The first law of thermodynamics states that energy can neither be created nor destroyed; it can only change form or be transferred from one object to another.
That principle may sometimes seem to not apply to our weight management efforts—the needle on the scale doesn’t move as much as we think it should based on what we ate or didn’t eat and how much we moved or didn’t move—but that’s only because we’re not always aware of all the factors that appear on either side of the “calories in vs. calories out” equation.
The thermic effect of food/feeding (TEF) is one of those factors. And a bit of understanding and taking advantage of it can help tip the scales in our favor (pun intended).
What is TEF?
Digestion is an active process. We chew and swallow food, produce enzymes to break it down further, absorb and transfer nutrients to our cells, and excrete waste. Obviously, we obtain more energy from the food we eat than what we expend breaking it down, but the process does still require energy. That energy requirement is what we call the thermic effect of food (TEF). While that should seem obvious now that it’s been pointed out, there are more details that make the TEF even more interesting and useful.
The thermic effect of any food is affected by a variety of factors, two of the largest being nutrient makeup and amount of processing the food undergoes before arriving on our dinner plate. On average, you’ll net the following percentages of calories based on a food’s nutrient makeup:
- Fat: 97-99%
- Carbs: 90-95%
- Protein: 70-80%
In other words, eating 100 calories of a pure fat, carb, or protein would net you 97-99, 90-95, and 70-80 calories, respectively. (If you’ve ever had the “meat sweats”, you now know why! Your body needs to work harder to break down those calories and produces heat as a byproduct.)
On the processing front, foods that are in a less-processed state require more calories to break down than foods that have been previously processed by a machine of some sort. That makes sense if you think about it; during processing, we effectively let a machine use electricity to perform a sort of “pre-digestion” process on a food in its natural state. That saves our bodies a bit of effort when we eat that food.
“How much of a difference does processing make?”, you might ask.
Obviously, that will depend on the nutrient makeup of the food/meal and how processed it is compared to a similar but less-processed meal. For the sake of example, this study performed in 2010 showed a roughly 47% reduction in the thermic effect of a processed “meal” as compared to one which was similar but less-processed. That means the more-processed meal netted more calories than the less-processed meal because it (the more-processed meal) required fewer calories to digest.
(The “meal” in this case was a couple cheese sandwiches, the less-processed of which used real cheese and whole grain bread while the more-processed used processed cheese and white bread. It can reasonably be argued that both meals were still more processed than a pan-seared steak, baked potato, and grilled veggie…)
Putting it into practice
While you might assume that my suggestion for using this information is to “eat more protein and less processed foods”, that isn’t necessarily the case. Ultimately, what you do with the information should depend on your goal.
If your goal is to lose weight and/or body fat, then you’ll generally want to slightly increase your energy expenditure—general activity + exercise (a tip for another time)—and perhaps decrease your net energy intake. That might mean gradually increasing your protein intake and eating a few more less-processed foods. (A good place to start would be keeping a food journal for a few days and then reviewing it either on your own or with a coach to help you determine where you could start to make small improvements.)
However, if you want to gain weight, likely by building muscle, you’ll probably want to increase your net energy intake while also maintaining or increasing your training and, subsequently, your energy expenditure… which means you’ll have to increase your net energy intake a bit more. Since it could be a bit challenging to get all the calories you’ll end up needing from less-processed foods, you may have to add—add, not replace—some more-processed foods into the mix. (See?!? In some cases, there’s a very well-defined reason to add a bit of ice cream or cookies to one’s diet!)
Whatever your situation, start small. After all, what you do consistently will have a greater effect on your results than how much you can do at one time if you then fall off the wagon!