To begin, how do those nutritional labels on food get their caloric information? The U.S. has a uniformed system implemented that assigns each gram of the macronutrients contained within the food item (e.g., fat, carbohydrates, protein, alcohol, etc.) the average caloric value. This system, officially named the "Atwater system," uses 4 calories per gram for protein, 4 calories per gram for carbohydrates, and 9 calories per gram for fat. These averages were derived from a laboratory instrument called the "bomb calorimeter." The representative macronutrient was placed in a sealed container surrounded by water. Then, the food was completely burned and the resulting rise in water temperature was measured. Remember back to science class? A calorie is a measure of the amount of heat energy ("enthalpy of combustion") needed to raise the temperature of 1 kilogram of water 1 degree Celsius.
(Side note from Dr. Attia: "If you’re wondering why fats contain more heat energy than carbohydrates or proteins, it has to do with the number of high energy bonds they contain. Fats are primarily made up of carbon-hydrogen and carbon-carbon bonds, which have the most stored energy. Carbs and proteins have these bonds also but “dilute” their heat energy with less energy-dense bonds involving oxygen and nitrogen." I also borrowed a handy chart from him, seen below.)
Now, before I put you guys to sleep, what we really need to ask here is how does the human body process caloric energy? Does the human body process energy the same way as a calorimeter? Without knowing any advanced science, I think it's safe to say that no, the body does not process energy the same way as a calorimeter. For the smartypants out there, here's a post that addresses the First Law of Thermodynamics. I think discussing thermodynamics is too much detail for our current purposes. It distracts from the issue at hand and we can arrive at a logical conclusion without it.
The main thing we normal folks need to understand is that the body uses different molecules for different functions. Energy isn't coming in with nothing happening between when you ingest food and when you exert energy. Your body isn't a giant pot of water, there's a lot more going on inside there than this mantra would lead you to believe. You can measure a calorie in just about any organic matter, including poison, spiders, toenail clippings, propane.... but the body reacts quite differently to different molecules. Our question should really be, how does the body react to the molecules we typically ingest and how does it use the macronutrients (e.g., fat, carbohydrates (SUGAR), protein, alcohol).
On a non-scientific level, let's also think about this anecdotally. Whenever someone says, "a calorie is a calorie; you just have to burn more calories than you take in," I picture a young girl, about 13, who is overweight. She has a deep desire to be accepted by her peers and is in the midst of forming her adult identity. She thinks if she can finally slim down, people will see her for who she really is, because right now they only see her as the "big girl." She's resolved that this is the year she is going to lose weight. This girl skips breakfast and has a soda (~200 calories) and a yogurt with fruit (~200 calories) for lunch. At night she eats a salad with a low calorie/low fat dressing that her concerned parent prepares (700 calories). She might lose a little bit of weight, but soon she feels awful and can't suppress her hunger so she binge eats until she finally feels full. Her cycle of weight gain continues along with her cycle of depression over her lack of control. When her parents and her pediatrician tell her she needs to eat less calories, she grows resentful and further depressed. She feels like a victim, but is treated like the perpetrator. The reason why "a calorie is NOT a calorie" matters in her case is because losing weight and maintaining a healthy weight have a lot to do with what foods are making her eat more calories. Why does she not feel full? Why does she continue to eat when losing weight is really all she wants? Why is her urge to eat so strong that it overcomes all other desires? Why is her urge to eat more frequent than other people? Why is her body storing energy instead of expending energy??
Our society has got to stop this dogma. This isn't merely a political issue over healthcare or a pissing match between scientists, but an issue that disproportionately affects the innocent. When we say losing weight is a matter of willpower over what we eat and what we expend, we are telling this innocent child, and the millions like her (including obese babies), that her willpower is not strong enough to "put down the fork." It creates a destructive pattern of thinking and does nothing to actually help. This is a major reason why instances of bulimia and anorexia are rising in the obese community. It is also one of many reasons the overweight and obese are disproportionately depressed, which, I am beginning to believe is more linked to the type of food they are eating than how they are treated, although that certainly isn't helping matters.
Yes, those who eat tons of calories tend to be those who are larger, but not always. What is so much more important is WHY, why are these people eating more calories. I'll discuss this in my next post on leptin, but feel free to read up on your own. :)
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