Are All Calories Created Equal?!
The Nuances Beyond "Calories In vs. Calories Out"
When it comes to nutrition, "Calories In vs. Calories Out" is a phrase frequently echoed by fitness professionals. It has become somewhat cool to be a part of the “Energy Balance Brigade”, and don’t get me wrong. I’m also a part of that brigade, energy balance is in fact the key to weight loss or weight gain. BUT I am far from a militant extremist that deems the 5-word phrase CALORIES IN VS CALORIES OUT to be the be-all of nutrition. If it were I’d have wasted several thousand hours and several thousand pounds studying the field.
Humans are not simple machines that consume energy and expend energy with absolutely no other factors affecting us. We are complex (some more than others) and nutrition is as complex a field as we are. Here we are going to discuss why not all calories are created equal. We’ll do this by focussing on the fact that humans consume food. We do not simply consume calories and several factors play a role in how much energy we actually get from food! Let’s dive straight into it, shall we?
The Science of Energy: More Than Just a Numbers Game
So we start with a cold hard physical truth. The law of conservation of energy. Energy cannot be created or destroyed, simply converted from one form to another. Calories are quite simply a unit of energy. So in this way, 1 calorie will always equal 1 calorie (or 4184 Joules).
Using the law of conservation of energy we can also see that it is true that to lose weight we must consume fewer calories than we expend. As if we do not consume enough energy to carry out all our metabolic functions we’ll need to source some from elsewhere, we cannot simply create energy. We instead convert chemical energy stored as glycogen or adipose tissue (and sometimes even as muscle protein) to mechanical energy allowing us to go about our day. This depletes our energy stores be it from glycogen or adipose tissue and we lose weight. BOOM. CALORIES IN VS CALORIES OUT!
But, it is a lot harder to achieve this consistently in day to day life as anyone who has attempted to alter their weight has found. This is because we eat food! We get our calories from (for the most part) carbohydrates, proteins and fats. And each of these is metabolised differently, the form/food groups in which we consume these will affect many things such as satiety, hormones, energy expenditure and other biochemical pathways.
You’ll know from personal experience that it is a lot easier to eat 1000kcals of ice cream than it is to eat 1000kcals of chicken or salad. This is majorly due to the energy density of these foods, Ice cream being relatively high in fat and fat carrying 9kcals/g as opposed to carb and proteins measly 4kcals/g (and alcohols 7). BUT there is more at play. The first thing we’ll touch on is a component of our energy expenditure called the Thermic Effect Of Food.
Thermic Effect of Food: The Hidden Energy Cost
Now another law of thermodynamics tells us that it is impossible to extract an amount of heat and use ALL of it to do the work. This refers to the efficiency of a system, the efficiency of energy transfer. The food we consume is no exception to this. In physiology, this law manifests itself as the aforementioned thermic effect of food (TEF).
The TEF is quite simply the bodies increase in metabolic rate after ingestion of a meal. It requires energy to digest, absorb and metabolise nutrients so not all the energy we ingest goes to moving. In a rather unshocking twist of events, the metabolic pathways of protein are less efficient than those of fats and carbs! This means that a significant amount of the energy we consume from protein is not stored! Let’s throw some numbers out, the TEF of protein is around 20-30%, for fat, it is around 1-3% and for carbs its 5-10%. SO let’s eat 100 kcals of each of these macros. 100 kcals of protein equates to 70-80 kcals of energy NOT put to metabolising it, 100 kcals of fat, 97-99 kcals and for carbs 90-95 kcals.
SO we can see here that already it is not as simple as just calories in vs calories out. Protein gets another gold star next to its name when talking about weight loss due to its effect on satiety too!
The Role of Satiety in Weight Management
Satiety is simply the feeling of being satisfied or full when it comes to food. LOTS of factors play into the regulation of food intake, both physiological and psychological and we still have a lot more to learn on this subject. One thing we do know, however, is that increasing protein intake can lead to weight loss without counting calories, simply because it makes you feel more full upon eating it. Moving away from macronutrients and into food groups, satiety is still very much a thing and I could write blog after blog on many regulators of satiety too. For now, though we’re just going to briefly touch upon the satiety index of certain foods. Satiety index is the measure of how full something makes you feel.
Foods high on the satiety index include eggs, fruit, beans, foods on the bottom end include simple sugars and things such as cake and cookies. Let’s rock a thought experiment, you consume a 500kcal meal. That 500kcal meal is a big old slice of cake. After said cake, you’re likely to consume more calories throughout the day than if you were to consume a meal that was 500kcals worth of eggs on toast with beans and some fruit! The calorie content of the meal is the same, the effect on appetite and eating throughout the day is significantly different!
Hormones, Carbohydrates, and the Glycemic Index
Diagram from the incredible team at www.mysportscience.com
We’ve spoken a lot about most people’s golden boy of nutrition (protein) and we’ve spoken a lot about satiety! Time to dive into the other ways that where you get your calories from matters.
Let’s look at the murky world of hormones. One hormone, in particular, is of note here, that is ghrelin. Ghrelin is commonly known as the appetite-stimulating hormone, when we eat, our circulating ghrelin levels decrease. BUT not all food types will reduce ghrelin as much as the other. A nice example here is that of glucose and fructose. Interestingly here fructose doesn’t reduce ghrelin levels as much as glucose, so 100kcals of fructose may not leave you as satisfied as 100kcals of glucose. BUT fructose is found in fruit, as is fibre which IS satiating so yet again the murky web of all calories being “equal” is yet more tangled.
Glucose and fructose brings up another point as they’re carbohydrates and lead us nicely onto talking all about refined carbs and the effect they have on blood sugar levels and the effect these blood sugar levels have on humans need/want/desire for food. We know that due to the simple structure of refined carbohydrates they are digested and absorbed swiftly! This means they cause a SPIKE in blood sugar, and thus a rapid drop due to insulin being released at a similar rate! This drop in blood sugar leads to the appetite being stimulated AGAIN and lo and behold, an increase in calories consumed. The rate at which food can raise your blood sugar is referred to as its Glycemic Index. People with unlimited access to high GI foods have been shown to consume 80% more calories than those with unlimited access to low GI foods. Showing yet another impact the source of the calories can have on you.
Key Takeaway
SO The take home message with this. YES calories are in-fact calories and YES you need to consume less than you expend to lose weight. BUT the form in which you consume these calories, where you get them from plays a huge role in many aspects of metabolism; Appetite, hormones, energy expenditure and the pathways that control absorption to name just a few. The crux of most peoples diets is adherence, yes you can lose weight eating just Ice Cream if you consume less calories in ice cream than your energy expenditure. But I challenge ANYONE to do that and a) not end up over consuming and b) not feel like absolute crap…
There’s always more to it with nutrition. We haven’t even scratched the surface and in my humble opinion the nutritionists of the future are psychologists that know a lot about food.
Need Help Navigating The World Of Nutrition?
I’m a performance nutritionist with a masters in Human Nutrition. See how I can help you here.
