What about Basal Metabolic Rate (BMR)?

This semester in my Nutrition and Metabolism (NSC308) class, we are learning BMR.

Basal Metabolic Rate or BMR for short is the minimum amount of energy expended in a fasting rate of about 12hrs or more. In class, we learned that BMR is the biggest contributor of energy output and works harder when our body is "at rest". BMR is also understood as our energy being needed to keep our body functions alive like our heart and liver.

Here's a good idea of how much energy our body organs use throughout the day!

If someone's less active, their basal metabolism is responsible for about 60-70% of total energy expenditure. Meaning, it's possible that their heartbeat may be faster, their respirations may be shorter, and the other organs like liver, brain, or kidneys may tend to work a little harder than usual. 

Here are some factors that INCREASE basal metabolism. (Do you have any of these?)

•Greater muscle mass

•Larger surface area

•Male biological sex

•Body temperature

•Higher levels of thyroid hormones (key hormone for Basal Metabolism)

•Nervous system activity, especially when the stress hormones are being released. 

•Growth

•Caffeine and Tobacco (Heads up on this one. Tobacco may not be recommended due to its many associated health risks).

•Recent exercise

Those are all great items, but what if we don't have those?

Basal metabolism decreases by 10-20% or about 150-300kcal a day when the calorie intake declines or when our body goes into "conservation mode". That means, the "conservation" period would only help us for a small period of time, especially if our bodies may experience famine or starvation. Calorie restriction may be a barrier to weight loss, especially if someone follows a strict diet that involves a low-calorie intake.

Factors that decrease basal metabolism:

•low thyroid hormone levels (hypothyroidism)

•restricted body/surface area and muscle mass

•Aging (after 30 years)

Naturally, our BMR drops at about 1-2% each decade past 30 years old due to lean body mass loss. That happens with advanced aging. So imagine losing the BMR 10-20% a day due to caloric restriction. Think about it. 🤔 

Physical activity helps maintain lean body mass and preserve BMR throughout adulthood. This temporarily concludes my notes about BMR. I may update this post in the future. The reference should be listed below. 

Reference:

Byrd-Bredbenner, C., Berning, J. R., Kelley, D. S., & Abbot, J. (2022). Wardlaw’s perspectives in nutrition: A functional approach (3rd ed.). McGraw Hill Education.