Calories versus Macros for Strength-Power Athletes?
Food provides the body with the energy to do work andthe building blocks for growth and repair of body tissue, principally in theform of the macronutrients: protein, fats and carbohydrates. Carbohydrates areprimarily an energy source, proteins are primarily building blocks formingstructural and functional components of the body, and fats provide both. Fibre,water and micronutrients are critical to the effective utilisation of thesemacronutrients in the body, however these will not be addressed today. The term‘calories’ describes the potential energy contained within macronutrients.
Resistance training is the primary focus in the strength-powerdisciplines of weightlifting and powerlifting. Such athletes rely on muscularstrength, power and explosivity to lift maximal weight, usually for single orlow volume repetitions. In competition, as athletes compete in specific bodyweightclasses, strength to bodyweight ratio can be arguably as important as absolutestrength.
Muscle strength is largely determined by muscle size andthe ability to execute a rapid and coordinated muscle contraction (Cribb etal., 2007; Maughan and Gleeson, 2010). Resistance training exerts mechanical loadstress on the body, providing a stimulus for adaptations that increase musclestrength – such as muscle growth and more efficient energy production (MacDougallet al., 1977; Kadi et al., 2004; Andersen et al., 2005).
Skeletal muscleis highly plastic in response to exercise stimuli. Muscle hypertrophytranslating to enhanced performance can be seen within a matter of weeks of anew training regime, in both trained and untrained subjects (Kadi et al., 2004; Andersen et al., 2005; Cribbet al 2007). Increases in muscle mass are primarily driven by increases in theamount of muscle protein. Considering this, it is perhaps unsurprisingthat nutrient availability modulates the body’s adaptations in response totraining, given that muscle growth alone requires energy and building blocks …i.e. the things provided by food. So, a basal level of energy (calories) and essential macronutrients appearsnecessary for strength performance.
Whilst this is clear, the relative importance of totalcalories versus specific macronutrient intake is unclear. Although there is anemphasis on consuming a high protein diet to support muscle hypertrophy withinthe strength-power athlete community, evidence for an optimal nutritionalstrategy for such athletes remains equivocal. Reflecting this, current nutritional guidelines forresistance training athletes differ between institutions. For example,the 2009 position stand from the American College of Sports Medicine (ACSM)recommends a daily protein intake of 1.2-1.7g/kg bodyweight (American Dietetic Association et al.,2009), whereas the 2018 position stand by the International Society for SportsNutrition (ISSN) recommends protein intake of 1.4-2.0g/kg bodyweight,increasing to 3.0g/kg for those on a hypocaloric diet and looking to retainlean mass (Kerksick et al., 2018).
The reason for this lack of clarity is the variance inthe findings of research on the matter. The reason why research findings differ?It is likely driven by differences in the subjects, exercise and nutritional interventionsmade in the different studies. Much research has been performed in untrainedand overweight populations, and it might be expected that their response totraining and dietary change may differ to that of an experienced strength-powerathlete whose physiology has already undergone significant training adaptations(Kadi et al., 2004; Andersen etal., 2005; Willoughby et al., 2007; Kerksick et al., 2010; Kreider et al., 2011; Weisgarber et al.,2012; Herda et al., 2013; Morton et al., 2018). I
So, what do weknow about total calories (regardless of macronutrient composition) versus specificmacronutrient intake for strength performance in experienced resistance trainedathletes?
Before webegin, it is worth noting that we will not address nutrient intake during acuteweight cutting phases where extreme calorie deficits, dehydration and otherprotocols may be undertaken preceding a competition to enable an athlete tocompete in a certain bodyweight class.
Calorie versusmacronutrient intake: strength performance
Many studiesthat have investigated the impact of diet on strength performance altered both macronutrient and total calorieintake (Hoffman et al., 2009; Bird et al., 2013; Antonio et al., 2015; Antonioet al., 2016a). This means it is not possible to conclude whether anyobserved performance effect is due to the change in total calories or specificmacronutrients. However, it isinteresting that the impact of increasing total macronutrient and calorie intakeon strength performance was mixed … some showed that diet did not impactperformance (Hoffman et al., 2009; Antonio et al., 2015, Antonio et al., 2016a),some showed it did (Hoffman et al., 2009; Bird et al., 2013). What this doesindicate is that increasing calorie or macronutrient intake does notnecessarily result in strength performance improvements … perhaps there is anupper limit to the body’s capacity to use food for training adaptations, whichwould be consistent with research that suggests an upper limit to the amount of protein that can be used for muscle building from any one meal (Moore et al., 2009; Atherton et al.,2010; Moore et al., 2012; Areta et al., 2013; Macnaughton et al., 2016; Schoenfeld and Aragon, 2018).
If calories aremore significant to strength performance than macronutrient composition, therewould be no impact on performance if macronutrient composition is manipulatedwhilst maintaining same total calorie intake. Looking at studies that haveperformed such manipulations, the picture is unclear (Burke et al., 2001;Hoffman et al., 2006; Kerksick et al., 2006; Cribb et al., 2007; Snijders etal., 2015). In each of these studies the participants undertook a newresistance training regime alongside any dietary change, and strengthperformance increased significantly regardless of diet; it is possible theimpact of this on strength performance was large enough to mask an impact ofdiet composition, particularly considering the variability in absolute and relative strength performance between participants and across time.
In four of thefive studies, the baseline diet of participants was high protein, within or abovethe recommended range of the ACSM and the ISSN for resistance trained athletes(>1.3g protein/kg bodyweight per day) (Burke et al., 2001; Kerksick et al.,2006; Cribb et al., 2007; AmericanDietetic Association et al., 2009; Snijders et al., 2015; Kerksick et al., 2018).Considering the hypothesis that there is an upper limit to the amount ofdietary protein that can be utilised by the body for muscle protein synthesisat any one time, this mayexplain why no strength performance effect is seen when proteinconsumption was further elevated (Mooreet al., 2009; Atherton et al., 2010; Moore et al., 2012; Areta et al., 2013; Macnaughtonet al., 2016; Schoenfeld and Aragon, 2018). It is also possible that areduction in the intake of carbohydrate as protein intake increased (tomaintain the same total calorie intake) had a balancing negative impact onstrength performance, as theenergy to drive the explosive and powerful skeletal muscle contractions inresistance exercise is derived principally from carbohydrates via anaerobic respiration. Whilst the typical durationand intensity of a whole-body resistance training session is not expected to exhaust muscle glycogen stores, such sessions have been shown to reduce muscle glycogen stores by up to 40%, itis still significant (MacDougall et al., 1977; Tesch et al., 1986; Robergs et al., 1991).
Calorie versusmacronutrient intake: body composition
Multiple studieshave focussed on manipulating macronutrient intake and assessing the impact onbody composition in resistance trained athletes. As strength-power athletescompete in weight class divisions, maximising strength to bodyweight is animportant factor in performance. Athletes therefore aim to optimise their leanmass to total body weight ratio, and so body fat percentage.
Current researchsupports a role of protein in promoting addition of lean mass and reducing bodyfat percentage. In four of the five studies manipulating macronutrient intakewithout changing total caloric intake (Table 2), at least one marker of bodycomposition (lean mass, fat mass and / or trained muscle size) significantlyimproved with higher protein intake (Burke et al., 2001; Kerksick et al., 2006;Cribb et al., 2007; Snijders et al., 2015). In the fifth study, although therewas a trend to higher lean mass accretion in the higher protein group, it wasnot statistically significant (Hoffman et al., 2006).
Where totalcalorie intake was increased by increasing protein intake, there was nosignificant impact of the increase on body composition, despite the fact the calorie intake of this groupexceeded that of the lower group by approximately 300-800kcal per day (Hoffmanet al., 2009; Antonio et al., 2014; Antonio et al., 2015; Antonio et al., 2016a;Antonio et al., 2016b). This may indicate the athletes were able to utilise theadditional energy, perhaps suggesting they were previously hypocaloric(Trexler, Smith-Ryan and Norton, 2014). It could also indicate the athleteswere able to utilise the additional protein for the turnover of tissue otherthan muscle.
Currentevidence remains equivocal as to the relative significance of total caloriesand macronutrient composition to strength performance in resistance trainedathletes. Evidence does support a significant role for protein in thepreservation and accretion of lean mass in response to resistance training.This is consistent with the current recommendation for resistance athletes tointake protein above that of the general population (American Dietetic Association et al., 2009; Kerksick etal., 2018). As muscle size is correlated with muscle strength (Cribb et al., 2007; Maughan andGleeson, 2010, p15), it might be hypothesised that over time such an increasein lean mass will contribute to strength gains.
It is perhapstoo simplistic to try and consider the body’s ‘energy’ and ‘building block’requirements independently; any macronutrient can provide both, differentmacronutrients can be converted into common ‘building blocks’, and maximal activationof the mTORC1 growth pathway requires the presence of both energy and certain buildingblocks. As such, use of any macronutrient for energy or as a building block islikely dependent on the relative energy and synthetic needs of the body at agiven point in time.
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