I write about food, nutrition and health, yet I avoid talking about calories. This might seem strange, since so much of diet and health culture is about calories obsession. Weight loss diets, food labels, restaurant menus, online food trackers, recipes, apps that track exercise and food intake, exercise machines that spit out calorie burning (mis)information. You could spend your whole day thinking about calories. Meanwhile all this calorie consciousness hasn’t made us healthier. The obesity epidemic is worse than ever and spreading rapidly in children.
I’m off the calorie bandwagon. Calorie obsession has distorted the way we think about food choices and eating. Time for a re-set.
What is a calorie?
A calorie is a measurement of energy potential. One calorie of heat will raise the temperature of 1 gram of water 1 degree Celsius, whether you use bread or wood chips or gasoline or Oreos as the fuel source. The energy in food is measured in kilocalories; one kilocalorie = 1000 calories. A kilocalorie (kcal) is defined as the energy required to raise the temperature of 1 kg of water 1 degree Celsius (1 kilogram of water is about 4-1/4 cups; 1 gram of water is about 1/5th teaspoon). The kcal system makes the numbers more manageable. Otherwise your 1200 Kilocalorie diet turns into a 1,200,000 calorie diet. Scary! Plus it saves space on food labels. Imagine if the label on the Oreos package listed one cookie as 53,000 calories rather than 53 kcal.
How do we measure calories in food?
Calories are not little gremlins lurking in our food. You can’t locate the 53 calories in an Oreo and take them out. The energy potential of food is stored in the carbohydrates, fat and protein contained in that food (alcohol also has calories).
The energy (calories) in a food can be measured in two ways:
- by burning the food and measuring the temperature change in water, using a bomb calorimeter. This process was invented in France in the 19th century, to evaluate explosives. The machinery has been modernized over the years, and is used to measure many energy in many different substances, including food.
- by the Atwater Method: analyze the food for fat, carbohydrate and protein content. Protein and carbohydrate have 4 kcal/gram; fat has 9. Count up all the grams of each component, multiply by the calories/gram and add it all up.
Calorie measurement is pretty straight forward. The problem is how the idea of calories is used by the diet and health industry. Eating has become a math problem. We’re encouraged to ‘eat by numbers’, not according to hunger. Add up your calories. Stick to a limit. If you can’t lose weight, it’s your fault because you aren’t adding up the calories correctly. I am not going to promote or support this mind-set. Here are 5 of my reasons:
1. Digestion is not a Bomb Calorimeter
Your gut doesn’t completely vaporizes food like a bomb calorimeter. Many foods are incompletely digested, particularly raw food. Fiber content of a meal, effective chewing, variations in digestive function, meal size, gut microbes and many other factors influence how much energy a person extracts from food.
Take corn. If you don’t chew up all those corn kernels, your digestive system can’t extract all the energy. A 100 kilocalorie serving of corn might only yield 75 kcals of energy. Recent research found the same effect for nuts. Result: calorie counts come with built-in inaccuracy, depending on a person’s digestion and other health issues.
2. Your daily energy requirement might not be so accurate
Researchers have developed several equations to calculate Basal Energy Requirement — how many calories a person burns every day for heart beat, digestion, breathing, thinking, muscle contraction (standing up, sitting down, moving your arms, talking, eating, etc), immune function, tissue renewal and repair, nerve transmission, cellular metabolism, and on and on. The equations depend on age, gender, height, and weight. These equations don’t account for muscle mass vs fat mass, a big problem considering that muscles need more energy than fat mass. And these equations don’t account for physical activity at all. Yet an individual might try to restrict her food choices to meet a daily calorie limit based on an equation that is not entirely accurate.
3. Calories burned by exercise are not accurate
Your total daily calorie needs = basal energy (see above) + calories burned for physical activity. The energy demands of dozens of activities have been estimated, but you might burn more or less calories to do the same activity. The calorie burn values on exercise machines are also averages. If you do all the calorie math, at best you get a ball park number for daily energy needs. At worst, you overestimate the impact of exercise. Even worse, some people immediately ‘eat back’ calories they supposedly burned on a treadmill or stair climber, using treat foods as a reward for exercising, even when they aren’t particularly hungry. Not a great weight control strategy.
If you’re interested in more information, this video explains energy requirements in a fun way.
4. Low calorie foods are “healthy”
This might the most pernicious outcome of our cultural calorie obsession. Thanks to low calorie weight loss diets, there’s a widespread belief that calories are bad. The inevitable conclusion: low calorie foods are healthy. We end up with nonsensical food rating systems that rank diet soft drinks or non-fat ice cream as healthier than olive oil or cheese or peanuts. People end up focusing on highly processed not-very-healthy foods strictly because of low calorie counts.
This gives food manufacturers the incentive to pump out all sort of “low calorie” or “low fat” junk food: low fat salad dressing, low fat/low sugar frozen desserts, low fat chips, low sugar candy, sugar-free soft drinks, low fat sugar free whipped topping, etc. People buy this processed stuff and think they’re making healthy choices.
5. Calorie counts on labels are not accurate
Did you know food labeling rules permit the actual calorie count in a food to be up to 20% higher than what is listed on the label. In other words, if a food label says 100 kcal/serving, it could actually be 120 kcal. If you depend on nutrition labels to guide your choices based on calories, you might be getting more than you expect.
As if labels aren’t bad enough, try getting a remotely ball-park sort-of accurate calorie count on home made food. Good luck. Sure you can take all the ingredients in a recipe and do the math with a nutrient database. But that presumes the database is accurate and that your measurements are 100% accurate. For example:
- Did you spoon the flour into the measuring cup? Or dip the cup into the flour bin? That makes a difference in amount of flour and calories.
- What percent fat meat did you buy? Did the fat cook out? Did you leave it in the pan or scrape it into the casserole?
- Is your cup of chopped broccoli exactly the same weight as someone else’s?
- Did you cook your pasta a minute or two longer because you prefer a softer texture? That makes a difference.
- Did you cut the lasagna into exactly the number of servings indicated? Did a bit more or less sausage end up in one of the servings? This all makes a difference.
- Did you pour the exact amount of wine into your glass to match the serving size? Or a bit more?
These are just some of the reasons I do not include nutrition information with recipes. It’s misleading to suggest that anyone will prepare a recipe exactly the same way I do.
Take Away Message
My advice is to ditch the calorie obsession. A much better plan is to focus on whole, mostly unprocessed foods. Eat according to hunger, not according to numbers. Don’t eat or drink all day long; leave some time between meals for your digestive system to process the food you just ate. Exercise every day (weather and circumstances permitting).
Eating should be about enjoying food and nourishment. Not an anxiety-producing math problem that makes you feel bad because you didn’t stick to some arbitrary limit.