Do calories matter in terms of fat loss? Conventional wisdom tells us that the answer is an unequivocal yes. In fact, it is commonly accepted that calorie balance is the key factor in an individual’s tendency to store body fat. Besides, the notion is intuitive and easy to understand. If you eat more calories than you burn, your body will respond by storing the surplus. You know, for a rainy day.
The reality, as is the case with many things, is much more complex.
A Discussion on Thermodynamics
Most of us are aware of the First Law of Thermodynamics and its assumed relevance to adiposity in humans. According to Wikipedia (1):
“The law of conservation of energy states that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings.” – Emphasis added.
In terms of human metabolism, this has been interpreted to mean that if energy is consumed, the body must burn it or store it. Again, the reality is much more complex, and the idea that we either store it or burn it is a false dichotomy. Our bodies also take some of what we eat to build or repair various structures in our cells. There is also the potential for the body to choose to not use the energy at all and excrete it.
The first law is a matter of bookkeeping. It only indicates that the total amount of energy doesn’t change. It doesn’t explain how efficiently the system uses the energy or in what form the energy ends up in at the conclusion of the processes involved.
We also have the Second Law of Dynamics, which isn’t nearly as well known as the first law, but is also applicable to discussions on nutrition and human metabolism. According to Wikipedia (2):
“The law defines the concept of thermodynamic entropy for a thermodynamic system in its own state of internal thermodynamic equilibrium. It considers a process in which that state changes, with increases in entropy due to dissipation of energy and to dispersal of matter and energy.” – Emphasis added.
The second law tells us that when a physical process acts upon energy in any form, there is a loss of usable energy during that process. Or to put it in terms of nutrition, when a person eats something, the body must convert the food into a form that it can use. During this process, there is some loss of the available energy.
An Over Simplification
What is often lost in the comparison is the human body is not an isolated system. It is a collection of many systems and there are many processes at work when we consume food in various forms. The Calories In/Calories Out (CICO) theory tends to imply that both sides of the equation are independent variables and doesn’t take into account other variables that effect how the energy is converted by processes of human metabolism. It completely ignores the Second Law of Thermodynamics, and possibly other factors as well.
For example, we have hormonal and psychological responses that effect how our bodies interact with the energy that comes from food. An example of this is insulin response (3). While there is some debate (4) on the scope of insulin’s role in fat storage, it does affect how our body deals with fat in our metabolism. Leptin is another possible factor in adiposity that needs to be studied further (5). Furthermore, what we eat can have an effect on what we will eat later. The same is true for exercise. We see this with the satiation effect of protein (6)(7) and the proclivity for the appetite of some to increase when they exercise (8).
We also have the thermic effect of food. This is another instance of the Second Law of Thermodynamics at work when the body converts food into usable energy. One of the most notable examples of this is how the body handles the different macronutrients in the food we eat. While the exact percentages vary, we know that fats, carbohydrates, and proteins provide different levels of usable energy to the body. In general our bodies can use about 98% of the energy available in fat, about 92% of the energy available in carbohydrate, and only about 75% of the energy available in protein (9).
There are also dependent variables in terms of exercise that can play a role in how our bodies interact with the calories we consume. As with dietary practices, there are many options available for the types of exercise we can engage in. As described by the FITT principle (9), we can adjust the Frequency, Intensity, Type, and Time of our activities to manipulate how many calories are expended both during and after exercise.
The CICO theory gives the impression that it doesn’t really matter what you eat as long as you control at least one side of the equation. This would mean that all you have to do to lose weight is make sure you burn more than you consume. If you eat 2000 calories of energy, regardless of whether it is made up of donuts or vegetables, then you must burn at least 2001 calories to create a deficit. The converse would be true as well; to gain weight you would need to burn less than you consume.
In this theory, it doesn’t really matter where your 2000 calories come from. You can choose highly processed foods like soda, pasta, and doughnuts or get your calories from nutrient dense foods like high quality meats and nutrient dense vegetables. Ultimately there is no difference.
Intuitively, this doesn’t make sense, and we are starting to see it in the scientific literature as well. While most nutrition and health experts would agree with the idea that there is a difference, it is often lost in the inflexible adherence to the CICO theory.
As we are often told, to lose weight all we have to do is create a negative calorie balance through calorie restriction and increased exercise.
Let’s Consider Another Theory
As stated above, eating and exercise are not independent variables. We need to also consider the metabolic and psychological responses we have when we consume and expend energy. As such, an alternative theory might be necessary, or at least beneficial, to have a better understanding of how to control our weight through diet. An alternative theory might suggest that fat accumulation is heavily influenced by the effects of the food we eat on how our body utilizes the energy we consume.
Peter Attia, a medical doctor and author of The Eating Academy, provides the following as an alternative hypothesis (10):
“Obesity is a growth disorder just like any other growth disorder. Specifically, obesity is a disorder of excess fat accumulation. Fat accumulation is determined not by the balance of calories consumed and expended but by the effect of specific nutrients on the hormonal regulation of fat metabolism. Obesity is a condition where the body prioritizes the storage of fat rather than the utilization of fat.”
Simplified, this theory posits that what you eat is at least as important as how much you eat. Calorie quality is on par with, or possibly more important than calorie density.
So…Do Calories Matter?
Of course they do. Energy balance is a factor in determining body weight. The issue is that it is certainly not the only factor and the process of losing or gaining weight is very complex. This complexity is further compounded by inherent differences in our biological makeup and gene expression. Weight control efforts that work for one individual might be completely wrong for another. This means that the answer to this question is not an unequivocal yes, but rather a yes with caveats.
In light of this, it is likely necessary for individuals to explore many possible dietary practices and exercise regimens to determine what works best for them. As the wide variance in scientific study clearly indicates, there are many potential solutions to the problem of obesity and unwanted weight gain.
For some it might be as simple as eating less and moving more, while for others it might be advantageous to monitor and control food quality and engagement in various different types of exercise that fits their personal situation. Expanding upon the traditional paradigm of the CICO theory will likely help many individuals who struggle with weight control. This, in turn, will allow them to better understand how their body and mind respond to their efforts in terms of weight loss.
Finally, in my opinion, it is imperative that we gain a better understanding of all the factors involved in weight maintenance and eating for optimal health. This would be best realized by adequately funding high quality studies publicly to ensure data free from corporate influence or personal agenda.
I would love to hear your thoughts on this topic and welcome your comments. Feel free to join the conversation in the comment section below.