Nutrition, Podcast, Science and Physiology

Energy availability with José Areta, PhD | EP#378

 February 20, 2023

By  Bernardo Gonçalves


Jose Areta - That Triathlon Show

José Arteta, PhD, is a lecturer at the School of Sport and Exercise Sciences at Liverpool John Moores University. His primary interest is in the area of training-nutrition interactions in humans, including energy availability and low energy availability specifically, which is the main topic of today's interview.

In this episode you'll learn about:

  • What is energy availability, and how is it different from energy balance?
  • What is considered low energy availability?
  • Symptoms and consequences of low energy availability
  • The uncertainty around measuring energy availability in the field, and difficulties with interpreting it
  • Diagnosis, detection and treatment of low energy availability
  • Sex differences in low energy availability
  • Weight loss and low energy availability

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José's background

02:58 -

  • I have been a lecturer at Liverpool John Moores University in the United Kingdom for five years.
  • I'm originally from Argentina and trained as a biologist with a Minor in zoology. 
  • My PhD was in exercise physiology and nutrition at RMIT University in Melbourne, Australia. 
  • I kept specialising in this topic at the Norwegian School of Sports Sciences, where I spent about three years as a postdoctoral researcher before ending up in Liverpool John Moores. 
  • The common thread throughout my research and my work in this area is how we can maximise adaptation to training by manipulating nutrients.
  • We can change a range of things to do that, like manipulating protein, carbohydrates and fat.
  • And over the last few years, I've been researching deeper and deeper the area of energy availability. (what happens to the body when you're not training or you're not eating enough energy concerning the energy expenditure)

Energy availability definition

04:45 - 

  • Its origin was from ecology studies in mammals in the wild, but now with an application to humans. 
  • The definition of the concept of energy availability took more of a mathematical calculation.
  • Energy availability is the energy available for physiological processes after subtracting the energy used in the exercise.
  • The arithmetic definition of energy availability is energy intake minus exercise energy expenditure, normalised to fat-free mass. 
  • There are a lot of nuances to how we calculate this and its origin. (it is more complicated than grabbing a calculator, start looking at their energy intake, calculating it from their apps and looking at their power meters and energy expenditure)

Difference between energy availability and energy balance

07:39 -

  • Energy balance is an output of the calculation of energy intake minus all the energy expenditure processes. (the value you get there in energy balance equals zero)
  • On the counterpart, energy availability is an input to the system. 
  • It's the energy available for the system to maintain normal homeostasis and the system's normal functioning. It's the energy intake minus exercise energy expenditure. It could be a positive number if you're in a normal state of adequate energy availability. 
  • In energy availability, a healthy energy balance is about 40-45 kcal/(kg of fat-free mass) per day.
  • You can have zero energy balance, but it can be a healthy or unhealthy one.
  • All the energy expenditure processes your body requires may not function perfectly if you are not consuming enough calories. For example, the resting metabolic rate may decrease, and the economy of movement may increase.
  • If you are doing the same amount of movement but decreasing the energy expenditure, you might reduce that need. 
  • When calculating energy balance, you look at the input and output, and you might think that someone is in a healthy energy balance because the result is zero. Still, a person might need to consume more calories than what we think might be optimal. 
  • Whereas if we consider energy availability, value is more comprehensive. If someone is for a prolonged period in values of energy availability 
  • That is low (10 kcal/kg.fat-free mass per day) and reach an energy balance in that case, and we can see that someone has low energy. However, they are still in a state of energy balance.
  • Values of energy availability give us an indication of what is the energetic state of an individual independent of all these metabolic adaptations.
  • The reason you can have a low value for energy availability but be in the energy balance is that if you are in a chronic state of low energy availability, the other energy expenditures of the body, including resting metabolic rate and non-exercise, pharmacogenetics processes.
  • However, as a caveat, we must know that this is theoretical.
  • There is not much experimental data supporting this because putting someone in a prolonged period of low energy availability is tough. 
  • One of the best examples is the Minnesota starvation experiment during the Second World War, where individuals were on a semi-starvation diet for six months. You can see the total energy expenditure matching these individuals' energy intake, showing an evident decrease in total energy expenditure to match the energy intakes over six months.
  • In this case, these individuals lost much of their body weight. 
  • By the end of six months, the body weight reaches some plateau where all the metabolic processes match the energy intake. 
  • Energy expenditure becomes more of a function of energy intake.

Calculating energy availability for a person that does not do specific training

14:56 -

  • There are limitations in the calculation of energy availability. 
  • The first origin of energy availability in mammalian ecology looks at the success of reproduction at different times of the season with different food availability. These studies are in labs where energy intake and exercise energy expenditure are tightly controlled. 
  • When we try to take this approach in this environment and bring it out to an environment that is much more unpredictable, it's a lot less precise and reliable.
  • The precision with which we can measure energy intake and expenditure in the field is low compared to what we can do in the lab.
  • For example, the typical error of measurement of energy intake is about 20%.
  • You also have a random error that can sometimes be up to 40%, depending on the methodology that you're using.
  • So this is very important to consider when you have someone with energy availability of 29 kcal/kg of fat-free mass per day. They try to fix that issue when they need help understanding that there are a lot of errors in calculating that value. 
  • On top of the calculation error, you are still determining what should be in the calculation and what energy expenditure we should calculate. 
  • It is relatively minor considering the amount of error you can get from the compounded error from energy intake and exercise energy expenditure. This formula takes only into consideration exercise energy expenditure for people that were in a lab-based situation and who were sedentary.  
  • We're currently trying to determine the best approach to bring this calculation to the field. 
  • However, it can give you a rough idea of what's happening with an athlete on the field, but we should highlight two things.
  • One of them is that you have to be very precise in the methodology used for calculation, which requires that you work with professionals to assess energy expenditure and energy intake.
  • The second thing is that you have to be careful about your measurement errors and the likelihood that the value you're getting is higher or lower. 

Threshold for low energy availability and the consequences

20:51 -

  • There's this general idea that there's this threshold of 30 kcal/kg of fat-free mass per day, under which your body starts to respond to insufficient energy. 
  • It comes from laboratory-based studies in well-controlled environments to understand the endocrine and physiological effects of reduced energy availability. But we must be careful in translating these endocrine and physiological responses to low energy availability to what they mean on the field. 
  • First of all, these studies were in sedentary females, but they have several limitations because we need more research to understand what happens in more active people. 
  • We also need to find out what responses exist to lower or higher energy levels and what happens with a more severe low energy availability for a shorter period.
  • In our review, we talk about this concept of low energy availability load (multiplying the time that you spend under 45 kcal/kg of fat mass )
  • We see a linear decrease in body mass correlated with severe low energy availability load.
  • Based on a few assessments, I would be careful in considering whether someone is in low, adequate or high energy availability. 

Consequences of low energy availability

24:52 -

  • Suppose you have a reduced amount of energy available for an extended period. In that case, it might negatively affect physiological health performance factors. 
  • It's essential to consider that energy might be a stressor the way exercise is. 
  • If energy generates some signal for adaptation, we might not get an optimal response to training if we don't use enough of it.
  • Looking at energy deficit or low energy availability might allow us to investigate the physiological responses to training with low energy. 
  • In the 60s-80s, female athletes would lose their menstrual cycle, and we did not understand why.
  • A range of studies could start teasing out that it was not the stress of exercise itself but the energy availability generating an endocrine disruption that would generate a hormonal profile that would be similar to the hormonal profile of female athletes that they didn't have these menstrual cycles. 
  • Three things associate with this: eating disorders, low bone mineral density and stress fractures. 
  • In its origin, the appearance of these related phenomena led to the description of the female athlete triad.
  • If you're in low energy availability, there's a high chance that you're going to have a disruption of your menstrual cycle (your reproductive function will be affected, and you will have low bone mineral density and stress fractures)
  • Then there was the development of their relative energy deficiency in sport, which is a different model that tries to explain what happened with low energy availability. 
  • They also describe low bone mineral density and issues with female reproductive function. They also extrapolate to males and many other factors caused by low energy availability. 

Other consequences of REDs or low energy availability

31:00 -

  • This information comes from cross-sectional studies that don't show a direct cause-effect relationship.
  • If you read the consensus statement about REDs, you will see many things supposedly caused by low energy availability with little evidence supporting it. Therefore, I couldn't stand behind this.
  • There's evidence to show that there might be some effects on haematological factors related to the production of red blood cells and haemoglobin mass.

Diagnosis and detection of low energy availability

33:24 -

  • We don't have a way to diagnose it.
  • So many endocrine parameters change when you put someone in a state of low energy availability. (IGF-1, leptin insulin, testosterone)
  • You maybe go to your clinician for a full analysis of all these black parameters, but, in the vast majority of the cases, these values are going to fall within sort of a physiological range (the clinician will tell you that it is on the lower ends but everything is normal).
  • However, this gives us the idea that your body has a physiological response to low energy availability.
  • So it is tough to diagnose from a blood test, for example.
  • Male endurance athletes tend to have a degree of hypogonadism (lower testosterone level) and a prevalence of amenorrhea in females (lower estrogen levels).
  • Detecting a chronic existence of low energy availability is much easier in females than in males. 
  • It doesn't mean a female would stop their menstrual bleeding if they have low energy availability, but the likelihood increases. 
  • They might have menstrual bleeding but don't ovulate, so there's a continuum of menstrual disturbances.
  • Other things to diagnose low energy availability has a low resting metabolic rate compared to a predicted formula. 
  • Resting metabolic rate is a rather noisy measurement, though.
  • No single tool will tell you a person has chronic low energy availability.
  • There are so many things associated with low energy availability that many signs could be a reason for someone suffering from this and not other things.
  • The field is at a stage where we cannot say someone has had low energy availability for an extended period. 

Practical take-home messages

39:45 -

  • I understand how alluring it can be for many endurance athletes to try to drop weight and improve their power-to-weight ratio to improve their performance.
  • Most athletes in endurance sports should pay attention to matching their carbohydrate intake to the training load.
  • Many athletes are under-fueling.
  • I'm not so conservative in terms of being fearful of someone being in low energy availability for a short period.
  • The problem is when it becomes chronic, and one of the main things we must be careful about is eating disorders.
  • I must give a full disclaimer here that I'm not an expert in eating disorders. Still, I think a lot of the time, the underpinning issues disorder eating or eating disorders rather than energy itself.
  • There are a lot of other issues, like anxiety and depression, that might as well have an endocrine effect, which goes beyond my knowledge.
  • If you are concerned that you are in an under-fueling camp, I will examine your carbohydrate intake.
  • Protein intake is essential, but start thinking about your training load with the volume and intensity of your training to the current carbohydrate recommendations for adaptation and performance.

Low energy availability and weight loss

43:44 -

  • The first thing to consider is why you're trying to lose weight.
  • Losing weight is easy comparatively.
  • You have to consider the potential risk and benefit for your performance and the potential for your health. 
  • You have to look at your training plan and pay attention to the high-intensity intervals of your training plan and how you will fuel those efforts. The more aggressive you are with your weight loss, the more careful you have to fuel the high-intensity efforts because they need muscle glycogen and carbohydrates.
  • Your training will suffer if you have low energy availability and chronically under-eating carbohydrates.
  • If you think about your nutrition on a meal-by-meal basis based on how hard you train and fuel the workouts accordingly, you will see a significant impact on how well you can manage that weight loss.

Prevalence of low energy availability among endurance athletes and higher training volume

46:21 -

  • First of all, it's important to understand we have to stop fearing and vilifying someone going into a little low availability and energy deficit. 
  • We must take a hard look at the potential adverse effects like stress fractures.
  • You might say high-level athletes and endurance athletes have a prevalence of low energy availability.
  • The cyclist papers show a prevalence of 100% of low energy availability if you look at specific days.
  • There is a relationship between athletes who do weight-bearing sports and Stress fractures and a relationship between higher training volumes and stress fractures.
  • These relationships can predict the likelihood of someone potentially being in low energy availability for an extended period. Considering cross-sectional data and comparisons between males and females, females are about three times more likely to have a stress fracture. 
  • Risk factors are high training loads in runners (for example, more than 11 hours a week), Being in a sport where individuals try to get linear.

Differences in males and women concerning sensitivity to low energy availability

49:59 -

  • I don't know the answer.
  • Only one study compares males versus females concerning low energy availability and markers like bone metabolism.
  • A comparison between studies suggests that females are more likely to be affected by similar energy availability levels. 
  • Epidemiological data shows you are more likely to have a stress fracture if you're a female. 
  • We might speculate that the cost of reproduction is higher. 
  • In females, we might have protective mechanisms. 
  • Over nine months of gestation for a woman, there's an energy expenditure of about 70 000 calories.
  • So it might be protective both for the baby and for the mother.
  • Whether the response to low energy availability is adaptive or maladaptive in females is information that I'm prepared to defend with any evidence.

Future research directions 

52:34 -

  • I would like to see the effect of low energy availability on muscle adaptation.
  • We have some data coming up on that. 
  • Understanding the low energy or low carbohydrate availability "zone".
  • I would like to see if low energy availability affects performance. 
  • If you have low energy availability, you also have low carbohydrate availability, and carbohydrates are essential for performance.
  • But controlling for that low energy availability might not harm performance unless you reach a breaking point.
  • We need to understand better whether you know energy.
  • I think it's like locomotion is so essential for survival that the body prioritises that above everything else.

Rapid fire questions

54:20 -

What's your favourite book or resource related to endurance sports?PubMed. 

And what's an important habit you have benefited from athletically, professionally or personally?  

Resilience. Keep moving forward despite failing.

Who is somebody that you look up to that has inspired you? 

In the academic world, Bengt Saltin and Louise Burke have been inspirational for me.


Bernardo Gonçalves

Bernardo is a Portuguese elite cyclist and co-founder of SpeedEdge Performance, a company focused on optimising cycling and triathlon performance. He writes the shownotes for That Triathlon Show, and also produces social media content for each new episode.

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