Calories in, calories out—simple math, eh? There’s another part of the calorie balance sheet that you may not be aware of. Diet-induced thermogenesis can add 5 to 15 % more to the calorie outflow bottom line. Your resting metabolic rate makes up 60 to 70 % of your energy output and activity adds 20 to 30 %.
Let me explain. When food is consumed, it requires energy to digest and assimilate the nutrients. Each macronutrient has a different effect on metabolism based on their diet-induced rate of thermogenesis. Protein has the greatest thermic effect at 20 to 30 %. It takes 20 to 30 % of the calories consumed from a protein source to actually digest and assimilate the macronutrient. Recall that energy is a measurement of heat, or heat loss. A high thermic effect of a food or meal shows a higher level of work is being done to digest that food. Ever sweat after eating a large meal? Fat has the lowest thermic potential at barely up to 5 %. Carbs have a bit of a range, being measured at 5 to 30 %. I contend there’s more to the story with carbohydrates—a lot more. Actually, it’s the reason behind the large range of measured thermic effect and it’s one of the greatest secrets to weight loss—especially in the anti-carb movement we’re living in.
The resurgence of low-carb/ketogenic diets has created a generation of people who assume carbs make you fat. Excess carbs will be stored as body fat—as will excessive amounts of any macronutrient. True. Carbohydrates are the body’s preferred source of energy, however; that makes it a double-edged sword. When carbs are present—blood sugar from a recently-eaten meal, stored carbs (glycogen) in the liver, or glycogen in the muscle—can and will be used when there is an energy deficit. Carbohydrate naysayers would say that when carbs are taken out of the diet, your body will use body fat sooner and in higher percentages. Also true. Case closed, right? We should all stop eating carbs! Not exactly.
When you eliminate carbs, you have the potential to slash your metabolism very quickly. Studies show that a low-carb diet can decrease your metabolism by almost 50 % in just a couple of months.
The best way of understanding macronutrients is to ditch a view that one is better than another or that any of them is “bad.” All three (protein, carbs, and fat) have necessary roles and all three can also be harmful in excess. Using the right amount at the right time makes all the difference.
Now you know the definition of thermic potential. It’s a linear equation—it takes a specific amount of energy to digest and assimilate the nutritional constituents of each macronutrient. Recall the nuance that this can actually be a bit of a range. The complexity of each macronutrient can change its thermic potential. For example, two difference sources of carbohydrates can be at different ends of a range. Two other points to consider are 1) the combination of macronutrients in the meal, and 2) the sheer size of the meal. There are times of the day and circumstances you may want a meal with no carbohydrates, all carbohydrates, complex carbohydrates, or simple carbs. This is perhaps the greatest example of how you can use the right macronutrients, in the right amount, and at the right time to achieve your best results.
Consider this as a major point to the book: protein does have the highest thermic potential, but carbs can have up to 30 % as well. It’s important to target the right meals with the right macronutrients and ratios to fuel (heat loss) the best activity (functional metabolism). In other words, it’s the merger of the thermic effect of food and activity (key point!) and using the calories eaten (efficiency). Timing, timing, timing. Function, function, function. Less hunger, more energy, better results from training, higher overall met rate…booyah!