A recent YouTube debate between two prominent personalities sparked my interest in the subject. One popular personality fired a shot for the "a calorie is just a calorie" side, and James Tiny Vest returned an intelligent volley that discussed why the thermic effect of food matters.
We all know how the "calorie is just a calorie" side of the debate goes. The thermic effect of food is minimized, and the proclamation is made that you can pretty much eat anything you want to lose weight IF your calories are under your daily maintenance level.
Related - Calculate Your Total Daily Energy Expenditure
Of the other side of the fence, James Tiny Vest responded with this insight:
"A calorie is not a calorie. Now let me tell you something. If you're still going and putting yourself in a caloric deficit, as someone that's interested in the progression of your physique, why would you be in a calorie deficit?"What James is implying here is simple.
The Thermic Effect of Food and Brown FatTEF, or the thermic effect of food, is basically the energy expended by the human body to process food. It is also known as specific dynamic action (SDA) or dietary induced thermogenesis (DIT).
There is also a second component to the thermic effect of food. Brown adipose tissue, or brown fat, is activated after a meal and produces heat. Approximately 5% of the human body is comprised of brown fat. Its main function is to turn the food we eat into heat.
Individuals with a lower BMI, or body mass index, tend to have more brown fat. This hints at an important thermogenic and physiological possibility. Because of the thermal effect of brown fat, higher concentrations could help fend off accumulation of more weight. More calories burned equals fewer calories stored.
Modern research is revealing that it may be possible to increase your levels of brown fat, and as a result, burn more calories. 
The neurons in our brain that also regulate hunger have a secondary function: they can encourage regular fat cells to turn into brown fat cells. Starving yourself, or eating too few calories, actually triggered these neurons to prevent - or slow - white fat from morphing into brown fat.
It makes sense, actually, if you think about it. When intaking fewer calories, why would your body want to make more brown fat and increase energy expenditure?
it should be noted that overconsumption of food can also hinder brown fat development.  Gorging on food not only increases the amount of white fat cells we have in the human body, but it also hinders the ability of brown fats cells to do what they do best - burn calories and create heat.
Thermic Effect of Eating Protein, Carbs, and Fats
At the core of "calorie is just a calorie" debate is the thermic effect of specific macronutrients - protein, carbohydrates, and fats. Each of these macronutrients requires a different amount of energy to digest. Is the difference so inconsequential that we can truly proclaim all calories are created equal? That is the question.
It is not uncommon to hear that 10% of the calories consumed are burned away during digestion. This is a rather generic estimation, but still somewhat useful.
Dietary fat is very easy for the human body to process, and has a lower thermal effect. On the other hand, protein is much more difficult for the body to process. It has a higher thermal effect. Carbohydrates are somewhere similar to fats.
Here are some more specific estimations from a the Journal of Nutrition: 
- Carbohydrates - 5 to 15% of the calories are burned during digestion.
- Fats - A high end 5 to 15% of the calories are burned during digestion.
- Protein - 20 to 35% of the calories are burned during digestion.
"Fats. They claim 5 to 15%. I disagree with that. I'm going to say that's a little high. I think that fats require so little (energy to digest). And if you go and do your own research you'll see where I am coming to these conclusions from."The thermal effect of macronutrient digestion is one of the three components of daily energy expenditure. The other two are activity-induced thermogenesis, and your basal metabolic rate (BMR).
It should be noted that DIT, or dietary induced thermogenesis, burns the least amount of daily energy.
There is research that indicates dietary induced thermogenesis levels are reduced for the obese. A meta-analysis by de Jonge and Bray looked at 49 studies. They found that those who were considered obese had far lower DIT levels. 
Granata and Brandon expounded on this research, saying that the theory was "attractive and plausible." They also noted that there were discrepant findings in the research that simply require further exploration of the topic. 
A few take-home points regarding the thermal effect of food.
Obesity and DIT. For the obese, DIT appears to be noticeably lower. Boiling this down to a real world application, this could fuel the argument that if you are overweight, overall calorie intake may be more important than macronutrient composition.
This doesn't negate the fact that a higher protein diet will still be a solid choice. But those that are obese will still need to watch food quality and calorie intake.
Food Intake. Overeating and undereating both appear to negatively impact potential brown fat levels in the human body. This could potentially lower an individual's metabolism during, and after a cutting diet involving reduced calories.
As we all know, calorie deficits work. Starvation diets are not good for you, but the topic is beyond the scope of this article, so we won't dive into them. It would be hyperbole to believe that a decrease in brown adipose tissue levels (even in a relative sense) would impact daily calorie expenditure to such a degree that fat would not be lost.
We all know this isn't reality for 99% of those that have tried calorie deficits.
Macronutrient Choices. Because of the high thermal effect of protein, and the ease with which fats are digested, shuffling around the macronutrient content of your food choices may help. This will only work if you're not already consuming a high protein diet.
If, say, your protein intake is only 10 to 15% of your daily calories, bumping it up to 30 to 40% will impact the amount of daily calories you burn. This difference will either allow you to eat slightly more food, or will allow for a very slight decrease in body fat levels while eating the same amount of daily calories.
What you DO want to avoid here are extreme diets. Moving daily protein intake to 70% of your daily calories might sound like a magic bullet on paper, but it's not a balanced diet and won't be sustainable nor enjoyable. Also, dropping carbs and fats to virtually nil won't be any fun either.
Diets should not restrict us to the point where they become an incredible burden. Sure, if you are a physique competitor of any kind, then this restriction might be necessary. But for the average Jane or Joe it's not.
Let's be honest here. The average person can make the following small adjustments to their diet and likely lose weight without ever needing to worry about the thermal effect of the macronutrients they intake.
- Drop most of the sugar and flour you eat.
- Avoid most processed and canned foods.
- Avoid fast food and deep fried foods.
- Get rid of drinks with calories.
- Make sure that 90% of your food intake comes from whole, clean foods. (One ingredient foods)
- Don't undereat or overeat any specific macronutrient, unless you have insulin sensitivity and need to reduce carbs. Stay balanced.
- Make sure you take in enough daily protein. Most people don't. Why? We live in a world filled with convenient food choices. Vending machines. Chain fast food restaurants. Donuts at work. Calorie-crammed coffee drinks. Processed, boxed foods. These are filled with cheap sugars and fats to keep cost down. It's easy for the average individual to undereat protein.
Increased protein intake helps, but how much is up to debate.
Digging Deeper into DIT - Dietary Induced ThermogenesisNow let's dig deeper into dietary induced thermogenesis and look at some additional studies. During a recent meta-analysis of 15 studies on food/alcohol intake and energy expenditure, we find the following: 
Alcohol Intake. When 22% of a meal's calories were removed and replaced by pre-dinner alcohol, energy expenditure increased by 7.2 to 8.6%.  A second study found similar results. When alcohol was swapped in and calories remained about the same, DIT increased by 7.1 to 9.0%. 
Protein Intake. Similar results were found when about 20% of a meal's calories were swapped out for more protein. One study found and increase in energy expenditure by 7.1 to 8.3%.  A second study yielded a more significant increase in DIT: a 10.5 to 14.6% increase in energy expenditure. 
Carb and Fat Intake. For carbohydrate and fat swaps, one showed no difference in energy expenditure at all.  Another study removed 65% of fat content and replaced it with carbohydrates. This yielded a slight increase in energy expenditure. 
Curiously enough, a third study involving the swapping out of fats for carbs found the opposite - that energy expenditure decreased.  This decrease in DIT occurred after only 28% of fats were substituted with carbs.
More research may be needed on energy expenditure when it comes to carb and fat swaps, but a logical conclusion is appearing: that fat and carbs burn about the same amount of energy to digest. This falls in line with the Journal of Nutrition percentages presented earlier in this article.
So there are a few conclusions we can draw from this research.
First, protein intake matters. Eat more protein and you will expend more energy. Second, alcohol intake may not be bad at all if your daily calories are kept the same. Moderation is key here. We are still after health and longevity, and it goes without saying that alcohol can be addictive.
Lastly, carbohydrates and fats really doesn't matter much. Obviously, if you swap out protein for carbs and fats, you will burn fewer calories. But it appears that swapping carbs for fats, or fats for carbs really won't change DIT to any substantial degree.
So is a Calorie Just a Calorie?So, is a calorie just a calorie? As with anything in life, the answer is complex and will vary from person to person. Is this a cop out? Far from it.
Overweight, Clean Eat. High Protein Diet. For those that are overweight, but already eat a clean diet that is rich in protein, calories matter. Calories should be reduced to lose weight. With that said, this drop should only be minor. Generally only several hundred calories below maintenance level.
Bumping up protein intake slightly will help, but obviously since you are already eating a lot of protein, there isn't much wiggle room here. It's best to add no more than 10 to 15% more protein to your diet while keep calories the same.
I wouldn't recommend pushing your protein intake about 40% of your total daily intake. For a man consuming a 3,000 calorie diet, this would mean a maximum of 300 grams of protein per day. This is a huge amount, obviously, but may help with energy expenditure. Using these guidelines, a woman consuming 1,800 calories per day would eat no more than 180 grams of protein per day.
Overweight. Poor Diet. Folks like this need to focus on cleaning up their diet, first and foremost. It's also beneficial to monitor calories. After all, they've been living in a free-for-all calorie world for ages. It's time to get serious about food choices. Getting calorie consumption down to a reasonable level is a primary goal.
With that said, these individuals should consider increasing their daily calorie intake. Fast food and processed food diets usually don't land on the high protein side of the fence.
So this is a double whammy. Between roping in daily calorie intake, and increasing protein intake, weight will be lost. Yes, dietary induced thermogenesis is still important here, but eating more protein will not help much if the individual doesn't change over to a new eating lifestyle.
A high calorie fast food, junk food diet with higher protein won't really help much. it might slow the rate of weight gain by a hair.
Average Weight. Slightly Healthy Diet. Here, the person is likely skinny fat. A normal(ish) weight, but doesn't look fit at all. They eat healthy(ish) a fair share of the time, but dislike how they look in the mirror.
Here, calories aren't as important.
What this person needs is resistance training and a slightly higher protein intake. The addition of muscle mass will noticeably improve the way they look, and work to minimize the impact of the fat they currently carry around on their bodies.
The combination of muscle mass additions, along with more protein intake, will work to improve metabolism and daily energy expenditure. This is a win win. Over time you will be able to eat more, look better, and perform better in all areas of life. It doesn't get any better than this.
You will likely drop some fat as well, albeit slowly.
The Skinny Guy or Gal. Here, calories matter. You will certainly need a reasonable amount of protein intake. Your frame is underweight. Packing on pounds while minimizing protein intake is a very bad idea. It's a recipe for a skinny-fat future.
What you want to do it keep a quality protein intake while eating slightly above maintenance levels by adding fats and carbs. Remember, overeating tends to reduce brown fat production. So in the long run aggressive calorie diets are not the way to go. They might help you gain weight now, but may also impact your metabolism when you finally reach a normal weight.
Final ThoughtsThere are many, many more possible body types and scenarios we could cover here. But honestly, I think you get the picture.
We often seek black and white answers in the diet and fitness world. The reality is this: there are rarely black or white solutions that apply to everyone. We are all unique, and have challenges and unique circumstance that can't be contained or quantified.
Some of us binge eat. This condition requires calorie moderation, a new eating lifestyle, and a huge commitment towards rewiring the way we approach food intake. Some of us eat healthy but have sloth metabolisms. We need to learn the importance of resistance training and a higher protein diet.
Instead of worrying about the "is a calorie just a calorie" debate, it's far better to equip ourself with a toolbox of information that allows us to make the best adjustments based on our current situation.
We know that:
- A higher protein diet not only helps burn more calories, but it also helps to build muscle. This is probably the best longterm metabolic strategy one can employ, especially if they like food. And who doesn't?
- Starvation diets are bad for longterm brown adipose tissue levels. They might potentially impact metabolism after weight has been lost. It goes without saying that an extreme diet like this, while it might encourage weight loss, will not give you the body you are after. You will lose both incredible levels of muscle AND fat, and will likely look awful after you are done.
- Aggressive bulks or high calorie diets, often employed by those that are underweight, powerlifters looking to add rapid strength, or gym bros who hope to pack on muscle mass quickly, are not good for brown adipose tissue development. After the bulk is done, a slower metabolism may be the result. Combine this will the resulting extra and unwanted fat, and it's a recipe for poor health and a weakened metabolism, even if you are bigger and stronger.
- Poor diets are more about food choices and calorie intake than anything. A new eating lifestyle must be learned, and yes, this generally includes more DIT-friendly protein.
- Extreme diets are not sustainable, nor generally healthy. You can try to increase protein intake to 70%, and fat to 10% of your daily calorie intake, but is this the "magic" fat loss solution you need? Yes, you will love fat. Maybe even eating the same amount of daily calories, but your body needs fat intake for proper brain health, organ health, and on and on and on.
If you want to lose fat my best advice is to drop calories just slightly, increase your protein intake, do some cardio, don't forget the importance of resistance training, make sure 80 to 90% of your calories come from whole foods, and to balance remaining calories between fats and carbs.