Becoming familiar with the information on food labels can be a smart move to increase the quality of your diet. With user-friendly apps like My Fitness Pal and Lose It, getting information on the foods you eat has become easier than ever. If your goal is healthy weight management, tracking your food intake can help to keep you accountable.
But just how accurate is the information on the nutrition panel? Surprisingly, the calories and other information provided on food labels may not be very precise at all.
If you were wondering how inaccuracies on the nutrition label may be impacting your health, keep reading. We’ll have answers to all of your questions on this topic, including:
- What is a calorie?
- How are the calories on food labels calculated?
- What is the thermic effect of food?
- How much of a calorie discrepancy is legally permitted on food labels in the United States?
- Is the other information on the food label also inaccurate?
- Are any changes coming to the nutrition facts panel?
- Is calorie tracking a useful method for weight management?
By the end of this article, you’ll be well-versed in the science behind food label information. The ability to sort fact from fiction in nutrition science will help you to be a more educated consumer. This can better enable you to make the best choices regarding your health.
What is a calorie?
Simply put, a calorie is a unit of measurement reflecting the amount of energy in food. It is the amount of heat energy needed to increase the temperature of 1 mL of water from 15ᵒC to 16ᵒC. Many countries measure food energy in kilojoules instead of calories (1 kcal = 4.184 kJ).
Metabolism involves significant amounts of energy, so when we are talking about “calories,” we are actually referring to kilocalories (kcal), 1000-calorie units. That 90-calorie glass of skim milk that you had at lunch would be considered 90,000 calories in a chemistry lab! The numbers become far more manageable when presented in their truncated form on food labels.
The calorie content of individual foods was initially being measured in a device called a bomb calorimeter. Foods were placed in the device, burned, and the change in water temperature was measured to determine the calories. Currently, the calories on most food labels are estimated using indirect calculations; we’ll cover these in the next section.
How are the calories on food labels calculated?
Food label information is more complicated than you may have surmised. Scientists determine the calories listed on food labels in the U.S. in several different ways. The most common methods are (from the FAO website):
The Atwater General Factor System
You calculate calories with this system using a single factor for each macronutrient, regardless of the food in which it is found. The factors are 4 kcal/g for total carbohydrate, 4 kcal/g for protein, and 9 kcal/g for fat.
These factors were corrected for losses in digestion, absorption, and urinary urea excretion. The calories on multi-ingredient foods are often calculated using this simple system.
With this system, a serving of crackers that contains 23 grams of carbs, 2 grams of protein, and 3 grams of fat would be 127 calories. This gets rounded up to 130 calories per serving on the food label.
The Atwater General Factor System with Modified Non-Digestible Carbohydrates and Sugar Alcohols
Insoluble fiber is often subtracted from the calorie count of high-fiber foods. Unlike soluble fiber, insoluble fiber is not a source of calories.
Soluble fiber is given a factor of 2 kcal/g. Sugar alcohols each have a different factor based on type. Otherwise, this system is identical to the General Factor System above.
The Atwater Specific Factor System
This system uses a different factor for each macronutrient, depending on the food in which it is found. Accounting for food matrices helps to provide more accurate nutrition information.
To give an example, proteins can have significantly different heats of combustion depending on their composition of amino acids. So while the protein in spaghetti has a factor of 3.91 kcal/g, the protein in potatoes clocks in at only 2.78 kcal/g. This difference may seem small, but it can add up fast depending on which foods are mainstays in the diet.
The specific factors for grains are dependent on how the grain is milled. While whole wheat flour has factors of 3.59 kcal/g for protein and 3.78 kcal/g for carbohydrate, refined white flour contains 4.05 kcal/g and 4.12 kcal/g, respectively.
American diets tend to be higher in foods that have higher specific factors. This means that we may be underestimating our calorie intake when the food label uses the general factor system. To confuse matters further, individual nutrition databases may contain information calculated using multiple methods.
Food labels may also use bomb calorimetry data or specific food factors for particular foods that have been approved by the FDA. The nutrition facts panel does not reveal which of these methods is behind the numbers provided.
The systems listed above all include metabolizable energy (ME), or the energy that remains after accounting for losses in feces, gases, urine, and body surfaces. These systems do not factor in the thermic effect of food, which varies by food type. They also fail to account for the length of cooking time, another factor that appears to have energetic consequences.
What is the thermic effect of food?
The thermic effect of food (TEF) is “the increase in energy expenditure associated with the consumption, digestion, and absorption of food.” It can be separated into two components (definitions adapted from Krause’s Food & the Nutrition Care Process):
Obligatory thermogenesis: the energy you need for nutrient digestion, absorption, and metabolism. This includes the energy required for the synthesis and storage of macronutrients.
Facultative thermogenesis: the additional energy you expend beyond obligatory thermogenesis due to metabolic inefficiency.
The TEF of certain macronutrients is much higher than others. Composing a diet that is less thermodynamically efficient (higher TEF) may lead to a lower calorie intake compared to the listing on the food label.
The thermic effect for carbohydrate is 5-10%, for fat is 0-3%, and for protein, it is 20-30%. TEF is generally estimated as up to 10% of total energy intake since most of us consume meals that are a mix of macronutrients.
There is some evidence that certain ultra-processed foods have a much lower TEF than “isocaloric” foods that are minimally processed. Choosing whole foods with lower thermodynamic efficiency may help to lower net energy intake. One hundred calories of processed cheese food will not behave in the body in the same way as 100 calories of cheese.
Some experts suggest that net metabolizable energy (NME) should be used instead of metabolizable energy, to increase the accuracy of calorie counts. Net metabolizable energy subtracts obligatory thermogenesis and energy loss to microbial fermentation from metabolizable energy. This would more accurately reflect the amount of energy that is available to the body for basal metabolism, growth, development, and physical activity.
The most significant differences between NME factors and the general Atwater factors occur for protein and fiber. The NME for protein is 3.2 kcal/g (compared to 4 kcal/g), while for fiber it is 1.4 kcal/g (compared to 2 kcal/g). Choosing a diet that is higher in protein and fiber may help you to create a calorie deficit for fat loss.
How much of a calorie discrepancy is legally permitted on food labels in the United States?
The issues above are not the only factors that contribute to the inaccuracy of calories listed on food labels. The FDA allows food manufacturers a wide margin of error, outside of the expected variability involved in the method of nutrient analysis used.
The calories listed on the label are legally allowed to be 20% in excess of the nutrient content of the food composite. That means that a “100-calorie” snack bar could actually contain 120 calories. Additionally, foods listed as zero calories may contain up to four calories per serving.
In short, food labels are permitted to have large calorie inaccuracies. Thus, two people who appear to have isocaloric diets may actually have widely different intakes. If an individual regularly eats an excess of calories, it could negatively impact a weight loss goal.
Is the other information on the food label also inaccurate?
Perhaps not surprisingly, there is a wide margin of error permitted for the other information on food labels as well. Nutrients added as part of a fortification process must be present in at minimum the amount listed on the label.
Thus, your calcium-fortified milk alternative must contain at least the amount of calcium listed. It may contain more.
Nutrients that are naturally occurring in foods must be present in amounts equal to at least 80% of the food label listing. These natural nutrients may include total carbohydrate, dietary fiber, protein, PUFAs and MUFAs, vitamins, or minerals. As with calories, manufacturers do not get penalized if levels fall outside of this range due to expected variability in analytical methods.
The FDA states that reasonable deficiencies of calories on labels “are acceptable within current good manufacturing practice,” with no lower limit specified. Reasonable excesses of total carbohydrate, dietary fiber, protein, PUFAs and MUFAs, vitamins, and minerals are accepted as well.
Are any changes coming to the nutrition facts panel?
Significant changes are coming to food labels by 2020 for major food manufacturers and by 2021 for smaller companies. Calories will be in larger type, and serving sizes will be changed to more accurately reflect typical portion sizes. In addition, added sugars, vitamin D, and potassium will be required on the label.
The current nutrition facts panel is over 20 years old. These updates are being made based on the latest nutrition information. These changes do not impact the methods used to determine the number of calories by weight of the food.
Is calorie tracking a useful method for weight management?
A low-calorie diet is considered one of the evidence-based methods for healthy weight management. Self-monitoring behaviors can help those who have lost a lot of weight keep the weight off long-term. As long as a person does not get too hung up on the numbers, calorie tracking is useful as a general guide.
That said, calorie tracking is not the right approach for everyone. It may be particularly hazardous for those who have a history of or are vulnerable to eating disorders. Additionally, individuals (including dietitians) tend to underreport their intake when keeping a food record.
When it comes to healthy weight management, you should compose your meals in a way that addresses your hunger. Continually having to draw on willpower to ignore hunger pangs is not sustainable, regardless of the weight management method you choose. Aiming for a diet that is rich in nutrient-dense food and low in energy-dense food can assist in creating a calorie deficit for weight loss.
As we’ve covered above, the calorie information on food labels is not very precise. Keeping this information in mind may help to prevent some from becoming obsessive about counting calories. Calorie tracking is only useful in seeing the big picture (e.g., consistently tracking 4,000 kcal days when your daily needs are 2,000 may lead to weight gain).
Final Thoughts About Calorie Counts On Food Labels
The current consensus is that it is not feasible to change the calorie counts on food labels to a standardized system based on NME. However, that does not mean that the information on the nutrition facts label is entirely worthless.
Choosing foods that are higher in protein and fiber may increase satiety and help to promote healthy weight management. The new food label will also help consumers to choose foods that limit added sugars. The focus on current nutrients of concern on the nutrition facts panel aids in increasing awareness regarding adequate intake.
Are you looking to increase the quality of your diet? Do not miss our recipe section. It’s the perfect place to discover some new family favorites that also happen to be packed with beneficial nutrients!
Summer is a registered dietitian located in Avon, Connecticut where she specializes in weight management, special diets, general nutrition, and avoidant/restrictive food intake disorder (ARFID). She is the developer and content creator behind the Summer Yule Nutrition website, where she shares evidence-based information on hot topics in food and nutrition.