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." [1] 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. [2]
Several years ago, Dr. Lonnie Lowery laid out a simple breakdown for the thermic effect of the three macronutrients:
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.
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). [3]
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.
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. [6] 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. [7]
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. [8]
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. [9]
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.
Increasing the thermic effect of food is all about creating a metabolic advantage. With that in mind, who would you guess is metabolically superior?
Or...
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. [13]
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:
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.
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:
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!
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