Weight Loss is 80% Diet, 20% Exercise, Is This True?

Weight Loss is 80% Diet, 20% Exercise, Is This True?

I’m sure you’ve heard at some point in your life that the key to weight loss consists of 80% diet and 20% exercise. But, is this really the case?

It’s no surprise that nutrition and exercise are both crucial parts of a healthy lifestyle, however, in order to lose weight one must be in a calorie deficit.

What is a calorie deficit?

Simply put, calories are the units of energy you get from foods and beverages, and a calorie deficit occurs when you consume less calories than you burn.

The calories you burn or expend each day (AKA calorie expenditure) include the following three components:

  1. Resting energy expenditure (REE). REE refers to the calories your body uses at rest for functions that keep you alive, such as breathing and blood circulation. This makes up about 60 to 75% of the energy that we expend.
  2. Thermic effect of food. This involves the calories your body expends digesting, absorbing, and metabolizing food. This makes up about 10% of the energy that we expend.
  3. Activity energy expenditure. This refers to the calories you expend during sports like exercise and non-exercise related activities, including fidgeting and performing household chores. This makes up about 15-30% of the energy that we expend.

If you provide your body fewer calories than it needs to support these three components of calorie expenditure, you put your body into a calorie deficit. Doing this consistently for a period of time results in weight loss.

On the other hand, if you constantly eat more calories than your body needs to support these functions, you’ll be at a calorie surplus and gain weight.

This is why your diet is the most important part of weight loss and exercise is the icing on the cake!

An exception to this rule are those who engage in boot-camp style classes and HIIT (high intensity interval training) exercises consistently because these workouts may result in a significant amount of calories burned. However, these types of workouts are not necessary for weight loss if one is in a caloric deficit!

It’s important to find an exercise that you genuinely enjoy rather than just doing it to solely burn calories whether that be hiking, bike riding, lifting weights, walking, swimming, etc!

Most people tend to just focus on how many calories they’ve burned in a workout but I encourage you to focus on building lean muscle. This is because building lean muscle boosts your metabolism, which can help you to lose weight!

Another mistake I tend to see is when individuals overestimate calories burned from exercise and use that as an excuse to eat whatever they want. For example, after lifting weights for an hour your fitness tracker tells you that you burned 300 calories but you consume 1,000+ calories on some donuts because you worked out. This will end up putting you into a calorie surplus which may lead to weight gain.

Bottom Line: Although it is more sustainable to create a calorie deficit from your diet, physical activity is still important for overall wellness! Use this information to structure a healthy, achievable path to weight loss.


Maryann Walsh, MFN, RD, CDE
Registered Dietitian/ Consultant