The Science of Weight Loss: Understanding the Basics of Energy Balance

As you embark on your weight loss journey, it is critical to understand the fundamental science that governs weight gain and loss. The key concept to grasp is energy balance – the relationship between the energy you consume through food and drinks and the energy you expend through physical activity and exercise. When you consume more energy than you expend, the excess is stored in your body, resulting in weight gain. Conversely, when you expend more energy than you consume, your body draws on stored energy, resulting in weight loss. Achieving and maintaining a healthy weight long-term requires making balanced and sustainable lifestyle changes to the energy equation. Understanding energy balance provides the foundation for developing an effective weight loss plan based on balancing the calories in versus the calories out. With this basic knowledge, you can make informed choices and set realistic goals to get started.

Understanding Energy Balance: Calories in vs Calories Out

To lose weight, you need to burn more calories than you consume. This is known as achieving a calorie deficit through the energy balance equation.

The energy balance equation is:

Energy in (calories consumed) – Energy out (calories burned) = Energy balance

If energy in exceeds energy out, you will gain weight. If energy out exceeds energy in, you will lose weight.

  1. Calories consumed: This refers to the calories you eat and drink. The average adult needs 2,000-2,500 calories per day to maintain weight. You must consume fewer calories, around 500-1000 calories less per day, to lose about 1-2 pounds per week. Keep a food diary to track your calories and make better choices.
  2. Calories burned: This refers to your basal metabolic rate (BMR), physical activity, and exercise. Your BMR is the minimum number of calories your body needs to function. Increase your activity level and exercise routine to burn extra calories. Aim for at least 30 minutes of exercise most days of the week in addition to increasing daily activity like walking more and taking the stairs whenever possible.

By making long-term lifestyle changes to both sides of the energy balance equation through diet and exercise, you can achieve sustained weight loss and better health. The key is making changes at a pace you can maintain and incorporating strategies that fit your needs and lifestyle. With time and practice, you can master the science of weight loss.

How to Determine Your Total Daily Energy Expenditure (TDEE)

To determine your Total Daily Energy Expenditure (TDEE), you need to calculate your basal metabolic rate (BMR) and factor in your activity level. Your BMR is the minimum number of calories your body needs to function while at rest. It is based primarily on your age, height, weight, and sex.

Once you have calculated your BMR, you must determine your activity factor, which reflects your overall activity level. The activity factors are:

  • Sedentary (little or no exercise): BMR x 1.2
  • Lightly active (light exercise/sports 1-3 days/week): BMR x 1.375
  • Moderately active (moderate exercise/sports 3-5 days/week): BMR x 1.55
  • Very active (vigorous exercise/sports 6-7 days/week): BMR x 1.725
  • Extra active (very vigorous exercise/sports & physical job): BMR x 1.9

To calculate your TDEE, simply multiply your BMR by the appropriate activity factor. For example, if your BMR is 1,400 calories and you exercise 3 times a week, your TDEE would be 1,400 x 1.55 = 2,170 calories.

Once you know your TDEE, you can create a calorie deficit by reducing your calorie intake and increasing your calorie output through exercise. Aim for a 500 to 1,000 calorie deficit per day through diet and exercise combined for healthy weight loss of about 1 to 2 pounds per week. Be sure to re-calculate your TDEE every 4 to 6 weeks as your BMR may decrease with weight loss.

With the knowledge of how to determine your TDEE, you now have a clear target for how many calories you should consume each day to successfully and sustainably lose excess weight. The key is making sure you do not exceed your TDEE if your goal is weight loss.

Strategies for Creating an Energy Deficit to Lose Weight

To lose weight, you must create an energy deficit by consuming fewer calories than you burn. There are a few effective strategies to achieve this:

Reduce your calorie intake. The most direct way to cut calories is to make better food choices and watch your portion sizes. Aim for a 500 to 1000 calorie deficit per day through diet alone for steady weight loss of about 1-2 pounds per week. Focus on lean proteins, high-fiber whole grains, fruits and vegetables. Limit high calorie foods like sweets, fried foods and sugary beverages.

Increase your physical activity. In addition to diet, exercise is key. Aim for at least 30 minutes of moderate activity most days of the week. This could include walking, jogging, biking or strength training. Increase your daily movement as well by taking the stairs when possible and going for walks on your breaks at work. The more active you are, the more calories you will burn to amplify your energy deficit.

Make sustainable lifestyle changes. Rather than going on a “diet”, make healthy changes you can stick with long-term. Don’t cut calories too low or eliminate entire food groups. Make gradual changes to your eating and exercise habits over time. Staying hydrated, getting enough sleep and managing your stress levels will also support your weight loss efforts.

Consistent monitoring. Regularly weigh yourself and track what you eat to stay on track. Make adjustments as needed to continue progressing. Even losing 1-2 pounds a week can add up to 20-50 pounds or more of weight loss over 6-12 months. Staying focused on your goals and motivated will help you achieve and maintain your success.

With the right strategies and dedication, you have the power to achieve sustained weight loss through an energy deficit. But remember—slow and steady wins the race. Make changes at your own pace for the best chance of long term success.


The bottom line is that weight loss comes down to energy balance. Consume fewer calories than you burn, and you’ll lose weight. Gain an understanding of how many calories you need and how many you’re actually eating. Making small changes to your diet and exercise routine can have a big impact over time. You have the power to achieve your goals by making sustainable lifestyle changes. While fad diets and exercise regimes may promise a quick fix, the science of weight loss is simple. Stay focused on the fundamentals of energy balance, be consistent, and you’ll steadily progress toward your target weight and improved health. With knowledge and commitment, you can accomplish amazing things. Read more

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