It’s food dogma: calories in, calories out. If you count more calories than you expend, you will gain weight; if you consume fewer calories, you will lose weight. Keeping track of it has never been simpler where you are with this calorie balance. Hundreds of diet-tracking applications, ranging from MyFitnessPal to Livestrong, provide dietary specifics for thousands of foods in their directories. They appear to be able to tell you exactly how many calories you need to lose or sustain your weight based on your age, height, and sex. Is it, however, really that simple?
Experts believe the answer is most likely no. Though regular diet control can help certain people lose weight (maintaining a weight loss is another story), calorie tracking isn’t as precise as it seems.
In reality, keeping track of the daily calorie intake does not necessarily correspond to the number of calories our bodies eat and burn.
Susanne Votruba, a researcher at the National Institute of Diabetes and Digestive and Kidney Diseases, states, “People should not focus on this as the Bible of food consumption and expenditure” (NIDDK).
What exactly is a calorie?
So, where did the calorie originate in the first place? Wilbur Olin Atwater, an American chemist, set out to calculate the amount of energy we bring into our bodies by simply blowing food up in the late 1800s. Atwater used a bomb calorimeter, which is an enclosed container containing a known volume of water that tests the amount of heat emitted during a chemical reaction. He’d put the food inside the device, turn on the power, and boom. The calorie is the unit of energy used to increase the temperature of one milliliter of water by one degree Celsius. The greater the energy of the food, the more it can heat the ambient water. (Calories on a diet label are kilocalories, which are the amount of energy used to increase a liter of water temperature by one degree.)
Of course, our bodies don’t need any molecule of food we consume, so Atwater even gathered and blew up the participants’ poop and pee. Atwater calculated nine calories in a gram of fat, four calories in a gram of carbohydrates, and four calories in a gram of protein-based on the energy discrepancy between what participants consumed and what they excreted. That’s the device we’ve got now. (Only on special occasions can we even blow up food.)
Unfortunately, humans have not bombed calorimeters, and not all diets are made equal. According to David Baer, a research physiologist at the US Department of Agriculture, Atwater’s method was reasonably reliable for the foods he measured. Still, it was never meant to be generalized to any morsel we put in our mouths today. “When you apply it to those ingredients, Atwater’s method just falls apart,” Baer notes.
According to Peter Ellis, a biochemist at King’s College London, Atwater’s method doesn’t tell us what happens to various foods when they pass through our human digestive systems or how our bodies consume those nutrients. “We’ve understood for a long time that how foods are digested varies greatly,” Ellis says.
All foods are not created equal.
Take, for example, nuts. According to the Atwater scheme, a few handfuls of nuts entered into your diet-tracking software might make a significant dent in your regular calorie target. However, evidence shows that we do not have access to any of those calories. According to Ellis, fat molecules in nuts are encapsulated inside cell walls consisting of dietary fiber that we can’t digest. It turns out that our digestive system isn’t very good at getting into those cells and extracting the fat. Ellis and his collaborators put this theory to the test by consuming a diet rich in almonds and only minimal quantities of other foods. The feces of the subjects were then gathered and examined. Many of the almond fragments had gone through the digestive system unchanged, even retaining their fat molecules, according to their findings, which were published in the American Journal of Clinical Nutrition.
Scientists from the US Department of Agriculture performed a related study of cashews, comparing the energy of the nuts participants consumed with what they excreted. The researchers discovered that the participants consumed less power from the cashew nuts than the Atwater causes predicted: just 137 calories on average, relative to 157 calories. Their findings were published in the journal Nutrients.
“As a result, the notion that all nutrients are digested to the same amount is untrue,” Ellis notes. It’s not all mad. Our bodies, according to Ellis, aren’t very good at accessing the starch and sugars present in beans and other seeds. These energy-rich molecules are hidden away within fibrous cell walls, similar to nuts. Then there’s the impact of boiling rice, which isn’t taken into account in the Atwater scheme. Processing can make the macronutrients in food (starch, fats, and proteins) more available to our bodies because the nutrition you get from a cooked meal is always more significant than the number of its components.
Finally, there’s interindividual variation—we’re not just as good at extracting nutrition from our food. According to Kathleen Melanson, a nutrition professor at the University of Rhode Island, those variations are primarily due to our gut microbiota. Some microbes assist us in extracting more energy from our food, while others siphon power away from us. The balance of gut microbiota determines the number of calories we consume.
According to Melanson, the gap in calories between 137 and 157 calories in a serving of cashews may not seem like much, but it’s enough to affect the accuracy of a diet tracker. “You can’t expect it to be right on time.” Over time, a ten to twenty percent difference will add up to hundreds of calories. Human error, Melanson adds, is almost definitely a more significant cause of inaccuracy—incorrectly tracking the amounts of foods or failing to monitor those ingredients. To begin with, people aren’t great at predicting how much they feed, let alone the consistency of Atwater’s method.
Should you keep track of your calorie intake?
Is calorie counting worth it, given the various possible causes of error? According to Brooke Tompkins Nezami, a behavioral nutrition scientist at the University of North Carolina at Chapel Hill, keeping track of what you eat will help you improve healthier eating patterns and even lose weight if that’s your intention. People who simply monitored their diet for eight weeks consumed two more servings of vegetables a day than they did at the start of the survey, according to a 2013 International Journal of Behavioral Nutrition, Physical Activity published a report on this subject.
According to Nezami, consistency is a more significant measure of performance than accuracy. In other words, people who use these apps aren’t counting calories daily; they’re just paying attention.
It’s possible that keeping track of calories isn’t necessary. People profit from just writing down what they consume rather than the calories, according to Nezami. This system could also be more beneficial for other citizens. “Calorie counting takes a long time. For certain people, it may be a burden. And that’s one of the reasons we started looking at alternate, perhaps more straightforward monitoring methods,” says Nezami. One of these approaches involves categorizing foods into three ranges depending on their calorie content: green, yellow, and red, and merely keeping track of how many “red” or high-calorie foods you consume.
Bottom line: If calorie counting helps you lose weight, do it. However, according to NIDDK’s Votruba, there’s no reason to fret about if you’re meeting your targets every day. “I think it’s fine and can be useful if users want to monitor and use these apps,” she says. “However, once it begins to govern your life, it is no longer worthwhile because it is providing you with an amount that may or may not be accurate.”