Nutrition Publication

NNIW69 - Sports Nutrition: More Than Just Calories – Triggers for Adaptation

Editor(s): R. Maughan, L. Burke. Sports Nutrition Series 69

Diet significantly affects athletic performance, and adoption of a dietary strategy that meets an athlete’s nutrition goals will maximize the possibility of competitive success. Over the years, the focus has shifted from a high intake of (animal) protein to the role of carbohydrate and water. Today, there is a growing recognition that the primary role of sports nutrition may be to promote the adaptations taking place in muscle and other tissues in response to the training stimulus. There is also much interest in the implications o manipulation of the fat and carbohydrate content of the diet.This publication contains the proceeding of the 69th Nestlé Nutrition Institute Workshop held in Hawaii in October 2010. The aim of the workshop was to explore the effects of nutritional manipulations on the metabolic responses to acute and chronic exercise. Another goal was to further identify the possible role of these dietary interventions in promoting adaptive changes in muscle, adipose tissues and other potential sites of limitation to exercise performance. Papers cover the three macronutrients carbohydrate, fat and protein, plus an additional chapter on water, together with the accompanying discussions.

Related Articles

Carbohydrate Ingestion during Exercise: Effects on Performance, Training Adaptations and Trainability of the Gut

Author(s): A. Jeukendrup, J. McLaughlin

Carbohydrate feeding has been shown to enhance endurance performance. During exercise of 2 hours or more, the delivery of carbohydrates to the muscle is the crucial step and appears to be limited by intestinal absorption. Factors of interest include practical ways to overcome this limitation, as well as the positive and negative effects of chronic carbohydrate supplementation. There is evidence that intestinal absorption can, at least partly, be overcome by making use of multiple transportable carbohydrates. Ingestion of these carbohydrates may result in higher intestinal absorption rates and has been shown to lead to higher rates of exogenous carbohydrate oxidation which can result in better endurance performance. It also seems possible to increase the absorptive capacity of the intestine by adapting to a high carbohydrate diet. Carbohydrate supplementation during exercise has been suggested to reduce training adaptations but at present there is little or no evidence to support this. Despite the fact that it has long been known that carbohydrate supplementation can enhance endurance performance there are still many unanswered questions. However, there is potential to develop strategies that enhance the delivery of carbohydrates and thereby improve endurance performance.

Altering Endogenous Carbohydrate Availability to Support Training Adaptations

Author(s): A. Philp, L. Burke, K. Baar

Glycogen was first identified in muscle over a century and a half ago. Even though we have known of its existence and its role in metabolism for a long time, recognition of its ability to directly and indirectly modulate signaling and the adaptation to exercise is far more recent. Acute exercise induces a number of changes within the body (i.e. sympathetic nervous system activation and elevation of plasma free fatty acids) and muscle (increased AMP-activated protein kinase (AMPK) activity and fat metabolism) that may underlie the long-term adaptation to training. These changes are also affected by glycogen depletion. This review discusses the effect of exercise in a glycogen-depleted state on metabolism and signaling and how this affects the adaptation to exercise. Although “training low” may increase cellular markers associated with training and enhance functions such as fat oxidation at sub-maximal exercise intensities, how this translates to performance is unclear. Further research is warranted to identify situations both in health and athletic performance where training with low glycogen levels may be beneficial. In the meantime, athletes and coaches need to weigh the pros and cons of training with low carbohydrate within a periodized training program.

Metabolic Regulation of Fat Use during Exercise and in Recovery

Author(s): L. Spriet

Fat is an important fuel for exercise but plays a secondary role to carbohydrate. Increasing fat use during exercise can decrease the reliance on carbohydrate (CHO) and spare CHO for later in training sessions or competitions that depend on CHO for success. The pathways that metabolize and oxidize fat are activated more slowly than CHO at the onset of exercise and reach a maximum at moderate exercise intensities. As exercise intensity increases to ~75% VO2max and beyond, fat metabolism is inhibited: using CHO will increase the amount of energy produced per litre of oxygen consumed. The capacity for fat use during exercise is increased by aerobic training and the dietary combination of little or no CHO intake and high fat intake. Fat oxidation is very dependent on the mitochondrial volume of muscle but other key sites of regulation include release of fat from storage forms and fat transport across plasma and mitochondrial membranes. This chapter examines the control of fat metabolism during moderate and intense exercise with an emphasis on human findings and the adaptations that occur with aerobic training and other acute nutritional manipulations. Recent work using molecular and cellular compartmentalization techniques have advanced the knowledge in this area.

Fat Adaptation Science: Low-Carbohydrate, High-Fat Diets to Alter Fuel Utilization and Promote Training Adaptation

Author(s): J. Hawley

The effect of manipulating an individual’s habitual diet on skeletal muscle fuel utilisation has been of longstanding interest to scientists and it is now well established that changes in dietary intake that alter the concentration of blood-borne substrates and hormones cause substantial perturbations in the macronutrient storage profile of muscle and exert profound effects on rates of substrate oxidation during exercise. Only recently, however, has it become appreciated that nutrient-exercise interventions can modulate many contraction-induced responses in muscle, and that fuel availability per se provides a ‘trigger’ for adaptation. Consumption of low-carbohydrate (CHO), high-fat diets in the face of endurance training alters patterns of fuel utilization and subsequent exercise responses. Human studies show how low-CHO, fat-rich diets interact with specific contractile stimulus to modulate many of the acute responses to exercise, thereby promoting or inhibiting subsequent training adaptation.

Dietary Protein to Support Muscle Hypertrophy

Author(s): L. van Loon, M. Gibala

Intact protein, protein hydrolysates, and free amino acids are popular ingredients in contemporary sports nutrition, and have been suggested to augment post-exercise recovery. Protein and/or amino acid ingestion stimulates skeletal muscle protein synthesis, inhibits protein breakdown and, as such, stimulates muscle protein accretion following resistance and endurance type exercise. This has been suggested to lead to a greater adaptive response to each successive exercise bout, resulting in more effective muscle reconditioning. Despite limited evidence, some basic guidelines can be defined regarding the preferred type, amount, and timing of dietary protein that should be ingested to maximize post-exercise muscle protein accretion. Whey protein seems most effective in stimulating muscle protein synthesis during acute post-exercise recovery. This is likely attributable to its rapid digestion and absorption kinetics and specific amino acid composition. Ingestion of approximately 20 g protein during and/or immediately after exercise is sufficient to maximize post-exercise muscle protein synthesis rates. Co-ingestion of a large amount of carbohydrate or free leucine is not warranted to further augment post-exercise muscle protein synthesis when ample protein is already ingested. Future research should focus on the relevance of the acute anabolic response following exercise to optimize the skeletal muscle adaptive response to exercise training.

Effect of Protein, Dairy Components and Energy Balance in Optimizing Body Composition

Author(s): S. Phillips, M. Zemel

Weight loss is achieved through the consumption of a hypoenergetic diet and/or increased energy expenditure through exercise. While weight loss is associated with numerous benefits the pattern of weight loss in terms of body composition changes is not always studied. In our view, the optimum pattern of weight loss is one in which fat mass is lost and lean mass is preserved. The preservation of lean mass has important consequences due to the role of this tissue in contributing to basal metabolic rate, controlling glycaemia, and contributing to lipid oxidation. We also propose that a preservation of lean mass would have important consequences in resisting weight regain after loss. We review dietary practices, including reduced consumption of dietary carbohydrate, consuming higher than recommended dietary protein, with an emphasis on dairy sources, as well as dietary calcium, to accelerate the loss of fat mass during dieting and preserve lean mass. Available evidence suggests that each practice has a highly plausible mechanistic and growing clinical rationale in terms of efficacy in promoting fat mass loss and lean mass retention during a hypoenergetic diet.

Effect of Cell Hydration on Metabolism

Author(s): F. Lang

Prerequisites for cell survival include avoidance of excessive cell volume alterations. Cell membranes are highly permeable to water, which follows osmotic gradients. Thus, cell volume constancy requires osmotic equilibrium across cell membranes. Cells accumulate osmotically active organic substances and compensate their osmolarity by lowering cytosolic Cl--concentrations. Following cell shrinkage, regulatory cell volume increase is accomplished by ion uptake (activation of Na+,K+,2Cl--cotransport, Na+/H+-exchange in parallel to Cl-/HCO3--exchange and Na+-channels), by cellular accumulation of organic osmolytes (e.g. myoinositol, betaine, phosphorylcholine, taurine) as well as by proteolysis leading to generation of amino acids and glycogenolysis generating glucosephosphate. Following cell swelling, cell volume is restored by ion exit (activation of K+-channels and/or anion channels, KCl-cotransport, parallel activation of K+/H+-exchange and Cl-/HCO3--exchange), release or degradation of organic osmolytes as well as stimulation of protein synthesis and of glycogen synthesis. The activity of cell volume regulatory mechanisms is modified by hormones, transmitters and drugs, which thus influence protein and glycogen metabolism. Moreover, alterations of cell volume modify generation of oxidants and the sensitivity to oxidative stress. Deranged cell volume regulation significantly contributes to the pathophysiology of several disorders such as liver insufficiency, diabetic ketoacidosis, hypercatabolism, ischemia, and fibrosing disease.

Practical Nutritional Recommendations for the Athlete

Author(s): R. Maughan, L. Burke

The aim of training is to achieve optimum performance on the day of competition via three processes or paradigms; training hard to create the required training stimulus, training smart to maximise adaptations to the training stimulus, and training specifically to fine-turn the behaviours or physiology needed for competition strategies. Dietary strategies for competition must target the factors that would otherwise cause fatigue during the event, promoting an enhancement of performance by reducing or delaying the onset of these factors. In some cases, the nutritional strategies needed to achieve these various paradigms are different, and even opposite to each other, so athletes need to periodise their nutrition, just as they periodise their training program. The evolution of new knowledge from sports nutrition research, such as presented in this book, usually starts with a stark concept that must be further refined; to move from individual nutrients to food, from ‘one size fits all’ to the individual needs and practices of different athletes, and from single issues to an integrated picture of sports nutrition. The translation from science to practice usually requires a large body of follow-up studies as well as experimentation in the field.