The Truth About Yo-Yo Dieting |Dr. Debbie Smrz,ND

You’ve cut carbs. Tried intermittent fasting. Pushed through cleanses, detoxes, maybe even keto. And for a while, it worked—until it didn’t. The weight came back (sometimes more), your energy crashed, and now it feels like your body is stuck in “resistance mode.”

It’s easy to think: “I’ve broken my metabolism. Nothing works anymore.”

To some degree – it’s true. Your metabolism has adapted to the changes you’ve made, for good and bad, let’s take a deeper dive into what’s going on after years of dieting ups and downs.

Yo-Yo Dieting / Calorie restriction and Thyroid

Each time you slash calories, your body’s survival instincts flip on. Your thyroid—the gland that sets your metabolic “thermostat”—may help manage production of T3, the active thyroid hormone that drives fat burning and energy. The body is pretty ingenious really, Oh, it says, for whatever reason you can’t give me enough fuel, I’ll create a system so that I can run on less, I gotcha. As a matter of fact, some studies show a reduction of T3 of up to 66%!

When a person comes to see me who has been doing intermittent fasting or continued calorie restriction for any length of time, their thyroid numbers will be down, pretty much . It’s not because their thyroid is malfunctioning – so not true hypothyroidism, but merely a response to dietary intake. IF works BECAUSE it allows you to eat less and still carry on with your day, so the good comes with the bad.

And what’s the potential bad? Weight gain with food introduction, low energy, constipation – the body is trying to help you to do less, metabolize less, need less.

The Role of Leptin (and Why “Eat Less” Stops Working)

Enter leptin: your body’s built-in fuel gauge. Produced by fat cells, leptin tells your brain how much energy you have in reserve.

Here’s how it works:

Dieting → fat cells shrink → leptin drops → brain thinks you’re starving → appetite spikes + metabolism slows.

Continuous low calorie diet Diet low levels of leptin brain thinks you’re hungry → appetite spikes + metabolism slows.

But, just like insulin, too much of it can lead to leptin resistance, or Years of swinging between low and high intake lead to confusion, making signaling less clear—your brain stops hearing the message. So, if you have been in an overfeeding state for a long period of time (the Yo in the Yo yo), this happens:

High levels of leptin (I’m full, stop eating) leptin resistance (it’s knocking but your body can’t hear it) so you still feel hungry, even though your levels are topped up.

Pretty much all hormones need the Goldilocks amount – neither too much or too little, just ‘right’, – otherwise your brain never gets the message and you feel hungrier, and your body locks into what feels like permanent weight management mode.

So….is the damage permanent?

Typically, your body can adapt back to running on a higher gear again. I would say that the majority of my menopausal patients know that they are eating too few calories, that the weight gain isn’t simply ‘menopause’, but they’ve been ‘watching what they eat (read – dieting, usually with periods of low calories followed by periods of high (yo yo), that they don’t even know where to start.

It’s about the goldilocks effect again, restoring hormone sensitivity: helping your thyroid, leptin, and insulin signals “talk” to your brain again.

4. Four Shifts That Retrain Your Metabolism

If you’ve felt stuck for years, here’s how to work with your body—not against it:

• Protein at breakfast – oh, does that mean stop skipping breakfast? Yup!
  Stabilizes hunger, supports thyroid output, and gives your metabolism a clear “on” signal for the day.

• Regular Strength Training – I know you were told that yoga and getting 10 000 steps a day would do it. Nope, movement is nice, but I need to see exercise.
  Muscle is metabolically active—it burns calories at rest and resists adaptation more than endless cardio ever will.

• Strategic refeeds (or diet breaks)
  Planned food adjustments reassure your body that it’s not in a famine, restoring leptin signaling so your metabolism stays flexible.

• Prioritize sleep & ease inflammation
  Poor sleep and chronic inflammation make your body resistant to every hormone that regulates weight. Recovery isn’t optional—it’s a metabolic reset button.

I know, easier said than done. You’ve trained your body for years to not eat breakfast, ‘you’re just not hungry’ and so now you’re afraid of the scale going up. But, what you’re doing now isn’t working, so you might see a small change, followed by a gradual decrease, but even more importantly, an change in energy, mood, digestion, metabolism and overall well being.

Years of yo-yo dieting have trained your body to defend itself. But adaptation works both ways. With the right inputs, you can retrain your metabolism to respond again.

Want to see where you stand right now? [Take my Metabolism Quiz] to find out if you’re Thriving, Borderline, Struggling, or Stuck—and what steps you need next.

And mark your calendar: next month I’ll be hosting a live webinar, “Metabolism and Midlife—What’s Changing & Why It Matters.” Bring your quiz scores—we’ll use them as your roadmap for lasting change.

Your Biggest Questions, Answered

Q: Is “metabolic damage” real?
Technically no. What you’re experiencing is metabolic adaptation—your body becoming more efficient at conserving energy with each diet. Efficiency feels like “damage,” but it’s reversible.

Q: Do I need to fix my thyroid?
For most, the thyroid itself is healthy—it’s simply adjusting hormone output based on signals from calorie intake, fat stores, stress, and sleep. That said, supporting your thyroid with all the nutrients it needs for proper conversion is critical. In some cases, the thyroid is sub optimal, and low dose thyroid medication may be warranted, and it is not uncommon for athletes (back to the gym again, where personal experimentation is high) that do take T3 as needed.

Q: Why do I manage weight faster each time?
How careful were you to ensure you lifted heavy and ate a lot of protein. Most likely, you lost fat AND muscle, so your metabolic rate slowed so when you eat your “old normal,” it’s suddenly a surplus.

Q: How long does it take to ?
Some notice changes within weeks of consistent protein, lifting, . For others—especially after years of yo-yo dieting—it can take months of reliable fuel and care.

Q: Can I stop this cycle for good?
Yes. By moving away from quick, extreme calorie cuts and toward sustainable habits: protein at every meal, strength training, managing stress, prioritizing sleep, and weaving in breaks instead of endless dieting.

👉 Ready to find out where your metabolism stands? [Take the Quiz Here] and bring your scores to next month’s webinar. Let’s put an end to yo-yo frustration—this time, for good.