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Understanding “Energy In vs Energy Out”

Personal Training

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In some form or another, the vast majority of individuals will have heard of Energy In vs Energy Out (EIEO), or Calories In vs Calories Out (CICO), as a concept.

Whether it’s in magazines, online articles, through working with a coach or following some form of nutritional guidance, this fundamental requirement for energy balance permeates the nutritional field. 

At the heart of CICO lies the first law of thermodynamics, a version of the law for conservation of energy. The first law states that in any transformation the total energy in a given system can be accounted for by the heat added to the system, the work done outputted on its environment and the change in energy content of all the components of the system.

As it relates to nutrition at its simplest form, energy balance in determined by the amount of calories consumed (calories in) vs the calories expended (calories out).

Whilst it’s possible to debate whether within complex dynamic systems such as humans, we can ever condense it down to be this simple with so many interactions at play between systems, very little in nutritional science makes sense without recognising this law of thermodynamics.

Part of the challenge in applying this concept successfully is appreciating the complexity on both sides of the CICO equation. We are a system that’s constantly yearning for homeostasis. As a result, there’s a multitude of factors at play that underpin both our energy intake and our energy expenditure.

We’ll begin with energy intake. 

The amount of food we consume during a day is closely tied to the regulation of appetite and hunger signalling. 

Both appetite and hunger signalling are a combination of the interactions between;

  • Cultural factors such as meal timing and the number of meals within a day
  • Environmental factors such as the presence of family and friends whilst eating vs eating alone, eating in front of the TV, seasonal changes and the weather), the environment around us (temperature of the room, colour of the walls…
  • Physical factors such as the influence of exercise/daily activity, psychological state (anxiety, depression, tiredness…), as well as actual physical health of the individual (i.e. during periods of ill health/disease/stress). 

We likely also cannot rule out the potential influence that both medications and drugs can have on appetite regulation. Certain Antidepressants and Corticosteroids have known secondary side effects of increasing appetite, whilst Antibiotics and forms of Chemotherapy can significantly suppress hunger signalling. Factors worth considering where appropriate.

Underneath the seemingly simple decision to choose whether to eat, what to eat and how much to eat, are a host of individual interactions between multiple systems.

Above all of these contributors however, is how much cognitive oversight and control we can consciously apply to managing energy intake. 

Essentially do we have sufficient control in the presence of these contributors to enable regulation of appetite to achieve energy balance?

Each of us will have a unique perspective on these factors of energy intake and appetite regulation. Food means different things to different individuals, we each have our own preferences for what, how and when. Certain individuals may have incredibly rigid structures around food intake, which enables them to achieve an outcome, others succumb to the cultural, environmental and physical contributors that lead to short term energy intake exceeding output resulting in long term weight gain. 

To see just how complex the process of energy intake is, I strong recommend spending a few minutes aiming to dissect the Foresight Obesity Systems Map (Vandenbroek et al. 2007). Within it you’ll see the endless positive and negative feedback loops between the influence of biology, activity environment, physical activity, societal influences, individual psychology, food environment and food consumption.

On the alternate side of our CICO equation we have our energy expenditure. In a similar fashion, the management of daily energy output is tightly regulated. 

Energy Output is often subdivided into four areas each contributing to the amount of energy we expend on a daily basis. 

The first of which is our Basal Metabolic Rate (BMR) often used synonymously with Resting Metabolic Rate (RMR). BMR is an estimation of energy expenditure for maintaining the most basic life-sustaining functions (breathing, cell production, circulation, nutrient processing etc…). 

BMR itself is influenced by multiple factors specific to the individual, such as age, sex, genetics, fetal micro-environment (time in the womb), hormonal status (specifically thyroid hormone) and lean body mass. BMR represents the vast majority (~60-70%) our energy expenditure under normal circumstances.

Our next variable on energy output is the Thermic Effect of Food (TEF). TEF describes the amount of energy required for the digestion, absorption and disposal of the nutrients we ingest. Put simply, it takes energy to break food down. 

This variable can contribute potentially 10-20% of our daily energy expenditure. TEF has however been shown to be influenced by age, physical activity (increased TEF in more active individuals), meal size (large vs small), meal composition (carbohydrate, protein and fat content, processed vs unprocessed), frequency and timing (AM vs PM).  

Our third variable is Non-Exercise Activity Thermogenesis (NEAT). This involves the daily movement we perform outside of organised physical exercise. This can include factors such as fidgeting, gesturing during conversation, climbing stairs, walking the dog, mowing the lawn, gardening, walking to and from work, playing with your kids. Essentially all unstructured activity and movement throughout the day. 

Tools such as FitBit, Apple Watch and Garmin are used as rudimentary estimations of NEAT by tracking measures such as Standing Time and Step Count.

The final variable is Exercise Activity Thermogenesis (EAT). 

Examples of EAT include participation in all forms of structured exercise, whether it be a circuit class, visit to a gym, playing a sport recreationally or professionally, or going for a swim. EAT represents the additional calorie expenditure outside of what would be associated with BMR, TEF and NEAT. 

Unfortunately many of the measures of EAT within commercial settings such as cardiovascular machines fail to distinguish between these variables, leaving individuals often to vastly overestimate the amount of EAT they’ve performed. For example a treadmill may indicate a 250kcal burn across a 30min run, however this doesn’t take into account the fact that without running we may have burned 100kcal regardless through BMR/TEF/NEAT, our estimation of EAT would therefore be more in line with 150 additional calories as opposed to 250kcal total.

When it comes to establishing an energy balance for the purpose of possibly maintaining, losing or gaining bodyweight, we need to recognise the variables at play on both sides of the CICO equation and understand where directed intervention needs to be placed.

In the presence of the individualised bio-psycho-social factors of energy intake, we’re likely first going to have to establish a degree of cognitive oversight over nutritional intake.

For some individuals this may require little effort within a controlled environment in which they can successful regulate appetite and maintain energy balance. For others, this may come in the form of direct intervention with a coach, nutritionist or dietician with the use of structured or flexible meal templates, food diaries or tracking tools, or changes to societal, personal or working environments to support greater appetite regulation. 

With regards to Energy Out in the context of BMR, we can begin to appreciate the variables at play that we can, and cannot, have influence over. We cannot change our age or gender in the context of BMR. We likely also cannot have an influence over genetics to any discernible degree. Likewise, our foetal microenvironment. 

However, there are potential influences within hormonal status on those individuals with disregulation of the Hypothalamic-Pituitary-Thyroid Axis through example such as Hypothyroidism, however this will almost certainly require formalised medical intervention. 

We’re therefore left with the influence that Lean Body Mass (LBM) has on BMR. The role of increasing muscle mass within individuals will be something discussed at length within future insights, however it’s important at this early stage to recognise its potential beneficial influence.

In terms of TEF, we have already discussed how age, physical activity, meal size, meal composition, frequency and timing, may all play a role within energy expenditure with TEF contributing to ~10-20% of daily expenditure. Moving individuals towards a more structured, whole-foods diet is likely to play a large role in how great an influence TEF can have on this equation.

Of all four contributing variables, NEAT is likely to have the biggest scope for overall change. Research has shown that daily physical activity above certain threshold (established as an activity level corresponding to 7116 steps…) enables an individual to better couple energy intake with energy expenditure. 

Bringing an individual up to this level (~8000 steps per day) is likely to be a powerful contributor for both appetite regulation on the level of intake and energy expenditure in the form of increasing low-intensity daily movement.

Finally we have the role that EAT may potentially play. Whilst we have already recognised that the additional energy expenditure of EAT, above what would be achieved regardless, may often be overestimated, multiple benefits still remain. 

We’re all acutely familiar with the health benefits of regular exercise and physical activity, from reducing the risk of cardiovascular and respiratory diseases, management of blood sugar and insulin, strengthening of bone density, increasing muscle mass, improving symptoms of anxiety, stress and depression as well as increasing sleep quantity and quality. These secondary benefits outside of simply increasing caloric expenditure should not be underestimated.

This insight has provided a brief look at the complexity at play within what seems a fundamental equation in terms of Calories In vs Calories Out. There are variables across both sides of the equation that have complexity underpinning them. Nutrition as a field is complex, working with an individual requires time and often large amounts of investment on both the side of the coach and client.

It benefits when working with individuals to recognise this complexity, understand the potential interplay taking place and begin to look at individuals not as equations but unique interpretations of multiple systems interacting at any given moment.

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