A Calorie is a Calorie! (And Elves Live in my Pants)
Q: Okay, Berardi, it’s time you cut the crap with all these “special” meal combinations in your diets like Massive Eating and Don’t Diet. A calorie is a calorie! Eat fewer calories than you need and you’ll lose weight. Eat more calories than you need and you’ll gain weight. It’s that simple!
A: Nothing about the human body is as simple as your statement implies. Sure, things appear to be simple when you have a very simple understanding of the most preliminary workings of human physiology and nutrient metabolism. Most dietitians, undergraduate students, and individuals who read a lot about nutrition learn just enough to think things are simple without fully understanding them. This is where they become dangerous advocates of such prejudiced statements as “a calorie is a calorie.”
Getting back to our undergraduate nutrition “experts,” I’m willing to bet that if you asked most of them to define exactly what a calorie is, they simply couldn’t tell you despite their “wealth” of knowledge. If that’s true, then get as far away from them as you can, just in case ignorance is contagious. Or better yet, print out this column so they can read it and learn something!
Okay, in all fairness, I’ll ease up and let you know that while these “calorie is a calorie” types are clearly ignorant in some respects, they’re at least definitionally correct. (And yes, I made that word up.) I’ll tell you what I mean in a minute.
Basically, what most people commonly call a “calorie” is really a misnomer. When you mistakenly say one gram of protein has four calories, what you should be saying is that one gram of protein has four kilocalories or four kcal. This is because one kcal actually equals 1000 “calories.” Over the years, people have mistakenly made the kcal and calorie synonymous in their usage so now one kcal is often mistakenly called one calorie.
With that understood, what exactly is a kcal? By definition one kcal is equal to the amount of energy required to raise one liter of water one degree Celsius. So the energy contained in one scoop of Grow! could either raise the temperature of a 110-liter jug of water by one degree C, or raise the temperature of a one-liter jug of water by 110 degrees C.
So, definitionally, a calorie is certainly a calorie, just like a degree Celsius is a degree Celsius. However, when someone asks the question “Is a calorie a calorie?”, they require more information. What they mean to ask is, “When I consume a calorie of protein, does my physiology respond the same way as when I consume a calorie of fat or carbohydrate?” The answer in this situation is a resounding no!
I could write volumes about this in support of my contention that functionally, a calorie is not a calorie, but don’t worry, today I’ll spare you. Instead let me address just a few points and give a few examples of why a calorie isn?t a calorie.
Let’s start out with a simple comparison that sounds a bit extreme but will illustrate my point. If I agreed with the idea that a calorie is a calorie, then I’d have to believe that my body would behave the same way if I ate 3000 calories a day from celery (yes, that’s a lot of celery) as it would if I ate 3000 calories a day from butter. Is a calorie just a calorie, or might some of the fibrous content in the celery fail to be absorbed, decreasing the amount of calories actually reaching the cells?
Since some of the fibrous calories will indeed fail to be absorbed, we can see that during the first step of physiological food processing (digestion), the inherent caloric value of food is already altered and fewer of the ingested calories reach the cells. So, 3000 calories of celery are certainly different from 3000 calories of butter. If you’re eating only celery and 3000 calories constitutes deficit eating for you, then you’ll get far less calories than you’d hoped.
In the end, my point here is that reading food labels doesn’t give a good indication of the exact amount of calories that’ll actually reach the cells for energy provision or storage. Functionally, a calorie is not a calorie.
The next main reason that people ask, “Is a calorie a calorie?” is because they want to try to manipulate their caloric intake so that it’ll be below, match, or exceed calorie needs. This is so they can lose, maintain, or gain weight. But the problem with thinking that a calorie is a calorie is that the very act of eating different foodstuffs can change metabolic rate. A good example of this is the thermic effect of food.
The digestion and metabolism of food actually increases the metabolic rate after a meal. Since protein foods have double the thermic effect of food verses carbohydrates or fats, it should be obvious that the metabolic rate will be higher when more protein is consumed. Again, functionally, a calorie is not a calorie!
When on a hypocaloric diet, protein needs are increased. In studies comparing groups on hypocaloric diets that are low in protein and those that are high in protein (calories are the same in both groups), the diets high in protein lead to increased metabolic rates, increased weight loss, and better preservation of lean mass. Clearly, a calorie is not a calorie in this case either.
While the previous paragraphs discussed different macronutrients, even different varieties of the same macronutrients have different physiological effects. When low glycemic carb diets are compared to high glycemic carb diets, it’s clear that the groups of individuals eating mostly high glycemic carbs have higher body fat percentages, higher fasting glucose and insulin levels, and have higher risks for cardiovascular disease. Functionally, a carbohydrate isn’t even a carbohydrate, let alone a calorie a calorie!
Studies done in rats have shown that when they eat diets of identical calorie levels, their body compositions are dramatically altered by the composition of fat in the diet. When omega-3 fatty acids make up a large percentage of the diet, the rats are lean and muscular. When omega-6 fatty acids make up a large percentage of the diet, the rats are obese. A fat isn’t even a fat, let alone a calorie a calorie! (You knew that was coming, right?)
I hope it’s getting clear that just because a calorie is a calorie by definition, that doesn’t mean this definition has any implications for changing our physiques. Just because a carbohydrate is a carbohydrate by structure, that doesn’t mean that different carbohydrate sources behave the same way in the body.
Here’s a cool study that illustrates my point quite well. This study was done to compare the effects of twelve weeks of a moderate hypocaloric (high protein) diet and resistance training in male police officers. In this study, there were three total groups - a control group that didn’t exercise, and two groups that did. In the two exercise groups, two different protein supplements were used to increase protein intake. Several very telling things emerged from this study:
Before the study began, the subjects’ diets were analyzed. It turned out that subjects had actually been consuming a hypocaloric diet that was approximately 10 to 20% below their calculated calorie needs (15% protein, 60% carbohydrate, 25% fat). Despite the calorie deficit, they were all between 22 and 35% body fat and had been gaining weight over the previous five years! So if a calorie were really just a calorie, they should’ve been leaner and losing fat, right? But no, they were gaining fat!
In the control group that didn’t exercise, the macronutrient composition of the diet remained the same as before the study (15% protein, 60% carbohydrate, 25% fat) but subjects made smarter food choices. They simply consumed fewer simple carbohydrates and ate more complex carbohydrates.
In addition, these subjects ate less food before sleep and more during the active hours of their days. If a calorie were a calorie, we wouldn’t expect to see any changes in their body compositions. However, these simple changes led to an average 5.5 pound weight loss and an average 2.5% decrease in body fat. If a calorie were just a calorie, then there shouldn’t have been a change in weight or body fat percentage!
- That’s already plenty of evidence to make the next person that says “a calorie is a calorie” eat his words, but let’s go ahead and kick him while he’s down, shall we? Let’s discuss the interesting changes between the two exercise/high protein groups.
These subjects consumed the exact same number of calories as they did before the study. In addition, the two groups consumed the same exact percentage of the different macronutrients as each other (26% protein, 52% carbohydrate, 20% fat) and did the same exercise routine. Interestingly, the subjects consuming one type of protein (a casein and milk protein product) lost almost 6.5 pounds more fat and gained nearly 4.5 pounds more muscle than those consuming another type of protein (whey).
Not only was body composition altered, but the subjects in the casein/milk protein group had a 31% improvement over the whey-only group in muscle strength. If a calorie is a calorie, the two groups should’ve had the same results. Clearly they didn’t, so, yet again, a calorie is not a calorie!
I could go on all day but I’ll stop here. From this discussion, I hope it’s clear that the old notion that a calorie is a calorie is a dying idea. Anyone who continues to make this assertion is completely wrong due to either a lack of current information or due to a closed mind. Whatever the reason, neither type of person has any place giving out nutritional advice.