Why some calories are more equal than others

The reason the diet/regime that worked for your friend has not worked for you is because not all calories are equal and, this is exacerbated by the way each of our unique bodies (and minds even!) digest and absorb different foods


What is a calorie?

 A calorie is a unit of measurement of how much energy is stored in a certain amount of food. One calorie is the amount of energy it takes to raise the temperature of 1kg of water by 1C.
You will have seen food packaging that refers to “Adult RI” (adult recommended intake) of 2000kcal and 2500kcal for women and men respectively. This amount is an 'average' and will vary widely depending on height, current weight and level of activity.

The first law of thermodynamics

“Energy can never be destroyed only changed from one form to another”. So, the energy in that chocolate bar will either be converted into energy that is used up because:

  • Your body needed it to keep your metabolism running (i.e. breathing, thinking, digesting, etc.)
  • Your body needed it for some type of activity (i.e walking around during your shift as a nurse, etc.)

Or it is converted into energy that gets stored as mass for later usage. The mass can be stored in our bodies:

  • as muscle, if your body regularly does high-intensity activities that require physical strength (i.e. an athlete, builder, etc)
  • or as fat

However, the story does not end there.

The second law of thermodynamics

“… any complex system will experience increasing disorder over time… the energy that drives organisms will always leak out depending on levels of inefficiency…”
Different foods have different levels of metabolic efficiency. Foods with high metabolic efficiency experience little leakage. We can retain and use (or store) almost all the energy from high metabolic efficiency foods.

Conversely, foods that have poor metabolic efficiency make your body work harder in order to digest and make use of the energy contained in them. Learning to use heat (fire) on our food is probably what kept the human race from dying out during the last Ice Age as it allowed us to get much more energy out of limited food supplies. Cooking may also be responsible for the rapid development of brainpower that occurred in human species over the last 100,000 years (the brain uses over 20% of the body’s total intake).

Problem is, this is no longer such an advantage now that we have central heating and readily available food. Cooked food has a far superior metabolic efficiency compared to raw fruit and veg. So, calorie for calorie, your body will get the benefit of a higher percentage of the energy in a baked pear than its raw equivalent.

Processed foods 

More recently, we have gone a step further in terms of food preparation and in industrialised countries, much of our diet is made up of processed foods. Processed foods have been found to be ultra-efficient when it comes to metabolic efficiency.
A 2010 US Study [1] found that 'whole foods' require much more energy to digest than equivalent processed foods. In the study, volunteers were assigned to eat:

  • Processed food sandwich – white processed bread and processed cheese.
  • Whole food sandwich – multigrain bread and cheddar cheese.

Both sandwiches had roughly the same nutritional content – 20% protein, 40% carbs and 40% fat; and portions were designed to be equivalent in terms of total calories contained.
The proportion of energy from the meal used to digest the whole food meal was 19.9% while the proportion for the processed food meal was 10.7%.

Why would this matter?

If I took twins and fed one of them the whole food diet; and, fed the other the processed food diet consistently, the processed food eating twin would gain double the amount of weight as his whole food eating brother; even though on the face of it they were consuming the same number of calories and nutrient. And what if stress is involved?

Woman cooking with stove

Stress and metabolism

A 2014 study [2] on the effect of stress on metabolic responses to meals that have similar calorie content, found that participants who reported stress during the previous 24 hours burned fewer calories than those who reported no stress.
Therefore, if I take my twins again – this time they eat exactly the same type of food, with same calories – however I subject one to on-going chronic stress; my stressed-out twin will gain more weight over a sustained period than the laid-back twin – all else being equal.

Stress and appetite 

Different types of stress can elicit different types of responses in different kinds of people. However, the observed trend is that acute/high stresses – e.g., chronic illness or a death in the family, may commonly decrease appetite levels; while milder/on-going stressors – e.g., ongoing relationship issues, work dissatisfaction, etc. tend to increase appetite and lead to seeking out more frequent meals and/or calorie-dense meals – typically known as stress-eating.

Sustained/chronic stress acts on the nervous system to release cortisol. Cortisol increases appetite and increases motivation. 

Having a hormone response like this was fantastic for humans back when we lived in caves and had to deal with predators as well as figure out where the next meal might come from. A hormone that made us eat high-calorie food and kept us motivated to continue eating whilst food was available, probably helped us survive long periods when there was little or no food; or even survive pregnancy (for women) when there was minimal food.
These days though, it just means we end up in front of the fridge after an argument with a colleague! An ability to deal with on-going stress can be key to eating well and managing one’s weight.

So, who said all calories are created equal?

As we can see, there’s much more to successful weight management than counting calories. To achieve lifelong change will require working on the whole person – physical and mental. 
A good nutritionist should have the skills to support you with understanding how to select the right foods for you and also how to design a life/lifestyle that will keep your hormones in balance thus avoiding stress-eating or other cravings.

If you would like to see more articles like this, contact me via my profile and I will share more insights, recipes and guides aimed at helping you feel great and full of vitality.

[1] Postprandial energy expenditure in wholefood and processed-food meals: implications for daily energy expenditure – Sadie B. Barr and Jonathan C. Wright
[2] Daily stressors, past depression, and metabolic responses to high-fat meals - Janice K Kiecolt-Glaser et al

The views expressed in this article are those of the author. All articles published on Nutritionist Resource are reviewed by our editorial team.

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London SW1Y & NW9
Written by Ola Molade
London SW1Y & NW9

Ola is a qualified Nutritionist and Transformational Coach who focuses on supporting people that work in high stress environments. Ola offers face-face and/or online consultations that help people wishing to develop new habits in relation to food and lifestyle choices.

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