Although calories often receive a bad reputation surrounded by myths, they actually help sustain life. Like a double-edged sword, the human body absolutely needs them to survive and thrive, but too many or too few can deter health.
Thus, knowing how many calories you should eat in a day is vital for health. Luckily, the body is smart and adaptive and possesses innate mechanisms that help regulate caloric intake on a daily basis.
Nonetheless, knowing your individual recommended calories per day can help guide nutritional and other lifestyle habits.
What Are Calories?
Calories are simply a measure of energy. They are units of energy in food and drink as well as some non-food substances like coal.
Specifically, a calorie, otherwise known as a kilocalorie is the amount of energy needed to raise the temperature of one kilogram of water one degree Celsius. They are provided by the three macronutrients – carbohydrate, protein, and fat – and eventually converted into ATP, the only usable form of energy.
For reference, micronutrients like vitamins and minerals help facilitate the metabolism of calories into ATP.
Empty vs Nutritional Calories
Calories can also be referred to as empty versus nutritional.
Empty calories refer to the calories from foods and drinks that provide energy but little nutritional value in the form of vitamins, minerals, antioxidants, fiber, amino acids, beneficial fatty acids, and phytochemicals among others.
Empty calories tend to come from processed and packaged foods in the form of added, refined sugar and fat and fillers. Common sources include:
• Donuts, pastries, and desserts
• Cakes and cookies
• Crackers and chips
• Processed meats and cheeses
• Juices, soda, energy drinks, and sports drinks
• White/refined carbohydrates (white bread, pasta)
• Candy
• Many condiments and sauces
Sometimes non-nutritive products like artificial sweeteners are also lumped into this category, though they do not actually provide energy.
In general, high consumption of empty calories is associated with health consequences like obesity, diabetes, heart disease, and stroke.
On the other hand, nutritional calories provide energy and additional beneficial compounds like the ones mentioned in the above paragraph (vitamins, fiber, etc.). They positively contribute to health by improving cells and reducing the risk of many chronic diseases. Food and drinks that provide nutritional calories are often referred to as nutrient-dense and examples include:
• Fruits and vegetables
• Whole grains (whole wheat, oats, rice, quinoa)
• Lean protein (poultry, fish, meat, eggs, high-quality dairy)
• Healthy fats (omega-3 rich foods, avocados, olive oil, nuts/seeds)
Recommended Calories per Day
If the number 2,000 stands out, that's because nutrition labels are based on a 2,000-calorie diet. Essentially, governing bodies created an entire food model system based on the idea that this number represents the average intake of billions of people. But how accurate is this number?
Calorie intake recommendations from the 2020-2025 Dietary Guidelines (DGAs) vary based on age, sex, height, current weight, pregnancy or lactation status, and physical activity. However, their entire appendix of caloric recommendations through the lifecycle is solely based on age, sex, and physical activity level.
These guidelines are established based on Estimated Energy Requirements equations established by the National Academies of Sciences, Engineering, and Medicine. They harp that they are estimates and that the best way to evaluate calorie needs in comparison to calorie intake is by monitoring and evaluating body weight status over time.
Nonetheless, their estimates typically range from 1,600 to 2,400 calories a day for adult women and 2,000 to 3,000 calories per a for adult men. Thus, that quintessential 2,000 number on food labels is somewhat accurate, but hardly encompasses the bio-individuality of the population at large. Aiming to consume a more individualized caloric amount will better contribute to weight maintenance and metabolic health.
Caloric Intake Equations
Because the DGAs only account for three factors – including age, sex, and physical activity level – evidence-based equations predict more accurate calorie recommendations for individuals. Dietitians regularly use these equations in hospital settings to determine meal plans and tube feedings, private practice as weight loss or gain parameters, and eating disorder centers to facilitate weight restoration.
The equations produce fairly accurate predictions that can serve as solid guidelines. This is vital for pursuits to lose weight, maintain current weight, or even achieve healthy weight gain. For example, 3,500 calories equal one pound. Thus, to lose one pound per week, one would subtract about 500 calories from their maintenance calorie amount per day (500 x 7 = 3500).
The two most popular types of predictive equations include those that calculate the basic metabolic rate (BMR) multiplied by an activity factor and kcals per kilogram of body weight.
Harris-Benedict Equation
The Harris-Benedict equation is one of the oldest predictive equations. However, based on new lifestyle habits, it tends to be less accurate than Mifflin St. Jeor (to be discussed next) and typically overestimates caloric needs. It calculates BMR and then applies an activity factor. In practice, this equation is sometimes used for athletes or those who need to gain weight.
For Women: BMR = 655.1 + (9.563 x kg) + (1.850 x cm) - (4.676 x age) *AF
For Men: BMR= 66.5 + (13.75 x kg) + (5.003 x cm) - (6.775 x age) * AF
*Activity Factors (AF)
• Sedentary (little to no exercise): 1.2
• Lightly Active (light exercise/sports 1-3 days/week): 1.375
• Moderately Active (moderate exercise/sports 3-5 days/week): 1.55
• Very Active (hard exercise/ sports 6-7 days/week): 1.725
• Extremely Active (very hard exercise/sports + physical job): 1.9
Harris Benedict Calorie Calculator
Mifflin St. Jeor
As mentioned, this equation is more accurate in practice because it accounts for the reduced amount of daily activity in today's society. In this way, it better predicts true caloric needs and tends to favor weight maintenance. Nowadays, dietitians use this in clinical settings like the hospital and eating disorder centers.
For Women: BMR= 10 x weight (kg) + 6.25 x Height (cm) – 5 x age (years) – 161 *AF
For Men: BMR= 10 x weight (kg) + 6.25 x Height (cm) – 5 x age (years) + 5 * AF
*Activity Factors (AF)
• Sedentary (little to no exercise): 1.2
• Lightly Active (light exercise/sports 1-3 days/week): 1.375
• Moderately Active (moderate exercise/sports 3-5 days/week): 1.55
• Very Active (hard exercise/ sports 6-7 days/week): 1.725
• Extremely Active (very hard exercise/sports + physical job): 1.9
Mifflin St. Jeor Calorie Calculator
Cunningham Equation
This third equation measures resting metabolic rate (RMR), which is closely related to BMR. This is the most accurate predictive equation for athletes, as it accounts for lean body mass or fat-free mass (FFM), which is more metabolically active than body fat tissue. However, it requires that one knows their lean body mass, which is calculated by bioimpedance analysis or DEXA scans, both of which can be costly.
RMR = 22 x FFM + 500 *AF
*Activity Factors
• Very light (office work, cooking, general activity): 1.2-1.3
• Low active (30 minutes of walking or similar): 1.5-1.6
• Active (at least 3 hours of moderate to vigorous activity per week): 1.6-1.7
• Heavy (planned vigorous activity, full-time athletes, hard-labor workers): 1.9-2.1
Calories per Kilogram Body Weight
This type of equation is typically only utilized by dietitians in the hospital setting. Certain disease states like burn victims, kidney disease, transplant receivers, tube feeders, and comas require very specific amounts of calories the body needs to heal, regardless of metabolic rates. Amounts range from 10 or 15 kcals/kg to 45 kcals/kg body weight.
Because these equations are so nuanced, specific calorie calculators cannot be provided.
The Takeaway on Recommended Calories per Day
The mere word calorie can cause quite a visceral reaction for many. However, at their most basic, calories are simply a measurement of potential energy. In general, empty calories are associated with poor health outcomes while nutritional calories reduce disease risk and optimize metabolic health, which equals healthful weight maintenance.
While the DGAs can offer loose guidelines for caloric recommendations, predictive equations are more individualized and therefore more accurate. Whereas Harris-Benedict was an original predictive equation, Mifflin St. Jeor has proved to be more reliable and valid and is most frequently used. However, the Cunningham is the gold standard for athletes because it accounts for lean body mass.
Rather than fear calories, understand the science of them to make informed decisions about health and wellbeing!
