Have you been lead to believe the following statements are true?
If you eat more calories than you burn you will gain weight.
If you burn more calories than you eat you will lose weight.
If you eat the same amount of calories that you burn your weight will not change.
In order to lose weight, all you have to do is burn more calories than you take in. Eat less, exercise more and you are bound to lose weight. Not so fast. These simplistic adages are just not true. We've all known someone who eats a ton of junk food, doesn't exercise, yet never seems to gain weight. Conversely, we've also known that unfortunate individual who does cardio everyday, is perpetually on a diet and can't seem to lose weight. The rules just don't seem to apply to certain people.
What is wrong with the "calories in = calories out" model of thinking? Let's start with the Law of Thermodynamics (AKA the Law Of Conservation of Mass). Your 9th grade science teacher told you it is an irrefutable fact; energy can neither be created nor destroyed. The law (of which there are 4) is indeed undeniable but not when it comes to the human body. The idea that "a calorie is a calorie" comes from a misunderstanding of the laws. Here is what the 1st law of Thermodymanics states
"In a thermodynamic process the increment in the internal energy of a system is equal to the increment of heat supplied to the system, minus the increment of work done by the system on its surroundings. This states that energy can be neither created nor destroyed. However, energy can change forms, and energy can flow from one place to another. The total energy of an isolated system remains the same."
The major problem with the application of this law to the human calorie model is that our bodies are not isolated systems. Far from it. The fat storage and muscle creation structures in our bodies are not closed loops. They interact with the digestive, endocrine and circulatory systems in addition to thousands of other biological processes.
If energy can’t be created or destroyed why wouldn’t a calorie always be a calorie? That’s where the second law comes in. "Entropy (loss of energy) of the universe increases during any spontaneous process." What this means is that it is impossible for a system to turn a given amount of energy into an equivalent amount of work. Simply put, a calorie ingested does not mean it will be digested.
Not all of the calories that are actually in a food will be absorbed, digested and available for the body to use. When we eat a calorie it is not always used for energy or stored as fat. Sometimes it is left unused and excreted. Up to 15% of your total daily food intake may end up in the toilet. Certain ingredients can actually block the absorption of nutrients ( molasses , calcium and fiber - the granddaddy of calorie blockers). Some types of fiber bind nutrients in the gut and decrease their absorption. This absorption block happens not only with micronutrients (calcium, iron, etc) but also with protein and fat. Additionally, some of the food we ingest is fermented by the bacteria in our gut; their calories simply become unavailable for us to absorb. These calories are actually burned off by the bacteria that are living inside us. Recent evidence suggests that our ability to derive calories from food depends significantly on the microbes we carry inside us. We are just beginning to understand the role of our complex microbiome .
The way a food is cooked (raw foods generally have less calories than cooked foods), the type of food you eat and individual differences in one's metabolism all affect the amount of calories your body absorbs. Moreover, there are a myriad of complex biochemical processes taking place simultaneously in the body. They all affect how calories are utilized. These processes are controlled by hormones, genes, enzymes and bacteria. Other factors that influence how the body uses calories
Basal metabolic rate (BMR) accounts for 60-85% of your total daily calorie burn by regulating all of your vital organs (heart, lungs, brain etc.). It is the amount of energy you require to sustain life at rest. Your calories go here first.
Thermogenesis is the process by which the body raises its temperature, and/or energy output (requiring copious amounts of calories). Examples of thermogenesis in the body: Certain foods specifically ones high in protein or foods like coconut oil , spices and green-tea; experiencing cold temperatures; the act of eating also negligibly increases thermogenesis called thermic effect of food (TEF).
During times of illness your body may utilize more calories to fight off infection.
Certain medications affect your hormones and promote weight gain/loss despite the calories you consume.
Prolonged stress will enhance your bodies capacity to store fat and use calories more judiciously.
Thought Experiment: Imagine you and your best friend were connected by the hip and both overfed by 500 calories per day while forced to eat the same exact food for two months. Obviously since you're connected, you went everywhere together and moved the same amount. After 60 days do you think you both would have gained the exact same amount of weight? Of body-fat? Chances are a big fat no.
This may sound crazy but calories don't exist except in our minds. They are not tangible, they exist as concepts. A calorie is like an inch, it is just a way to measure something. Calories describe the amount of heat created when a nutrient is burned in a lab oven called a calorimeter. You don't have one of these ovens in your body. When you eat food the nutrients within are mostly converted to fuel to power all your bodily functions. Calories are the measurement of the energy the body makes from the food you eat, not the actual energy (which is called adenosine triphosphate - ATP). Remember that from science class?
What drives food to be stored as fat? Multiple biochemical reactions including hormones, genes, and enzymes control how much fat you store. Storing fat is a complex bodily process I'd rather not rehash here for you for fear you'll fall asleep. If you want to learn more about it I encourage you to read this book: "Why We Get Fat" by Gary Taubes. The thing to remember is that hormones (especially insulin ) play the biggest role in converting nutrients into stored fat. Hormonal interactions are highly interdependent so a change in one hormone will affect another. They can be unsettled by many things in our environment (pesticides, medications, stress, sleeplessness , food, age etc). Hormones are constantly in flux. The science tells us: controlling our hormones is a key to controlling our stores of body fat.
Factoid: Eating fat does not necessarily cause you to store fat. In fact, it may actually help you lose fat!
The calories in/calories out model is a simplistic theory that doesn't do enough to explain why we get fat. Eating less and exercising more doesn't work for most people long term (losing and keeping weight off has a very high failure rate - many people are going about it all wrong by following the calorie model). Under-eating and moving more will help you drop weight but good luck maintaining that state of being for life. Taking in less calories than you expend treats the symptom (over storage of fat) not the cause. Eating the right nutrients, balancing your hormone levels and exercising correctly will treat the cause and rid the body of its symptoms - being fat. Changing your body may not be simple but it doesn't have to be hard. Pay more attention to what you eat, not how much, and I promise you'll feel and look better in the long run. Experiment with what works for you by making a few key lifestyle changes and gradually take your body to the optimal place of health and happiness.