Considerable debate has taken place over the safety and validity of increased protein intakes for both weight control and muscle synthesis. The advice to consume diets high in protein by some health professionals, media and popular diet books is given despite a lack of scientific data on the safety of increasing protein consumption. The key issues are the rate at which the gastrointestinal tract can absorb amino acids from dietary proteins (1.3 to 10 g/h) and the liver’s capacity to deaminate proteins and produce urea for excretion of excess nitrogen. The accepted level of protein requirement of 0.8g · kg−1 · d−1 is based on structural requirements and ignores the use of protein for energy metabolism. High protein diets on the other hand advocate excessive levels of protein intake on the order of 200 to 400 g/d, which can equate to levels of approximately 5 g · kg−1 · d−1, which may exceed the liver’s capacity to convert excess nitrogen to urea. Dangers of excessive protein, defined as when protein constitutes > 35% of total energy intake, include hyperaminoacidemia, hyperammonemia, hyperinsulinemia nausea, diarrhea, and even death (the “rabbit starvation syndrome”). The three different measures of defining protein intake, which should be viewed together are: absolute intake (g/d), intake related to body weight (g · kg−1 · d−1) and intake as a fraction of total energy (percent energy). A suggested maximum protein intake based on bodily needs, weight control evidence, and avoiding protein toxicity would be approximately of 25% of energy requirements at approximately 2 to 2.5 g · kg−1 · d−1, corresponding to 176 g protein per day for an 80 kg individual on a 12,000kJ/d diet. This is well below the theoretical maximum safe intake range for an 80 kg person (285 to 365 g/d).
Shane Bilsborough and Neil Mann
Sheila A. Kopp-Woodroffe, Melinda M. Manore, Christine A. Dueck, James S. Skinner and Kathleen S. Matt
Chronic energy deficit is one of the strongest factors contributing to exercise-induced menstrual dysfunction. In such cases, macro- and micronutrient intakes may also be low. This study presents the results of a diet and exercise training intervention program, designed to reverse athletic amenorrhea, on improving energy balance and nutritional status in 4 amenorrheic athletes. The 20-week program provided a daily sport nutrition supplement and 1 day of rest/week. The intervention improved self-reported energy intake (El) and balance in all participants. The program increased protein intakes for the 3 athletes with a protein deficit to within the recommended levels for active individuals. Micronutrient intakes increased, as did serum concentrations of vitamin B12, folate, zinc, iron, and ferritin. These results indicate that some amenorrheic athletes have poor nutritional status due to restricted Els and poor food selections. A sport nutrition supplement may improve energy balance and nutritional status in active amenorrheic women.
Eric C. Haakonssen, David T. Martin, Louise M. Burke and David G. Jenkins
Body composition in a female road cyclist was measured using dual-energy X-ray absorptiometry (5 occasions) and anthropometry (10 occasions) at the start of the season (Dec to Mar), during a period of chronic fatigue associated with poor weight management (Jun to Aug), and in the following months of recovery and retraining (Aug to Nov). Dietary manipulation involved a modest reduction in energy availability to 30–40 kcal · kg fat-free mass−1 · d−1 and an increased intake of high-quality protein, particularly after training (20 g). Through the retraining period, total body mass decreased (−2.82 kg), lean mass increased (+0.88 kg), and fat mass decreased (−3.47 kg). Hemoglobin mass increased by 58.7 g (8.4%). Maximal aerobic- and anaerobic-power outputs were returned to within 2% of preseason values. The presented case shows that through a subtle energy restriction associated with increased protein intake and sufficient energy intake during training, fat mass can be reduced with simultaneous increases in lean mass, performance gains, and improved health.
Armand E.O. Bettonviel, Naomi Y.J. Brinkmans, Kris Russcher, Floris C. Wardenaar and Oliver C. Witard
The nutritional status of elite soccer players across match, postmatch, training and rest days has not been defined. Recent evidence suggests the pattern of dietary protein intake impacts the daytime turnover of muscle proteins and, as such, influences muscle recovery. We assessed the nutritional status and daytime pattern of protein intake in senior professional and elite youth soccer players and compared findings against published recommendations. Fourteen senior professional (SP) and 15 youth elite (YP) soccer players from the Dutch premier division completed nutritional assessments using a 24-hr web-based recall method. Recall days consisted of a match, postmatch, rest, and training day. Daily energy intake over the 4-day period was similar between SP (2988 ± 583 kcal/day) and YP (2938 ± 465 kcal/day; p = .800). Carbohydrate intake over the combined 4-day period was lower in SP (4.7 ± 0.7 g·kg-1 BM·day-1) vs. YP (6.0 ± 1.5 g·kg-1 BM·day-1, p = .006) and SP failed to meet recommended carbohydrate intakes on match and training days. Conversely, recommended protein intakes were met for SP (1.9 ± 0.3 g·kg-1 BM·day-1) and YP (1.7 ± 0.4 g·kg-1 BM·day-1), with no differences between groups (p = .286). Accordingly, both groups met or exceeded recommended daily protein intakes on individual match, postmatch, rest and training days. A similar “balanced” daytime pattern of protein intake was observed in SP and YP. To conclude, SP increased protein intake on match and training days to a greater extent than YP, however at the expense of carbohydrate intake. The daytime distribution of protein intake for YP and SP aligned with current recommendations of a balanced protein meal pattern.
Oliver C. Witard, Ina Garthe and Stuart M. Phillips
.4 g·kg BM −1 ·day −1 actually gained a modest but significant amount of LBM. We propose that in fact of the two stimuli, the practice of resistance exercise is going to be far more potent than increasing protein intake as a stimulus for promoting retention of LBM. High Protein Diets for Health and
athletes and weight loss studies suggest that a combined approach of creating a caloric deficit, combined with increased protein intake and the implementation of a consistent exercise stimulus, appears to allow for total weight loss, while attenuating the loss of muscle mass (for review, see Phillips
Amy J. Hector and Stuart M. Phillips
al., 2014 ; Hector et al., 2015 ; Pasiakos et al., 2013 ) resulting in net negative protein balance and loss of skeletal muscle mass ( Pasiakos et al., 2013 ). To offset this negative net muscle protein balance, strategies such as increasing protein intake and the practice of resistance exercise that
.D. ( 2010 ). Increased protein intake reduces lean body mass loss during weight loss in athletes . Medicine & Science in Sports & Exercise, 42 ( 2 ), 326 – 337 . PubMed doi:10.1249/MSS.0b013e3181b2ef8e 10.1249/MSS.0b013e3181b2ef8e Need , A.G. , Horowitz , M. , Morris , H.A. , & Nordin , B
Michael J. Ormsbee, Brandon D. Willingham, Tasha Marchant, Teresa L. Binkley, Bonny L. Specker and Matthew D. Vukovich
). Furthermore, many have opted to supplement their diets with protein, despite the lack of research investigating the impact of increased protein intake during a combined strength and endurance training program. It is assumed that the long-term effect of protein supplementation during a concurrent exercise
Hellen C.G. Nabuco, Crisieli M. Tomeleri, Rodrigo R. Fernandes, Paulo Sugihara Junior, Edilaine F. Cavalcante, Danielle Venturini, Décio S. Barbosa, Analiza M. Silva, Luís B. Sardinha and Edilson S. Cyrino
weeks of increased dietary protein intake plus RT decreased MetS Z -score values, WC, %BF, and increased lean body mass of healthy older women. Increased protein intake in combination with RT was effective in increasing SMM by 3.9%, confirming previous studies of the effectiveness of this type of