HeraSphere #42: Burning fat: the science and the protocols

Hi friends,

A few months ago, I lost 4 pounds of fat. I know because I have a Hume body composition scale, and I watched the total body fat number move in the right direction over months of clean eating and consistent exercise. I was really proud of it.

Then work got intense, the holidays arrived, and my workouts dropped off. I kept eating well. And I gained it all back over the past 6 months.

What made it worse was seeing my that visceral fat had gone up. I was frustrated. Honestly, I was annoyed at myself. I felt like I had done everything right and yoyoed back anyway.

My body was responding to hormonal and metabolic conditions I didn't fully understand. The rules I had been using, the ones most of us learned in our 20s and 30s, don't apply anymore. Fat loss after 40 is requires understanding what has changed in our bodies.

This is part one of a two-part series on fat burning and muscle building. You cannot sustainably lose fat without building and protecting muscle. And you cannot build muscle effectively without understanding how fat metabolism works first. Part one covers why fat accumulates differently now, how it actually burns, and why it comes back when you stop moving. Part two covers what it takes to build the muscle that makes all of this stick.

The TL;DR

• The fat loss rules from your 30s don't apply anymore. When estrogen drops, your body reroutes fat storage toward visceral fat around your organs, and triggers cravings for sugar precisely when your body needs protein.

• Chronic stress and poor sleep are fat storage mechanisms. Both raise cortisol, which spikes insulin, which locks fat cells shut and directs energy toward visceral storage — independently of what you eat.

• Eating dietary fat does not make you fat. Refined carbohydrates and sugar spike insulin, the hormone that locks fat cells shut and drives visceral fat storage. Dietary fat does not. The cardiovascular picture is more nuanced.

• How you exercise matters more than how long. Sprint intervals followed by heavy strength training trigger the precise hormonal sequence that unlocks fat burning. Comfortable steady-state cardio does not.

• Gaining fat back despite eating clean is not a willpower failure. Leptin, the hormone that protects against fat regain, drops when you stop training. Fast fat loss accelerates that drop.

Why Your Body Stores Fat Differently Now

• There are two primary types of fat. Subcutaneous fat sits just under the skin: the soft layer on hips, thighs, and upper arms. It is visible, it is what most of us fixate on, and it is relatively harmless. Visceral fat accumulates deep inside the abdominal cavity, packed around your liver, intestines, and stomach. You can’t see it or pinch it, but it drives inflammation, accelerates insulin resistance, and raises cardiovascular risk. The good news: it responds faster to the right interventions than subcutaneous fat does.

• Estrogen governs where your body stores fat. When estrogen is present, fat accumulates subcutaneously — hips and thighs. As estrogen drops in perimenopause, the liver starts reading circulating fat molecules differently and routes them toward visceral storage. This happens independently of how much you are eating. Research shows that women gain an average of 1.5 pounds per year during perimenopause, most of it going to the abdomen, even when overall weight stays stable.

• If you are on hormone replacement therapy (HRT), the rules still apply. Menopause hormone therapy slows some of these body composition changes and improves insulin sensitivity, but it does not reverse them. HRT is a tool in the toolbox, but everything in this issue applies whether you are on hormone therapy or not.

• Your body needs protein. Your brain is ordering sugar. As estrogen drops, muscle breaks down faster and the body's demand for protein rises. At the same time, rising cortisol signals the brain to seek fast glucose. Your muscles need amino acids to rebuild. Your brain sends you to the pantry for crackers. Your cravings are a result of hormonal miscommunication, not your waning willpower.

• Chronic stress is a fat storage mechanism. Sustained cortisol elevation — from work pressure, poor sleep, and hormonal upheaval — raises insulin independently of what you eat. Elevated insulin directs energy toward visceral fat storage. For women carrying significant mental load, this is often the missing piece that explains why everything else is in place and the visceral fat number still climbs.

• Poor sleep makes all of this worse. Inadequate sleep raises cortisol, spikes insulin, locks fat cells shut, and suppresses leptin — the hormone that protects against fat regain. Sleep is a critical metabolic input to fat loss.

• Muscle loss accelerates fat gain. Estrogen drives the creation of new muscle cells and governs the nerve signals that produce strong muscle contractions. When estrogen drops, both slow down. Less muscle means fewer calories burned at rest and less capacity to oxidize fat during exercise. Part two covers what to do about it.

Dietary Fat Does Not Make You Fat

• The "eating fat makes you fat" idea is one of the most damaging nutrition myths of the last 50 years. It drove decades of low-fat products loaded with sugar and refined carbohydrates that made metabolic health worse. Dietary fat is broken down into fatty acids, not glucose, so it does not spike insulin. Insulin is the switch that locks fat cells shut and directs energy toward visceral storage.

• Dietary fat is not a free food. At 9 calories per gram, it is more than twice as calorically dense as protein or carbohydrate. Eat enough in a caloric surplus and you will store the excess. But the metabolic pathway is different from refined carbs. A meal of salmon, olive oil, and roasted vegetables does not produce the same hormonal response as a croissant with the same calorie count. The insulin response, the satiety signal, and where the energy gets stored are all different.

• Refined carbohydrates and sugar drive visceral fat in midlife women. When glucose floods the bloodstream, insulin spikes, lipolysis shuts down, and incoming energy gets directed toward visceral storage. A Women's Health Initiative study following over 88,000 postmenopausal women found that reduced carbohydrate intake was associated with the lowest risk of weight gain, while low-fat diets were associated with the highest. The same carbohydrate load that was manageable at 35 accumulates as visceral fat at 45 because the insulin response has changed.

• Not all carbohydrates behave the same way. Refined carbs and added sugars are the problem. Complex carbohydrates from fruit, vegetables, legumes, and whole grains digest slowly, produce a gentler insulin response, and feed the gut microbiome diversity that is critical for perimenopausal women. The goal is not zero carbs. It is fewer refined carbs, timed strategically around activity.

• Keto is one version of this approach, with real evidence and real caveats. Ketogenic protocols — restricting carbohydrates to under 50 grams per day — have shown meaningful results for postmenopausal women: reduced visceral fat, improved insulin sensitivity, and preserved lean mass. For women who find moderate carb reduction insufficient, it is a legitimate option to explore with a physician. The caveats are real: keto can raise LDL cholesterol in some women, may reduce bone density over time (a particular concern during menopause when osteoporosis risk is already elevated), and very low carb can compromise gut microbiome diversity.

• Prioritize mono and polysaturated fats. Polyunsaturated fats — fatty fish, walnuts, flaxseed, olive oil — improve insulin sensitivity, lower fasting glucose, and reduce inflammation. Saturated fat in whole food sources does not spike insulin and is not the direct driver of visceral fat storage — but a note worth making here: this section is about fat metabolism and insulin response, not cardiovascular risk. Saturated fat raises LDL cholesterol in many people, and cardiologists broadly recommend limiting it for heart health, particularly in postmenopausal women whose cardiovascular risk rises after estrogen loss. These are two different questions: what drives fat storage, and what drives heart disease. If you have elevated LDL or a family history of cardiovascular disease, talk to your cardiologist before leaning heavily into saturated fat sources.

How Fat Actually “Burns:” The Three Stages

• Stage 1: Lipolysis, the unlock. Fat is stored in cells as triglycerides: three fatty acids attached to a glycerol backbone. Lipolysis breaks that bundle apart and releases the fatty acids so they can travel to muscle cells and be burned. The trigger is adrenaline, released in response to exercise intensity. The harder the effort, the more adrenaline, the more fat gets unlocked. Insulin shuts this down completely. High insulin and unlocking store fat cannot coexist.

• Extending the low-insulin window is the real reason intermittent fasting works. Fasting lowers insulin, which keeps fat cells unlocked and lipolysis running. A 12 to 14 hour overnight fast — finishing dinner by 7pm and eating breakfast between 7 and 9am — is enough to produce this effect for most women. Longer protocols of 16 hours or more can raise cortisol enough to counteract the benefit in perimenopausal women. More is not always better here.

• Stage 2: Transport. Once released, free fatty acids travel through the bloodstream to reach muscle cells. Long-chain fatty acids cannot enter the mitochondria on their own: they need a molecule called carnitine to carry them across the mitochondrial membrane. This is why 20 minutes of easy cardio mobilizes fat but does not burn much of it: the session ends before the transport and oxidation chain completes.

• Stage 3: Oxidation, the actual burn. Inside the mitochondria, fatty acids are broken down in cycles to generate ATP — your body's energy currency. Fat oxidation increases with exercise intensity up to roughly 65% of your maximum heart rate. Above that, carbohydrate becomes the dominant fuel. Zone 2 cardio burns fat during the session. Sprint intervals burn more carbohydrate during the effort but drive higher fat oxidation for hours afterward through sustained adrenaline response.

• What this means for how you eat around workouts. Keep insulin lower in the hours before training. Prioritize protein and healthy fats before exercise, and save starchier carbohydrates for after — when muscle cells are primed to absorb glucose for recovery rather than store it as fat.

What to Actually Do: The Workout Protocol

• Sprint first, then lift: the sequenced session. Dr. Vonda Wright, orthopedic surgeon and longevity researcher, recommends opening each strength session with 30-second all-out sprint intervals before moving to weights. The sprint floods the system with adrenaline, unlocks Stage 1 lipolysis, and depletes muscle glycogen. The weight training that follows happens while fat oxidation is already running and adrenaline is still elevated. Three to four rounds of 30-second all-out efforts with full recovery between rounds, then straight into compound lifts.

• Heavy strength training, 2 to 3 sessions per week. Squats, deadlifts, hip thrusts, rows, presses: compound movements with real load. This builds the muscle mass that expands mitochondrial capacity, directly counteracts estrogen-driven muscle loss, and maintains leptin sensitivity. Dr. Sims and Dr. Wright converge on the same point: for women in perimenopause, the weight room is the primary intervention, not the cardio machines.

• Standalone sprint sessions if you cannot combine, 2 sessions per week. All-out efforts of 8 to 30 seconds with full recovery between rounds still trigger the adrenaline surge and post-exercise fat oxidation window. Brief and hard.

• If you are starting from zero. Ten minutes of bodyweight movement three times a week: squats, pushups, hip hinges, light overhead press. The sprint component can begin as a 30-second brisk walk at your fastest pace, progressing to a jog, then a true sprint as fitness builds. Add load once the movements feel solid.

• Zone 2 and daily movement is necessary but not sufficient. Walking and easy movement support cardiovascular health and daily energy expenditure. They do not trigger the hormonal adaptations that drive body composition change. Moderate-intensity steady-state cardio sits in no-man's land: too hard for easy recovery, too easy to trigger adaptation. One meaningful exception: fasted zone 2 cardio beyond 90 minutes produces greater fat oxidation than fed cardio at the same duration. Under 90 minutes, the difference is negligible. Your 45-minute walk is valuable, but will not be a primary fat loss intervention.

• Your morning coffee before a workout is doing something real. Caffeine amplifies the adrenaline response to exercise, driving Stage 1 fat mobilization. Thirty to 60 minutes before training is the practical window. Cut it off by early afternoon: the sleep disruption undoes far more than the fat oxidation it produces.

• A note on alcohol. Alcohol suppresses fat oxidation while it is being metabolized, raises cortisol, disrupts sleep, and lowers leptin sensitivity. For a woman who eats clean, trains consistently, and has a glass of wine, alcohol is often the variable quietly breaking the equation.

Why the Fat Came Back: The Leptin Problem

• Leptin is the hormone that signals your brain you have enough energy in reserve. Produced by fat cells, it keeps hunger in check and metabolism running normally. When you lose fat, leptin drops. Your brain reads this as famine, ramps up hunger, slows metabolism, and pushes the body to restore fat stores.

• Exercise maintains leptin sensitivity. Resistance training and high-intensity exercise keep leptin receptor sensitivity functional. If you stop training for a few months like I did and leptin sensitivity degrades, making fat regain likely even without overeating. The fat loss built on consistent movement can’t be maintained by diet alone.

• Estrogen compounds the problem. Lower estrogen further compromises leptin signaling. Fat loss without sustained training, plus rising cortisol from work stress, plus declining estrogen: that combination is why my fat came back and landed viscerally.

• Slow fat loss protects against the leptin crash. Half a pound to one pound per week keeps leptin from dropping sharply and makes results easier to sustain. Crash diets accelerate the leptin drop, intensify hunger, and make regain more likely.

Where to Start

• Clean eating and 10,000 steps a day is a solid foundation. It is not a complete strategy. Low refined carbs keeps insulin down and fat cells unlocked. Zone 2 walking burns fat during the activity. But without the sprint-then-lift sequence to trigger the adrenaline response and preserve muscle, results will plateau and are vulnerable to regain the moment life intervenes. The diet and the steps are the floor. The intensity and the load are what build on top.

• Protect your sleep first. Seven to nine hours is a metabolic intervention. Chronic sleep deprivation undoes the work of everything else you may be doing.

• Reduce refined carbs and added sugar second. This lowers chronic insulin elevation and reopens the fat mobilization pathway. Swap refined carbs for complex ones and watch portion sizes around sedentary periods.

• Add the sprint-then-lift sequence third. Two sessions a week. Thirty seconds all-out, full recovery, three to four rounds, then straight into weights. More hormonal effect than an hour of moderate cardio.

• Protein is the bridge to Part 2. One gram per pound of body weight per day protects the muscle you already have while you work on the fat loss side. The full breakdown — and exactly what to eat to hit the target — is in the next issue.

What I'm Actually Doing Differently

Understanding the mechanism changed what I prioritize.

Strength training has always been my weakness, literally and figuratively. I kept sidelining it. It is now the non-negotiable anchor of my week. I now understand why Dr. Vonda Wright opens every session with sprints before lifting. Part 2 will explain why the weight room should be yours too.

Now that I know the new rules of fat loss, I know how to prioritize my workouts.

My standing desk adapter and walking pad are my insurance policy. On days when a structured workout is not happening, I can still get 8,000-10,000 steps by walking during video calls. I select 1-2 hours of meetings when I’m able to walk and talk, at a slow pace of about 1.6 miles per hour.

Part 2 on gaining muscle is coming next week. We are going to talk about building the muscle that makes all of this stick.

Burn baby burn!

Lilly

P.S. If you have a friend who has been eating well, doing everything "right," and still can’t seem to change her body composition: send this her way.

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Note: While I love diving deep into research and sharing what I've learned about women's health and wellness, I want to be crystal clear: I'm a passionate health advocate and researcher, not a medical professional. Think of me as your well-informed friend who does extensive homework – but not your doctor.

Everything I share in HeraSphere comes from careful research and personal experience, but it's meant to inform and inspire, not to diagnose or treat any medical conditions. Your body is uniquely yours, and what works for one person might not work for another. Always consult your healthcare provider before making significant changes to your diet, exercise routine, or wellness practices, especially if you have underlying health conditions or take medications.

ICYMI, here are a few past issues that you may enjoy: