Calories & TEF

by Marlene Harris, NSCA-CSCS

One of the more obscure facts in nutrition is this; in order to process food into a usable form, our bodies need to invest energy into breaking the chemical bonds within the various macro-nutrients. Even less discussed is the individual contribution of each macro-nutrient (protein, carbs, & fats) to this energy investment, which is referred to as “TEF”. TEF stands for “Thermic (heat) Effect of Food”, and is science speak for the metabolic impact of your food intake. To sum it up, we have 2 layers of TEF; the overall effect of food intake, then the impact of each of the macro-nutrients individually.

Layer #1: In general, the average overall TEF for your total daily caloric intake is about 10%. As an easy example, if you eat around 2,000 calories per day, about 200 of those calories will be spent breaking down the foods you’ve eaten into usable parts (depending on the composition of your meals, as you’ll see below). This leaves you with a net calorie intake of around 1,800 calories (again, depending).

Which brings us to Layer #2: The TEF for proteins, carbs, and fats, individually, as outlined below.

Protein: 20-35 % of the calories you take in as protein are burned just in breaking it down into its component parts, the amino acids. The bonds between the amino acids are robust, and require more energy to break than those in carbs or even fats. This means that for every 100 calories in protein you eat, you’ll burn 20-35 calories in processing that fuel source. As such, your net caloric intake is somewhere between 65 and 80 calories, depending on the protein source. Yes, to complicate things further, different protein sources=different TEFs, but we won’t go any further with that thought, so relax!

     Carbohydrates: 5-15% of the calories you take in as carbs will be burned in their processing. This means that for every 100 calories in carbs you take in, you’ll burn 5-15 calories in breaking them apart for your body’s use. Obviously, the bonds between carb molecules are much easier to break than is true for proteins. This is what make it a faster energy source; its broken down faster. As with proteins, different carb sources have different TEFs as well. The TEF for broccoli will be much higher than the TEF for a soda cracker.

     



Fats: 3-5% of the calories you take in as fats will be burned in processing, or, so for  every 100 calories of fat, you’ll burn just 3-5 calories in processing. Unlike the type of fat stored in our love handles, hips, thighs etc., apparently, our body doesn’t have to work very hard to break the bonds in dietary fat. Despite this, dietary fat isn’t a quick energy source like many carbs—you won’t feel a quick energy jolt from fat intake.
     Important Side-Bar Note: Fat is a paradox; when in a substantial caloric deficit (think: very low calorie & starvation), our bodies prefer to break down our muscle for fuel rather than our stored fat. Yes, our muscle is actually easier for our body to break down than our stored fat. Yet when it comes to dietary protein, it’s more difficult to break down than dietary fat. Strange, but biologically, muscle is more expensive calorically tor our body to maintain than fat, which is why muscle (particularly Type 2/strength muscle) will be sent packing if no stimulus indicating use/need is present, especially in a low calorie intake situation. (Hint: that stimulus most certainly includes strength training!). In case you’re curious (and I know you are…), 1 pound of muscle will cost you roughly 30-50 calories per day metabolically, but 1 pound of fat will only cost you around 2 measly calories per day. Let’s say person A has 10 more pounds of muscle than person B. Setting all other metabolic considerations aside for simplicity, person A would burn roughly 300-500 more calories every day than person B. Think about it!  

Returning to the topic at hand, what implications does TEF have in terms of meal construction? Let’s have a look! For the sake of simplicity, I’ll use the middle of the range #’s for each of the macro-nutrients: 28% for protein, 10% for carbs, and 4% for fat.
Scenario #1: You eat a 600-calorie meal that contains 350 calories in protein, 250 calories in carbs, and 100 calories in fat. Using %’s in the middle of the TEF ranges, you’d burn around 98 calories in busting up the protein, 25 calories in processing the carbs, and a measly 4 calories in fat processing for a total cost of around 127 calories.

Scenario #2: Say you compose a different 600-calorie meal as follows: 350 calories in carbs, 100 calories in protein, and 250 calories in fat. Again using %’s in the middle of the TEF ranges, you’d burn around 35 calories in carb processing, around 28 calories in protein busting, and a 10-calorie investment in fat processing. Total TEF cost= around 73 calories. A rather significant 54 calories less than the metabolic cost of the meal in #1. Let’s extend this out over a 3-meal day: #1=381 calories expended, #2=219 calories burned in processing. Over a week, the numbers become even more jolting: #1=2,667 calories burned in processing, #2=1,533, a difference of 1,134 calories (closing in on an entire day’s worth!) Imagine what the difference would look like after a month! (Go ahead, do the math, I dare ya!) Let’s do 1 more scenario.

Scenario #3: You construct another 600-calorie meal that looks like this: 350 calories in fat, 250 calories in protein, and 100 calories in carbs. Here’s your approximate burn rates (using the middle %’s of the ranges): 14 calories for fat, 70 calories for protein, and about 10 calories for carbs, totaling around a 94-calorie investment. A bit higher metabolic cost than #2, but not quite as good as #1.

Take home messages:
   1). The values used in the examples are simplified for illustrative purposes and should not be taken as set in granite, but…
   1). When it comes to calories, quantity matters, but so does quality. In addition to nutrient, vitamin, and mineral content, TEF is a part of meal quality. A higher TEF will serve you more favorably for increasing your metabolic rate, even given the same # of calories.  
   2). When it comes to metabolic demand of processing, protein is king of the hill. This means that including a larger portion of protein in your meal will actually cause you to burn more calories digesting it due to the extra work your body has to do in processing it. Besides this, there’s only one nutrient that builds muscle, and (Spoiler Alert!)  it’s NOT fat, and it’s NOT carbs…
   3). The higher metabolic demand for protein processing also creates better satiety, the sense of fullness and satisfaction ala “I can stop eating now”. Better satiety also means you’ll stay satisfied longer, and be able to have better, more consistent energy for a longer period between meals. Both highly important to fat loss and productivity!
    4). Hopefully this discussion has also got you thinking about why I always say that whole, nutrient dense foods are best when creating meals. You not only get a better array of nutrients from foods in their natural form working synergistically in your system, but whole foods also come at a metabolic cost, which can help stoke the fires of your metabolism.

One Last Note:  Here’s an interesting tidbit I stumbled across while researching this topic, and yet another reason why it’s better to be leaner than not. Apparently, the leaner you are, the more efficiently you torch your chow. Here’s a quote from a major study on the subject: “Lean people have a thermic effect of food that is approximately 2 to 3 times greater than obese people during rest, after exercise, and during exercise.”
The study: Segal KR, Gutin B, Albu J, Pi-Sunyer FX. Thermic effects of food and exercise in lean and obese of similar lean body mass. Am J Physiol. 1987 Jan;252(1 Pt 1):E110-7.