Tag: sports nutrition

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Fat Burning – using body fat instead of carbohydrates as fuel

In this article the fat burning processes are well explained and the latest scientific research dispels many popular myths. Mike

Fat oxidation through intense exercise

Fat burning is a very popular and often-used term among endurance athletes. But is it really important to burn fat – and, if so, how can it best be achieved? Asker Jeukendrup looks at the latest research

The term ‘fat burning’ refers to the ability to oxidise (or burn) fat, and thus to use fat – instead of carbohydrate – as a fuel. Fat burning is often associated with weight loss, decreases in body fat and increases in lean body mass, all of which can be advantageous for an athlete.

It is known that well-trained endurance athletes have an increased capacity to oxidise fatty acids. This enables them to use fat as a fuel when their carbohydrate stores become limited. In contrast, patients with obesity, insulin resistance and type II diabetes may have an impaired capacity to oxidise fat. As a result, fatty acids may be stored in their muscles and in other tissues. This accumulation of lipid and its metabolites in the muscle may interfere with the insulin-signalling cascade and cause insulin resistance. It is therefore important to understand the factors that regulate fat metabolism, and the ways to increase fat oxidation in patients and athletes.

Fat oxidation during exercise

Fats are stored mostly in (subcutaneous) adipose tissue, but we also have small stores in the muscle itself (intramuscular triglycerides). At the onset of exercise, neuronal (beta-adrenergic) stimulation will increase lipolysis (the breakdown of fats into fatty acids and glycerol) in adipose tissue and muscle. Catecholamines such as adrenaline and noradrenaline may also rise and contribute to the stimulation of lipolysis.

As soon as exercise begins, fatty acids are mobilised. Adipose tissue fatty acids have to be transported from the fat cell to the muscle, be transported across the muscle membrane and then be transported across the mitochondrial membrane for oxidation. The triglycerides stored in muscle undergo similar lipolysis and these fatty acids can be transported into the mitochondria as well. During exercise, a mixture of fatty acids derived from adipocytes and intramuscular stores is used. There is evidence that shows that trained individuals store more intramuscular fat and use this more as a source of energy during exercise (1).

Fat oxidation is regulated at various steps of this process. Lipolysis is affected by many factors but is mostly regulated by hormones (stimulated by catecholamines and inhibited by insulin). The transport of fatty acids is also dependent on blood supply to the adipose and muscle tissues, as well as the uptake of fatty acids into the muscle and into the mitochondria. By inhibiting mobilisation of fatty acids or the transport of these fatty acids, we can reduce fat metabolism. However, are there also ways in which we can stimulate these steps and promote fat metabolism?

Factors affecting fat oxidation

Exercise intensity – One of the most important factors that determines the rate of fat oxidation during exercise is the intensity. Although several studies have described the relationship between exercise intensity and fat oxidation, only recently was this relationship studied over a wide range of intensities(2). In absolute terms, carbohydrate oxidation increases proportionally with exercise intensity, whereas the rate of fat oxidation initially increases, but decreases again at higher exercise intensities (see figure 1). So, although it is often claimed that you have to exercise at low intensities to oxidise fat, this is not necessarily true.

In a series of recent studies, we have defined the exercise intensity at which maximal fat oxidation is observed, called ‘Fatmax’. In a group of trained individuals it was found that exercise at moderate intensity (62-63% of VO2max or 70-75% of HRmax) was the optimal intensity for fat oxidation, whereas it was around 50% of VO2max for less trained individuals (2,3).

However, the inter-individual variation is very large. A trained person may have his or her maximal fat oxidation at 70%VO2max or 45%VO2max, and the only way to really find out is to perform one of these Fatmax tests in the laboratory. However, in reality, the exact intensity at which fat oxidation peaks may not be that important, because within 5-10% of this intensity (or 10-15 beats per minute), fat oxidation will be similarly high, and only when the intensity is 20% or so higher will fat oxidation drop rapidly (see figure 1).

fatburn1 - Fat Burning - using body fat instead of carbohydrates as fuel

This exercise intensity (Fatmax) or ‘zone’ may have importance for weight-loss programmes, health-related exercise programmes, and endurance training. However, very little research has been done. Recently we used this intensity in a training study with obese individuals. Compared with interval training, their fat oxidation (and insulin sensitivity) improved more after four weeks steady-state exercise (three times per week) at an intensity that equaled their individual Fatmax (4).

Dietary effects – The other important factor is diet. A diet high in carbohydrate will suppress fat oxidation, and a diet low in carbohydrate will result in high fat oxidation rates. Ingesting carbohydrate in the hours before exercise will raise insulin and subsequently suppress fat oxidation by up to 35%(5) or thereabouts. This effect of insulin on fat oxidation may last as long as six to eight hours after a meal, and this means that the highest fat oxidation rates can be achieved after an overnight fast.

Endurance athletes have often used exercise without breakfast as a way to increase the fat-oxidative capacity of the muscle. Recently, a study was performed at the University of Leuven in Belgium, in which scientists investigated the effect of a six-week endurance training programme carried out for three days per week, each session lasting one to two hours(6). The participants trained in either the fasted or carbohydrate-fed state.

When training was conducted in the fasted state, the researchers observed a decrease in muscle glycogen use, while the activity of various proteins involved in fat metabolism was increased. However, fat oxidation during exercise was the same in the two groups. It is possible, though, that there are small but significant changes in fat metabolism after fasted training; but, in this study, changes in fat oxidation might have been masked by the fact that these subjects received carbohydrate during their experimental trials. It must also be noted that training after an overnight fast may reduce your exercise capacity and may therefore only be suitable for low- to moderate- intensity exercise sessions. The efficacy of such training for weight reduction is also not known.

Duration of exercise – It has long been established that oxidation becomes increasingly important as exercise progresses. During ultra-endurance exercise, fat oxidation can reach peaks of 1 gram per minute, although (as noted in Dietary effects)fat oxidation may be reduced if carbohydrate is ingested before or during exercise. In terms of weight loss, the duration of exercise may be one of the key factors as it is also the most effective way to increase energy expenditure.

Mode of exercise – The exercise modality also has an effect on fat oxidation. Fat oxidation has been shown to be higher for a given oxygen uptake during walking and running, compared with cycling(7). The reason for this is not known, but it has been suggested that it is related to the greater power output per muscle fibre in cycling compared to that in running.

Gender differences – Although some studies in the literature have found no gender differences in metabolism, the majority of studies now indicate higher rates of fat oxidation in women. In a study that compared 150 men and 150 women over a wide range of exercise intensities, it was shown that the women had higher rates of fat oxidation over the entire range of intensities, and that their fat oxidation peaked at a slightly higher intensity(8). The differences, however, are small and may not be of any physiological significance.

Nutrition supplements

There are many nutrition supplements on the market that claim to increase fat oxidation. These supplements include caffeine, carnitine, hydroxycitric acid (HCA), chromium, conjugated linoleic acid (CLA), guarana, citrus aurantium, Asian ginseng, cayenne pepper, coleus forskholii, glucomannan, green tea, psyllium and pyruvate. With few exceptions, there is little evidence that these supplements, which are marketed as fat burners, actually increase fat oxidation during exercise (see table 1).

fatburn2 - Fat Burning - using body fat instead of carbohydrates as fuel

One of the few exceptions however may be green tea extracts. We recently found that green tea extracts increased fat oxidation during exercise by about 20%(4). The mechanisms of this are not well understood but it is likely that the active ingredient in green tea, called epigallocatechin gallate (EGCG – a powerful polyphenol with antioxidant properties) inhibits the enzyme catechol O-methyltransferase (COMT), which is responsible for the breakdown of noradrenaline. This in turn may result in higher concentrations of noradrenaline and stimulation of lipolysis, making more fatty acids available for oxidation.

Environment – Environmental conditions can also influence the type of fuel used. It is known that exercise in a hot environment will increase glycogen use and reduce fat oxidation, and something similar can be observed at high altitude. Similarly, when it is extremely cold, and especially when shivering, carbohydrate metabolism appears to be stimulated at the expense of fat metabolism.

Exercise training

At present, the only proven way to increase fat oxidation during exercise is to perform regular physical activity. Exercise training will up-regulate the enzymes of the fat oxidation pathways, increase mitochondrial mass, increase blood flow, etc., all of which will enable higher rates of fat oxidation.

Research has shown that as little as four weeks of regular exercise (three times per week for 30-60 minutes) can increase fat oxidation rates and cause favourable enzymatic changes(10). However, too little information is available to draw any conclusions about the optimal training programme to achieve these effects.

In one study we investigated maximal rates of fat oxidation in 300 subjects with varying fitness levels. In this study, we had obese and sedentary individuals, as well as professional cyclists (9). VO2max ranged from 20.9 to 82.4ml/kg/min. Interestingly, although there was a correlation between maximal fat oxidation and maximal oxygen uptake, at an individual level, fitness cannot be used to predict fat oxidation. What this means is that there are some obese individuals that have similar fat oxidation rates to professional cyclists (see figure 2)! The large inter-individual variation is related to factors such as diet and gender, but remains in large part unexplained.

fatburn3 - Fat Burning - using body fat instead of carbohydrates as fuel

Weight loss exercise programmes

Fat burning is often associated with weight loss, decreases in body fat and increases in lean body mass. However, it must be noted that such changes in body weight and body composition can only be achieved with a negative energy balance: you have to eat fewer calories than you expend, independent of the fuels you use! The optimal exercise type, intensity, and duration for weight loss are still unclear. Current recommendations are mostly focused on increasing energy expenditure and increasing exercise volumes. Finding the optimal intensity for fat oxidation might aid in losing weight (fat loss) and in weight maintenance, but evidence for this is currently lacking.

It is also important to realise that the amount of fat oxidised during exercise is only small. Fat oxidation rates are on average 0.5 grams per min at the optimal exercise intensity. So in order to oxidise 1kg of fat mass, more than 33 hours of exercise is required! Walking or running exercise around 50-65% of VO2max seems to be an optimal intensity to oxidise fat. The duration of exercise, however, plays a crucial role, with an increasing importance of fat oxidation with longer exercise. Of course, this also has the potential to increase daily energy expenditure. If exercise is the only intervention used, the main goal is usually to increase energy expenditure and reduce body fat. When combined with a diet programme, however, it is mainly used to counteract the decrease in fat oxidation often seen after weight loss (11).

Summary

Higher fat oxidation rates during exercise are generally reflective of good training status, whereas low fat oxidation rates might be related to obesity and insulin resistance. On average, fat oxidation peaks at moderate intensities of 50-65%VO2max, depending on the training status of the individuals(2,8), increases with increasing exercise duration, but is suppressed by carbohydrate intake. The vast majority of nutrition supplements do not have the desired effects. Currently, the only highly effective way to increase fat oxidation is through exercise training, although it is still unclear what the best training regimen is to get the largest improvements. Finally, it is important to note that there is a very large inter-individual variation in fat oxidation that is only partly explained by the factors mentioned above. This means that although the factors mentioned above can influence fat oxidation, they cannot predict fat oxidation rates in an individual.

Asker Jeukendrup is professor of exercise metabolism at the University of Birmingham. He has published more than 150 research papers and books on exercise metabolism and nutrition and is also consultant to many elite athletes

References
1. J Appl Physiol 60: 562-567, 1986
2. Int J Sports Med 24: 603-608, 2003
3. Int J Sports Med 26 Suppl 1: S28-37, 2005
4. Am J Clin Nutr 87: 778-784, 2008
5. J Sports Sci 21: 1017-1024, 2003
6. J Appl Physiol 104: 1045-1055, 2008
7. Metabolism 52: 747-752, 2003
8. J Appl Physiol 98: 160-167, 2005
9. Nutrition 20: 678-688, 2004
10. J Appl Physiol 56: 831-838, 1984
11. Int J Obes Relat Metab Disord 17 Suppl 3: S32-36; discussion S41-32, 1993

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Recovery – how the right nutrition can help prevent overtraining

overtraining nutrition - Recovery - how the right nutrition can help prevent overtraining

More in the series on recovery and the prevention of overtraining which again emphasises the importance of having a good balanced nutrition programme. – Mike


Specific nutritional practices can prevent overtraining and accelerate exercise recovery

overtaining nutrition1 - Recovery - how the right nutrition can help prevent overtraining

Where should we draw the line between appropriate ‘heavy training’ and overtraining? And are there specific nutritional practices that can prevent overtraining and accelerate exercise recovery? Mike Saunders explains and shows that these two concepts are intimately linked.

In simple terms, overtraining is the result of intense training stimuli (and other stressors) combined with inadequate recovery. If appropriate recovery is not provided during hard training, you experience a downward spiral in which continued heavy training creates diminishing returns, and performance levels continue to get worse. However, determining precisely when the ‘overtraining line’ is crossed is very difficult. This is because the symptoms of overtraining are highly individualised and varied – a laundry list of physical, psychological, immunological and biochemical symptoms.

A consistent end result of overtraining is the impairment of physical performance. When you are overtrained, you can expect to see elevated perceptions of exertion/fatigue during exercise, decreased movement economy, slower reaction time and impaired performance times. To make things worse, overtraining status is usually only diagnosed with the benefit of hindsight. In other words, by the time you know you are overtrained, it is too late to handle it effectively!

Overtraining terminology

Recently, the terminology around overtraining has been improved. Researchers from the Netherlands and Belgium have described the overtraining process as occurring in three progressive stages (see box 1)(1):

  1. Functional overreaching
  2. Non-functional overreaching
  3. Overtraining syndrome

overtaining nutrition2 - Recovery - how the right nutrition can help prevent overtraining

Functional overreaching is the normal process of fatigue that occurs with sustained periods of heavy training. Although these periods of hard training cause short-term impairments in performance, this effect is reversed with a relatively short pre-planned recovery period. For example, a 1-week block of hard training may cause moderate levels of fatigue, impairing your peak performance for a few days. However, when you balance this hard training period with a period of adequate recovery, you can quickly return to a level matching and ultimately exceeding your initial level of performance.
Non-functional overreaching is a more severe level of fatigue reached when your performance and energy are not restored after a planned short-term recovery period. This often happens if you work too hard during your recovery days, if you underestimate the impact of the non-training stresses in your life, or if you simply train too long and hard before a recovery period. As a result, you may still feel fatigued following your planned recovery period. This is where flexibility in your training programme becomes very important. If coaches recognise the continued fatigue of an athlete, they can delay the next heavy training phase or competition. This is often enough to reverse the fatigue and restore performance levels.

However, if coaches and athletes ignore fatigue in the non-functional overreaching stage, further heavy training simply results in deeper levels of fatigue. This can become a vicious cycle in which athletes continue heavy training in an attempt to reverse their declining performance, only to exacerbate the problem by further impairing their recovery. True overtraining syndrome is reached only in the most severe cases, and can be quite debilitating. Symptoms of overtraining syndrome overlap with chronic fatigue syndrome and clinical depression, and can only be reversed with several weeks or months of recovery(1).

Balancing training and recovery

The model of overtraining discussed above illustrates the critical balance of well-timed recovery periods within a training program. Your training phases can be specifically designed to cause functional overreaching at strategic times. However, effective training programmes are  created to include adequate recovery to prevent both non-functional overreaching and overtraining syndrome.

As an example, professional cyclists often perform team training camps that provide a significant early-season training stimulus. The volume of training performed at these camps can induce significant fatigue. However, training camps can produce important improvements in performance if the heavy training is balanced with an appropriate period of short-term recovery.

Recent studies from our Human Performance Laboratory at James Madison University (USA) provide some quantitative evidence to support these concepts. We studied professional cyclists who completed at least three consecutive days of high-volume training, averaging almost 100 miles/day. Not surprisingly, the heavy training caused significant changes in a number of overreaching/overtraining symptoms. These included increased levels of mental and physical fatigue, increased muscle soreness and elevated markers of muscle damage.

About half of the cyclists then performed an ‘easy’ day of training on the fourth day – about 30 miles at low intensity. For these highly trained athletes, this was enough recovery to initiate improvement of all of the symptoms mentioned above.

Overtraining and diet

Appropriate nutrient intake and timing can play an important role in influencing the overtraining process. It has long been established that adequate carbohydrate intake is required to maintain muscle glycogen levels during heavy training. This is critical to sustaining high training volumes, as muscle glycogen is a primary fuel stored in muscles and used during endurance training and racing. In addition, we know that exercise stimulates enhanced uptake of carbohydrate in the muscles. This so-called ‘insulin-like effect’ of exercise remains for a short time following exercise. As a result, the consumption of carbohydrate immediately after training (within 30 minutes) produces faster replenishment of muscle glycogen than if carbohydrate intake is delayed. Thus, it is now common practice for endurance athletes to consume a carbohydrate-rich recovery beverage or snack immediately following demanding training sessions.

More recently, scientists have begun to investigate how carbohydrate intake and timing influence specific aspects of the overtraining process. Researchers from the University of Birmingham examined how dietary carbohydrate intake influenced overreaching symptoms during a period of intensified running training(2). When performing 11 days of intensified training consuming relatively low carbohydrate intake (5.4 grams per kilo of bodyweight per day), the runners experienced significant worsening in mood states, fatigue, muscle soreness, and declines in running performance. These factors were considerably (though not entirely) reversed when the athletes performed the same training demands with higher carbohydrate (8.5g/kg/day) in their diets.

The same research group performed a similar study in cyclists(3). Athletes consumed sports beverages with low or high carbohydrate content during exercise (low=2%; high=6%) and immediately following exercise (low=2%; high=20%). When consuming the low-carbohydrate drinks over eight days of intensified training, the athletes experienced significant declines in their mood states, increased perceived effort during exercise, and declines in cycling performance. All of these factors improved when the high-carbohydrate beverages were consumed during/following training.

Following the eight-day period of intensified training, the cyclists received fourteen days of reduced volume training to promote recovery. This resulted in significant improvements in cycling performance (exceeding baseline levels) but only when the athletes drank the high-carbohydrate beverages. By contrast, performance remained suppressed below baseline levels with the low-carbohydrate drinks.

Thus, altering the carbohydrate levels of the cyclists’ sports drinks was enough to influence their responses to training. As a result, the intensified training represented a functional overreaching stimulus when appropriate carbohydrate was provided, but a non-functional overreaching stimulus without adequate carbohydrate. This is an excellent illustration of how ‘optimal recovery’ represents much more than simply lowering the demands of training (see figure 1).

overtaining nutrition3 - Recovery - how the right nutrition can help prevent overtraining

Co-ingestion of carbohydrate and protein

The effects of protein intake on recovery from endurance training have been understudied compared to carbohydrate. As a result, there is no clear consensus among scientists regarding the role that protein plays in the overtraining process. However, recent studies suggest that there may be some additional recovery benefits associated with consuming a mix of carbohydrate and protein following heavy endurance training.

Carbohydrate-protein and glycogen replenishment Combined intake of carbohydrate-protein may influence a number of factors that are important for recovery in endurance athletes. For example, some studies have shown faster rates of muscle glycogen replenishment when carbohydrate-protein is consumed immediately following endurance exercise (compared to carbohydrate alone).

Other studies have suggested that the additional benefits of added protein are negligible if the carbohydrate doses are very high (over 1.2 g/kg). At a minimum, it appears that carbohydrate-protein ingestion is a highly practical way to ensure high rates of glycogen replenishment following exercise, especially when you are not consuming a high-calorie recovery drink or snack. This is particularly relevant in conjunction with the other potential benefits of carbohydrate-protein ingestion discussed below.

Carbohydrate-protein and protein balance Combined carbohydrate-protein intake may also have positive effects on protein balance for endurance athletes. Researchers at Maastricht University in Holland observed that carbohydrate-protein consumption increased protein synthesis and decreased protein breakdown in endurance athletes, compared to when they consumed carbohydrate alone(4).

Investigators at McMaster University (Canada) made similar observations of enhanced protein balance with carbohydrate-protein ingestion following aerobic exercise(5). In addition, they reported that the fractional synthetic rate (FSR) within the muscle was improved with carbohydrate-protein intake (see figure 2, overleaf). Collectively, these studies suggest that protein synthesis in the muscle may be improved with carbohydrate-protein intake. Though the long-term effects of improved protein synthesis and protein balance have not been studied in endurance athletes, this evidence suggests that protein may be helpful in stimulating muscle recovery and promoting positive muscle adaptations following heavy endurance training.

overtaining nutrition4 - Recovery - how the right nutrition can help prevent overtraining

Carbohydrate-protein and muscle recovery Carbohydrate-protein ingestion has been associated with improvements in various other markers of muscle recovery in endurance athletes. For example, researchers from our Human Performance Laboratory at James Madison University have observed that carbohydrate-protein ingestion results in lower blood creatine kinase (CK) levels (an indicator of muscle damage)(6,7), less muscle soreness(7), and improved muscle function(6)following heavy endurance exercise (see Figure 2).

We have observed these benefits in carbohydrate-protein versus carbohydrate-only drinks matched for both carbohydrate content and total calories(6). In addition, we have observed these effects when we studied carbohydrate-protein beverages consumed during endurance exercise(6) or immediately following exercise(7). In one study, we examined carbohydrate and carbohydrate-protein recovery beverages during six days of consecutive training in collegiate distance runners(7). While consuming the drinks containing carbohydrate-protein, the athletes had lower blood CK levels and less muscle soreness, despite performing identical training loads between the two periods.

Carbohydrate-protein and subsequent performance

A critical question for coaches and athletes is whether the improved muscle recovery markers observed when consuming carbohydrate-protein drinks relates to any tangible benefits with respect to sport-specific performance. In other words, if carbohydrate-protein intake improves ‘recovery’, does this lead to enhanced performance during subsequent exercise?

Studies investigating this issue to date have produced mixed findings. For example, in our aforementioned study of runners, we did not observe differences in running performance following the six-day training period between the two beverages. However, this was probably due to the fact that the athletes were reducing their training levels in preparation for a race. Thus, they were probably well recovered prior to the race under both beverage conditions.
This evidence leads to an important observation: no supplement can be expected to enhance your recovery if you are already fully recovered. If you only perform light exercise, and take relatively long recovery periods between workouts, then the composition of your post-exercise nutrition regimen is far less critical, and perhaps irrelevant altogether if your regular diet is appropriate. However, if you perform heavy exercise on a regular basis, then it is important that your recovery nutrition includes adequate carbohydrate to maximise your post-exercise recovery. Under these conditions of heavy exercise and short recovery periods, it also seems likely that carbohydrate-protein sustains high performance levels better than carbohydrate alone.

Evidence supporting this concept can be observed in recent studies on this topic, including our study of runners discussed above. As mentioned previously, carbohydrate-protein did not produce performance improvements in runners who were tapering slightly prior to a race. However, the athletes who continued to perform the highest training mileage throughout the six days had the greatest improvements in muscle recovery with the carbohydrate-protein. This same group of ‘harder-training’ athletes also had a stronger tendency towards faster race performance with the carbohydrate-protein drink.

More convincingly, US researchers at the University of California-Davis examined the effects of carbohydrate-protein drinks during a short period of heavy cycling training(8). They assessed changes in blood CK and time to fatigue during three consecutive days of exercise. These variables got significantly worse over the three days of hard training when the cyclists consumed carbohydrate-only drinks. However, these declines were prevented when carbohydrate-protein drinks were consumed.

Similarly, researchers from Canada tested recovery and performance during two 60-minute cycling performance tests, separated by six hours(9). Carbohydrate or carbohydrate-protein recovery drinks were provided immediately after the first exercise trial. The cyclists were able to generate higher power output and better performance in the second exercise session following the carbohydrate-protein beverage, compared to the carbohydrate-only drink.
Not all studies have shown significant improvements in subsequent performance following carbohydrate-protein intake. However, the positive effects of protein seem to appear more regularly in the studies that provide the more demanding training/recovery periods. Thus, the longer and harder you train, the more important the details of your recovery nutrition, including the inclusion of protein, become.

The bottom line

In summary, overtraining is a complex issue, which can have important consequences for endurance athletes. Functional overreaching can be an intended outcome of heavy training periods, provided it is balanced with an appropriate period of recovery. The consumption of adequate nutrients, especially in the period immediately following heavy exercise training, can augment recovery from exercise. Thus, recovery nutrition can assist in the prevention of non-functional overreaching, and allow you to get the most out of your training. In short, this means making sure that your daily carbohydrate intake (especially immediately post-exercise) is adequately high to maintain your muscle glycogen levels during training. In addition, adding protein to your post-exercise recovery drinks and meals appears to have further benefits to promote optimal recovery from heavy exercise.

References

1. Sports Med 2006; 36: 817-828
2. J Appl Physiol 2004; 96: 1331-1340
3. J Appl Physiol 2004; 97: 1245-1253
4. Am J Physiol Endocrinol Metab 2004; 287:E712-E720
5. J Appl Physiol 2009; 106: 1394-1402
6. Int J Sports Nutr Exerc Metab 2008; 18 :363-378
7. Int J Sports Nutr Exerc Metab 2006; 16: 78-91
8. Int J Sports Nutr Exerc Metab 2008; 18 : 473-492
9. J Int Soc Sports Nutr 2009; 5(24): [in press]

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Sports Nutrition – Medium-Chain Triglycerides

triglyceride - Sports Nutrition - Medium-Chain TriglyceridesThis is a follow up article on the previous one I posted entitled “Sports Nutrition – It is essential you include fat in your diet” and which expands on the use of medium-chain triglycerides (MCTs). Mike.

Medium-chain triglycerides (MCTs) are a special class of fatty acids. Normal fats and oils contain long-chain fatty acids (LCTs). Compared to these fatty acids, MCTs are much shorter in length. Therefore, they resemble carbohydrates more than fat. As a result, they are more easily absorbed, digested, and utilized as energy than LCTs.

Medium-chain triglycerides are found naturally in milk fat, palm oil, and coconut oil. Commercial MCT oil, available as liquid and capsules, is obtained through lipid fractionation, the process in which MCTs are separated from other components of coconut oil. Medium-chain triglycerides were originally formulated in the 1950s as an alternative food source for patients who are too ill to properly digest normal fats and oils. The long chains of LCTs require a lot of bile acids and many digestive steps to be broken down into smaller units that can be absorbed into the bloodstream. Once in the bloodstream, they are absorbed by fat cells and stored as body fat. In contrast, the medium-chain triglycerides are more water-soluble and are able to enter the bloodstream quicker because of their shorter lengths. Once in the bloodstream, they are transported directly into the liver. Thus, MCTs are an immediately available source of energy and only a tiny percent is converted into body fat.

Medium-chain triglycerides were first used in the mid-1900s to reduce seizures with the help of the ketogenic diet. In the 1980s, MCTs became popular in sports as a substitute for normal dietary fats or oils. They quickly became a favorite energy source for many athletes, such as marathon runners, who participate in endurance sports. These athletes require a quick source of energy, which is readily supplied by carbohydrates. However, diets high in carbohydrates may cause rapid increase in insulin production, resulting in substantial weight gain, diabetes, and other health problems. Dietary fats or oils are not a readily available source of energy. In addition, they are believed to make the body fatter. MCT is also a form of fat; therefore, it is high in calories. Yet, unlike normal fats and oils, MCTs do not cause weight gain because they stimulate thermogenesis (the process in which the body generates energy, or heat, by increasing its normal metabolic, fat-burning rate). A thermogenic diet, which is high in medium-chain triglycerides, has been proposed as a type of weight loss regime.

General Use

Endurance Sport Nutrition

Medium-chain triglycerides are often used by athletes to increase their endurance during sports or exercise regimes. MCTs are an immediate source of energy, and as such, the body can use them as an alternative energy source for muscle during endurance exercise. However, if consumed in moderate amounts (30 to 45 grams), MCTs are not very effective in either decreasing carbohydrate needs or in enhancing exercise endurance. Increased consumption may help. One study evaluated six athletes at different points during a 25-mile cycling trial. They were given either a medium-chain triglyceride beverage, a carbohydrate drink, or a combined MCT-carbo-hydrate mixture. The fastest speed was achieved when the athletes used the MCT-carbohydrate blend. The worst performance was associated with sport drinks containing MCT alone (without carbohydrate). Therefore, to gain significant increases in endurance, it is generally recommended that an athlete consume at least 50 grams of MCTs per day in combination with some carbohydrates. However, dosages exceeding 30 grams often cause gastrointestinal upset, which can diminish an athlete’s performance.

MCT products available in the market may have high water content or contain unwanted ingredients. Therefore, athletes should buy MCT-only products, and mix a small amount into carbohydrate soft drinks. Alternatively, they can purchase premixed MCT sport drinks, such as a brand known as SUCCEED.

Thermogenic Diet

MCTs are popular among body builders because they help reduce carbohydrate intake, while allowing them ready access to energy whenever they need it. MCTs also have muscle-sparing effects. As a result, they can build muscles while reducing fats. However, this does not mean that these athletes will become healthier, because an improvement in body physique does not always correlate with higher fitness levels.

Pre-Competition Diet

Compared to carbohydrates, medium-chain triglycerides are a better and more efficient source of quick energy. They help conserve lean body mass because they prevent muscle proteins from being used as energy. Therefore, some athletes load up on medium-chain triglycerides the night before a competition. However, MCT intake should be raised gradually to allow the body to adapt to increasing MCT consumption. If MCT consumption abruptly increases, incomplete MCT metabolism may occur, producing lactic acid in the body and a rapid rise of ketones in the blood, which can make the person ill.

Weight-Loss Diet

Studies have shown that MCT may increase metabolism, which is the rate that the body burns fat. It is believed that sustained increases in metabolic rate cause the body to burn more fat, resulting in weight loss. However, for any kind of meaningful weight loss, a person would have to consume more than 50% of total daily caloric intake in the form of medium-chain triglycerides.

Treatment of Seizures

A ketogenic diet, or diet containing mostly medium-chain triglycerides, offers hope for those who have seizures that cannot be controlled by currently available drugs. Excessive consumption of MCTs produces ketones in the body; therefore, this type of diet is called a ketogenic diet. It has proven effective for some epileptic patients.

Nutritional Supplements

MCTs are the preferred forms of fat for many patients with fat malabsorption problems. Many diseases cause poor fat absorption. For instance, patients with pancreatic insufficiency do not have enough pancreatic enzymes to break down LCTs. In children with cystic fibrosis, thick mucus blocks the enzymes that assist in digestion. Another fat absorption condition is short-bowel syndrome, in which parts of the bowel have been removed due to disease. Stressed or critically ill patients also have a decreased ability to digest LCTs. Unlike LCTs, medium-chain triglycerides are easily absorbed by patients with malabsorption conditions. These patients benefit most from oral preparations that contain MCTs as the primary source of fat (up to 85% of fat caloric intake). Several scientific studies have shown MCT to be effective in treating fat malabsorbtion, chronic diarrhea, and weight loss in patients with Acquired Immune Deficiency Syndrome (AIDS).

Many MCT products can be found in local health food stores or ordered through pharmacies. Before purchasing these products, patients should consult their doctors or registered dietitians for advice concerning appropriate dosage and use. MCT oil is not used for cooking. However, it can be used for tube feeding in critically ill patients. Healthy people may take it orally, by itself or mixed with water, juice, ice cream, or pudding.

Preparations

Available medium-chain triglyceride products include:

  • MCT oil
  • sports drinks
  • energy bars
  • meal replacement beverages

Precautions

  • People with hepatic encephalopathy, brain and nervous system damage that occurs as a complication of liver disorders, should not take MCT.
  • High consumption of medium-chain triglycerides can cause abdominal pain, cramps, and diarrhea.
  • Long-term high-level MCT consumption is associated with increased risk of heart disease and other conditions. Even moderate consumption of medium-chain triglycerides can increase cholesterol and triglyceride levels. Therefore, no more than 10% of a person’s diet should come from MCTs.
  • Diabetic athletes and those with liver disease should not use MCT products.
  • MCT oil should not completely replace all dietary fats, as this would result in a deficiency of other fatty acids—essential fatty acids—that the human body needs from food sources. To avoid essential fatty acid deficiencies, a person should also include omega-3 and omega-6 fatty acids in their diets. Good sources of omega-3 include fish, fish oils, or flaxseed oil. Omega-6 fatty acids are often found in vegetable oils and evening primrose oil. The omega-3 fats have several additional health benefits, such as alleviating inflammation and protecting the body against heart disease.
  • A person should not take medium-chain triglyceride products on an empty stomach, as this may cause gastric upset.
  • MCT oil is not for cooking. It is usually consumed in its uncooked form as sport bars, or mixed with a carbohydrate drink, protein shake, or other products.
  • MCT oil leaches into plastic bags and containers. Therefore, non-plastic containers should be used for MCT oil storage.

Side Effects

There are a few adverse effects associated with MCT use. Eating foods containing medium-chain triglycerides on an empty stomach often causes gastrointestinal upset. Regular consumption of MCTs may increase cholesterol and triglyceride blood levels.

Interactions

There have been no reported interactions between MCTs and other drugs.

Resources

Books

Antonio, Jose, and Jeffery Stout. Supplements for Endurance Athletes. Champaign, IL: Human Kinetics, 2002.

Ivy, John, and Robert Portman. The Performance Zone: Your Nutrition Action Plan for Greater Endurance and Sports Performance (Teen Health Series). North Bergen, NJ: Basic Health Publications, Inc., 2004.

Ryan, Monique. Sports Nutrition for Endurance Athletes. Boulder, CO: Velo Press, 2002.

Stapstrom, Carl E. Epilepsy and the Ketogenic Diet: Clinical Implementation & the Scientific Basis. Totowa, NJ: Humana Press, 2004.

Periodicals

(No author). “Medium-Chain Triglycerides May Help Promote Weight Loss.” Obesity, Fitness & Wellness Week (March 29, 2003): 5.

(No author). “Medium Chain Triglycerides.” Alternative Medicine Review (October 2002): 418–20.

Donnell, S.C., et al. “The Metabolic Response to Intravenous Medium-Chain Triglycerides in Infants After Surgery.” Alternative Medicine Review (February 2003): 94.

St-Onge, M.P., and P.J. Jones. “Physiological Effects of Medium-Chain Triglycerides: Potential Agents in the Prevention of Obesity.” Alternative Medicine Review (June 2002): 260.

St-Onge, M.P., et al. “Medium-Chain Triglycerides Increase Energy Expenditure and Decrease Adiposity in Overweight Men.” Obesity Research (March 2003): 395-402.

Organizations

American Dietetic Association (ADA) Consumer Information Hotline. (800)366-1655..

Other

Klein, Samuel. “Lipid Metabolism During Exercise.” Health-World Online. Abstract from NIH Workshop: The Role of Dietary Supplements for Physically Active People. .

PDRhealth.com article. “Medium-Chain Triglycerides.” .

[Article by: Mai Tran]