Breakfast or Fasting? Training in a Fasted State

It is, to say the least, striking to leaf through books on nutrition in sport and vaguely read some reference to fasting, or even observe that the possible adaptation responses to training in this state are not even mentioned. In our opinion, it should be a chapter to be addressed, due to the importance of its good or bad use, and especially because of the existing scientific literature on the subject. Therefore, in this article we are going to try to answer the question: what it consists of, for whom it is most recommended and why, when and how much we should make use of this strategy and some application recommendations.

A distinction can be made between training in a fasted state (no food) and a complete fast (no food or water). We will talk indistinctly about training on an empty stomach or in a fasted state, when we have spent the night without eating any food (at least between 8 and 12 hours), whether solid or liquid, and we are ready to do our morning training. It is worth mentioning that the absence of water will not be part of our application, since maintaining a high state of hydration is essential to perform any type of exercise or sport, so that the body can have enough tools to, among other things, thermoregulate properly, especially in extreme heat conditions.

When we propose to train on an empty stomach, liver glycogen stores are low after the body has drawn on this reserve overnight as long as we have had a quiet night, since the nervous system primarily uses glucose as an energy substrate to maintain the vital functions of the body, specifically that of the central nervous system. Hence the importance of knowing that, when exercising in the absence of prior intake of Carbohydrates (CHO), and considering a given intensity of exercise, there is a risk of suffering premature failure of glycoregulation and hypoglycemia derived from the function of the liver, which is responsible for regulating the concentration of blood glucose or glycemia through the process known as glycogenolysis.

Some might wonder if drinking a coffee or tea without sugar is analogous to training on an empty stomach. In totally strict terms, it is not possible to consider it as such, since a cup of coffee, no matter how low its caloric content may be (1 cup-100ml = 9 Kcal), provides carbohydrates, fats and proteins that are the protagonists of energy metabolism, and with it an insulin response, which we will see later how it affects both the activation of the metabolism of one or the other substrate and its relationship with the resynthesis of muscle glycogen. However, in practice, many athletes find it very uncomfortable to go out to train without drinking anything, or even opt for the effects that caffeine has on the body as an ergogenic aid (activation of the nervous system thus improving the level of concentration and alertness, delaying the onset of fatigue and even attenuating the state of drowsiness). so we will assume that, for practical purposes, drinking a cup of coffee or tea without sugar will lead to a state akin to the fasting state.

At this point, it is worth pausing to briefly recall the energy metabolism systems responsible for supplying the energy necessary for physical activity, and thus be able to meaningfully understand what the literature says in relation to this topic. There are two ways

to obtain energy to perform in our sport: one, anaerobically (without oxygen involvement) and the other, aerobically. From the former, we can obtain energy through the phosphagen system and by anaerobic glycolysis, potentially used in explosive sports such as the family of combat sports, weightlifting, long jump and high jump, and shorter athletics and swimming events, among others. In a very general way, we can understand the first system (PCr) as obtaining a large amount of energy in a short period of time of approximately 0-15 seconds. In the second, anaerobic glycolysis can obtain a very rapid amount of energy derived from the metabolism of CHOs, but the result of this process leaves in the bloodstream, as a waste product, the lactic acid responsible for muscle fatigue and which reaches its maximum expression in activities of maximum intensity for an approximate period of time between 15 seconds to 2 minutes, such as a 400m athletics event or a 200m freestyle swimming event. To conclude with the reminder of the metabolic processes of obtaining energy, we have the most important source in endurance sports, the process of obtaining aerobic energy (with oxygen), which takes place in the cellular mitochondria and can oxidize both CHO (aerobic glycolysis), proteins and fats, providing the latter with the highest energy intake (9kcal/g) in relation to CHO and proteins (4kcal/g). It should be noted that energy systems do not acquire an absolute value at any time (energy continuum), that is, if prolonged exercise is carried out at low intensity, the system the body will preferentially use to meet its energy demands will be the oxidation of fats due to its high efficiency, but it will also keep active the other systems whose contribution will be much lower but in continuous activation.

From the laboratory to the track! Once these concepts have been refreshed, we are going to review the scientific literature and give a practical interpretation of it, which is what we need to include this type of training in our routine.

One of the most recent and most comprehensive studies carried out so far is the one carried out by K. V. Proeyen et al. at the University of Leuven (Belgium) in 2011. They had 20 physically active men who followed a weekly cycling training plan, which consisted of two 90-minute sessions and two 60-minute sessions, for 6 weeks and at the individual intensity of 70% of their maximum oxygen consumption (VO2Max). In addition, 10 of them made up the group that trained on an empty stomach (A) and only with water during the session, and the other 10 performed the same training with the intake of a breakfast (D) of approx. 160g CHO and during the CHO session diluted in water (1g·kg-1·h-1). Well, these researchers with several studies in this field observed, among other things, that the two groups similarly improved oxygen consumption (+9-10%) and capillary density (10%), but some significant differences were determined in favor of group A:

1) The improvement in the amount of power measured in Watts (+21%) in group A, realized at the moment of maximum rate of fat oxidation, calculated using the formulas validated in the 90s by Peronnet & Massicotte related to VO2 and VCO2. This result means that it is beneficial for endurance training, since by making use of the most efficient metabolism we have, that of fats, we are able to produce more power and convert it into better performance.

2) As we know, insulin is the hormone responsible for regulating the level of blood glucose by "accompanying" it inside the muscle cells for metabolism. Well, it turned out that in group A this hormone remained more stable in a period of 2 hours of exercise, while in group D it remained compensated for only the first hour, and then fell to normal pre-test values.

3) The content of two of the enzymes involved in the Krebs cycle (oxidation) within the mitochondria was increased by 37% in the case of Beta Acetyl CoA Dehydrogenase (β-HAD), and by 47% in the case of Citrate Synthase (CS).

Despite being a very clarifying study, we continue to investigate the literature on analogous studies that try to compare fasting performance, thus finding a study led by K. De Bock in 2005 that, despite having a different design, its results do not leave us indifferent. They obtained a sample of 10 physically active men who performed a pre-test on a cycle ergometer (exercise bike) in an fasted state (group A) and at an intensity equivalent to their 75% of VO2 Max, and in the 4 hours after the end of the test they carried out recovery in the laboratory together with a high carbohydrate intake. At the end of the three weeks, they carried out the same procedure under conditions of eating breakfast (group D) before exercise (150g CHO) and carbohydrate drink during exercise. The results were also very interesting, again in favour of fasting exercise:

1) A significant drop in intramuscular triglyceride content was observed, specifically from 18% to 6%, after the 2-hour test, in group A and not in group D, only in Type I fibers, also known as oxidative fibers, involved in endurance exercise. This statement corroborates the evidence of Van Loon et al. in 2003, in a study that measured these same variables or indicators.

2) In group A, the blood content of lipolysis-stimulating hormones, such as adrenaline, noradrenaline and cortisol, except leptin, increased. In addition, HSL (sensitive hormone lipase), responsible for hydrolyzing triglycerides, during exercise, into 3 fatty acids and glycerol subsequently released into the blood, is activated by increasing the adrenaline:insulin ratio (Donsmark et al. 2004), as the amount of insulin falls by a third in the two groups.

3) Muscle glycogen stores were better recovered after 4 hours of CHO intake in the laboratory by the fasting group. The explanation may lie in the improvement in glycogen resynthesis due, despite maintaining the same blood glucose level, to the significant drop in insulin in group A. (McGarry and Dobbins, 1999; Deeney et al. 2000; Yaney et al. 2000).

4) Finally, these researchers observed that during the 2-hour test on a cycle ergometer, group A maintained lower RER coefficients (VCO2/VO2) than group D and, therefore, a better range of fatty acid oxidation throughout the test.

From all these data extracted from these studies, we can conclude that fasted exercise:

1. It results in an increase in intramuscular lipid breakdown predominantly in type I fibers.
2. Improves the use of fatty acids as an energy substrate.
3. Helps to stimulate post-exercise muscle glycogen resynthesis.
4. Its greatest benefits are obtained at low to moderate intensities and respecting the principles of progression and individualization training, among others.
5. The intake of CHO prevents the use of lipids as a metabolic pathway.

To conclude in an optimal way and following our philosophy "from the laboratory to the track", we are going to try to capture in the following numbering the general considerations and application suggestions that can be extracted from our review on fasted training:

•   Subject's experience. The frequency and quantity of fasted training should be in accordance with: first, the characteristics of the subject, i.e., age, sex, sports habits, training zones, or diseases such as diabetes, in which extreme caution should be exercised due to a drop in blood glucose; and second, their level of experience, if we think, for example, of a person who has just started training, since their heart rate in response to exercise will be higher than desired for this type of training. So, if the intensity is high for this beginner athlete, we will achieve the opposite effect, that is, stimulating the metabolism of carbohydrates instead of fats, working close to their anaerobic threshold. On the other hand, if our athlete has a lot of experience or fasted training was already a regular part of their training, we can increase the times per session and increase the weekly training volume of this type of training to achieve a better adaptation.
•   Hydration. It goes without saying at this point that hydration is non-negotiable. To achieve optimal performance, our body must remain fully hydrated at all times, so that vital functions and, especially, those related to exercise such as thermoregulation, the net balance of the Krebs cycle, etc., are not compromised.
• As we have pointed out above, this training only makes sense at low or, with some nuances, moderate intensities. These nuances are, for example, in a frequently used fasting training applied to a trail runner or orienteering, it can be utopian to maintain a low intensity zone for a long time, given the unevenness of the terrain. When we talk about low intensities, we basically refer to rhythms below or a little above Ventilatory Threshold 1, or better known as aerobic threshold (65-70% VO2Max). If we have not yet made a determination of the training zones, we must think about maintaining a rhythm for a long time and comfortably (a subjective effort rating of 1-2 out of 10), those rhythms that give us the feeling of being able to maintain indefinitely but without being an extremely slow pace, because that would represent an insignificant stimulation of our body to cause that overcompensation desired.
•  Energy gel or bar. Despite following the hydration and intensity guidelines, it does not hurt to have a gel or a bar in the pocket of the windbreaker, the jersey or on the edge of the pool, in order to prevent the arrival of possible "bonking" by draining muscle glycogen stores too much and avoid the cost that this entails. for physiological purposes, for the recovery of that depletion.
•  Post-exercise. In order to facilitate the resynthesis of muscle and liver glycogen, during the period after the end of training it is recommended to consume approximately 1,5 g· Kg-1H-1 of carbohydrate.

! Combined sports. In combined sports such as triathlon or duathlon, it is well known that all training that is carried out in any of the modalities is generally transferred in a positive way to the other disciplines, also known as cross-training (Millet et al., 2002). Despite this, it is suggestive to be able to combine fasting training in each and every one of the endurance sports practiced, as the greater the global adaptations and the greater the benefits for our performance. In addition, it is considered that an appropriate use would not exceed, in terms of volume, 2 hours per session in swimming or running and 2 to 3 hours in cycling, based on the criteria of relative score range by discipline (Cejuela & Esteve, 2011)

Distance. Maintaining all the general considerations and always attending to the basic principles of training, the tendency to use fasting training has a direct relationship with the distance of the race, that is, the greater the distance we prepare, the greater its training must be, due to the importance that falls on the use of fats as a metabolic substrate.

Periodization. It has been amply demonstrated that fasted training becomes effective at low intensities. So, as it is a training that has a relatively low impact on our body and, in addition, the existence of adaptations and acute responses to training in this state has been demonstrated, it is convenient to propose that the largest volume of training should be encompassed around the competitive period, since the intensity of the sessions will always be lower and adaptable to our planning. Finally, the tendency to use methodological approaches that stand out for their excellent results, such as polarized training (Boullosa et al. 2010; Muñoz, et al. 2014; Stöggl & Sperlich, 2014), means that fasting training can easily participate and carry an important weight in our planning.

Therefore, applying fasted training in the athlete's daily routine, taking into account the above considerations, can be a tool within anyone's reach, very easy to use and quantify, although it should always be done with prudence, and if in doubt, a specialist should be consulted.

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BIBLIOGRAPHY

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• Proeyen K. V.; Szlufcik K.; Nielens H.; Ramaekers, M.; Hespel. P. B Beneficial metabolic adaptations due to endurance exercise training in the fasted state. J Appl Physiol 110: 236-245, 2011.
• Stöggl, T., & Sperlich, B. (2014). Polarized training has greater impact on key endurance variables than threshold, high intensity, or high volume training. Frontiers in Physiology, 5, 33. doi:10.3389/fphys.2014.00033
• Van Loon LJ, Koopman R, Stegen JH, Wagenmakers AJ, Keizer HA, Saris WH. Intramyocellular lipids form an important substrate source during moderate intensity exercise in endurance-trained males in a Fasted state. J Physiol 553: 611–625, 2003.

AUTHOR

Alberto Ferriz Valero (Bachelor of Science in Physical Activity and Sport. University of Alicante)

Roberto Cejuela Anta (PhD in Physical Activity and Sports Sciences. University of Alicante).