How Does Eating a Meal Affect Your RMR Results?

3 MIN READ • BY The BodySpec Team • May 17, 2019

A person picks up a pea shoot with a toothpick from a paper bowl filled with falafel and salad.

Have you ever wondered why you should be fasted before getting a resting metabolic rate (RMR) test?

The primary reason is that the act of eating increases your metabolism for approximately 4 hours. So coming in while your body is actively digesting a meal means that you are not in a rested state during your test.

But, just how MUCH does having a meal shortly before having an RMR done impact the results? It turns out, it increases it a LOT!

The Experiment

To test this out, our Wellness Consultant Amanda did three rested, fasted and un-caffeinated RMR’s back-to-back-to-back to get a baseline measurement.

After completing the three baseline RMR’s, she had breakfast.

The meal consisted of:

3/4 cup old fashioned oats
1 scoop of VegaOne Coconut Almond Protein Powder
2 tablespoons of Naked Nutrition Powdered Peanut Butter
2 teaspoons ground brown flax seeds
Dash of cinnamon
12 ounces of water
8 medium strawberries

The meal came in at a total of 492 calories, 36 grams of protein, 65 grams of carbohydrates and 13 grams of fat.

Once she finished breakfast, she performed three more RMR’s at 10 minutes after eating, 36 minutes after eating and 58 minutes after eating.

The Results

Prior to eating, Amanda’s average fasted RMR came out to be 1708.7 calories.

After eating, her RMR rose to an average of 2366.7 calories, with the highest reading coming in during the third test.

That's a whopping increasing of 38.5% from her pre-meal average!

A scatter plot showing pre and post meal resting metabolic rate measurements. Baseline RMR is around 1700, increasing to over 2500 after a meal.

Note: Amanda is a conditioned 34 year-old female with a height of 5’7” and weight of 146lbs, and her metabolism is slightly faster, in general, when compared to women of her age.

If you do this experiment yourself, your mileage may vary. Because everyone’s metabolism is slightly different, based on body composition, conditioning from training and genetics, the magnitude of RMR change due to eating will differ from person to person, but will still result in a higher than actual RMR.

So why does this matter?

The Resting Metabolic Rate is meant to be a starting point upon which lifestyle and activity energy expenditure are added. Based on goals set by the client, adjustments are made to caloric intake targets to either maintain, gain or lose weight.

But if you come in with your RMR measurement already elevated, the resulting calculation of calories required to meet your goals will be skewed upwards - meaning you'll likely be eating more than you need to!