The calorie counts on many low-carb foods appear to vastly understate the actual calorie count. Are you actually eating more calories than you think?
I recently heard from a long-time listener who was upset by what she felt was highly misleading nutrition information on one of her favorite products.
“Alice” explained that she’d been eating a lot of tortillas, in the form of breakfast tacos, wraps for lunch, and tortilla and peanut butter roll-ups for snacks. She had found a few different low-calorie tortillas, with anywhere from 30 to 50 cal according to their labels.
“But when I calculated the calories myself, by multiplying the grams of carbohydrate by 4, grams of protein by 4, and grams of fat by 9,” she wrote, “the result was almost double what the nutrition labels showed. If you are someone that only has a wrap on occasion, it's not a big deal. But if you are someone like me who eats several wraps per day, you might be eating a lot more calories than you think you are. How can they get away with this?”
In fact, the nutrition counts provided on these labels were perfectly legal, as well as reasonably accurate. There are a few reasons why the calorie counts on Nutrition Facts labels may not add up the way you think they should. One has to do with common misunderstandings about how many calories the so-called macros (carbs, fats, and protein) provide.
The 4-4-9 myth
It’s commonly believed that 1 gram of carbohydrate contains 4 calories, 1 gram of protein has 4 calories, and 1 gram of fat has 9 calories. These numbers are called Atwater equivalents, and they represent the average values for these macronutrients. In fact, a gram of carbohydrate may have anywhere from 0 to 4.5 calories, depending on the source of carbohydrate. There are also variations in the number of calories per gram in fats and proteins from different sources, although the range is quite a bit smaller.
Manufacturers have a number of options for calculating their calorie counts. The simplest way is to use the Atwater equivalents. For a lot of foods, this is going to be pretty close. But for some foods, using Atwater equivalents would significantly overstate the calories. This is especially true for foods that have been engineered to be lower in carbohydrates than they normally would, such as the low-carb tortillas that Alice was buying.
The total carbohydrate count that you see on the Nutrition Facts label includes starches and sugars, as well as fiber and sugar alcohols. But because these last two categories are largely indigestible, they contribute a lot fewer calories per gram than other carbohydrates. When you see a package that lists “net carbs” in addition to total carbohydrates, that’s often a food with a lot of indigestible carbohydrates.
Understanding net carbs
Net carbs is not an officially recognized way of stating the nutrient content of foods—and this number cannot be included in the Nutrition Facts label. It’s considered front-of-package labeling, or marketing language. The number of net carbs is calculated by subtracting fiber and sugar alcohol from the total carbohydrate count. But this does not give you any information about calories. In other words, multiplying net carbs by 4 calories per gram isn’t an accurate way to calculate calories, either.
Manufacturers also have the option to use more accurate values for different types of carbohydrates when calculating calorie counts. For example, instead of multiplying the total carbohydrate by 4, they can multiply the soluble fiber by 2 calories, sugar alcohols by 0 to 3 calories (depending on which one they are using), and the rest of the carbohydrates by 4.
So the good news for Alice is that these Nutrition Facts labels were not as far off as she feared. But there are a couple of other reasons why the calorie counts may not add up perfectly, such as rounding.
Rounding and margin of error
The manufacturer must calculate calories using the actual amounts of protein, fats, and carbohydrates. However, on the Nutrition Facts label, they can round those values up or down to the closest whole number. So a food that lists 2 grams of protein on the label might actually contain 1.8 grams or 2.2 grams of protein.
The total amount of calories per serving is also rounded up or down to the closest 5 calorie increment (for foods with less than 50 calories per serving or less) and to the closest 10-calorie increment for foods with more than 50 calories per serving. Foods with less than 5 calories per serving can be rounded down to zero.
And finally, the FDA allows for a margin for error on Nutrition Facts. A food could contain up to 20% more calories than stated without running afoul of the regulations. But you may be reassured to know that a recent survey measuring the actual calorie content of packaged foods found that most were within 5% of the amount stated on the label.
The bigger problem with counting calories
The calorie counts that we see on food packages (or in our diet tracking apps) are not exact measurements. And it’s even more difficult to pin down the exact number of calories our bodies burn. Formulas or apps that calculate how many calories you can afford to eat, based on your age, size, and exercise habits are providing only a very rough estimate—and may in fact be wildly inaccurate.
A better indicator of how your calorie intake matches your calorie expenditure is your bathroom scale. But keep in mind that day-to-day changes in your body weight do not reflect actual changes in body fat. These short-term changes are driven mostly by transient fluctuations in fluid and waste. This is why I recommend looking instead at your 7- or 15-day average instead. If this number is trending up, it’s a pretty good indication that you are taking in more calories than you are using. If it’s trending down, you’re taking in fewer. If it’s flat, you’re in homeostasis; your energy intake is perfectly balanced with your energy output. If that’s not the desired outcome, then you’ll need to make some adjustments.