A patient sent Joanne the following email. “I overheard a coworker talking about food/calories/etc. and noted her saying, ‘We should all be on a 1,500-calorie diet as women.’ For some reason this really got to me and I normally don’t let these stupid comments affect me, especially when I know better. Thoughts?”
Yes, I do have thoughts about this, several in fact, but for the sake of time and space, I will leave aside tangential issues of practicing dietetics without a license (If someone without a medical license made a statement along the lines of, “As women, we should all be taking [insert name of a medication] daily,” would you be cool with that?) and the virtually-constant propagation of nutrition myths throughout our culture. Instead, let’s focus on just how incorrect this coworker’s assertion is.
Caloric needs are surprisingly difficult to determine. The most accurate method is direct calorimetry, which utilizes a metabolic chamber in which the subject occupies a compartment that measures the heat that he or she emits during whatever state of activity happens to be taking place at the time. Unless you enroll in a research study that involves one of these chambers, you will most likely never gain access to one in your lifetime.
Indirect calorimetry, which involves measuring oxygen and carbon dioxide intake and expulsion, respectively, is less invasive in some ways and easier to utilize. Large hospitals typically have metabolic carts that can perform such measurements in their research laboratories, and lesser models exist for office settings. The tradeoff, however, is accuracy, as even the best indirect calorimetry tools are a step down from direct calorimetry.
Next we have the Fitbits of the world, devices that use algorithms to estimate caloric needs based on a crude set of variables. Dietitians use similar equations sometimes as well, and when I do, I always stress to patients that the results are just rough estimates that cannot and should not be taken too literally.
These equations have numerous sources of error, such as the reliance on subjective measures of physical activity. Anybody can Google how many calories certain activities supposedly burn, but really these numbers are general rules of thumb at best. Running a mile burns 100 calories, we are told, but is this right? What about the size and body composition of the runner, or his or her mechanics? Does he or she have short, quick strides or long, less frequent steps? What about swings of the arms, point of contact between the foot and the ground, head bobbing, or any number of other factors that can influence the results?
One of my patients occasionally asks me how many calories one burns during sex. Unless you get two people to have intercourse in a metabolic chamber, who knows? Even then, the heat generated would pertain only to those unique individuals in that specific encounter, so what do you do, divide by two and make the assumptions that their efforts were equal and that these results apply at other times and to other people as well? Logistical hurdles and the countless variables involved make estimating caloric expenditure a guessing game not just for sex, but for pretty much any activity.
As a consequence, estimates of caloric needs are just that – estimates – and vary widely from person to person. My degree in mathematics reminds me that I like numbers as much as the next guy if not more, and I can certainly understand the appeal of having a short, sweet, and specific target for which to aim, but really the best method to determine your caloric needs is to set quantifiable data aside and look internally to your hunger and fullness signals. Despite all of the proliferating nutrition myths and overarching messages we are taught from childhood on that we cannot trust ourselves regarding food, our bodies are actually pretty good at telling us what and how much they need. We just need to relearn how to pay attention and trust those signals again.
Ahhh, the 1,500-calorie diet. It’s amazing how some arbitrary number has gotten stuck in the minds of so many people. 1,200 calories is also a popular number. Flip through any of your typical women’s health magazines and you are likely to read that all women should be consuming no more than 1,500 calories per day to be “healthy.” Unfortunately, there really is no such thing as the “perfect” number of calories for each and every person. 1,500 calories (or 1,200 calories or 1,750 calories) is a myth. It makes no sense to say that every woman should be on a 1,500-calorie diet; we all are unique human beings with unique needs.
As I tell my patients over and over – every body has different caloric needs. Age, height, weight, gender, muscle mass, and activity level are just some of the factors that can affect our calorie needs. Even the Mifflin-St. Jeor equation, the equation most often used by most dietitians to determine calorie needs, does not take into account all of these factors. Our caloric needs will vary over our lifespan for a number of reasons. Women who are pregnant or breastfeeding need many more calories, while as we age, we typically need fewer calories. Anyone who has lived with a teenager can attest to the fact that calorie needs go way up during adolescence! When someone is recovering from an injury, his or her caloric needs might be elevated. For instance, the caloric needs of burn patients can be as much as double what the “average” person’s needs are. The best way to figure out what your calorie needs are? Eat as you normally would. If you see no large shifts in your weight (think plus or minus five pounds), you are meeting your calorie needs!
When working with patients who struggle with eating disorders, I try to steer clear of talking about calories. Many of my patients have spent countless hours logging the calories they ate (and burned), and most of these patients would say that they were “obsessed” with doing so. I had one patient who would log her calories daily, and if she consumed more than 1,300 per day, she felt like she had “failed.” Another patient would try to stick to no more than 1,800 calories per day, and if she went over by just a few calories, she would binge because she had “blown it.”
Instead of talking about calories, I try to use the “exchange” system with my patients. Exchanges are groups of foods that have similar nutritional profiles. For instance, a carbohydrate exchange (sometimes called “grain” or “starch” exchange) contains approximately 15 grams of carbohydrate per serving. This might look like an average piece of bread, a ½ cup of cooked pasta or rice or ½ of a large potato. By using exchanges, we can take the focus off of calories and how we need to limit them and instead talk about making sure we get enough carbohydrates, protein, fats, vegetables, etc. Calories have a negative connotation for many of my patients, while exchanges feel a bit more abstract and neutral.
In short, instead of setting an arbitrary calorie goal for oneself, I think it would be much more beneficial to set other goals. Getting five fruits and vegetables per day, being physically active for 60 minutes per day, and eating intuitively would be much better goals (in my opinion) than making sure one never goes over 1,500 calories per day.