Performance Nutrition

Becoming Fat Adaptive: Theory and Application

It is widely documented and accepted that carbohydrate (CHO), fat and to a lesser extent protein is utilised as fuel for exercise performance. Unlike CHO metabolism, which is closely reflects the energy requirements of the working muscle, fat utilization is multifactorial. In general, as the exercise intensity increases, there is a shift from fat-based to CHO-based fuel, known as the “crossover” point (figure 1). This finding was first shown in the late 1930’s in the classic Christensen & Hansen respiratory exchange study. In all cases the longer the exercise bout the greater the contribution from fat to total energy metabolism. 

Figure 1. Blood glucose and FFA flux rates as a function of relative exercise intensity. Hawley, J.A (2002). Effect of increased fat availability on metabolism and exercise capacity. Medicine & Science in Sports & Exercise, 34, 1485-1491.

At rest and during low to moderate-intensity exercise a relatively high percentage of the energy produced comes from FA oxidation (figure 1). Endogenous CHO stores are limited and only sufficient to fuel ~3hrs of continuous, sub-maximal exercise (70-80% VO_2max). Throughout the literature there has typically been a focus on CHO ingestion to enhance endurance performance (carb-loading). An alternative approach that could potentially enhance endurance performance would be to utilise an alternative fuel source to CHO and/or slow its normal rate during exercise. Fat, comprising intramuscular triglyceride, blood lipids and adipose tissue is in abundance and even in the leanest athlete is capable of fuelling low to moderate-intensity exercise for several days from endogenous stores! Interestingly, one of the classical responses to endurance training is that well-trained athletes have a greater capacity for to oxidise fat during submaximal exercise.

The rate of fat oxidation during exercise is predominantly determined by the rate of carbohydrate (CHO) utilization and the availability of circulating fatty acids (FA). The shift from fat to CHO as the intensity of exercise increases is as a result of the failure of FA metabolism to increase above levels seen at lower exercise intensities and a subsequent suppression of FA’s in the blood. Collectively, increased availability of glucose, the switch from Type I (slow twitch) to Type II (fast twitch) muscle fibres and the production of blood lactate (a strong inhibitor of lipolysis) all favour the use of glucose. Thus significantly minimising the rate of FA oxidised my skeletal muscle. Another reason for this substrate shift is the lower ATP production rate per unit of time from fat compared with CHO, combined with the fact that more oxygen is needed for the production of a certain amount of ATP from fat vs. CHO.

With this in mind any intervention that increases FA’s into circulation has the potential to enhance fat oxidation and slow the rate of muscle glycogen utilization. Pre-exercise muscle glycogen content is strongly correlated to subsequent endurance capacity, it is not surprising that there are numerous strategies proposed to increase FA availability and therefore promote fat metabolism.

In summary, storage of CHO in the form of glucose is limited and the ability to perform moderate to high-intensity exercise will decline with a decrease in glycogen. With this in mind, any adaptation leading to an increased capacity to enhance FA metabolism, thus sparing endogenous CHO may coincidently improve endurance capacity. Theoretically there are a few considerations to help achieve an increase plasma FA and up regulate, increase transport and oxidation of FA. The section below will provide a synopsis of techniques and strategies used.

• Endurance Training – This results in numerous structural and metabolic adaptations which favour FA oxidation. The capillary density of muscle tissue increases which develops the exchange surface area, promotes blood flow and thus the delivery of oxygen and substrates. Therefore trained muscles are able to oxidise more substrate allowing for greater oxygen consumption at maximal intensities. Additionally, trained muscles also store more fat within the cell. Thus, training enhances total fat oxidation by increasing intramuscular fat storage and by increasing maximal FA flux. Increasing FA metabolism with endurance training, will therefore preserve endogenous CHO stores, resulting in prolonging the time-period during which intense exercise can be performed. 

• Caffeine Ingestion – Caffeine is a purine and similar in structure to adenine, which forms the basis for ATP. The effects of caffeine are wide spread, effecting muscle, adipose and central nervous tissue by indirectly facilitating the level of cyclic adenosine monophosphate (cAMP). There has been a plethora of research on the effects of caffeine on metabolism, since the first exercise physiology study (Costill et al. 1978), showing a significant increase in both elevated fat oxidation and cycling time to exhaustion. The findings of various studies suggest that ingestion of 3-5mg.kg^-1 of caffeine (80kg athlete = 240-400mg.kg^-1; Dbl. Espresso ~300mg) is sufficient to create and ergogenic effect. The theory states that caffeine increases the sympathetic nervous system, which in turn liberates fatty acids from adipose tissue and/or intramuscular stores. This indirect mechanism of caffeine ingestion therefore provides a rational for its use in mobilizing FA’s and thus sparing muscle glycogen resulting in performance enhancement.

• MCT Ingestion (coconut oil) – Medium Chain Triglycerides (MCT’s) predominantly contain FA’s. Due to their small molecular size, these medium chain fatty acids (MCFA) have several physical characteristics namely more soluble with a lower melting point, which separates them from long-chain fatty acids (LCFA). Long Chain Triglycerides (LCT’s) are strong inhibiters of gastric emptying, when added to CHO where as MCT’s are emptied extremely rapidly. MCT’s require less bile and pancreatic juices for digestion, resulting in both faster and a more complete hydrolysis of MCT, this absorption rate is almost as fast as glucose. These physical properties have led to the suggestion that MCT’s could therefore be a valuable source of energy for contracting skeletal muscle during submaximal exercise. Research (Van Zyl et al. 1996) investigating ingestion of MCT on metabolism and performance has shown that during a 2hr. submaximal exercise bout (60% VO_2max) immediately followed by a 40km TT ingesting MCT’s with CHO improved TT performance by 2.5% ahead of CHO alone. These findings suggest that MCT’s are effective at increasing fat oxidation at rest and in exercise, thus reducing the rate of muscle glycogen breakdown and delaying the onset of exhaustion.

• Fasting – This is another dietary manipulation to induce specific training adaptations. The low circulating insulin vs. the elevated plasma epinephrine (adrenaline) associated with fasted exercise, stimulates rate of adipose tissue lipolysis and peripheral fat oxidation.  Consistent training with low initial glycogen levels due to dietary CHO restriction between training sessions results in beneficial effects on basal muscle glycogen content, mitochondrial oxidative capacity as well as fat oxidation during moderate intensity exercise. Recent research (Van Proeyen et al. 2011) showed that a 6-week period of consistent endurance training in a fasted state induced a greater increase of fatty acid binding protein. This finding is consistent with the prevailing opinion, that exercise in a CHO-restricted state eventually causes molecular adaptations in muscle cells to up regulate the capacity for energy production via fat oxidation. Many endurance athletes perform endurance training sessions after an overnight fast (where liver glycogen is largely depleted) hoping that performance will improve during competition when ample CHO is ingested. In this regard it has been shown that endurance training in the fasted state, compared to training with CHO (identical training program) blunted net glycogen breakdown. Therefore, although fasting increases the availability of FA’s and the rate of fat oxidation during exercise, such perturbations do not have a positive effect on subsequent exercise performance, due to the reduction in endogenous glycogen stores. Therefore if multiple training sessions are to occur in the same day it is imperative to replenish endogenous glycogen stores.

• High Fat Diet – The concept that altering an athlete’s habitual diet several days prior to exercise can modify patterns of fuel substrate utilization and impact on subsequent performance has been around since 1940’s. The exogenous substrate supply plays an important role in modulating the acute metabolic responses to endurance exercise. CHO intake before and during exercise stimulates the contribution of blood glucose for muscle contraction and thus inhibiting fat oxidation. Alternatively, ingestion of high-fat nutrients stimulates energy production by fat oxidation, whist supressing CHO utilization. It has also been shown that endurance training in conjunction with a high-fat diet stimulates metabolic adaptations in muscle cells to facilitate energy production by fat oxidation.The results from a number of studies have shown that acute (1-3 days) exposure to a high-fat, low CHO (HFLC) is associated with a lowering of resting muscle glycogen stores and a reduction in exercise performance. This impairment in exercise capacity is due likely to both, premature depletion of lowered muscle glycogen and the absence of any worthwhile increase in the capacity for fat utilisation during exercise to compensate for the reduction in CHO availability. On the other hand, in some well-trained athletes, long term (>7-days) adaptation to such diets (LCHF) have been shown to substantially enhance the capacity for fat oxidation during submaximal exercise, with evidence that the major shifts in the pattern of substrate metabolism (from CHO to fat) can be achieved with 5-6 days. At present, this is still insufficient scientific evidence to recommend that athletes should “fat load” during training and before major competitions. However this scenario presents a practical opportunity to enhance ultra-endurance performance (>6 hrs) if an athlete trains for most of the year on a CHO diet and then undergoes a short term period of fat adaptation followed by the traditional CHO-loading protocol in the final build up to an event. Thus, nutritional periodization for endurance and specifically ultra-endurance events should aim to enhance the contribution from fat to oxidative energy metabolism, resulting in the sparing of endogenous CHO stores. It is important to understand that there is a possibility that there are “responders” and “nonresponders” to dietary fat-adaptation strategies.

References

        

Burke LM, Hawley JA. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Medicine and science in sports and exercise. 2002;34(9):1492-1498.

Draper N, Marshall H. Exercise Physiology for Health and Sports Performance. Pearson Education; 2013.

Hargreaves M, Hawley JA, Jeukendrup A. Pre-exercise carbohydrate and fat ingestion: effects on metabolism and performance. Journal of sports sciences. 2004;22(1):31-38.

Hawley JA. Effect of increased fat availability on metabolism and exercise capacity. Medicine and science in sports and exercise. 2002;34(9):1485-1491.

Hawley JA, Brouns F, Jeukendrup A. Strategies to enhance fat utilisation during exercise. Sports Medicine. 1998;25(4):241-257.

Jeukendrup A, Randell R. Fat burners: nutrition supplements that increase fat metabolism. Obesity reviews. 2011;12(10):841-851.

Van Proeyen K, Szlufcik K, Nielens H, Ramaekers M, Hespel P. Beneficial metabolic adaptations due to endurance exercise training in the fasted state. Journal of Applied Physiology. 2011;110(1):236-245.




Coconut Oil (Coconoil)

Coconut oil is an edible oil, which is idea for cooking due to its high resistant heat properties. Coconut oil is a structured lipid (fat) known as a Medium Chain Triglycerides (MCT’s). MCT’s (Coconoil) is sold as a supplement to replace normal fat because it is said not to be stored in the body. Therefore MCT’s help athletes to lose body fat. Upon ingestion MCT’s are rapidly broken down and hydrolysed in the small intestine and converted into glycerol and medium-chain fatty acids (MCFA), where they directly enter the blood, increasing fat transportation. In addition MCFA can cross the mitochondrial membrane (site of energy production in the cell) of liver and muscle independently, where they are oxidised. MCFA’s demonstrate better gastric emptying rates that isocalorific carbohydrate (CHO) beverages at rest.

MCT’s have attracted attention of researchers for the possible application to the diet of athletes due to is ease of absorption, rapid rate of oxidative metabolism (as fast as glucose) and possible glycogen sparing properties, thus delaying fatigue. Recently, ingestion of MCT’s has been advocated as a possible means of enhancing exercise performance during prolonged endurance events by elevating plasma free fatty acid (FFA) levels and thus sparing muscle glycogen.. Additionally MCT’s demonstrate a greater rate of oxidation both at rest and at exercise than long-chain fatty acids.

In conclusion, research supports the replacement of dietary fat with MCTs, due to it being effective at increasing fat oxidation at rest and in exercise, thus reducing the rate of muscle glycogen breakdown and delaying the onset of exhaustion.

References

Angus DJ, Hargreaves M, Dancey J, Febbraio MA. Effect of carbohydrate or carbohydrate plus medium-chain triglyceride ingestion on cycling time trial performance. Journal of Applied Physiology. 2000;88(1):113-119.

Burke L. Practical sports nutrition. Human Kinetics Publishers; 2007.

Calbet J, Mooren F, Burke L, Stear S, Castell L. A–Z of nutritional supplements: dietary supplements, sports nutrition foods and ergogenic aids for health and performance: part 24. British journal of sports medicine. 2011;45(12):1005-1007.

Goedecke J, Clark V, Noakes T, Lambert E. The effects of medium-chain triacylglycerol and carbohydrate ingestion on ultra-endurance exercise performance. International journal of sport nutrition and exercise metabolism. 2005;15(1):15-27.

Jeukendrup A, Gleeson M. Sport nutrition: an introduction to energy production and performance. Human Kinetics; 2010.

Jeukendrup A, Saris W, Schrauwen P, Brouns F, Wagenmakers AJ. Metabolic availability of medium-chain triglycerides coingested with carbohydrates during prolonged exercise. Journal of Applied Physiology. 1995;79(3):756-762.

Kern M, Lagomarcino ND, Misell LM, Schuster V. The effect of medium-chain triacylglycerols on the blood lipid profile of male endurance runners. The Journal of nutritional biochemistry. 2000;11(5):288-292.

Van Zyl C, Lambert E, Hawley J, Noakes T, Dennis S. Effects of medium-chain triglyceride ingestion on fuel metabolism and cycling performance. Journal of Applied Physiology. 1996;80(6):2217-2225.