What is Food? Part II: A Source of Energy

In the previous post I asked the question, “What is Food?”

In short, the conclusion was that there is no such thing as food!

Rather, the term “food” is a label we apply to living organisms that we choose to eat, and that all living organisms can be assessed as a potential food source based on how they measure up as a source of the following factors:

  • Energy
  • Raw Materials
  • Toxins and Anti-Nutrients
  • Pleasure

In this post, I’m going to look at food as a source of energy.


I think we can safely assume that everyone is aware that food is a source of energy.

This knowledge on its own doesn’t seem to be helping the majority of the population make good decisions about what, when, and how much to eat, however, so I think the topic needs some further investigation.

Perhaps one major issue, is that the majority of people, and most of the mainstream advice, focus purely on the energy aspect of food, overlooking the fact that it is so much more, but I digress, that is subject matter for parts III and beyond…

The conventional wisdom says that all that matters is calories in vs calories out. Proponents of this theory often quote the first law of thermodynamics (Energy can neither be created nor destroyed, only changed from one form to another), to argue their case that if you eat 3000kCal, unless you burn 3000kCals of energy through a combination of your BMR (base rate metabolism) and physical activity, any surplus calories will be stored as fat.

Equally, they argue, to lose fat you must consume fewer calories than you burn.

There are others, however, that argue that not all calories are created equal, and that certain macronutrients are more likely to be converted to fat than others. Some argue that it is fat that makes you fat, as it is twice as high in kCals per g and does not need to be converted before it is stored, others that it is carbohydrates that make you fat, as they stimulate the release of insulin, the storage hormone when they are consumed.

Contentious as ever, I would argue that they are all somewhat off the mark.

First, lets look at the calories in vs calories out theory.

I am certainly not questioning the first law of thermodynamics – It is true that energy cannot be created or destroyed, only changed from one form to another. This does not necessarily mean, however, that all the energy in a food which is consumed must be either burned or stored by the body.

This scientist clearly has a better understanding of the principles of energy conservation than most dieticians, as he has recognised the fact that poo is potentially a lucrative source of renewable energy!

When calorific values of foods were first calculated, it was done by simply burning the food in a device called a bomb calorimeter. The food in question is burned to dust, and the total amount of energy given off is measured.

The human body, however, is not a bomb calorimeter. We do not excrete carbon dust. As seen from the link above, there is still sufficient energy left in our faeces to generate electricity!

Scientists are now beginning to understand that the proportion of the energy stored in a food that can be extracted by the person eating it can vary wildly, and that there are in fact many factors which can affect the process.

Genetics/Gut Flora

Some people are simply more efficient at extracting energy from their food. Give two people exactly the same meal, and each will extract a different proportion of the calories from it.

This could in part be down to their genetics – just as some people can lift more weight, run faster or see further, there is also going to be variability in digestive efficiency.

Perhaps more significant than this however, is a person’s gut flora. Studies have shown that the type of bacteria in an individual’s stomach has a huge effect on the number of calories that can be extracted from the diet. Obese individuals have been shown to have different types of gut flora to lean individuals, gut flora that extracts a much higher percentage of calories.

Studies in mice have shown that simply transferring the gut flora from an obese mouse into a germ-free mouse (a mouse with no gut flora) will make it spontaneously gain fat with no increase in calories. (Check this article for a good summary of the research)

Raw vs Cooked

Cooking and other food preparation techniques such as soaking, blending, grinding, fermenting, etc, all work to make foods more digestible. In his book Catching Fire, How Cooking Made us Human, Dr Richard Wrangham argues that humans have adapted to a diet of cooked foods, and are no longer able to efficiently extract calories from raw foods, hence the success for raw food diets for rapid weight loss (and their inadvisability as a long term option!).

Meal Size?

This is pure speculation, but one might expect that the larger the volume of food consumed in one sitting, the harder it would be for the body to extract all the calories from it. For example, if you were to eat 3000kCals in 2 x 1500kCal meals or 6 x 500kCal meals spread throughout the day, one might expect that the body would be more able to effectively deal with the 6 smaller meals, and extract more of the calories, than from the larger deluges from the 1500kCal feasts. Perhaps an additional way in which a more IF style eating pattern can help.

Assuming that weight gain or weight loss can be calculated by subtracting a person’s BMR + Energy expenditure through activity from the total calories contained in their food is clearly and over simplification.

Are all Calories Created Equal?

Ignoring alcohol for the time being, the stored energy in food comes in three different forms: Protein, Carbohydrates and Fats. (Actually, this is probably a gross over simplification – Just like the term food, the macronutrient names are labels assigned by humans to molecules we decide should be grouped together based on similarities of chemical structure. The effects, roles and uses of different proteins/carbs/fats can vary widely).

There is now general agreement that although a gram of protein may contain 4kCals, due to its high thermic effect of feeding (i.e. it takes considerable energy to break it down), it should really be classed as nearer to 3. The chemical process of converting protein to stored body fat is also very costly in terms of energy and highly inefficient (though this does not mean it is not possible).

Though it does take energy to break down carbohydrates into digestible monosaccharides, it is considerably less than the cost of digesting protein, and therefore the potential net calorie gain is more likely to be closer to 4kCals, though this will vary depending upon the type of carbohydrate, and all the factors listed in the previous section. Unlike protein, carbohydrates can be readily converted into fat stores with little energy waste.

Fat contains 9cKals per gram, is relatively easy to digest, and requires little energy to be put into storage.

Based on the above, it’s easy to see why dietary fat was suspected of being the villain in driving unwanted weight gain – It contains more than twice the energy gram for gram than the other macronutrients, in a form which is easily accessible and store.

The low-carb proponents point to the fact eating carbohydrate rich foods stimulate the release of insulin, predominantly a storage hormone, though perhaps this overlooked the fact that the body can also store fat via other methods.

In my opinion, both sides are a little patronising towards the “intelligence” of the human body. To explain, let me use an analogy:

A person has a log cabin, within which pretty much everything is made from good quality hard wood.

Inside the cabin, they have a wood burning stove. This stove is used to heat the cabin, cook food, and various other tasks such as firing earthen ware, forging simple iron tools etc.

The cabin gets three kinds of deliveries:

High Quality Hardwood Timber – This is hard to cut, doesn’t burn well, awkward to store, but is important for keeping the cabin in good repair, building furniture etc.

Firewood – This burns fast and hot, is great for heating things up quickly or when an intense flame is needed. It’s easy to store and can be accessed quickly from the cupboard next to the stove.

Coal – This gives a slower and more sustained heat. It is stored in the coal shed where it can be accessed relatively easily.

Under normal circumstances the person would use each of the substrates for the appropriate task as and when needed. They’d probably have a regular order on for all of them, which they could adjust up or down as necessary if they found themselves using more or less of either than usual.

Depending upon the timing of deliveries, the inhabitant of the cabin may use the fuel as soon as it is delivered, or use some out of the stores, and then replenish it when more arrives.

If firewood starts to run unusually low or runs out altogether, coal can be burned exclusively and will still do the job, even if it is not entirely perfect for all situations, and vice versa.

Because it is expensive, difficult to cut, and doesn’t burn well, the inhabitant is reluctant to burn the high quality hardwood timber for fuel. They would only do so in dire circumstances when supplies had been cut, and there was not enough firewood or coal left to provide enough energy to heat the cabin and cook.

If the situation got really severe, and all supplies got cut off for a prolonged period, they may even have to resort to stripping down the walls and furniture and burning this for fuel, but this would be a last resort!

For some reason, however, it seems that some cabin dwellers just keep over stocking on coal and/or firewood, consistently over ordering more fuel than they can use, with their storage areas getting fuller and fuller to the point of over flowing.

Perhaps they’ve lost the key to the coal shed and can’t seem to get through to the delivery man to tell him to stop coming to fill it up, maybe they just love chopping firewood, even if they’ve got more than they can burn, or perhaps they’ve just got in the habit of ordering the same amount and can’t get around to changing it…

One possible solution is to cancel either the coal delivery or the firewood delivery. This could certainly solve some of the problems, they’d have less fuel coming in, and could adapt to using whichever fuel they received for all purposes. Is it an ideal solution though? I’d say far from it.

Would a better option not be to find the key and unlock the coal shed, get in touch with the delivery man, learn to just chop enough wood as you need to burn (while still really enjoying cutting it), and get in the habit of only ordering as much of each type of fuel as you really need?

OK, I know it’s not a perfect analogy, but I hope you get the gist.

The point I was trying to make, is that neither carbohydrates nor fat are necessarily more or less fattening than the other. If you eat too much of either, both can make you gain unwanted body fat. In countless studies, both low carb and low fat diets have been shown to be equally effective for weight loss, as have low calorie diets with moderate amounts of both.

Another argument of course is that it’s the type of carbs or fats that make a difference – Are they fast or slow releasing etc. Going back to the analogy again however, if your coal burned faster or slower, should this really make a difference to your stock levels providing you continue to order more at the rate at which you use it?

What makes people gain fat is the consistent and unrelenting over consumption of calories.

I’ve talked before about why people get fat, and it’s a topic that deserves revisiting in detail in the near future.

Why is it that some of us don’t seem to be able to regulate our appetite in the same way as others?

The reasons are many and varied, but below is a brief summary split into two main categories:

  • Physiological


Inflammation seems to be at the root of pretty much every modern disease. It’s causes are numerous and varied, from toxins in food and the environment, emotional stress, physical stress from over-training/working, lack of sleep, dysbiosis of the gut flora, illness, the list can go on and on.

In terms of appetite dysregulation, inflammation appears to cause signalling problems with hormones such as leptin, insulin and grehlin to name but a few, effectively meaning that the thermostat/petrol gauge is broken and we no longer no when to stop eating!

Nutrient Deficiency?

Paul Jaminet, author of The Perfect Health Diet has convincingly argued that one contributing factor to the over consumption of calories could be nutrient deficiency. The body is crying out for much needed raw materials, but all it gets is empty calories…


It appears that an imbalance of the gut flora can lead to problems with calorie and nutrient extraction, satiety, and of course affects stress and inflammation. Oh it’s a tangled web indeed!

  • Psychological

Though all of the above are real and significant contributors to obesity, I am becoming ever more convinced that simply eating when we are not hungry is the major causal factor in unwanted fat gain. Why we eat when we’re not hungry is again a complex question with many possible answers.

Fear of Hunger

“Lose weight without the hunger pains” “Keep Hunger Locked Up ’till Lunch” “Keep Hunger at Bay” We’ve been conditioned into thinking that hunger is an abnormal state that should be avoided at all costs. Eat as soon as you wake up, graze throughout the day, carry snack bars around with you, but don’t worry if you forget as there’ll be a vending machine on every corner just in case…

Hunger has been demonised, made into the villain. For most people, the unknown is scary, and most people have no idea what it’s like to actually be hungry!

This interview with professor and MD Dr Lovell-Smith on his research dissertation into the importance of the perception and recognition of true hunger, or the “empty hollow sensation” is fascinating.

This is, in my opinion, one of the major benefits of intermittent fasting. It teaches you not only what true hunger actually feels like, but also that it is not something to be feared, but rather something to be appreciated. It can make you more alert, more active, you can achieve PBs in the gym, get around to organising the spare room or writing that blog post… Plus when you do finally eat, you really relish and enjoy every mouthful, rather than wolfing food down thoughtlessly without even registering its consumption.

Do yourself a favour. If you’ve not tried IF yet, do it now. You need no special equipment, preparation or anything else. Simply don’t let any food pass your lips for the next 24 hours. (NB Small medical disclaimer: If you’re pregnant, have a medical condition, or have to operate heavy machinery or perform brain surgery etc, please use some uncommon sense).


This is really an extension of the above category. Many of us may not be consciously aware of having a fear of hunger, or a lack of awareness of what true hunger feels like, but still mindlessly eat unnecessary calories out of habit and convention.

The timings of meals and sizes of portions we eat tend to be dictated not by our cravings, or basic calorific needs or our activity levels, but by the size of our plates, the recommended serving size on the box, or the portion size served by the restaurant.

If two people eat the same size bowl of cereal for breakfast, the same pre-wrapped sandwich for lunch, the same packet of crisps, snack bar and can of SSB throughout the day, and the same packaged meal for tea, what are the chances that they both actually required the same number of calories?

This problem is made worse by the fact that most of us have been conditioned to “always clear your plate” – Good advice during war ration times perhaps, but not so much now we’ve been invaded by supermarkets and every street is occupied by a Tescos…

Emotional Eating

This is perhaps the most dangerous kind of over-eating, where food is used as some kind of extrinsic reward.

Eating out of boredom, eating to reward yourself for “good behaviour”, eating to try and fill an emotional void – In some cases perhaps even eating something “bad” be it intentionally or unconsciously in some kind of twisted self-harm-esque manner.

So the question of why people over consume calories is a complex one, with many inter-related and nuanced factors. There are however, a couple of useful facts that can help us in the short term to get things on track whilst we begin to address all the physiological and psychological issues highlighted above.

People tend to eat the same volume of food each day

There are many different factors that regulate appetite, some operate over the long-term, others the short term. One such short-term factor is the simple physical presence of undigested food sitting in your stomach. Irrespective of all the above listed points, most people tend to eat the same volume of food each day, regardless of calorie content.

Protein is more satiating than other macronutrients

Another short term factor is the amount of protein in a food. Protein stimulates the body to produce more of the hormone ghrelin than either fat or carbohydrate. This is a hormone responsible for producing the feeling of fullness after a meal.

When I do finally get around to writing that post on how to actually make decisions on which foods to eat (which I will do eventually I promise…) these two factors are going to play an important role.

Before I conclude this post on calorie basics however, I thought it useful to address two other FAQs I get on the subject:

1) Is a calorie deficit necessary for weight-loss?

Yes, and no, is the short answer.

Any regular reader to this blog will know that I’ve never been a fan of short answers though!

There is most definitely more to it than simple calories in vs calories out. There is plenty of anecdotal evidence out there of people that claim they have lost body fat whilst on very high calorie diets. Quite possibly with a super clean diet, optimum exercise plan combining hypertrophy training and HIIT, plenty of sleep and a stress free life, I could see this working, maybe.

I don’t however, see much science to back this up. Neither can I imagine that even if it is a realistic option, that you wouldn’t lose fat faster, and more easily with some form of calorie deficit.

That said, a calorie deficit certainly does not guarantee fat loss. A calorie deficit with suboptimal food choices, no training or over-training, lack of sleep and poor stress management can easily result in lean tissue loss and even fat gain!

There is also no reason to say that a calorie deficit need be severe or chronic (I.E. all the time). Trying to stick to a low calorie diet 7 days per week is a sure fire recipe for disaster. I firmly believe cyclical dieting to be the most effective strategy, both physiologically and psychologically. Using strategies such as Intermittent Fasting you can alternate between periods of calorie deficit and calorie balance, or even surplus, over a period of time such as a week or even a day.

2) Is a calorie surplus necessary for muscle-gain?

I’ve seen plenty of people gain a lot of mass through protocols such as GOMAD. How much of it, if any, was muscle is another question however, as are the effects it may have on your long term health (or bank balance if you’re drinking organic grassfed buffalo colostrum by the gallon which I’m sure is what all the cool kids are doing).

Now my take is that it all depends upon what you call surplus. It certainly does take energy to build muscle, that is indisputable. Your body requires energy for running its day to day processes – Keeping your heart pumping, lungs breathing, liver filtering, etc, etc. It also requires energy for movement. These are pretty high priority tasks. From an evolutionary perspective, muscle is a pretty low priority luxury. Its not that useful, can even slow you down, and uses valuable calories that could be used elsewhere. We’re a successful species because of our big brains, not our big biceps…

The GOMAD and EEIS (Eat everything in sight) type strategies seem to hinge on the premise that if you keep bombarding your body with more calories that it can ever possibly use, it’ll figure that it can spare some to build and feed some muscle.

Though this may work, you will invariably gain some fat in the process, and chances are when you cut the calories back in order to strip the layers of flabby fat off your new found muscle your body could well decide the new muscle can’t be afforded any more!

I would say that a better strategy would be to make your body prioritise muscle. Follow a well designed, high intensity strength training program that gives your body no choice but to try and grow some muscle to keep up. Your body will respond by asking for more calories via stimulating your appetite.

Keith Norris addresses this same question here and I like his appropriation of Gary Taubes’s example of the growing child: A child eats lots of calories because he is growing, he doesn’t grow because he eats lots of calories. As we see all too often, feeding a child lots of extra calories will not make them grow bigger or faster, just fatter and sick.

1 thought on “What is Food? Part II: A Source of Energy”

  1. Pingback: What is Food? Part V: A Potential Source of Pleasure - Live Now, Thrive Later

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