We talk a lot about abdominal weight gain, but rarely about the hormone driving it.

Every year, people gain more than half of their annual weight between Thanksgiving and New Year’s and never lose it (New England Journal of Medicine, 2000). We blame the cookies and cocktails, but the root cause of holiday weight gain often runs deeper: cortisol.

Cortisol itself isn’t bad. You need it: it helps you wake with energy, think clearly, raise heart rate when needed, and maintain blood pressure. It’s adaptive and protective. The goal is to cultivate a healthy cortisol rhythm—high when you need it, low when you don’t.

The problem is chronic cortisol.

When cortisol stays elevated, it sets off a cascade: blood sugar swings, an uptick in belly fat, poor sleep (which worsens metabolism), immune suppression, and hormonal chaos.

The good news I tell my patients all the time: your hormones are in your hands. 

Here’s how your daily habits can help reshape your cortisol curve to get you through the most stressful time of year.

⚡️ Forward this protocol

The fastest, evidence-backed way to lower cortisol right now: cyclic sighing. 

In a head-to-head trial of different stress-reduction techniques, cyclic sighing—two quick inhales through the nose, one long exhale through the mouth—outperformed meditation, box breathing, and cyclic hyperventilation on three fronts (Cell Reports Medicine, 2023):

• Greatest immediate stress reduction

• Most sustained drop in physiological arousal

• Best improvement in mood 

Try it for 1 minute:

1. Inhale through your nose

2. Take a second, shorter inhale

3. Long, slow exhale through your mouth

4. Repeat 5–10 times

🤓 What to know: Cortisol is the hormone that runs your day and your metabolism.

Your cortisol follows a daily rhythm (highest in the morning and lowest at night) which is essential for energy, metabolism, immunity, and sleep. 

Cortisol is made in the adrenal glands but controlled by the HPA axis and your vagus nerve → strong vagal tone helps keep cortisol flexible, while poor sleep and chronic stress flatten or spike the curve.

🌀 Why cortisol matters for metabolic and hormonal health

1. Cortisol increases appetite.

• High cortisol increases ghrelin (hunger hormone), reduces leptin (regulates appetite, energy and weight) sensitivity, and drives cravings. 

2. Cortisol elevates blood glucose and reduces insulin sensitivity.

• Cortisol mobilizes glucose for quick energy. 

• Chronic cortisol elevation → higher baseline glucose → elevated insulin → impaired metabolic flexibility.

3. This leads to “cortisol belly.”

• Over time, this leads to insulin resistance and more abdominal fat (Obesity Medicine, 2025).

• Even in women who aren’t overweight, high cortisol promotes visceral fat storage around the organs (Psychosomatic Medicine, 2000).

4. Cortisol suppresses immune function.

• Short-term, cortisol down regulates inflammatory pathways (Cells, 2023).

• Chronic elevation does the opposite, suppressing key immune cells and weakening viral defense (Journal of Clinical Medicine, 2024). This is why people get sick right after stressful holidays.

5. Cortisol destabilizes sex hormones.

• High cortisol → high insulin → higher testosterone and estrogen production.

• This mimics PCOS-like patterns, worsens PMS, disrupts ovulation, and can impair fertility (Frontiers in Endocrinology, 2023).

🔬 How to Measure & Track Cortisol 

Most “cortisol tests” on the market are useless. At Parsley, we use two validated tests:

1. 5-Point ZRT Cortisol Test (Saliva) 

Measures cortisol at 5 points across a single day: 

• Low morning cortisol → fatigue, brain fog

• Midday cortisol dips → energy crashes, cravings

• High nighttime cortisol → wired-and-tired, poor sleep

• Flat cortisol curve → burnout, HPA axis suppression

2. DUTCH Hormone Test (Urine)

• Measures cortisol and cortisone (how you metabolize cortisol)

• Also evaluates estrogen, progesterone, DHEA, and testosterone pathways

• Ideal for women where stress + sex hormones are interacting (PMS, perimenopause, PCOS-like presentations).

🩸Why Parsley Longevity Labs don’t include a random cortisol blood test

Because cortisol naturally fluctuates throughout the day, single-point blood tests are mostly irrelevant (unless you have Addison’s or Cushing’s).

⚠️ Wearables & cortisol: promising but not comprehensive.

HRV and sleep tracking offer some insight into stress load. But they’re not substitutes for testing free cortisol in saliva or urine.

I dream of a continuous cortisol monitor that shows how your stress shifts across your cycle, workload, sleep, and relationships. But until Santa delivers, we work with what we’ve got.

💪 What to do: Get morning light, downshift daily, choose sleep over alcohol.  

There’s no way to completely avoid holiday cortisol swings (if you’ve cracked the code for a zero-stress December, please email me immediately). 

But you can meaningfully reduce it with an intentional, evidence-based routine:

☀️ Step 1: Get morning light within 60 minutes of waking

• Natural light anchors your circadian rhythm and strengthens your cortisol awakening response (CAR) → This translates to better energy, mood, and blood sugar.

• What to do: Step outside for 5–10 minutes, or even better, prioritize a morning walk. 

😌 Step 2: Downshift daily with breathwork, meditation or sauna. 

These practices activate the vagus nerve, your body’s brake pedal for cortisol.

• Breathwork (5 min): Best for acute stress. Cyclic sighing outperforms meditation for immediate relief (Cell Reports Medicine, 2023).

• Meditation (15 min): My daily non-negotiable—even if a child is physically sitting on me. Increases vagal tone, reduces HPA axis activation, and improves emotional regulation.

• Sauna: Heat therapy boosts endorphins, then lowers cortisol via parasympathetic rebound (Experimental Gerontology, 2021).

🏋️ Step 3: Prioritize movement—especially strength + low-intensity cardio

Best exercise for cortisol regulation:

• Zone 2 cardio: Fast walking, easy cycling—discharges stress hormones.

• Strength training: Improves insulin sensitivity, which flattens cortisol-driven glucose spikes.

• Skip HIIT: During high-stress weeks, it can push your cortisol too high.

💤 Step 4: Choose sleep over alcohol

• One night of bad sleep can spike cortisol the next day, increase cravings, worsen insulin resistance, and lower your stress resilience.

• If you’re having a holiday drink, try to stop by 6 p.m.

💊 Step 5: Supplement Strategically

The right supplements help your HPA axis recalibrate, so cortisol can rise and fall appropriately. My top 3: 

• HPA Adapt → Contains herbs that modulate HPA signaling—helpful when cortisol is too high at night or too low in the morning.

• Magnesium glycinate (200–400 mg) → Supports relaxation, sleep quality, and reduces nighttime cortisol.

• L-theanine (100–200 mg) → Promotes calm focus and smooths out cortisol-driven anxiety without sedation.

💛 The Momgevity Files

On Saturday night, fully feeling myself in my favorite new sparkly holiday dress, I made the unusual choice to not follow my own advice and have a Negroni at roughly 11 p.m. It felt, let’s say, in the spirit. 

I’m not shaming myself for having a drink. The holidays create an ambient pressure system, like a weather event we all live through for a month. That pressure can drive unpredictable behavior. And unpredictability can be a good thing! 

But with two glasses of wine already in me, and a full Sunday ahead (ice hockey, soccer, and a board deck to finish), my unpredictability turned out to be less of a bold move and more of a tumble. I definitely felt the aftermath when I woke up.

We all have unconscious ways of reacting to stress, often defaulting to coping mechanisms we’ve learned or mirrored. It takes real self-awareness to slow down and unwind that reaction cycle—to choose ourselves over the easy paths all around us. 

The holidays are full of collective peer pressure around consumption: shopping, food, alcohol, how we relate, how we spend money, even how we dress. Some of that is shared cultural joy, and some of it is uncomfortable norming. Where we land between the two depends on our ability to slow down and really listen to ourselves.

So on Sunday, I turned to health as a practice—not a punishment. I rehabbed my aching head with a gluten-free muffin slathered in Kerrygold butter, two Epic beef jerky sticks, two double espressos, a very large water with Endura electrolytes, and two much-needed ibuprofen. I power-napped for thirty minutes mid-day. I weight trained in the evening when my energy came back. I sauna-ed out the toxins. I leveled out my see-sawing blood sugar with salmon and salads for dinner. 

My longevity philosophy is that I’m stopping the aging clock—but I’m not stopping my life. I live in the world, and I want to live in the world, including all its holiday messiness and the stress I can’t avoid or didn’t create but roll with anyway. For me, health is the place I return to in order to find center—not the thing I chase. That difference means everything this time of year.

Stay strong, stay curious and breathe, 

Robin

⚡️ One more thing…

What to get for the person who has everything: a 1:1 visit with a Parsley clinician to review your labs (from any company!) and build a personalized health plan. Sign up for BYO Labs here!

As always, this newsletter is for informational and educational purposes only and is not intended as medical advice. Always consult your healthcare provider before making any health decisions or changes to your treatment plan.