By Dr. Naomi Parrella, MD — Family and Obesity Medicine physician; Chief Medical Officer, Zero

A patient sat down across from me last week and said, "I'm doing what used to work, and my body isn't responding the way it used to."

I have heard that sentence from a 42-year-old woman whose periods had just started shifting. From a 56-year-old man whose strength training plateaued. From a 33-year-old new mother. From a 47-year-old executive whose sleep changed and never came back. From a 68-year-old retired teacher trying to protect her bones.

It is not a willpower problem. It is a conversation — between hormones and tissues — that has changed.

Once you understand who is at the table and what they are saying, the path forward becomes clearer. And kinder.

I want to walk you through twelve hormones every adult should know by name. Rather than introduce them one at a time, I am going to organize them into five small teams, because that is how they actually work in your body. Then I will show you the four daily moves that support all five teams at once.

One foundation point before we begin, because it shapes everything that follows: men and women carry all of these hormones — including estrogen, testosterone, and progesterone. What differs is the amount, the rhythm, and the timing across life. A woman's body produces and uses testosterone every day. A man's body produces and uses estrogen and progesterone every day. Both matter for both.

Team 1 — Hunger and Fullness

Leptin, Ghrelin, GLP-1, GIP

These four are constantly negotiating one question: am I hungry, or am I satisfied?

Ghrelin rises before meals and quiets after you have eaten. It is the eat now signal.

Leptin comes from your fat tissue and tells your brain, we have enough — you can stop searching. When leptin signaling works, you feel satisfied after a real meal. When it does not — a state called leptin resistance, common with chronic over-eating, ultraprocessed food, and disrupted sleep — your brain keeps hearing find more even when your body has plenty.

GLP-1 and GIP are released by your gut when you eat. They slow your stomach, sharpen your insulin response, and tell your brain you are satisfied. The medications people are asking me about almost daily — semaglutide, tirzepatide — work by mimicking these signals at much higher levels than your body produces on its own.

What this team needs from you: real food your gut can recognize. Enough protein and fiber to trigger a meaningful GLP-1 and GIP response. And consistent sleep, because leptin does most of its work while you rest.

Team 2 — Fuel and Storage

Insulin, Glucagon

These two are the thermostat for your blood sugar.

Insulin rises after you eat. Its job is to move sugar out of your blood and into your cells, and to tell your liver and fat tissue, we have plenty — store some. Insulin is a storage hormone, which means while it is up, fat burning is turned down — your body is in storage mode, not burn-fat-reserves mode.

Glucagon is insulin's mirror. When you have not eaten for a while, glucagon rises and tells the liver, release some stored fuel — the body needs it.

You want both of these working. A healthy metabolism is not one that lives in insulin all day. It is one that can move fluidly between fed and not-fed, between insulin and glucagon. When we eat constantly, snack on refined carbohydrates, and graze from morning to bedtime, insulin stays elevated and glucagon barely gets a turn. Over years, that pattern is one of the central drivers of insulin resistance, fatty liver, and stubborn weight around the middle.

What this team needs from you: real meals with protein, color, and fiber — and meaningful breaks between them, so glucagon gets to do its work. This is where fasting earns its place.

Team 3 — Energy and Pace

Thyroid, Cortisol

These two set the speed of your whole system.

Thyroid hormones decide how quickly your cells turn food into energy. When thyroid is low, everything slows — temperature, mood, hair, digestion, the rate you burn calories at rest. When it is high, everything speeds up uncomfortably. Most adults sit somewhere in between, but thyroid function quietly drifts with stress, undereating, nutrient gaps, and life stage.

Cortisol is your daily rhythm hormone. Cortisol is not your enemy. It is what wakes you up in the morning, gets you through hard days, and helps you respond to challenge. The problem is not cortisol — it is cortisol that never comes down. Chronic stress, broken sleep, and prolonged severe under-eating keep cortisol elevated when it should be falling, and over time that pattern is associated with central weight gain, metabolic syndrome, and disrupted sex hormones.

What this team needs from you: sleep your body can rely on, daylight in the morning, food that does not keep you in a constant state of deficit, and recovery between hard things — emotional and physical.

Team 4 — Identity and Strength

Estrogen, Testosterone

These are the hormones we usually file under reproduction, but their reach is much bigger than that. They shape muscle, bone, brain, mood, sleep, skin, and how your body handles every other hormone on this list.

Both men and women have both — what differs is the amount, the rhythm, and the timing across life.

Estrogen supports insulin sensitivity, bone density, brain function, and mood. In women, estrogen rises and falls across the menstrual cycle and shifts dramatically through perimenopause and menopause. In men, estrogen is present at lower levels every day, and it matters — for bone, brain, libido, and cardiovascular health.

Testosterone supports muscle, mood, libido, energy, and metabolic health. In men, testosterone declines gradually from the 30s onward, by roughly one percent per year on average — a slow drift that is easy to miss until it is no longer subtle. In women, testosterone is present every day at lower levels, and it matters — for muscle, drive, mood, and sexual health, particularly through the midlife years.

The most under-appreciated effect of these hormones, in both sexes, is on muscle. Estrogen and testosterone both help you build and hold muscle tissue. As they shift — through aging, through perimenopause, through andropause, through chronic stress, through under-eating — the body lets muscle go more easily. And muscle is the organ that determines how well every other hormone on this list performs.

What this team needs from you: resistance training. Enough protein to actually build tissue — most adults do well between 0.7 and 1.0 gram per pound of goal body weight, spread across the day. Sleep. And, for many people, an honest conversation with a clinician about whether hormone support is right for them.

Team 5 — Calm and Connection

Progesterone, Melatonin, Oxytocin

These three are the hormones that bring your system back into balance — the ones that bring it down, together, and into rhythm with itself. They are also among the most underdiscussed hormones in standard medical training, which is part of why patients often arrive in my office having never heard them named outside of pregnancy or sleep aids.

Progesterone is most often filed under reproduction, but its reach is much wider. Progesterone has a calming, sleep-supporting, anti-anxiety effect on the brain through its action on GABA receptors — the same receptors many anti-anxiety medications target. In women, progesterone rises in the second half of the menstrual cycle and falls steeply through perimenopause, and that decline is part of why sleep, mood, and anxiety so often shift in women in their 40s, even before periods become irregular. Men carry progesterone too, at lower levels, where it plays a supporting role in mood, sleep, and as a precursor to other hormones.

Melatonin is your circadian hormone. It rises in the evening as light fades, signals to every cell in your body that it is time to wind down, and quietly orchestrates the overnight repair work that the rest of your hormones depend on. Melatonin levels naturally decline with age — by the 50s and 60s, peak nighttime melatonin can be a fraction of what it was in the 20s. Light exposure at the wrong time of day, especially screens late at night, is the modern lifestyle factor that disrupts it most.

Oxytocin is the hormone of connection — released through warm physical contact, intimacy, breastfeeding, and meaningful social interaction. The reason it belongs on this list is not sentimental. Oxytocin actively suppresses the HPA stress axis, lowers cortisol, supports cardiovascular health, and is being studied for its role in mood, pain, and even appetite regulation. In a culture that has quietly engineered out much of the everyday human contact previous generations took for granted, this hormone is one of the most under-supported in adult life.

What this team needs from you: protected sleep in a dark room, daylight in the morning, time outside in the afternoon, and real human contact — not just digital. For women in perimenopause, an honest conversation with a clinician about sleep, mood, and progesterone is often as important as the conversation about estrogen.

How All of This Connects

I want to spend a minute on something I see in clinic almost every day, because once you understand it, everything in this article starts to make more sense — and a lot of self-blame patients carry around starts to come off.

It begins with muscle. As we age, as estrogen and testosterone shift, as sleep gets shorter and life gets busier, the body lets muscle go. That matters more than most people realize, because muscle is the largest site of insulin-driven glucose uptake in the body. When there is less of it, the same meal raises blood sugar more, the pancreas has to release more insulin to bring it back down, and over time the cells stop responding to that insulin the way they used to. Insulin levels stay elevated for longer after every meal — and that is where the part most patients have never had explained to them comes in.

When insulin is high, your fat cells stay locked. They cannot release the energy they are holding. So you can be carrying a substantial reserve of stored fuel and still feel like your body is running on empty, because the door to that reserve is closed.

This is what most people are actually feeling when they describe it as cravings, or "I have to eat right now," or hunger that does not match how much they just ate. It is not weakness. It is biology. The brain is asking for fuel because it cannot reach the fuel that is already there.

And then the loop tightens. Ultraprocessed food and foods designed to spike blood sugar create the biggest insulin response of anything we eat, which keeps fat cells locked even longer, which keeps the brain asking, which makes the next ultraprocessed snack feel almost involuntary. Stress and broken sleep push cortisol up, which raises insulin resistance directly and increases cravings for high-glycemic foods. Progesterone falls in midlife and sleep gets worse, so melatonin does less of its overnight repair. Oxytocin — the daily counterweight to all of this — gets crowded out by digital life. And the muscle keeps quietly going.

A growing waistline is not a moral failing. It is the visible footprint of all of this happening at once. So is the 3 p.m. crash. So is the snack you swore you would not eat at 9 p.m. So is the stubborn weight that does not move even when you are doing what you have always been told to do.

This is also why I am hopeful when patients understand it. Every one of the four daily moves I am about to describe is designed to interrupt this loop somewhere. Protein and resistance training rebuild the muscle that protects insulin sensitivity. Hydration supports the entire signaling system. Meaningful breaks from food — particularly with an earlier eating window — let insulin fall and fat cells open, so the body remembers it has access to its own stored fuel. And sleep, recovery, and real human connection are how cortisol comes back down and the whole system gets to reset.

You are not stuck. You are caught in something that has a way out — and the way out is the same four moves, done with a little more understanding of why they matter.

A Note on Stage of Life

Hormones do not move in a straight line. They move in seasons and change at different stages of life. Both sexes have them; the seasons and stages of life just look different.

For Women

In your 20s and early 30s, the system is forgiving. Cycles are typically regular. You can skip meals, sleep poorly, train hard, and bounce back. This is the season when habits get built — well or poorly — for the decades to come.

In your late 30s and 40s, perimenopause begins, often years before periods stop. You may notice shifts in cycle length, sleep, mood, recovery, and how your body responds to the same effort that used to work. Falling progesterone is often the first hormonal change of this season — and it is one of the reasons sleep and anxiety can shift before any other symptoms appear. This is the most common stage of life that I see patients sit down and say the sentence at the start of this article.

In your late 40s, 50s, and 60s, perimenopause moves into menopause. Estrogen drops more steeply, and bone, brain, sleep, mood, and metabolic health all become more sensitive to the basics — protein, sleep, movement, recovery, connection. This is also the stage of life when the work pays back the most. Patients who attend to muscle, sleep, and food rhythms in this decade are often the strongest, sharpest, and most resilient women I see.

In your 70s and beyond, protecting muscle becomes the headline of the entire conversation. Strength is independence.

For Men

In your 20s, testosterone is at its peak. Recovery is fast, sleep is forgiving, and the system tolerates a great deal. As with women, this is the season of habit-formation.

In your 30s, testosterone begins a slow, gradual decline — on average about one percent per year. Most men do not notice it. The first signs often look like lifestyle: slower morning energy, slightly worse sleep, a little more belly fat than there used to be.

In your 40s, andropause symptoms can begin to appear and are often missed or attributed to stress. Lower libido, slower recovery from workouts, mood shifts, sleep that does not restore the way it used to, visceral fat redistributing around the middle. This is often the stage of life when professional and family stress is also at its peak, and the hormonal shift gets buried under the rest.

In your 50s and 60s, the cumulative effect of declining testosterone becomes more clinically meaningful. Without intervention, muscle loss accelerates, and the risk of metabolic syndrome, type 2 diabetes, and cardiovascular disease rises. Sleep changes — including new or worsening sleep apnea — interact with hormones in ways that are often missed in routine care. This is the decade when men benefit most from honest conversations with a clinician about labs, sleep, body composition, and whether hormone support is appropriate.

In your 70s and beyond, the same headline applies as it does for women: strength is independence. The single best predictor of how well any of us live in our 80s is how much muscle we still have at 70.

You are not behind. You move through different stages of life. The four moves that follow work in every one of them.

The Four Moves That Support Every Team at Once

Twelve hormones. Five teams. And almost everything they need from you comes down to four daily practices.

1. Eat Enough Protein, Every Day

Protein is the most underused tool for hormonal health. It signals satiety through GLP-1 and GIP. It blunts the insulin spike of a mixed meal. It protects muscle as estrogen and testosterone shift. It gives your thyroid the raw materials it needs. For most adults, that means somewhere between 0.7 and 1.0 gram of protein per pound of goal body weight, easier when spread across the eating times rather than aiming for all at once.

2. Drink Water Like It Is Part of the Plan

Hydration affects nearly every hormone on this list — through the kidneys, the gut, and the brain. Most of the patients I see are mildly under-hydrated and do not know it. Real water, consistently, before you are thirsty. Many people find that fat loss becomes easier when they are well-hydrated.

3. Let Your Body Have Meaningful Breaks from Food

This is where fasting belongs in the picture. Not as a punishment, and not as a contest, but as a normal physiological state your hormones expect to spend part of the day in.

Time-restricted eating — choosing a daily eating window and letting your body fast outside of it — is the most studied form of fasting in adults, and the evidence is clearer than the noise on social media suggests:

  • For most adults, a consistent 12-to-14-hour overnight fast is a reasonable, gentle starting point. Insulin falls - which means fat cells can finally open and the body can reach its own stored fuel. Glucagon rises, leptin recalibrates, and melatonin gets to do its overnight work without late-night digestion competing for attention.
  • For metabolic health specifically — including in midlife women, postmenopausal women, and men — randomized trials of 8-hour eating windows have shown improvements in body weight, body composition, insulin sensitivity, and blood pressure, particularly when paired with adequate protein and resistance training.
  • The timing of the eating window matters. Multiple randomized trials now suggest that eating earlier in the day produces better outcomes for blood sugar, fat mass, and insulin resistance than eating the same window later. If you can choose, choose earlier.
  • For perimenopausal women, the evidence is more reassuring than the loudest voices on social media suggest. Recent trials show that time-restricted eating in this group is well-tolerated, supports body composition goals, and does not appear to disrupt sex hormones meaningfully — particularly when protein is sufficient and the window is reasonable, not extreme.
  • For men in midlife, time-restricted eating combined with resistance training is one of the most evidence-supported strategies for addressing the visceral fat and insulin resistance that often arrive alongside declining testosterone.
  • Where to be more cautious: pregnancy, breastfeeding, history of an eating disorder, frailty in older adults, type 1 diabetes, people on medications that lower blood sugars, and anyone underweight or already in significant caloric deficit. Fasting is not the right tool for every stage of life.

The goal is establishing rhythms, not extremes — and the rhythm should fit the life you are actually living.

4. Protect Your Sleep, Your Recovery, and Your Connection

Sleep is when leptin recalibrates, cortisol resets, growth hormone rises, melatonin orchestrates overnight repair, and sex hormones do much of their quiet work.

Real recovery ideally includes: daylight in the morning. Time outside during the day. Movement that is not training. Quiet. And — often missed — real human connection.

Oxytocin is not a soft hormone. It is one of the most powerful daily regulators of the stress axis, and it is released through ordinary human contact: a hug, a phone call with someone who knows you, time with a partner, a friend, a pet. No supplement and no protocol replaces this. It is safety, social bonding, feeling connected to another being.

A Note on GLP-1 Medications

A meaningful share of patients reading this are taking, or considering, a GLP-1 or dual GLP-1/GIP medication — semaglutide, tirzepatide, and others. These medications can be transformative, and they are create an environment where the four moves matter more, not less.

With significant weight loss on these medications, roughly 25 to 40 percent of the weight lost can come from lean mass, including muscle. A 2025 analysis presented at the Endocrine Society's annual meeting found that, in patients on semaglutide, being older, female, or eating less protein was each associated with greater muscle loss.

*Side Note: A recent study was published in Cell Reports Medicine in 2026 that showed that lean body mass on a DXA is not the same as skeletal muscle loss. Liver shrinkage, fluid shifts, intramuscular fat reduction all contribute to that number. Also in that study, in direct measurements — grip strength, knee extension, physical performance — patients were not weaker. Relative muscle strength improved, even for semaglutide which had the largest drop of lean mass in the STEP 1 study. So, while this was a reassuring signal that not all lean mass lost is muscle, it is still much easier to lose muscle as we age and also on GLP1's.

The good news is that this is largely modifiable. Trials and case series consistently show that adequate protein intake and resistance training meaningfully attenuate lean mass loss during GLP-1 therapy.

The four moves above are how you make these medications work with your long-term health, not at its expense.

A Note from Me

When patients tell me their body is not responding the way it used to, what is almost always happening is that the conversation between their hormones and their tissues has gotten quieter — because of stress, sleep, age, life stage, under-eating protein, missing connection, or all of the above.

The work is not to fight your body. Rather, it is to give it something to listen to.

Feed your muscle. Hydrate the system that carries every signal. Let your body have the rhythm of fed and fasted it was built for. Sleep like it matters, because it does. And do not underestimate the hormone you release through ordinary human contact.

That is the whole map — twelve hormones organized into five teams, all of them quietly waiting on the same four daily moves from you. None of it is dramatic. All of it adds up.

— Dr. Naomi Parrella, MD

This article is for general educational purposes and is not a substitute for individual medical advice. Please talk with your own clinician before making changes to your nutrition, fasting, or medications.