Everything you need to know about the thermic effect of food.
What is TEF? How can you maximize it? Does it even matter?
You may be thinking, "Oh yeah, I remember somebody talking about this. I need to eat more protein. It's the key to fat loss or something..." Yes and no. Fortunately, TEF, or the thermic effect of food, is much more interesting and complex than just eating more protein.
This article will serve as your manual for maximizing the thermic effect. If you know nothing about TEF or you already know a little, this article will provide you with the practical information you need to increase the calorie burning power of your nutrition. As a bonus, it'll also provide you with some random science stuff to wow your co-workers at the water fountain.
Let's get started!
The thermic effect of food is the increase in energy expenditure (above your resting metabolic rate) that occurs subsequent to eating as a result of your body digesting and processing nutrients. David Barr described it as diet-induced thermogenesis in his recent article,21st Century Eating.
This phenomenon also goes by "thermic effect of a meal" and "postprandial thermogenesis" – lots of different names, same topic. TEF has become very popular of late, but like most things, it's actually been around for a very long time.
In 1902, M. Rubner, a German scientist, noted "an increase in heat production following food ingestion."  In 1930, Lusk et al reported a difference in "specific dynamic action" between protein, carbohydrates, and fats. His findings that protein, carbohydrates, and fats increased the metabolism by 30%, 6%, and 4% respectively weren't too far from the mark, despite the fact that his methods and techniques would be considered archaic by today's standards. 
Several years ago, Dr. Lonnie Lowery laid out a simple breakdown for the thermic effect of the three macronutrients:
- 200 g protein (which is 800 calories) x .25 = 200 kcal
- 300 g carbs (which is 1200 calories) x .04 to .06 = 72 kcal
- 100 g fat (which is 900 kcal) x .04 to .06 = 54 kcal
As you can see, these numbers are right in line with Lusk's initial calculations. But now let's look at some info that wasn't known prior to World War II.
TEF and Meal Timing
Is your eating schedule all over the place? One day you'll get six meals in, but the next couple days you'll only get in two or three? Did you know that this irregularity in your feeding schedule is actually reducing your TEF?
Researchers out of Queen's Medical Centre reported that eating an irregular meal pattern (three to nine meals per day) results in a significantly lower TEF than found in subjects eating a regular meal pattern (six meals per day). 
Now even though the difference in TEF was found to be significant, I'm not suggesting (and neither did the researchers) that over the short term this will make a huge impact on fat loss. However, just like small behavioral changes made consistently over time can lead to significant changes, the increased TEF due to meal regularity can positively impact your physique in the long run.
TEF and Exercise
A common statement made about the benefits of exercising (namely weight lifting) is that it increases your metabolism. This is usually attributed to increases in lean body mass. Muscle is metabolically active and thus you'll burn more calories at rest. This is a good argument, but it can't be the only reason, right?
It's not. Studies have shown that people who habitually exercise have a greater TEF when compared to sedentary people, even if the two groups have similar fat free masses. [4, 5] And what's even more interesting is that this increase in TEF isn't age dependent. That's strike one against the "your metabolism slows as you age" theory.
One of the problems with these studies is that they clumped all kinds of exercise together. What about resistance training specifically?
One study out of UNLV looked at the TEF after just one bout of resistance training (2 x 10 for 10 exercises) and found that the TEF was significantly increased.  Finally, some real instantaneous results! I can see the infomercials now: "With just one workout you can turn your body into a fat burning furnace!" Actually, I think that one already exists.
I believe this is (at least initially) a more significant metabolic enhancer than increases in lean body mass because it's an instantaneous increase. This is especially true when you take into consideration the time it takes to pack on enough muscle to make a significant impact on your resting metabolic rate.
On a side note, exercise has also been shown to increase the TEF of carbohydrates following exercise. This is great news for carbohydrate sensitive folks because with increased insulin sensitivity and increased TEF, you can't go wrong getting your starch fix after an intense workout. 
Here's one final study on exercise and metabolism. Burke et al looked at the differences in the resting metabolic rate and thermic effect of food in aerobically trained women. Don't worry that they're aerobically trained and not anaerobically trained; a previous study showed no difference in the increased TEF between aerobically and anaerobically trained subjects. 
This aerobic/anaerobic similarity is cool because it means you get a bump in your metabolism after your morning meal (following cardio) and your post-workout meals following an afternoon weight training session. While the researchers found no difference in TEF between the three groups of women (separated by level of fitness), they did find that the women who had the highest level of energy flux (e.g. G-Flux) had the highest metabolic rate. 
TEF and Energy Restriction
When you start severely restricting your calories, all kinds of crazy things happen to your body and your metabolism. Does calorie restriction affect TEF? There isn't a lot of research in this area, and the present data disagrees on whether or not TEF is reduced when calories are restricted. Interestingly enough, the conflicting data is coming from the same lab.
But regardless of whether or not TEF decreases when dieting, the data is in agreement that the thermic effect due to protein is maintained and in some cases increased. [10, 11, 12] This data seems to further endorse the importance of increasing protein levels in your diet during periods of energy restriction.
It's important to note that in the above two studies, the additional thermic effect from increasing protein intake wasn't enough to blunt the reduction in metabolic rate due to the calorie restriction.
TEF and Body Composition
Increasing the thermic effect of food is all about creating a metabolic advantage. With that in mind, who would you guess is metabolically superior?
- The guy on the fourth year of his bulking cycle who's carrying around fifty extra pounds of fat?
- G-Flux Jimmy, who resides in Ripped City and hasn't seen a double digit body fat since his twelfth birthday?
G-Flux Jimmy, no contest. Yeah, being hyooge is cool and all, but being fat, not so much. Controlling body composition is crucial to your health and fitness goals, and it heavily influences your TEF. 
Researchers at Columbia University took two groups of men, lean (<15% body fat) and obese (>25% body fat) and examined the differences in TEF in different situations (at rest, during exercise, and after exercise). The results were pretty amazing. Compared to the obese subjects, the TEF of the lean subjects was:
- 70% higher at rest
- 175% higher after exercise
- 316% higher over the course of 30 minutes of exercise
I know there's already a myriad of reasons to lose the extra body fat you've been carrying around, but this is just another.
Making Sense of TEF
To help make sense of all the scientific studies and abbreviations in this article, I've compiled a list of take-home points to help you assimilate this info ASAP and get it into action:
- At its most basic level, digesting and processing protein takes significantly more energy than carbohydrates or fat, and carbohydrates take more energy to process than fats.
- Most nutritionists estimate a person's TEF to be 10% of their energy intake.
- A regular meal schedule not only allows for better feeding compliance, but it positively impacts TEF which could cause significant changes in the long term.
- Lose the gut and you'll crank up your TEF.
- Exercise has positive metabolic repercussions regarding TEF, even after just one workout.
- Increasing your protein levels while restricting your calories will allow for maximum TEF.
It's important to note that while the thermic effect of food is a neat topic and that the various strategies outlined above can help maximize TEF, it's still only part of a greater plan. Total calories, food selection, and energy expenditure trump TEF any day of the week and they should be your main focus!
- Rubner, Die Gesetze des Energieuerbrauchs bei der Erniihrung. Leipzig and Vienna: Franz Dauticke. 1902.
- Lusk, G., Journal of Nutrition, 1930. 3: p. 519.
- Farshchi, H., M. Taylor, and M. IA, Decreased thermic effect of food after an irregular comparted with a regular meal patter in healthy lean women. Intermation Journal of Obesity, 2004. 28(5): p. 653-660.
- Jones, P.P., et al., Role of Sympathetic Neural Activation in Age- and Habitual Exercise-Related Differences in the Thermic Effect of Food, J Clin Endocrinol Metab, 2004. 89(10): p. 5138-5144.
- Poehlman, E., C. Melby, and S. Badylak, Relation of age and physical exercise status on metabolic rate in younger and older healthy men. J Gerontol., 1991. 46(2): p. B54-8.
- Denzer, C. and J. Young, The effect of resistance exercise on the thermic effect of food. Int J Sport Nutr Exerc Metab, 2003. 13(3): p. 396-402.
- Witt, K., et al., Exercise training and dietary carbohydrate: effects on selected hormones and the thermic effect of feeding. Int j Sport Nutr, 1993. 3(3): p. 272-89.
- Schmidt, W., et al., The effect of aerobic and anaerobic exercise conditioning on resting metabolic rate and the thermic effect of a meal. Int j Sport Nutr, 1994. 4(4): p. 335-46.
- Burke, C., R. Bullough, and C. Melby, Resting metabolic rate and post drandial thermogenesis by level of aerobic fitness in young women. Eur J Clin Nutr, 1993. 47(8): p. 575-85.
- Luscombe, N.D., et al., Effects of Energy-Restricted Diets Containing Increased Protein on Weight Loss, Resting Energy Expenditure, and the Thermic Effect of Feeding in Type 2 Diabetes Diabetes Care, 2002. 25(4): p. 652-657.
- Luscombe, N., et al., Effect of high-protein, energy restricted diet on weight loss and energy expenditure after weight stabilization in hyperinsulinemic subjects.Int J Obes Relat Metab Disord, 2003. 5(27): p. 582-590.
- Gougeon, R., Effect of Insulin and Energy Restriction on the Thermic Effect of Protein in Type 2 Diabetes Mellitus. Obes Res, 2001. 9(4): p. 241-250.
- Segal, K., et al., Thermic effect of Food at Rest, during Exercise, and after Exercise in Lean and Obese Men of Similar Body Weight. J Clin Invest, 1985. 76: p. 1107-1112.