I get asked some version of this question almost every day: What should I be doing to keep my metabolism up? Why am I gaining weight and what can I do about it?

Patients, friends, my Instagram comments — everyone's confused. And honestly? It makes sense. We are living in the most data-rich, nuance-heavy, information-overloaded moment in metabolic medicine history. GLP-1s, CGMs, wearables, hormone therapy, peptides — the tools have never been better. But the noise has never been louder, either.

So I went back to the science. A year of deep dives, 50,000+ patients, and a decade of practice later, here's what I keep coming back to.

If you want to know where your metabolism actually stands — hormones, insulin, body composition — that's exactly what we assess at Parsley Health.

The single most important thing you can do for your metabolism right now: build muscle.

Skeletal muscle absorbs ~80% of post-meal glucose — it is your largest metabolic organ. Women with low muscle mass are 63x more likely to die early. For men, the risk is 11x.

Everything else on this list works better when you're also building muscle.

Muscle isn't just about strength — it's where blood sugar goes after you eat.

Skeletal muscle absorbs ~80% of post-meal glucose (Comprehensive Physiology, 2021). Women over 65 with low muscle mass are 63x more likely to die early than their stronger counterparts (Journal of Bone and Mineral Research, 2019). For men, that risk is 11x.

This is the most underutilized metabolic lever I see in practice. And the most impactful.

For women: Estrogen upregulates GLP-1 receptors, protects mitochondrial function, and keeps visceral fat in check. It starts dropping in your late 30s and falls 85–90% at menopause. Women combining HRT with tirzepatide lost 17% body weight vs. 14% without HRT — and were 2.5x more likely to hit ≥20% total weight loss (Menopause, 2026). If you're on a GLP-1 and it's underperforming, look at your estrogen first.

Testosterone matters for women too. Most HRT plans still leave it out — which means libido, muscle, bone, and energy are left on the table. 

For men: Low testosterone directly drives insulin resistance, visceral fat, and metabolic inflexibility. TRT in hypogonadal men significantly improves body composition and metabolic syndrome markers (Frontiers in Endocrinology, 2026).

Start testing at 35. Don't guess.

Fasting insulin becomes abnormal 10–15 years before type 2 diabetes is diagnosed.

Your glucose can look completely normal while insulin is quietly rising to compensate — that's insulin resistance doing metabolic damage in stealth mode. It's one of the earliest warning signs we have, and most standard panels don't include it.

This is one of the first tests we run at Parsley. Start here.

Nearly 40% of US adults have prediabetes. Most don't know it — because A1C won't catch it.

A1C is an average. It completely misses glucose variability, which is independently linked to dementia risk and accelerated biological aging. And here's what a CGM reveals that no lab test will: there's no universally "healthy" meal. Your response to the same bowl of rice is different from everyone else's — shaped by your microbiome, sleep, stress, and genetics.

I prescribe the Freestyle Libre 3.0; Lingo and Stelo are available without a prescription.

One quick hack from the data: 10 squats every 45 minutes outperforms a 30-minute walk at lowering post-meal glucose spikes (Scandinavian Journal of Exercise and Science in Sports, 2024). Your muscles are glucose sponges. Use them.

1 in 4 women ages 35–50 have low bone density. Most have no idea. I was one of them.

But DEXA isn't just about bones. It's the only test that tells you your actual body composition: lean mass vs. fat mass vs. bone mineral density. Your weight can stay exactly the same while you're trading muscle for fat — and getting metabolically worse. The scale will never show you that.

Also critical if you're on a GLP-1: semaglutide is associated with a 2.6% reduction in hip bone density at 52 weeks. The FDA now flags this. You need a baseline.

Over 30? Get one. About $100. Takes 10 minutes.

Fasting past 16 hours activates autophagy — your body's cellular recycling program (International Journal of Molecular Sciences, 2025). It clears damaged proteins linked to Alzheimer's, eliminates precancerous cells, and resets metabolic health.

But how you break your fast matters as much as the fast itself.

VO₂ max is the strongest single predictor of all-cause mortality we have. Increasing it by just 1 MET is associated with a 10–20% reduction in mortality risk (Circulation, 2013).

And: 1 minute of vigorous exercise = ~6.6 minutes of moderate exercise for longevity (Nature, 2025). If you can talk normally during your workout, it doesn't count.

Berberine improves insulin resistance and supports natural GLP-1 production — via butyrate signaling that prompts your gut to make more of its own GLP-1. That's real, and useful.

But it does not bind GLP-1 receptors. The mechanism is completely different from semaglutide. Calling it nature's Ozempic dramatically overstates the evidence and sets people up for disappointment.

What berberine is good for: improving insulin sensitivity, supporting metabolic health as part of a food-first strategy, and potentially delaying or avoiding a prescription.

Try it for 4–6 weeks before going pharmaceutical — especially if your primary goal is blood sugar optimization rather than significant weight loss.

A 3-week ketogenic diet produced a 47% rise in BDNF and a 22% increase in cerebral blood flow in recent research. Evidence also supports keto for improving insulin sensitivity and clearing metabolic dysfunction.

The way I use it: a 3–6 week metabolic reset to break insulin resistance, reduce inflammation, and restore fat-burning capacity. After that, reintroduce clean carbs and use CGM data to guide what you eat.

Non-negotiable while in keto: 80–100g protein minimum. You do not want to be burning muscle for fuel.

Under 5 hours of sleep cuts insulin sensitivity by 24% (Sleep Medicine Reviews, 2019). That's on par with a bad diet.

But it's not just duration — it's consistency. Even 1–2 hour swings in sleep timing disrupt circadian-regulated mitochondrial biogenesis. Your body does its deepest metabolic repair during consistent, dark-hour sleep.

The goal: a metabolism that's flexible — not just fast.

I just landed in LA. Leaving today was one of the hard ones — my four-year-old kept saying, "don't travel without us ever again, mommy." Oof.

I hate leaving my kids. I also love it sometimes. Being in my own energy, even on a work trip, is its own kind of longevity reset — a reminder of who I am and how I think as a rare solo-operator in the world.

Today, being on my own is giving me a moment to check in on my health, which is — I have to say — a little wonky as I head into a big week. I'm the co-host of Season 3 of the Luminescence podcast, and we're recording all 15 episodes back to back. Then I go straight into hosting my first female longevity retreat with One Commune in Topanga. I'm so excited. I also want to feel top notch.

Which makes it annoying that I've had acid reflux and bloating since my Italy trip. I think the Venice water got me. (Or maybe it was all the pasta. 🤷‍♀️)

So I'm using this time away to do a mini-cleanse: lower carb, lots of plants, protein, and EVOO, tons of water with lemon, early bedtimes, and two weeks of Biocidin herbal antimicrobial drops to nip whatever's going on — plus extra probiotics. My favorite concoction right now: coconut water, lemon, and parsley, blended. If that doesn't move the needle, I'll do a proper 30-day gut healing protocol with some testing on top.

Sometimes you have to take your own medicine. In this case, that's literal — but I mean it both ways.

I can do all the things: travel, work, social life, parenting, partnering, friending. And sometimes, even I can't hold up. The garden needs tending. The gut needs a reset. Inconvenient — but at least I have the tools. What else can we ask for?

If this list made you realize you don't actually know your numbers — fasting insulin, hormone levels, body composition — that's exactly where to start. At Parsley, we build personalized metabolic plans around your actual data, not guesswork.

Start with Parsley Health →

Stay strong, stay curious, and breathe,

Robin

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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.