A Calorie Is Not A Calorie
While the gurus and pundits of the past believed that all calories were created equal, and while much of the current dietetics herd still believes it, I'm here to tell you why it just ain't true. To do so, I'll focus on three main arguments: the Thermic Effect of Feeding (TEF), cross-cultural studies, and the effects of isoenergetic diets using different foods.
The TEF, as I've said many times before, represents the additional caloric expenditure (above resting metabolism) that it takes to digest, absorb, and process the food you eat. Studies on the thermic effect of different foods have been important in describing the different effects of the macronutrients on metabolism.
The TEF lasts from between one to four hours after eating a meal. When adding up the thermic effects from each of your meals, this extra metabolism represents between 5% and 15% of your total daily energy expenditure. Therefore, if your daily energy expenditure is 3,000kcal, about 150 to 450kcal of that comes from the TEF. Interestingly, different macronutrients tend to have different effects on metabolism.
Welle et al. (1981) and Robinson et al (1990) demonstrated that during a normal six hour period of rest and fasting (basal metabolism), subjects burn about 270kcal. When eating a single 400kcal meal of carbs alone (100g) or fat alone (44g), the energy burned during this six hour period reached 290kcal (an additional 20kcal). Interestingly, when eating 400kcal of protein alone (100g) the subjects burned 310kcal during this six hour period (an additional 40kcal). Therefore, protein alone had double the thermogenic power vs. fat or carbs alone!
Swaminathan et al (1985) demonstrated that during a normal fasted 90-minute period, both lean and obese subjects burned about 110 calories. When consuming a 400kcal, fat only meal (44g), the lean subjects burned 125kcal (+15kcal) while the obese subjects only burned 110kcal (+0Kcal).
This indicates that while the lean can up-regulate metabolism when eating fat, the obese may, in fact, have a defect in their thermogenic response mechanisms for fat. When fed a 400kcal mixed meal (P+C+F), the lean subjects burned 130kcal (+20kcal) during the 90-minutes while the obese burned 125kcal (+25kcal) during the 90-minutes. These data demonstrate that mixed meals are more thermogenic than fat only meals and that lean people have a better TEF response than the obese.
So now that you understand that different macronutrients (at the same energy intake) can alter calorie balance within a single meal, here's another interesting argument for the fact that all calories were not created equal. In a study by Campbell et al (1991), 6,500 rural and urban Chinese were compared to the US population norms for energy intake, macronutrient breakdown, and health. This is an important comparison due to the fact that obesity and cardiovascular diseases have reached epidemic proportions in North America while the prevalence is much lower in China. Check out this data on average nutrient intake:
U.S.:
* Energy - 30.6kcal/kg
* Carbohydrate - 42% (224g)
* Fat Intake - 36% (85.86g)
* Alcohol - 7%
* Fiber - 11g/day
* Protein - 15% (80g)
* % Protein from Animal - 70% (56g)
* BMI (wt/ht*ht) - 25.8
China
* Energy - 40.6kcal/kg
* Carbohydrate - 71% (504g)
* Fat Intake - 14% (44g)
* Alcohol - 5%
* Fiber - 33g/day
* Protein - 10% (71g)
* % Protein from Animal - 11% (7g)
* BMI (wt/ht*ht) - 20.5
It's interesting to note that while the Chinese have a much lower body mass index (as represented by weight in kg/height squared in meters) and a much lower prevalence of obesity and cardiovascular disease, they eat about 25 to 35% more food than we do! Now, the Chinese tend to be more active than we are, but when the numbers were corrected for activity levels, the differences remain!
Looking at the macronutrient breakdowns, the Chinese are on a high-carb diet, no doubt. But they're not fat. And while their protein intake, by percentage, is lower, they do get nearly as much total protein, by gram amount, as we do. Perhaps we could take a lesson from the Chinese. Clearly not all calories are created equal because if they were, the Chinese would be fatter than we are! But instead, the average 100kg Chinese person gets to enjoy a 4060kcal diet while keeping his lean physique.
I know, I know, that study is only epidemiological and therefore lacks some explanatory power, but stay tuned as I present two final studies to demonstrate that all calories were not created equal.
In a study by Demling et al (2000), the researchers demonstrated that food choice and timing could be more important than total calorie intake. Before the study began, overweight police officers, eating about 2100 to 2300kcal per day, tipped the scales at 216lbs with 56lbs of fat mass (25% fat) and 158lbs of lean mass. They were eating about 74g protein, 380g carbs, and 56g fat. Since this is clearly a hypocaloric diet, they should've been losing weight. But they weren't.
Unfortunately for these poor guys, they were eating only 10% of their calories at breakfast and a whopping 50% of their calories right before bed. In addition, 50% of their carb intake was sugar! After diet counseling, these guys still ate the same diet in terms of macronutrients, but they ate 70% of their calories during the active parts of their day and 80% of their carb intake was complex and low on the GI scale. At the end of twelve weeks these guys lost 3lbs of weight and 5lbs of fat while gaining 2lbs of lean mass. And this was without changing exercise habits! While these changes weren't huge, it's clear that food choices and timing make a difference.
In another study by T-mag's own Doug Kalman et al (2001), Doug showed that a 1200kcal, high-protein (47%P, 36.5%C, 16.5%F) diet was more effective than a 1200kcal, moderate-protein (24.5%P, 48.3%C, 27.2%F) diet for fat loss. Subjects in the high-protein group lost 6.3lbs of body weight, 5.3lbs of fat weight, and only 1lb of lean weight. The moderate protein group lost 3.1lbs of body weight, no fat weight, and 4.5 whopping pounds of lean weight. Try telling these subjects that a calorie is a calorie!
In the end, there clearly are ways to burn more calories and lose more weight while eating diets differing in macronutrient content but similar in energy intake. In addition, if you can believe it, there may even be ways to eat more food while staying leaner. Just ask the Chinese.
