I may be many things, but although I do quantify myself as intelligent I'm no scientist. I am, however, friends with brilliantly science-minded folk who are conveniently also well spoken, well written, and willing to write intriguing guest posts for me discussing the science of weight loss and gain.
To that end, I present my friend Charles and his assessment of human biology with regards to thermodynamics and the conservation of energy (thank you, Charles!)
In every discussion of diet or weight control I see, someone implies it's just a matter of calories in minus calories out; if more calories go out than in, then fat will disappear. To someone who knows nothing of science, this sounds like science. I've heard it referred to as a law of thermodynamics; actually it's the law of conservation of energy. If one attempts to apply it to diet and fitness, one demonstrates one has no understanding of science. While calories in - calories out is a law of physics, it is about as relevant to human diet and exercise as saying runners gain weight due to relativistic mass increase as they approach the speed of light. It's true, but flat-out dumb. It's irrelevant in practice when describing humans because neither variable is measurable. The calorie labelling is barely relevant to what an individual body absorbs, and calorie figures for exercise applied to individuals are laughable. (Even a relatively simple exercise like walking; imagine how much terrain or gait difference would influence calories required for movement.)
To make any kind of scientific measurement of calories in - calories out, you would need to not only burn the food in a calorimeter, but the excretions. You would need to have the individual live and exercise in a calorimeter during the experiment, and you would need to (impossibly) burn the individual to ash in a calorimeter both before and after the experiment to measure changes in their bodies. Fat is certainly not the only potential change, nor the only calorie-relevant one.
Calories in - calories out is probably repeated with the intent of being an encouraging idea, but I doubt it's encouraging now if it ever was. There's too much access to estimated values, which never include any uncertainty data. People follow what they imagine is a scientific system, and it doesn't have any actual predictive value because it was never science.
As a brief afterword, what my friend wrote above puts me in mind of the fact that I can easily check three different online calculators to try and find out how many calories I've burned for my height, weight, age and gender for a 45 minute, 4 mph walk and get as a result: 232 calories, 420 calories, and 556 calories. I hate that. How am I supposed to accurately stay within my desired calorie regimen for the day when it's impossible to say how much I'm burning via workouts? So frustrating.
I had been giving thought to purchasing a heart rate monitor watch that supposedly tracks my calorie burn for an entire day after I've input my biometrics and it monitors my heartbeats and steps taken, but now I'm seriously wondering if such devices are not a waste of money.