Calorie is a Calorie Debunked

Calories consumed minus calories burned = the simple formula for weight loss or gain. For those monitoring their weight, they often find that this formula does not work. In the United States, 73.6 % of adults aged 20 and over are overweight or obese. (1). About 45 million Americans go on a diet every year, may of them unsuccessful in shedding the extra pounds. Those that are actually counting calories end up frustrated and feeling discouraged. What is going on?

We need to step back and start with the question, what is a calorie? A calorie is a unit of energy. From a thermodynamic standpoint, it is defined as the amount of energy needed to raise the temperature of 1 kilogram of water by 1 degree Celsius. Calories in our food come from one of the three macronutrients: fat, carbohydrates, and protein. One way macronutrients and calories are calculated is with a tool called a bomb calorimeter, which is a device that measures heat release of organic substances. Humans are not bomb calorimeters and we do not extract every calorie from the food we eat. Metabolizable energy is the difference between the total energy of food consumed and the energy that passes out of the body undigested in feces and urine. Wilbur Atwater, a 19th-century chemist, determined a mathematical equation to indirectly estimate the number of calories in food products after subtracting the energy measured in feces. His experiments revealed proteins and carbohydrates have about 4 calories per gram and fats have 9 calories per gram. So, using this equation, here is an example of how calories of food are calculated:

A food that contains 10 grams [0.35 ounces] of protein (10 x 4 = 40) and 5 grams [0.2 ounces] of fat (5 x 9 = 45), would have a total caloric value of 40 + 45 = 85 calories.

The U.S. Department of Agriculture still uses these calculations today to come up with an official calorie number for every food. Of note, the FDA allows for a 20 percent margin of error for nutrients listed on a food label, including calories, meaning that these calorie counts aren't incredibly accurate.

The Atwater system is outdated and inaccurate. Here are some examples that disprove the calorie is a calorie myth:

1. The thermic effect of food (TEF) is a reference to the increase in metabolic rate that occurs after ingestion of food. When you eat food, your body must expend some energy (calories) to digest, absorb, and store the nutrients in the food you have eaten. The TEF is approximately 10 percent of the energy of a mixed diet and will depend on several factors, including your age, meal timing, and macronutrient composition — carbs, fat, and protein — of your meal. (2)

The energy required to digest each macronutrient (its TEF) can be expressed as a percentage of the energy provided by the macronutrient:

· Fat TEF is 0–5%.

· Carbohydrate TEF is 5–10%.

· Protein TEF is 20–30%.

Generally, meals higher in protein produce a higher TEF compared with those lower in protein and high-carb meals produce a greater thermic effect when compared with high-fat meals. (3) But many factors can modify these results. Meals high in fiber may also increase the TEF. Conversely, meals made mostly of highly refined or processed foods may produce a lower TEF. (4) There is a growing body of research indicating that the TEF may vary depending on the time of day meals are consumed. (3) Physical activity, regardless of age or body composition, can also increase the TEF. (5) Age can also play a factor in TEF, decreasing as you age. (6)

2. Our bodies extract fewer calories than listed on the nutrition label. This has been noted with nuts, such as almonds and walnuts. A 2012 study published in the American Journal of Clinical Nutrition found that the energy content of certain foods, such as nuts, cannot be accurately calculated by the Atwater system. (7) So, what can alter digestibility of nut macronutrients? Fiber! Fiber alters calories by means of altering the percentage you absorb. Dietary fiber is not broken down by human digestive enzymes but is acted upon by gut microbes. Some of the fiber you consume is not for you but for your gut microbes. Cooking method also matters when it comes to absorbing calories. Cooking unlaces microscopic structures that bind energy in food and allows our gut to digest the food. The calorie system does not account for the differences between raw and cooked food, pureed versus whole, or plant versus animal cell structures. For example, if you eat a steak rare, you will likely be consuming several hundred calories less that if it was well-done. Same goes for vegetables, raw vegetables absorb less than cooked ones. Processed foods are basically pulverized ingredients which likely results in maximum calorie absorption.

3. The Atwater equation does not take human individuality into account. No two people are identical. Differences in height, body fat, liver size, levels of stress hormones, microbiome differences and other factors influence energy required to maintain the body’s basic functions. Even something as seemingly insignificant, such as the time we eat, may affect how we process energy.

None of this means that the calorie is a useless concept. Calorie counts remain a helpful guide to relative energy values despite the inaccuracies listed above. We know that standing burns more calories than sitting; cookies contain more calories than spinach. But the calorie is broken in many ways, and there's a strong case to be made to take a more holistic look at what we eat. Food calories affect the body very differently depending on their source and the overall context in which they are consumed. Where health is concerned, count more on the QUALITY of the calories you consume rather than the calorie count. So, in the end, not all calories are equal.

Reference:

1. Centers for Disease Control and Prevention (April 20, 2022). Nationan Center for Health Statistics obesity and overweight. https://www.cdc.gov/nchs/fastats/obesity-overweight.htm

2. World Health Organization, Food and Agriculture Organization of the United Nations, & United Nations University. (2004). Human energy requirements. Retrieved from https://www.fao.org/publications/card/en/c/e1faed04-3a4c-558d-8ec4-76a1a7323dcc/

3. Calcagno, M., Kahleova, H., Alwarith, J., Burgess, N.N., Flores, R.A., Busta, M.L., & Barnard, N.D. (2019). The thermic effect of food: A review. The Journal of the American College of Nutrition, 38(6), 547-551.

4. Barr, S.B., & Wright, J.C. (2010). Postprandial energy expenditure in whole-food and processed food meals: implication for daily energy expenditure. Food Nutrition Research, 54. https://doi.org/10.3402/fnr.v54i0.5144

5. Denzer, C.M., & Young, J.C. (2003). The effect of resistance exercise on the thermic effect of food. International Journal of Sport Nutrition and Exercise Metabolism, 13(3), 396-402.

6. Du. S., Rajjo, T., Santosa, S., & Jensen, M.D. (2014). The thermic effect of food is reduced in older adults. Hormone Metabolism Research, 46(5), 365-369.

7. Novotny, J.A., Gebauer, S.K., & Baer, D.J. (2012). Discrepancy between the Atwater factor predicted and empirically measured energy values of almonds in human diets. The American Journal of Clinical Nutrition, 96(2), 296-301.