A patient recently said to me at the Innisfil clinic: "I think my metabolism is off or broken ever since I've been in perimenopause."

Another one (in a virtual appointment) said something along the lines of: "I know PCOS can slow down metabolism and I think that the stress of the last few years has done a number on my body."

Sure, there are factors that influence your metabolism (including good ole chronological ageing!), but metabolism is (and isn't!) super straightforward.

So, before you fall down the Google, ChatGPT, or Tiktok rabbit hole of "metabolism hacks", let me explain what metabolism is.

What actually IS metabolism?

In casual conversation, we talk about "metabolism" kind of like a synonym for "how fast I burn fat."

Physiologically, there's more to it (obviously!):

Metabolism refers to the sum of all the chemical processes in your body that convert energy (food and drink) into the fuel required for you to stay alive. We're talking about breathing, blood circulation, repairing cells, growing new tissue, etc.

All living things do this to survive!

The Math of Your Metabolism and Metabolic Rate

There are many factors that can influence your metabolism and metabolic rate (some of them permanent and some temporary!).

• age
• body size
• physical activity
• body composition (fat, muscle, etc.)
• hormonal factors (hello perimenopause, PCOS, etc.)
• past history of caloric restriction/eating disorders/yo-yo dieting
• health conditions
• genetics
• and more!

To understand where your energy goes, we look at something called your TDEE, which stands for Total Daily Energy Expenditure. It’s basically the total number of calories you burn in 24 hours.

TDEE includes your:

1. Basal Metabolic Rate (BMR): Sometimes, this is also called your resting metabolic rate (RMR) or resting energy expenditure (REE). This is the heavy lifter: you just existing on this planet. For most people, this accounts for somewhere between 60-70% of your daily caloric burn.
2. Physical Activity Energy Expenditure: This usually makes up about 20-30% of your daily caloric burn, and includes all manners of movement, from formal exercise like running and lifting weights to the non-exercise activity you might do, like playing with kids, cooking, and brushing your teeth.
3. Thermic Effect of Food (TEF): This contributes a tiny bit to your day-to-day caloric use simply to chew, digest, and store fuel from your diet.

How do hormones and habits tie into my changing weight and metabolism?

This is a complex question that has a nuanced and variable answer based on who you are.

In the second episode of Phase to Phase: The Hormone Health Show, Dr. Ashley White framed metabolism from a weight management perspective in an interesting way that has really stuck with me:

Your appetite dictates what goes in, and your metabolism dictates how you utilize that.

Here are a few considerations as you think or work through this:

• The biggest determinant of your metabolic rate is your "fat-free mass" (mostly muscle). Muscle is metabolically expensive tissue; it costs your body energy to keep it around. The more you have, the higher your BMR. Plus, you'll also protect your bones and your heart at the same time!

• If you've spent years chronically restricting calories, your body may have adapted to become "thrifty" to protect you. This "metabolic adaptation" means your body learns to survive on less fuel, and this can persist even after you stop dieting. What's done is done, so we move forward from here and try to build muscle and work on what we can!

• Hormone-based conditions like PCOS and thyroid issues, as well as the hormonal shifts of perimenopause absolutely play a role in how this energy is partitioned and used.

• Appetite regulation is influenced by sleep, hormones, stress, exercise, family history and behaviours, mood disorders, and SO MUCH MORE! This is where people often struggle.

(Check out that episode with Dr. Ashley White here--she does a great job of explaining some of these concepts with respect to weight loss if that's what you're hoping to accomplish!).

How to calculate your own metabolic rate

You can try using a calculator that uses the Harris-Benedict or Katch-McArdle equations online which will approximate your basal metabolic rate (and even adjust based on your physical activity levels). This one from the Cleveland Clinic is a simple one.

Metabolism Takeaways for 2026

If you are feeling stuck, tired, or like your math isn't adding up regarding energy in vs. energy out, please know you aren't broken. You're likely dealing with the ups and downs of life that bring inconsistencies with it (most of us struggle with this!), a complex biological history, and/or a lack of guidance.

Instead of trying to "hack" your metabolism, focus on the basics:

1. Fuel your body adequately (especially protein and fibre)
2. Increase your activity levels (especially focus on building muscle, but don't forget about cardio!)
3. Address your lifestyle and hormones (sleep, stress, and hormone change)

If you're in Ontario, I'd be happy to support you with any or all of the above in Innisfil, East Gwillimbury, or virtually.

I'm also running my Strong Foundations: 5-Week Nutrition and Weight Management Reset starting Tues, Jan 13 virtually if that's of interest.