30 years ago unless you worked in the medical, biochemical or nutritional sectors it is quite possible that you had never heard of calories. Today, ‘Calories’ have become a ‘thing’, part of the vernacular, a unit of currency and a topic of discussion that has penetrated all areas of life and permeated all demographics. Every food label or food marketing campaign highlights them, every health advocate or body conscious person talks about them or tracks them, and still, many ‘weight-loss’ enthusiasts live in fear of them!! Calories, and their association with our body weight and perceived state of health, are now front-and-center, and for many reasons, rightly so. But what exactly are calories and how much do we actually now about them.
Calories are not tangible entities but are actually units of measurement in the same way that inches, grams and degrees are units of measurements. Calories are units of heat energy. Specifically defined, a calorie is the amount of energy necessary to raise the temperature of 1 liter of water by 1 degree C. When we eat food, we are essentially ingesting the energy stored within the molecules of that food. The amount of energy we gain from a particular food is determined by the calorie density of that food, and the quantity we eat.
As stated above, calories are a form of heat energy. The First Law of Thermodynamics indicates that heat energy cannot be created or destroyed but can only be transferred from one place to another or converted into other forms of energy. So in essence, all the calories we consume are either utilized by the body or stored within the body.
Put simply, when we eat food, it is broken down into its constituent parts (macronutrients, micronutrients, phytonutrients, wastes) and the energy within those food molecules (calories) is transferred into our bodies. Once inside, that caloric energy it is used (metabolized) to create new forms of energy, which power all biological processes such as breathing, digestion, cellular regeneration, physical movement and even thinking.
Any caloric energy that is not used in this way is stored as chemical energy within the cells of the body for future use. Although some of this excess energy (calories), primarily glycogen (sugars), is stored in the blood stream, liver and muscle tissues, and ready for immediate deployment, this is a relatively small reserve. Once these glycogen stores are full, any additional surplus calories are locked away in fat cells around the body. Here they will remain until there is a specific requirement for that energy or there is an absence of sufficient glucose or glycogen to provide ‘quick’ energy.
Just to keep alive our bodies are always burning calories for energy to support the function of the vital organs and nervous system even at rest. This sum of calorie burn is referred to as our Basal Metabolic Rate (BMR) and can be roughly estimated. Any and every movement, action or stress placed on the body, over and above this basic functioning, requires extra calories to be burned to supply the necessary energy for those actions. The more active we are, the more energy require.
‘Energy balance’ refers to the relationship between the number of calories that we consume, through food and drink and the number of calories that we expend through daily living and functioning, within that same period of time. If we consume more calories than we expend over the course of a day, then we are said to be in a positive energy balance. Conversely, consuming fewer calories than we are burning is referred to as a state of negative energy balance. It is generally accepted that significant or prolonged periods of positive energy balance will result in some gain in body mass (weight), while a negative energy balance should be accompanied by a reduction in body mass.
At this stage, it is important point out that the terms ‘positive’ and ‘negative’ in this context could indeed be replaced with ‘surplus’ and ‘deficit’ and are not intended to suggest a better or worse state for people to be in.
Whether someone chooses to eat in perfect accordance with his or her energy requirements, or not, is often a personal choice driven by ones behaviors and/or specific body weight or body composition goals. In modern society, however, a lack of understanding in this area coupled with ever-increasing access to heavily refined and processed foods, has meant that more and more people are over-eating, relative to their energy demands, and as such, are living in a constant state of positive energy balance or caloric surplus. As stated earlier, this surplus energy has to be stored by the body and mostly that occurs in fat cells, and this in turn typically results in increased body weight and increased body fat.
As humans we have evolved to be natures ultimate adaptors and we are equipped with most of the tools needed to survive. One of our fundamental survival mechanisms is our physiological ability to store lots excess energy, which in the days of feast and famine was a very necessary and beneficial attribute. The flaw in this adaptation, however, is that we have an almost unlimited capacity to store extra energy. In modern western culture, where prolonged periods of calorie restriction (famine) seldom occur, and we have access to virtually unlimited calories, this increasingly self-destructive trait, is leading to a significant rise in levels of obesity and associated chronic illnesses.
Although obesity is without question one of the fastest growing health concerns in the western world and this is well documented, it is worth noting within the Energy balance discussion, that prolonged or severe calorie restriction or negative energy balance can also be linked to a host of adverse health risks.
In its most basic and fundamental form the process of calorie counting and the Energy Balance Equation are mathematically straightforward calculations. In some cases this data translates just as simply to the real world, in the form of an individual’s weight-loss or weight gain. On a population basis, however, it would be remiss to believe that this is always the case, or to ignore the fact that there are many more determining factors at play when it comes to sustainable body weight management, and more importantly, general state of health.
While the overall quantity of calories IS the most important factor when it comes to acute weight loss or weight gain, what the energy balance equation doesn’t account for is the type of, and source of calories that we consume. As the often-touted saying goes, in its ‘food state’, a calorie, is a calorie, is a calorie. However it is important to acknowledge that, in reality, not all calories are created equally and as such not all calories behave the same when they enter the complicated network of systems and signalling that is the human body. Both the macronutrient source (fat, carbohydrate, protein, alcohol) and the nutritional profile or density of calories play a very important roll in determining how those calories are treated when they enter the body and also the impact that those calories can have on things like hormone function, digestive absorption, inflammation, satiety and hunger signalling.
It is critical to understand that the food we eat and the dietary choices we make, not only serve as our main source of energy for powering our bodies, but also represent our primary source of vital vitamins, minerals and phytonutrients. The presence of these micronutrients, in rich supply in our food, is essential for cell growth, development and regeneration and ultimately one of the most important components when it comes to health and optimal performance. One of the major issues facing us today is that many of the food products on our shelves, while bountiful in calories, are devoid of such essential nutrients and leave us overfed but under nourished.