In The Biggest Medical Myth of All Time, we reviewed some of the evidence that losing excess body fat is not as simple as the supposedly tried-and-true formula of eating less and exercising more. And that’s because our bodies are not simple machines, like cars or televisions or the iPhone 3GS. In this post, we’re going to examine the calorie balance theory: Calories In – Calories Out = Fat Lost/Gained, and build an understanding of why we can’t fool our fat-o-stats with a step-aerobics video and a freezerful of Lean Cuisines.
“The New Math”
- TEE=Total Energy Expenditure.
- REE=Resting Energy Expenditure, the rate of oxygen consumption when fasting and completely at rest.
- TEF=Thermic Effect of Food, the increment in oxygen consumption seen just before, during, and after a meal.
- EEE=Exercise Energy Expenditure, the increment in oxygen consumption attributable to volitious exercise, such as jogging, playing hockey, etc.
- NEAT=Non-Exercise Activity Thermogenesis, all non-volitious activity over and above lying completely still.
Resting Energy Expenditure (REE)
Much research has compared the REE between lean and obese persons, and, while slight differences are sometimes reported, for the most part, REE can be attributed to the maintenance of lean body mass—muscle, bone, skin, hair, etc. Even highly trained athletes don’t show a significantly higher REE than couch potatoes of the same size and body composition.2 When people alter their intake acutely for a short period of time, or modestly for a long period of time, however, the REE, when measured per unit of lean body mass, will show a commensurate adjustment, albeit a small one. Let me make that clear: if a person has dieted (or gorged) for a suitable length of time, he will burn a different number of calories at complete rest than will a person of exactly the same size and body composition who hasn’t altered his diet. Some studies will fail to show this, but likely only due to methodological differences (sample size, study length, measurement technique).
Thermic Effect of Food (TEF)
Now here’s where things get interesting. As far back as the 19th century, scientists were fascinated by what was then called Specific Dynamic Action, the significant increase in metabolic rate that occurs when we eat and for several hours after. Early researchers observed that TEF varied with the size and composition of the meal and so logically drew the conclusion that TEF represented the energy cost of digestion and assimilation of the meal, which is how it is still often defined today. This isn’t entirely accurate, however. Researchers began to notice that there were significant variances in TEF between individuals, even when eating the same exact meal under the same circumstances. That fact suggested that TEF was not solely the processing cost of food.
Exercise Energy Expenditure (EEE) and Non-Exercise Activity Thermogenesis (NEAT)
The calories burned as a result of activity over and above REE can be divided into Exercise Energy Expenditure (jogging, tennis, pilates, etc.) and Non-Exercise Activity Thermogenesis (showering, fidgeting, channel-changing). The former is pretty straight-forward; it’s basic physics: work = mass X distance and force=mass X acceleration. The distance you move something—like your arm or a barbell—through space, and the force you use to do so can be combined to calculate the calories burned in the process. Okay, there’s a bit more to it than that, as there are effects from exercise training and efficiency, and interactions with the fuel source (sugar or fat), but for the most part, moving a given weight a given distance at a given intensity has a set value, regardless of our body’s fat content. The same could be said of NEAT, except for one important difference. For most of us, EEE is the result of a willful, conscious act; whether we enjoy the activity or not, we make the decision to spend 30 minutes or an hour or the whole afternoon playing golf, painting the den, or using the elliptical trainer. NEAT is much more about unconscious movements—the number of times we get up and walk to the window to look outside, how often we feel the urge to head to the water cooler for a gossip-fest, whether or not we are drumming out our favorite song on our desk while reading email—in short, how inclined we are to fidget, pace, or otherwise “waste” energy. So why do we make this distinction? Because our inclination toward non-exercise activity is a key element in balancing the energy expenditure equation. Let’s look at some science behind that statement. A group of researchers at Mayo Clinic was given a great deal of credit for their research into the NEAT concept about a decade ago, but in reality, the idea of compensatory changes in NEAT goes way back to the mid-twentieth century.
NOTES
- Neumann R.O. Experimental determination of human food requirements with particular consideration of essential protein need. Arch Hyg 45: 1–87, 1902 ↩
- Schulz, LO. Effect of endurance training on sedentary energy expenditure measured in a respiratory chamber. Am J Physiol. 1991 Feb;260(2 Pt 1):E257-61. ↩