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How Weight Loss Happens: The Science of Energy Balance

How Weight Loss Happens: The Science of Energy Balance

Achieving weight loss involves a basic understanding of your body’s metabolism and energy needs. This article will give you a crash course in the science of energy balance and how you can use this knowledge to reach your weight loss goals.

By Andres Ayesta, MS, RD

Key Points:

  • Energy balance is the key factor in weight gain or loss. It refers to the balance between the calories consumed and the calories burned each day.
  • Weight loss requires creating a calorie deficit by burning more calories than consumed.
  • Weight gain happens when more calories are consumed than burned.
  • Energy expenditure is influenced by basal metabolic rate, exercise, non-exercise activity thermogenesis, and the thermic effect of food.
  • Achieving sustainable weight loss involves gradual calorie reduction, balanced macronutrient intake, regular physical activity, and seeking professional guidance when needed.

What is Energy Balance?

Energy balance refers to the number of calories you consume vs. the number of calories you “burn” every day. This is the one factor that will dictate weight gain or loss, independently of anything else.  

To lose weight, you need to create a calorie deficit by burning more calories than you consume through your diet. This forces the body to use stored energy (fat) to meet its energy needs, resulting in fat loss over time.

Conversely, weight gain occurs when you consume more calories than your body burns, which is known as a “calorie surplus”. The third possible scenario is eating the same number of calories your body burns, which means your body weight will stay the same (this is called “maintenance”) [1].

Factors Affecting Energy Expenditure

Energy expenditure, or how many calories your body burns, is determined by four main factors:

Basal Metabolic Rate (BMR): 

BMR is the number of calories your body needs to perform its essential functions for survival, such as breathing, maintaining your body temperature, and beating your heart. It is influenced by factors such as age, body composition, and genetics [2,3].

Exercise Activity Thermogenesis (EAT):

Increasing physical activity causes your body to burn more calories. Cardiovascular exercises, strength training, and other forms of movement contribute to energy expenditure. Strength training also aids in building muscle mass, which elevates BMR as muscles consume more energy even at rest compared to fat [1]. If you would like to learn more about nutrition for building muscle, this article provides an overview. 

Non-Exercise Activity Thermogenesis (NEAT): 

NEAT also involves physical activity, but it encompasses activities outside of intentional exercise that involve some kind of movement (eg. walking to the store, fidgeting, standing, etc.) [2].

Thermic Effect of Food: 

This is the energy your body uses for digestion, absorption, and storage of nutrients. Protein-rich foods have a higher thermic effect compared to carbohydrates and fats. This means protein requires more energy to digest and can slightly increase overall energy expenditure [1].

Creating a Calorie Deficit for Weight Loss

If your goal is weight loss, you will need to create a calorie deficit by either increasing the number of calories you burn each day, decreasing calorie intake from food, or (preferably) a combination of both [1].

When it comes down to food choices and weight loss or weight gain, it doesn’t really matter which foods you choose—the outcome with weight will always depend directly on your energy balance (how many calories you are consuming) [4]. 

For example:

  • You could eat less nutritious foods (pizza, cookies, hamburgers, etc.) and still lose weight if you happen to be in a calorie deficit.
  • On the other hand, you could eat nutrient-dense foods all the time, such as fruits, vegetables, healthy fats, and lean protein, but you would still gain weight if you were in a calorie surplus.

Is it better to eat healthy foods to lose weight?

So, food choices don’t necessarily “matter” when it comes to energy balance, but they are still important!  Nutrient-dense foods will help you feel fuller and more satisfied while being in a calorie deficit, making it easier to lose weight. Additionally, these foods can help prevent vitamin and mineral deficiencies and have a noticeable impact on our body’s health and nutrition status, beyond the weight we gain or lose [4]. 

A healthy diet primarily consists of whole, nutrient-dense foods, with occasional flexibility. Strive for approximately 80% of your diet to consist of healthy options, while the remaining 20% allows for enjoyment of less nutritious foods. Remember, these percentages are estimations and not strict measures, emphasizing that impressive results can still be achieved without perfection [5].

Achieving Sustainable Weight Loss

Here are a few key steps you can take to create a calorie deficit and reach your weight loss goals, without feeling restricted.

Reduce calories gradually

Rather than drastically slashing calories, aim for a moderate and sustainable reduction in energy intake. This minimizes feelings of deprivation and prevents muscle loss [4]. One way to be more precise and efficient with weight loss is by using an app to track calories or macros.

This involves first determining your total daily energy expenditure (TDEE), and then setting a calorie goal for the day that is slightly lower than that number. Your TDEE is affected by your current weight, your age, your sex, your height, as well as other more complex factors [4]. There are many calorie calculators online which can help you estimate your calorie needs; however, if possible, it is best to work with a professional to personalize your calorie goals to your unique needs. If you would like to learn more about determining your calorie needs, check out this article.

Aim for Balanced Macronutrient Intake

Focus on consuming a balanced diet that includes adequate amounts of protein, carbohydrates, and healthy fats. Make sure to prioritize protein intake, supplementing with protein powder if necessary. This will help promote greater satiety, preserve muscle mass, and make weight loss easier [4,6]. 

Regular Physical Activity

Exercise as well as moving more throughout the day (i.e., increasing NEAT) can help optimize weight loss efforts [2]. Strive for a mix of aerobic and strength training exercises to enhance energy expenditure and improve body composition. But remember: even if you are training hard, it is difficult to compensate with exercise for a diet that is too high in calories.


Weight loss is determined by the science of energy balance. Creating an energy deficit through a combination of reduced calorie intake and increased energy expenditure will result in losing fat over time. By understanding the factors influencing energy intake and expenditure, you can meet your body’s needs, while eating in a way that allows you to reach your goals. Remember, adopting healthy habits, practicing moderation, and seeking professional guidance when needed can help you achieve and maintain your weight loss goals in the long run.

About The Author:

Andres Ayesta is a sports dietitian and the founder of Planos Nutrition, with over 12 years of experience helping people transform their nutrition and lifestyle. He works with busy professionals and parents to help them lose weight, improve their confidence, and show up as the best version of themselves, using a personalized, evidence-based nutrition blueprint.

With a bachelor's degree in Nutrition and Dietetics from the University of Southern Indiana and a master's degree in Exercise Science and Sports Nutrition from the University of Central Florida, Andres has earned numerous certifications, including Certified Strength and Conditioning Coach (CSCS) and Certified Specialist in Sports Dietetics (CSSD). He is a licensed Registered Dietitian in the state of Florida and provides coaching programs worldwide. To connect with Andres, you can find him on TikTok @andresthedietitian or Instagram @andresayesta


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