Nutrition 101: Calories

By Stephanie Nelson, MS, RD MyFitnessPal Sr. Lead Nutrition Scientist 

Reviewed By Melissa Jaeger, RD, LD MyFitnessPal Head of Nutrition

A common misconception about calories is that they are another word for food. Instead, calories are actually a measure of energy. Food gives us energy, and calorie intake is a measure of how much energy we get from a particular food. 

Calories also refer to the energy it takes to get through our day. We use calories every day for everything we do; laying in bed, breathing, blinking, walking, typing, and exercising. The total amount of calories we burn in a day is our Total Daily Energy Expenditure (TDEE). 

How are calories calculated?

The amount of calories we burn in a day, TDEE, can either be directly measured or estimated. For direct measurements, you would need a lot of expensive equipment in a laboratory, and these measurements are completed through processes called Doubly Labeled Water or Indirect Calorimetry. 

Instead, we can estimate our TDEE through equations based on the major factors that influence our calorie burn: height, weight, age, sex, and physical activity, by plugging them into an equation based on direct measurements from other people.

In MyFitnessPal, we use the Mifflin St. Jeor equation (1). We request the relevant information when you sign up for MyFitnessPal, and calculate your TDEE to estimate the number of calories you burn in a day.

How do calories influence body weight?

If we eat the same amount of calories as we burn in a day, this is called calorie balance, and our weight stays stable. However, if we eat more calories than we burn in a day, this is called calorie surplus, and these extra calories are stored as fat, causing weight gain. In order to lose weight, we must eat fewer calories than we consume, called a calorie deficit.

The size of our calorie deficit determines how quickly we lose weight. When we lose weight too quickly, we lose muscle along with body fat (2), and our hunger hormones get out of sync (3) even after we discontinue our calorie deficit. So what’s the right calorie deficit to optimize weight loss? 

The maximum calorie deficit a person should have is dependent upon their body size, specifically, the relationship between their height and weight, known as BMI. (Calculate your BMI here) According to the NIH (4), the maximum recommended calorie deficits are:

• BMI <27: 250 calories per day
• BMI 27-35: 500 calories per day
• BMI >35: 1000 calories per day

Conventional estimates say that a 500 calorie deficit per day should lose about 1 pound per week (4). However, this is just an estimate and it’s important to remember that weight loss is not linear, so try not to put too much stock in weekly weight loss rates. Instead, focus on building healthy habits that support your calorie goals.

How to use food tracking for weight management

Tracking your food can be an effective way to manage your calorie balance to achieve your goal (5). Understanding the amount of calories you eat and burn in a day can help you modify your diet appropriately.

However, it’s important to understand that both your calorie goal and the calories you log are estimates, and not exact numbers. Therefore, it’s not necessary to hit your goals perfectly every day (6). Try using calorie tracking like a zip code rather than an exact address; as long as you’re in the neighborhood, you’re on the right track.

Tracking isn’t just about calories and weight management. Regardless of your weight goal, being aware of your calorie intake is important for maintaining a high-quality diet, for food portion management, and meeting nutrient intake recommendations. But calories aren’t the full story. Where the calories come from (nourishing, nutrient-dense foods while balancing the treats you love) and the makeup of your calorie intake from carbohydrates, fat, and protein, are also important aspects of your health journey. Paying attention to the bigger picture ensures a balanced diet while maximizing satiety and fullness, so you make the most of the calories you consume!

References

1. Thom G, Gerasimidis K, Rizou E, et al. Validity of predictive equations to estimate RMR in females with varying BMI. J Nutr Sci. 2020;9:e17. Published 2020 May 26. doi:10.1017/jns.2020.11
2. Edda Cava, Nai Chien Yeat, Bettina Mittendorfer. Preserving Healthy Muscle during Weight Loss. Advances in Nutrition. 2017;8(3): 511-519. ISSN 2161-8313. https://doi.org/10.3945/an.116.014506.
3. Sumithran P, Proietto J. The defence of body weight: a physiological basis for weight regain after weight loss. Clin Sci (Lond). 2013;124(4):231-241. doi:10.1042/CS20120223
4. Pi-Sunyer FX, Becker DM, Bouchard C, et al. Clinical Guidelines on the identification, evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report.; 1998. https://www.nhlbi.nih.gov/files/docs/guidelines/ob_gdlns.pdf.
5. Wiechert M, Holzapfel C. Nutrition Concepts for the Treatment of Obesity in Adults. Nutrients. 2021;14(1):169. Published 2021 Dec 30. doi:10.3390/nu14010169
6. Helsel DL, Jakicic JM, Otto AD. Comparison of techniques for self-monitoring eating and exercise behaviors on weight loss in a correspondence-based intervention. J Am Diet Assoc. 2007;107(10):1807-1810. doi:10.1016/j.jada.2007.07.014