At the most basic level, your weight is influenced by the relationship between the number of calories you take in (the food and fluids you consume) and the number of calories you expend (essential bodily functions and activity):

Energy Balance = Calories In – Calories Out

To lose weight, you must achieve a negative energy balance (taking in fewer calories than you expend). For weight gain, you need a positive energy balance (taking in more than you expend).

At first glance, the "calories in, calories out" (CICO) equation looks like an elementary math problem; eat less, move more, and you'll surely be on your way to weight loss. Even a math dunce can grasp that simple concept.

Unfortunately, it's not that simple. Many factors influence both the "calories in" and "calories out" components. In fact, if you base your diet solely off the CICO equation, you'll probably see lackluster results. However, learn the intricacies that influence this equation, and you can set up a successful weight-loss plan!

Calories In

This portion of the CICO equation represents the food and fluids you consume. However, the calories you consume also influence the number of calories you expend. Your body expends energy digesting, absorbing, and distributing the nutrients from the food you eat. This is referred to as the thermic effect of food (TEF). Not every food has the same TEF:

  • Protein : 20-35 percent of calories burned as TEF
  • Carbohydrates: 5-10 percent of calories burned as TEF
  • Fat: 0-5 percent of calories burned as TEF
Protein, Carbs, and Fats

Protein has a significantly greater TEF than carbohydrates or fat. So, if you eat a meal high in protein, your body will expend significantly more calories compared to eating the same number of calories from the other macronutrients. Imagine the impact this has on total calorie expenditure when two people follow an 1,800-calorie diet, yet one person consumes 35 percent of their calories from protein and the other just 15 percent.

Another way the type of food you choose impacts the entire CICO has to do with satiety, or how full you feel after a meal. Protein has a more satiating effect than carbohydrates or fat. This is because protein triggers the release of several satiety hormones that send messages to your brain to cease hunger signaling. Because of this, a person eating a higher-protein diet is more likely to stick to a calorie goal than someone filling up on empty calories.

Researchers found this to be true when they reviewed the impact of a high-protein diet on calorie expenditure, satiety, and weight loss across more than 50 studies. The results suggested that higher-protein diets may result in more weight loss and fat loss than a lower protein diet in the short term.[1]

Calories Out

The total number of calories you expend per day, also referred to as your total daily energy expenditure (TDEE), goes far beyond your exercise habits.

Basal metabolic rate: Your basal metabolic rate (BMR) refers to the number of calories you burn at rest if you lie in bed for 24 hours. These calories are expended to carry out functions essential to survival, like breathing, blood circulation, and oxygen and nutrient delivery. Your BMR may account for up to 70 percent of your TDEE.

BMR, Eat, Neat

Exercise activity thermogenesis: Your exercise activity thermogenesis (EAT) refers to the number of calories you expend via your exercise habits. Of course, the duration and frequency of your workouts obviously influence this number, but the type of exercise you engage in heavily impacts this amount, too.

Some forms of exercise, such as resistance training and high-intensity interval training, have a lasting impact on your metabolic rate after the exercise session ends (and up to 24 hours later). This means you not only expend more energy during these types of workouts, but your energy expenditure remains elevated for a prolonged period afterward.

Non-exercise activity thermogenesis: Your non-exercise activity thermogenesis (NEAT) refers to the number of calories you expend in all other non-exercise specific activity such as standing, walking, fidgeting, and executing tasks throughout the day. This number of calories is highly individualized. Someone who works a manual-labor job is going to expend far more calories than someone working a sedentary 9-5 desk job.

Thermic effect of food: As I mentioned earlier, you expend a significant number of calories simply digesting, absorbing, and distributing nutrients from the food you eat. Your TEF may account for up to 10 percent of total calories expended per day.

The Verdict

The same two people eating the same number of calories each day may experience drastically different results based on their food choices, types of exercise, and daily activity.

So, is CICO worthless and outdated?

No! The CICO equation still needs to be involved in your diet planning. You must take in fewer calories than you expend to drive weight loss. However, it's important that your diet plan doesn't stop there. You must consider the macronutrient composition of your diet, your exercise choices, and your daily activity levels, too. By taking everything into account, you'll be able to plan for optimal progress.


  1. Halton, T. L., & Hu, F. B. (2004). The effects of high protein diets on thermogenesis, satiety and weight loss: a critical review. Journal of the American College of Nutrition, 23(5), 373-385.

About the Author

Paul Salter, MS, RD

Paul Salter, MS, RD

Paul Salter, MS, RD, CSCS, received his BS in dietetics from the University of Maryland and his MS in exercise and nutrition science from the University of Tampa.

View all articles by this author