't always based on evidence and may increase the risk of contamination.
• The authors indicated that protein supplements are used after exercise, especially after key training sessions or competitions, when the adaptation linked with protein synthesis is desired. Among practical applications, their use as a convenient form of nutrition while travelling or on a tight daily schedule was also listed.
• Among typical applications, supporting growth of lean body mass in response to resistance training was also listed. In the section on changes in body composition, the authors emphasise that protein is the basic ingredient of supplements directed at gaining lean body mass.
• In the table on changes in body composition, the authors stated that the optimal daily protein intake for supporting growth of lean body mass is around 1.6 g/kg of body weight, and intake up to 2.2 g/kg of body weight daily wasn't linked with adverse effects. In the same section, a recommended intake of around 0.3 to 0.5 g/kg of body weight per meal, 3 to 4 times daily, in close timing with training, was also indicated.
• In the section on fat tissue reduction, the authors stated that meta-analyses confirm a small but significant influence of higher protein intake on the loss of fat tissue and maintenance of lean body mass during weight loss.

Key conclusions

• The analysis included 49 studies with 1863 participants. The interventions lasted from 6 to 52 weeks, and the participants trained for strength 2 to 5 times a week.
• Protein supplementation significantly increased strength gain measured by the one-repetition maximum test. The mean extra effect was 2,49 kg (95% confidence interval: 0.64 to 4.33 kg). At the same time, no significant influence was shown on maximal voluntary contraction measured by isometric or isokinetic methods.
• Protein supplementation also significantly increased lean body mass gain. The mean extra effect was 0,30 kg (95% confidence interval: 0.09 to 0.52 kg). The authors also noted a favourable influence on the cross-section of muscle fibres and the cross-section of the thigh muscle, though for some of these indicators they marked the need for cautious interpretation.
• The analysis showed that the effect of supplementation on lean body mass was more visible in people training for strength earlier than in untrained people. In the meta-regression, training status was linked with greater effectiveness of supplementation for lean body mass changes, and in the subgroup analysis the effect was clearer in trained people.
• The effectiveness of supplementation for lean body mass gain decreased with age. The authors indicated that the effect was smaller in older people, which may partly result from lower supplementation doses used in studies of this group.
• One of the most important findings of the work was that the benefits of supplementation didn't grow further after exceeding total protein intake at the level of around 1.62 g/kg of body weight daily.The authors note that in practice it may be reasonable to aim for around 2.2 g/kg of body weight dailyif the goal is to maximise lean body mass gain, but the plateau point itself should be interpreted cautiously.
• The studies used different protein sources. Among the interventions were supplements with whey protein, casein, soy, milk protein, pea protein, food products and blends of various protein sources.
• The authors emphasise that resistance training itself remains a significantly stronger stimulus for strength and muscle mass development than adding a protein supplement. Supplementation can support this effect, but doesn't replace appropriately programmed training or proper total protein intake throughout the day.
• In the final conclusions, the authors summarise that protein supplementation may support strength and muscle mass gain during prolonged resistance training, especially when total daily protein intake is lower than around 1.6 g/kg of body weight. At the same time, they note that the significance of elements such as the exact moment of intake, the dose after training or the specific protein source appears smaller than the significance of total daily protein intake.

Key conclusions

• After pooling data from 13 randomised controlled trials, a generally positive, small to moderate influence of whey protein on the restoration of muscle function in the period from less than 24 hours to 96 hours after resistance training was shown. The authors report that the range of the effect in the temporal analysis fell between 0.4 and 0.7..
• In the temporal analysis, the size of the effect for whey protein was: <24 h: ES = 0,6, 24 h: ES = 0,4, 48 h: ES = 0,4, 72 h: ES = 0,7 ratio, and 96 h: ES = 0,4The authors note, however, that these values shouldn't be interpreted as definitive confirmation of effectiveness at each time point, but rather as a description of a general trend supporting a faster return of muscle function.
• Four of the eight included studies showed a generally favourable influence of whey protein relative to the control group, while the remaining four didn't show such an effect. At the same time, no study showed a generally negative influence of whey protein.
• In the 13 randomised controlled trials, whey protein was given in single servings of which the median dose was 25 g.. The dose range fell between 20 g and around 120 g.In 62% of the trials whey protein was given after exercise, in 23% before exercise, and in 15% both before and after exercise. In most studies supplementation was also continued during the recovery period.
• The authors emphasise that across all 13 randomised controlled trials a dose was used corresponding to the amount of whey protein recognised as sufficient for optimal anabolic response after exercise, that is around 20 g or more..
• The analysis didn't show clear benefits of whey protein in relation to creatine kinase activity and muscle soreness after resistance training. This suggests that the potential effect of supplementation concerns more the restoration of muscle function than all the classic markers of muscle damage.
• The authors draw attention to important limitations of the work. Significant heterogeneity occurred between studies, and important confounding factors may have been, among others, differences in training protocols, participants' training status, the type of control groups and the lack of full control of protein intake from the daily diet in some of the studies.
• In the final conclusions, the authors summarised that whey protein may show a small to moderate effect supporting the restoration of muscle function after resistance training, but they emphasised that the current conclusions rest on only 8 studies and 13 randomised controlled trials, so further, better-designed studies are needed.

Key conclusions

• Intake of 100 g of protein after exercise produced a greater and more prolonged anabolic response, exceeding 12 hours, than intake of 25 g of protein. The authors describe this as a dose-dependent increase in amino acid availability and intensification of protein synthesis at the level of the whole body and the muscles.
• The amino acid concentration in the plasma rose in a dose-dependent way. After intake of 25 g of protein, amino acid concentrations in the plasma were higher than after placebo for the first around 5 hours, while after intake of 100 g the increase was greater and persisted for the whole 12-hour post-meal period.
• The appearance in the circulation of amino acids from the consumed protein was significantly greater after intake of 100 g than after 25 g of protein across the whole 12-hour observation period. The authors report that over 12 hours, on average 53 ± 7 g of amino acids was released into the circulation after intake of 100 g of protein, and 16 ± 1 g after intake of 25 g.
• The incorporation of amino acids from the consumed protein into the muscles was also dose-dependent. After intake of 25 g of protein the increase was visible mainly in the first 4 hours, while after intake of 100 g the incorporation rose essentially linearly across the whole 12-hour observation period. Over 12 hours this corresponded to around 13 gthat is 13% of the consumed protein.
• Muscle protein synthesis assessed across the whole 12-hour period after exercise showed a clear dose-dependent pattern: 100 g > 25 g > placeboThe authors indicate that the rate of synthesis of myofibrillar proteins was around 20% higher after intake of 100 g of protein in the first 4 hours and around 40% higher in the period 4 to 12 hours compared with 25 g of protein.
• Protein intake also increased whole-body protein synthesis and improved total protein balance. At the same time, the influence on the rate of whole-body protein breakdown was small, and the increase in amino acid oxidation was small compared with the increase in protein synthesis. The authors emphasise that their data don't support the thesis that a larger serving of protein simply "goes to oxidation."
• In the muscles, the free concentrations of leucine, isoleucine and valine were significantly higher after intake of 100 g of protein than after 25 g of protein or placebo across the whole 12-hour post-meal period. At the same time, the general increase in anabolic signalling in the muscle cell was transient, which suggests that the longer-sustained protein synthesis was linked mainly to the prolonged availability of amino acids as a substrate.