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Understanding “Energy In vs Energy Out”

Personal Training

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In some form or another we’ve all heard the basic concept of Energy In vs Energy Out (EIEO).

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

At the heart of EIEO lies the first law of thermodynamics, 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 simple nutrition, our 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 EIEO equation. We’re all a multitude of systems that’s constantly yearn for stability and homeostasis. As a result, there’s a wide array of control mechanisms within the body that underpin both our energy intake and our energy expenditure.

Let’s take a look first at the Energy Intake side. 

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 with distractions such as in front of the TV, seasonal changes and the weather, the environment around us such as the temperature of the room, colour of the walls, to name but a few.
  • 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). 

* As a brief side-note, we also likely cannot rule out the potential influence that both medications and drugs can have on appetite regulation. It’s widely know that certain Antidepressants and Corticosteroids have secondary side effects of increasing appetite. Whilst Antibiotics and forms of Chemotherapy can significantly suppress hunger signalling. Factors potentially worth considering depending on circumstance…

Underneath the seemingly simple decision to choose whether to eat, what to eat and how much to eat, are a host of interactions between multiple systems. Yet essentially the question becomes do we have sufficient control in the presence of these known factors to enable regulation of appetite and achieve energy balance?

Each of us will have unique perspectives and experiences in terms of energy intake and appetite regulation. Food means different things to different individuals, we each have our own preferences for what we like to eat, in what way and when.

There will be those amoung us that may have incredibly rigid structures around food intake. Possibly a useful behaviour to have in some circumstances, an hinderance in other potentially…

Others may be more heavily influenced by the cultural, environmental and physical contributors that can 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.

It’s never just as simple as telling an individual to eat more or less.

On the opposing side of our EIEO equation, we have our Energy Output.

In a similar fashion, the management of daily energy output is tightly regulated. Energy expenditure can be subdivided into four areas, each contributing to the amount of calories we burn 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%) of our energy expenditure under normal circumstances.

Our next variable with 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 down the food we turn into energy.

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. 

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 EIEO 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. We need to develop some awareness of what we’re taking in on a daily basis.

For some individuals this may require little effort within a controlled environment in which they can successful regulate appetite and maintain energy balance in which intake looks similar day-to-day. 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, firstly considering BMR, we can begin to appreciate the variables at play that we may and may not have influence over. Put simply we cannot alter our age or sex in the context of changing BMR. We also likely can’t have an influence over genetics to any discernible degree at this point in time. Likewise, the influence of our time spent inside the womb of our mothers…

However there are potential influences that are changeable in terms of down regulated hormonal status such as those suffering with Hypothyroidism, however this will almost certainly require formalised medical intervention. 

So we’re left therefore 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. The more muscle we have, the higher BMR is…

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 ~7000 steps…) enables an individual to better couple energy intake with energy expenditure. 

Bringing an individual up to this level and possibly beyond in time, is likely to be a powerful contributor for both appetite regulation and energy expenditure in the form of increasing low-intensity daily movement.

Finally we have the role that EAT may potentially play.

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.

The key here to remember is that nutritional science and coaching is a complex field, 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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