JeffN wrote:TEF is the thermal effect of food. It is amount of calories you burn digesting the food you eat. While the macronutrient composition of the diet may effect it slightly, it is safe to estimate it at 10% of the calories you consume. Some people mistakenly use TEF to think that eating or eating more will cause them to burn more total calories or raise or "jumpstart" their RMR/BMR. It won't as TEF is separate from RMR/BMR and is always only a small portion of the total calories needed to be ingested to get the effect. So to burn or "jumpstart" your body to burn an extra 300 caories from TEF one would have to eat 3000 more calories. This leaves a net increase of 2700 calories. Hardly a "jumpstart" to net 2700 calories in
The claim has often been made, which I have often been asked about, that consuming a high carbohydrate diet, like the one recommended here, results in an increased (or higher) metabolism. To answer this, we have to first clarify all the issues related to metabolism, as I did above. Then, we have to understand that the question is not really related to BMR (basal metabolic rate), but to TEE (total energy expenditure,which is often thought of as our metabolism), and thermogenesis.
There are three main things that contribute to thermogenesis, formal exercise (Exercise Associated Thermogenesis), daily activities (Non Exercise Associated Thermogenesis) and the thermal effect of food (TEF) also known as Diet Induced Thermogeneisis (DIT). As described above, these three are parts of TEE (total energy expenditure) but not BMR.
Therefore, this question, in relation to whether switching to a diet like the one recommended here, does this diet increase thermogenesis, and more specifically, the thermal effect of food and if so, how much of an increase is it.
In a mixed diet, and for most mixed diets, we estimate TEF to be about 10-15%. The TEF of fat is about 0-3%, carbs 15-25% and protein 20-30% and these are estimates, which can vary. In addition, within each food group, the least processed the food is, and the more fiber in the food, the higher the TEF. So, there is no one single number we can use.
However, looking at the numbers, it is easy to see why one would think that switching from a higher fat, highly processed diet to a higher carb, minimally processed diet, would raise the TEF part of thermogenesis.
Let's run some sample numbers and use 3% for fat 20% for carb and 25% for protein to see if this is true and if so, how big is the benefit.
Take someone eating 1800 calories, 35% fat, 15% protein, 50% carb who is in energy balance (1800 in, 1800 out)
Fat - 35% = 630 calories x 3% = 19 calories TEF
Protein - 15% = 270 calories x 25% = 68 calories TEF
Carb - 50% = 900 calories x 20% = 180 calories TEF
Total TEF = 267 (which is 14.8% of calories)
Now, lets switch them to 1800 calories, 10% fat, 15% protein and 75% carb
Fat - 10% = 180 calories x 3% =5 calories TEF
Protein - 15% = 270 calories x 25% - 68 calories TEF
Carb - 75% = 1350 calories x 20% = 270 calories TEF
Total TEF = 343 (which is 19% of calories)
As you can see, without even factoring for the impact of the higher fiber and the less processing, by switching from a higher fat to a higher carb diet, you burn more calories from TEF
Here, it is an 76 calorie benefit, which, while it is a 28% increase in TEF, the impact, is only an 4% of total energy expenditure (1800 calories).
So, yes, we do get an advantage in TEF (which is not directly metabolism but part of the Total Energy Expenditure equation) but it is minimal at best
The problem with isolating this impact is if you follow the logic, switching to a higher protein diet, would create and even higher TEF. Not much, but slightly higher.
In Health
Jeff