Tell me if you've heard this before. You're sleeping. You're eating the way you were told to eat. Your labs come back normal, and you still know something is off.
That's the woman I had in mind for this conversation.
After twenty years in hormone and longevity medicine, here's what I keep coming back to. Most of what supports your hormones comes down to the foundations, like light, darkness, and when you eat, and so many of them cost you nothing.
My guest, Sarah Kleiner, is board-certified through the Quantum Biology Institute and the creator of My Circadian App. She came to this work the hard way. In her forties, she went through two pregnancy losses and two rounds of IVF with no viable embryos. Then a single conversation with Jack Kruse pointed her toward leptin and circadian biology. When she asked her fertility doctor to test her leptin, she was told it was an insignificant hormone. Her levels came back very low. She rebuilt her rhythm with morning sunlight, dark evenings, and a shift in how and when she ate, and she later got pregnant with her son without IVF.
We get specific. Sarah explains what leptin does while you sleep and why she sees leptin resistance show up before insulin resistance. She covers the early hunger signals that something may be off and how to test leptin so the result means something. We talk through yellow versus orange and red blue light blockers, and why an incandescent bulb on your desk is worth it. We also cover why sitting in the shade still counts and why the same meal lands differently at 8 AM than at 8 PM. I also share why I built MenuPause around rotating eating patterns, especially if you've been doing carnivore, keto, or Keto-Green for a long time.
Most of the women who find Sarah's work are in perimenopause and menopause. These small, consistent shifts give your body clearer instructions to work with. And the best years of your life are waiting for you.
KEY TAKEAWAYS
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Leptin works like your body's accountant. Overnight, it reports to your brain how much stored energy you have, then passes instructions along to your thyroid, your sex hormones, and your metabolism. Blue light at night, eating close to bed, or staying up late can interrupt that nightly conversation.
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In Sarah's experience, leptin resistance shows up before insulin resistance. It's rarely tested, which is one reason "normal" labs can miss what you're feeling.
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Some early signs your leptin signaling may be off are feeling hungry again soon after you eat, never feeling satisfied, or having no appetite in the morning at all. Sarah skipped breakfast for about ten years and felt nauseous at the thought of eating in the morning.
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If you test leptin, do it fasted in the morning, 12 to 14 hours after your last meal. Eating beforehand skews the result, and so does fasting too long.
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Your morning reset is simple. Go outside soon after you wake up, before your phone and before the overhead lights. After sunset, keep your home dim and switch to orange or red light. Use yellow-tinted blue blockers during the day at screens, and orange or red ones after dark.
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When you eat matters, not only what you eat. Research we discuss shows your body handles the same meal better earlier in the day, which is why I encourage breaking your fast by 10 AM.
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You don't need to overhaul your house. An incandescent bulb on your desk, a seat by the window, and working outside when you can, even in the shade, are where Sarah tells people to start.
Time Stamps
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00:00 Why the foundations matter more than hacks and peptides
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04:02 Sarah's path from corporate America to circadian biology
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07:22 Two IVF rounds and a wall with conventional care
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10:04 What a morning circadian reset looks like
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22:09 Yellow, orange, or red? Choosing blue light blockers
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24:48 What leptin is and why Sarah calls it a master hormone
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28:10 Sarah's own low leptin, and the doctor who dismissed it
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29:42 Early signs your leptin signaling is off
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39:31 Why "calories in, calories out" misses timing
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42:48 The underrated habit of working in the shade
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46:14 Where to find Sarah and how My Circadian App works
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49:20 MenuPause and why I rotate eating patterns
Memorable Quotes
"You can't out supplement the sun and nature." (Dr. Anna Cabeca)
"I always say consistency over perfection every single day of the week." (Sarah Kleiner)
"The best years of your life are not behind you. They are waiting for you." (Dr. Anna Cabeca)
RESOURCES MENTIONED
From Sarah
People and research referenced
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Jack Kruse, an early influence on Sarah's circadian and leptin work
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Dr. Gerald Pollack, for his research on exclusion zone water and infrared light
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Dr. Glen Jeffery, for his research on red and infrared light and mitochondrial function
From Dr. Anna
Connect With Sarah Kleiner:
Website - https://www.sarahkleinerwellness.com
Substack - https://substack.com/@sarahkleinerwellness
Instagram - https://www.instagram.com/sarahkleinerwellness
Podcast - https://www.sarahkleinerwellness.com/podcast
YouTube - hhttps://www.youtube.com/@SarahKleinerWellness
Free ebooks: https://www.sarahkleinerwellness.com/all-free-resources
Connect with Dr. Anna:
Website: dranna.com
Instagram: instagram.com/thegirlfrienddoctor
YouTube: youtube.com/@thegirlfrienddoctor
TikTok: tiktok.com/@drannacabeca
Facebook: facebook.com/thegirlfrienddoctor
If someone you love keeps saying "my labs are normal, but I don't feel like me," send her this episode. And subscribe on YouTube so you catch the shorts from this conversation.
Disclaimer
This episode is education, not medical advice, so please talk with your own physician before making changes to your health routine.
