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| With average daily protein intakes of only 90±24 g (Gillen 2017), many female athletes are probably missing the sweet spot of ~1.7g/kg/d. |
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Stuart M. Philips and colleagues are among those researchers who have been dabbling with the idea of increased protein requirements in athletes and non-athletes, young and old, sick and diseased for years (Phillips 2007; Phillips 2017). As the Canadian scientists point out in one of their latest reviews (Phillips 2017), there are two main methods to measure human beings protein balance. There is...
- measurement of an individual's nitrogen balance - This method has been used for more than 60 years, despite its various shortcomings (Young 1986); and it is also the methodology that underpins the "RDA", a term of which Phillips writes in his review in Front Nutr. in 2017 that it would "inherently imply that the protein intake is 'recommended,' and it is all that you are 'allowed' to eat" (Phillips 2017). Now, I don't have to quote an expert for you to understand that this is, "[o]f course, [...] strictly speaking [not] true" (ibid.).
- the more recent alternatives are the indicator amino acid oxidation (IAAO) method and the 24h-indicator amino acid oxidation and balance method (24h-IAAO/IAAB)- Having been explicitly developed as an alternative to the nitrogen balance (free reviews can be found in Elango et al. 2008 & 2012), they yield significantly higher values for optimal protein intakes in than nitrogen balance studies, especially in older individuals.
Even though, I believe that this is the first time some of you read about this, the above ain't 'news' in the strict sense of the word and wouldn't have made it into this article, if it wasn't necessary to know that the IAAO method has recently been applied by Wooding et al. (2017) to determine a dietary protein requirement in active females performing variable-intensity intermittent exercise using the indicator amino acid oxidation (IAAO) method.
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| If we go by the Institute of Medicine's AMDR concept, 0.8g/kg is the absolute minimum, not the recommended protein intake. |
Optimal intakes for our exemplary 55-year-old man, on the other hand, would be somewhere within the AMDR of 65–228 g protein/day (assuming an energy requirement of 2,600 kcal/day or 10.9 MJ/day) - in other words, the "optimal" range, i.e. the range where the Institute of Medicine says that it takes "into account the trends related to decreased risk of disease identified in epidemiological and clinical studies" is, as Phillips highlights in his previously cited review from 2017 "well above the RDA (up to 2.8 g/kg/day) that are associated with good health".
We do already know that endurance athletes need more, much more ...
As Wooding et al. point out, their "group previously used the minimally-invasive indicator amino acid oxidation (IAAO) method to demonstrate that protein requirements in endurance athletes are ~50% greater than sedentary individuals" (Wooding 2017). That, however, is still a pretty conservative estimate, as it marks the protein requirements, not the optimal intakes that will "maximises whole body protein synthesis" and thus enhance recovery from, and potentially adaptation to, an exercise stimulus" (ibid.) - a value the scientists sought to determine in their latest study which involved six healthy, active young adult females (see Table 1).
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| Figure 1: Modified LIST in which participants followed an audio prompt to complete the variable-intensity intermittent exercise pattern 10 times per block. There were four blocks separated by 5-min breaks, totaling 75-min of exercise plus a 5-min warm-up and cool-down at a self-selected pace (Wooding 2017). |
"Participants were required tobe healthy (PAR-Q+), have habitual activity levels of more than 45 min/d on 5 d/wk of moderate vigorous physical activity (I-PAQ for adults aged 15-69), a predicted VO2max ≥44.6 mL O2/kg/min (Leger Multistage Fitness Test), no current use of hormonal contraceptives, and a predictable menstrual cycle (25-33d) during the previous year as determined by interviews and the participants’ records of the 2-3 months prior to study enrollment" (Wooding 2017).Each participant completed 5-7 metabolic trials (n = 36) during the predicted luteal phase. The women consumed a 2-d adaptation diet containing 1.2 g/kg/d of protein prior to each trial. Wooding et al. chose this intake "in order to minimize metabolic variability during the trial day" and to "provide a level that was previously determined to be sufficient for non-exercising males by IAAO" (ibid.) (15). These adaptation diets contained sufficient energy to meet the subjects' individual habitual daily caloric expenditure of ~2700kcal/d.
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| Figure from an exemplary study by Kriengsinyos et al. (2002), |
As Elango et al. explain in their 2012 paper, "the IAAO technique is based on the concept that when one indispensable amino acid (IDAA) is deficient for protein synthesis, then all other amino acids including the indicator amino acid (another IDAA, usually L-[1-13C]phenylalanine) are in excess and are therefore oxidized" (Elango 2012). That's logical, after all, dietary protein can only either be stored or oxidized. If a rate limiting amino acid is missing, storage is not an option and oxidation will take place. As the intake of said limiting amino acid increases, the oxidation of the indicator amino acid will decrease - a decrease that reflects the increasing incorporation of amino acids into protein. Yet, once the requirement is met for the limiting amino acid, there will be no further change in the oxidation of the indicator amino acid with increasing intake of the test amino acid (see breaking point in the figure). The inflection point where the oxidation of the indicator amino acid stops decreasing and reaches a plateau is referred to as the ‘breakpoint’. The breakpoint, identified with the use of two-phase linear regression analysis, will then "indicate the estimated average requirement (EAR) of the limiting (test) amino acid" (Elango 2012) - in the example from Kriengsinyos et al. (2002), the breakpoint for lysine is 36mg/kg/d.
"Briefly, the test involved four 15-min blocks in which a 17-m variable-intensity shuttle pattern was repeated 10 times with 5-min rests between each block. The entire test was 75 min in length, which also included a 5-min warm-up and cool-down at a self-selected pace. The running pace in our study was based on the percentage of average maximum speed obtained by the entire group of participants during the aerobic assessment (3.45m/s) instead of the percentage of individual VO2max. In this way, the same audio prompt was used for all participants with the following 17-m shuttle paces: 1.7m/s (walk), 2.1m/s (jog) 3.1m/s (run), and an all-out sprint. The average energy expenditure during the LIST was 8.7 ± 0.2 kcal/kg (range 8.5-9.1kcal/kg, determined from accelerometer)" (Wooding 2017).Following exercise, participants consumed their first of eight hourly mixed meals containing the test protein intake (0.2-2.66 g/kg/d) and sufficient energy and CHO content in the form of test beverages containing crystalline amino acids, protein-free powder, fruit flavoring powder, grapeseed oil, and maltodextrin as well as protein-free cookies. The actual measurement was done by including a priming dose of NaH13CO2 (0.176 mg/kg) and L-[1-13C]phenylalanine (1.86 mg/kg) in every hourly meal beginning at meal #5. The turnover of this tracer was determined from urinary [13C]phenylalanine enrichment.
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| Figure 2: Relationship between protein intake and F13CO2. Six participants completed 5-7 metabolic trials each (n=36). F13CO2 breakpoint was used to estimate protein requirements and recommended daily allowance (Wooding 2017). |
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| Overview of new, IAAO based protein intake minimums and recommendations in different groups of athletes; the figures across the bar denote the values in units of the current RDA of 0.8 g protein /kg/d (Wooding 2017 women in team sports; Kato 2016 male endurance athletes; Bandegan 2017 bodybuilding men) |
What the study adds to the existing evidence are definite numbers for the minimal and recommended protein intake of female team-sports athletes, a subject group that is often overlooked in clinical research.
More specifically, Wooding's data reveals that an acute bout of variable-intensity exercise results in an increase of young women's protein requirements to 1.41 g/kg/d and an approximate RDA, i.e. an intake that can be expected to be sufficient for 95% of the population, of 1.71 g/kg/d. As previously hinted at, this result is consistent with the scientists' previous observations in endurance-trained males on a day in which they trained (Kato 2016) and in bodybuilders on a rested day (Bandegan 2017) - all numbers you know from the SuppVersity Facebook or Twitter News | Comment!
- Elango, Rajavel, Ronald O. Ball, and Paul B. Pencharz. "Indicator amino acid oxidation: concept and application." The Journal of nutrition 138.2 (2008): 243-246.
- Elango, Rajavel, Ronald O. Ball, and Paul B. Pencharz. "Recent advances in determining protein and amino acid requirements in humans." British Journal of Nutrition 108.S2 (2012): S22-S30.
- Gillen, Jenna B., et al. "Dietary protein intake and distribution patterns of well-trained dutch athletes." International journal of sport nutrition and exercise metabolism 27.2 (2017): 105-114.
- Hoerr, ROBERT A., et al. "Recovery of 13C in breath from NaH13CO3 infused by gut and vein: effect of feeding." American Journal of Physiology-Endocrinology And Metabolism 257.3 (1989): E426-E438.
- Kato, Hiroyuki, et al. "Protein Requirements Are Elevated in Endurance Athletes after Exercise as Determined by the Indicator Amino Acid Oxidation Method." PloS one 11.6 (2016): e0157406.
- Phillips, Stuart M., Daniel R. Moore, and Jason E. Tang. "A critical examination of dietary protein requirements, benefits, and excesses in athletes." International journal of sport nutrition and exercise metabolism 17.s1 (2007): S58-S76.
- Phillips, Stuart M. "Current Concepts and Unresolved Questions in Dietary Protein Requirements and Supplements in Adults." Frontiers in Nutrition 4 (2017).
- Thomas, D. Travis, Kelly Anne Erdman, and Louise M. Burke. "Position of the academy of nutrition and dietetics, Dietitians of Canada, and the American college of Sports Medicine: Nutrition and athletic performance." Journal of the Academy of Nutrition and Dietetics 116.3 (2016): 501-528.
- Trumbo, Paula, et al. "Dietary reference intakes for energy, carbohydrate, fiber, fat, fatty acids, cholesterol, protein and amino acids." Journal of the American Dietetic Association 102.11 (2002): 1621-1630.
- Wooding, Denise J., et al. "Increased Protein Requirements in Female Athletes after Variable-Intensity Exercise." Medicine and science in sports and exercise (2017).
- Young, Vernon R. "Nutritional balance studies: indicators of human requirements or of adaptive mechanisms?." The Journal of nutrition 116.4 (1986): 700-703.