Inventing the Calorie

The calorie was developed in the early 19th century as a unit to measure energy. If you’re familiar with the kilowatt hour, commonly used to gauge electrical energy, or the joule, which is utilized across various scientific disciplines, you can appreciate the calorie's purpose. It was specifically designed to quantify thermal energy, defined as the energy required to increase the temperature of one kilogram of water by one degree Celsius.

You might wonder how a unit measuring water temperature can provide insight into food.

(Note: The term "Calorie" with a capital C refers to this specific measurement; the lowercase "calorie" indicates the energy needed to raise one gram of water by one degree Celsius. However, in everyday discourse, the capitalized version is predominantly used.)

Yet, this raises an essential question: How can this unit of thermal measurement translate to insights about food? For clarity, we can look to Wilbur Atwater, a chemist from the mid-1800s, who developed a method that may seem peculiar today.

Atwater conducted an unusual experiment: he incinerated various foods within a sealed chamber submerged in water. This setup, known as a bomb calorimeter, enables measurement of how much the water temperature rises as the food burns. By calculating this temperature change, he could estimate the energy released from the food, presuming that the human body extracts energy in a similar manner.

This method, while strange, was innovative for its time. In 1896, many medical professionals still believed in outdated treatments, like bloodletting. Nonetheless, Atwater’s bomb calorimeter work laid the groundwork for our ongoing discussions about calorie burning.

Consider these questions: “Is that dark chocolate cranberry granola bar a healthy choice?” or “Should I indulge in those tortilla chips and guacamole?”

Answering these queries demands a careful evaluation of the myriad nutrients in these foods, alongside your overall dietary intake and activity levels. Even a seemingly simple food like a banana is a complex blend of vitamins, minerals, enzymes, and micronutrients.

Now, for a straightforward question: “How many calories are in this banana?” We devised the calorie concept to quantify energy. While burning food in a controlled environment may seem odd, it simplifies the intricate debate about food quality into a single number. It's easy to see why this appeals to food manufacturers.

Atwater dedicated years to studying food composition, believing his calorie framework would serve as a practical tool for assessing food and identifying high-calorie meals that contribute to weight gain. However, over the last century, food companies discovered they could exploit this system to promote nutritionally questionable processed foods.

The calorie-counting system is efficient. Food manufacturers can derive calorie counts from ingredient lists without needing to burn their products. Using Atwater’s established values, they assign average calorie amounts to fats (nine calories per gram), carbohydrates (four calories per gram), and proteins (also four calories per gram). This streamlined approach means no one has to waste time conducting caloric experiments on frozen dinners.

This calculation is particularly beneficial for large corporations producing mass-market foods. After all, a large banana, with its 125-calorie count, is not vastly different from a Twinkie, which comes in at 150 calories.

Reducing foods to a single figure raises concerns. Are calorie counts even reliable?

Increasingly, evidence suggests they are not.

One notable issue arises with fiber, which our bodies generally do not digest. For years, it was believed that fiber holds no calories since we can't digest it. However, recent research indicates that gut bacteria can ferment fiber, producing fatty molecules that your body can utilize for energy.

Your body is not a flawless food-burning machine.

In the U.S., the food industry is still permitted to exclude fiber from total calorie counts. In Canada and the EU, fiber is factored in but at a reduced calorie rate (two calories per gram).

The fiber debate pales in comparison to the broader issues surrounding calorie counting. The primary concern is that calorie counts reveal the total energy content in food without addressing how accessible that energy is. For instance, a meal may contain 1,000 calories, but that does not guarantee your body can utilize all of them. Digestion is complex, and the body employs various metabolic pathways to process different nutrients, with some components inevitably passing through unused.

Moreover, the body can more readily access calories from cooked or processed foods. For instance, digesting raw spinach requires more effort than cooked spinach, as cooking breaks down tough cell walls and simplifies complex carbohydrates into more absorbable sugars. In some cases, cooking can mean your body expends less energy to digest, which may affect the overall caloric absorption.

The more natural and less processed the food, the more likely it is to be undervalued by the calorie system.

Research has shown that individuals absorb fewer calories from certain nuts than anticipated. For example, raw almonds contain about a third fewer calories than believed. Roasted almonds deliver 23% fewer calories than indicated, while roasted, chopped almonds fall short by around 20%.

Clearly, preparation methods like cooking and chopping impact calorie absorption. To maximize caloric intake from almonds, one would need to grind and cook them, such as in an almond cookie. This underscores the idea that only highly processed convenience foods have accurately represented calorie counts.

In other words, the more natural and unprocessed the food, the more likely it is to be misrepresented within the calorie framework.

There are numerous additional criticisms of the calorie system. We haven't even touched on how food interactions affect metabolism or the variances among individuals' gut bacteria colonies. Perhaps the most significant overlooked factor regarding food is satiety—the sensation of fullness after eating.

Research consistently shows that consuming proteins and fats leads to greater feelings of fullness compared to carbohydrates. This is because proteins and fats take longer to exit the stomach and trigger hormones that signal the brain to stop eating. In contrast, carbohydrates are rapidly absorbed into the bloodstream, prompting quick insulin fluctuations that can stimulate appetite.

Thus, it becomes evident that we would benefit more from focusing on whole, unprocessed foods rather than fixating on calorie counts.

Wilbur Atwater likely would have concurred. He often advocated for a simple, economical diet, believing Americans needed to incorporate more proteins, legumes, and vegetables while reducing sugar and fat consumption. He also recognized that most people were insufficiently active—an astute observation, given that average body weights were about 50 pounds lower at that time.

What Atwater did not foresee was how his calorie-counting framework would be misused. His experiments with food combustion led to a culture fixated on calorie counting and a proliferation of processed foods.

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