Why "Calories In, Calories Out" Fails Women: A Beginner’s Guide to Hormones, Metabolism & Weight Loss
- Amy Simpson
- Feb 13
- 7 min read
Updated: 3 days ago
If you’ve ever been told to “eat less and move more” but still struggle with stubborn weight, energy crashes, or intense cravings—you’re not alone. Women’s metabolism is far more nuanced than a simple calories-in, calories-out equation. This guide shares my clinical strategies for sustainable fat loss, eating in rhythm with your cycle, and building lean muscle.
Science-Backed Alternatives to "Calories In, Calories Out"
Our bodies are deeply influenced by hormones, stress, and blood sugar regulation, meaning traditional weight loss advice (often based on research conducted on men) can actually backfire for women.
The key to sustainable fat loss, stable energy, and balanced hormones lies in understanding how cortisol, insulin, and the menstrual cycle impact metabolism.
🚫Caveat - There is a lot of talk on social media about cortisol, so I want to be clear here that cortisol is a critical hormone. "Cortisol face" is likely a reference to a very serious endocrine disease called Cushing's. This needs to be treated by an endocrinologist and is not cured with a juice or cleanse.
I think it's also important to point out that acute post-exercise cortisol is your body’s secret weapon for adaptation. What I am referring to in this blog is chronically elevated stress hormones in response to over-training and under-eating that has been sold to women as the way to "get toned and stay thin".
How Cortisol and Stress Impact Women's Metabolism
Women are naturally more sympathetically driven than men, meaning our "fight or flight" response - and cortisol production - activates more easily (this is further increased during early motherhood and perimenopause). While cortisol is an essential daily hormone that we need to thrive, chronically high levels from stress, poor sleep, chronic dieting, over exercising overtime can:
Increase blood sugar levels
Disrupt insulin balance
"Slow" metabolism
Promote fat storage, especially visceral fat around the middle
👉 The solution? Instead of ongoing extreme restriction like 1,500 calories or skipping breakfast, prioritise strategic cycle-based nourishment (optimal protein + healthy fats + fibre) that helps stabilise blood sugar, support metabolic function, and prevent stress-induced fat storage. Let's break it down 👇
Why Skipping Meals and Cutting Calories Can Backfire and What to Do Instead:
Many women are told that eating less and exercising more is the fastest path to weight loss. But in reality, chronically under-eating and overtraining can throw the metabolism into chaos.
Skipping breakfast, fasting, and overdoing fasted cardio can keep cortisol elevated for too long. While these trends are often celebrated in male-focused fitness spaces (hello, 16:8 fasting), for women, regularly skipping meals—especially breakfast—has been linked to higher visceral fat, insulin resistance, and type 2 diabetes.
Here’s what can happen when women undereat for too long:
↑ Cortisol → ↑ Blood sugar → ↑ Insulin → ↑ Fat storage
↓ Thyroid activity → Slower metabolism, lower mood, reduced fertility
↑ Hunger hormones → Stronger cravings → More chance of binge eating
In clinic, I often hear women say they skip breakfast and have light lunches—only to find themselves ravenous and grazing all afternoon. Sound familiar?
👉What to do instead: Eating in a way that regulates stress, balances blood sugar, and fuels your metabolism.
Eat enough, stop restricting and signalling a deficit to your brain.
Eat at least 30g of protein for breakfast. Eating protein at breakfast signals safety to our brain and we stop pumping out morning cortisol we also set the tempo for the day's blood sugar. Learn more about the benefits of eating breakfast here.
Flip the fast! Instead of skipping breakfast, have an early dinner (5pm) and skip any after dinner snacks. We are less sensitive to insulin in the afternoons so we cannot process a huge dinner in the way we can process a huge breakfast.
Have at least 3-4 hours to digest dinner before going to bed. This enables optimal digestion and leaves sleep for other critical metabolic and detoxification processes.
The Luteal Phase - Why You Crave Carbs Before Your Period and What to Do About It:
If you happen to crave chocolate, bread, or pasta before your period? Or feel bloated around this time? It’s not a lack of willpower - it’s biology.
During the luteal phase (the second half of your cycle), progesterone rises and naturally increases insulin resistance and drives you to seek out more food. This is your body’s way of prioritising carbohydrates and protein in order to grow a healthy uterine lining in the case of pregnancy.
We have a cycle for 35-40 years of our life! Yet, this critical biological process (i.e. nourishing a potential baby) is missing from the 'calories in, calories out' / 'eat less, move more' argument.
👉What to do instead: Instead of fighting your menstrual cycle, work with it by:
Choose slow-digesting, fibre-rich carbs (e.g., sweet potatoes, quinoa, legumes) to stabilise blood sugar and clear excess hormones from the gut during the luteal phase.
Prioritising protein and healthy fats at every meal and snack to reduce sweet cravings and serve the uterus's demands so it stops asking you to seek out food.
Adjusting workouts to lower-impact movement (e.g., strength training, yoga) instead of high-intensity cardio to help reduce excess hunger, dehydration, and stress.
How Over-Training Can Cause Fat Around the Middle and How to Exercise for Fat Loss and What to Do Instead:
Overtraining and consistently training in a fasted state can increase cortisol, the body's primary stress hormone. In women, chronically elevated cortisol levels especially without enough fuel or recovery can lead to muscle breakdown, hormone imbalances, and a shift toward storing fat around the abdomen.
Paradoxically, instead of burning fat, the body may hold onto visceral fat as a survival response to stress and perceived energy scarcity.
🚫Caveat - Remember, the best exercise is the one you enjoy! Choose activities that feel good and fit your lifestyle, whether it’s strength training, yoga, walking, or dancing. The point of this blog is to emphasize how much fuel we need, not to add stress! Consistency is key, so find what makes you feel empowered and keep moving - just fuel for the occassion.
👉 Here's how to build muscle and lose fat:
Lift heavy weights - build muscle
No, lifting weights won’t make you bulky—promise. In fact, muscle helps burn sugar, acting like a glucose sponge that improves blood sugar control and lowers your risk of insulin resistance, visceral fat, and type 2 diabetes. That’s what people really mean when they say “fast metabolism.”
For women in midlife, heavy resistance training is one of the best tools for staying strong, managing blood sugar, and preventing bone loss. As oestrogen drops, we lose muscle and strength faster—but lifting weights (heavy enough that you fatigue by 5–8 reps) can help slow that down. And you don’t need hours at the gym—just 2 focused sessions a week using big, compound moves is enough to make a real impact.
👉Speak to your physio like the superstars at 3D Physio or work with a personal trainer who understands female physiology to develop a heavy training plan. The right support will ensure that you see quick results and prevent the risk of injury.
High Intensity Interval Training - lose fat
Sprint-style training isn’t just for athletes, it’s a game-changer for women in perimenopause and beyond. Dr. Stacy Sims, a leading women's sport physiologist, recommends Sprint Interval Training (SIT) and High-Intensity Interval Training (HIIT) to support muscle retention, boost insulin sensitivity, and shift stubborn fat—especially as oestrogen levels decline with age.
The best part? These sessions are short and sharp—not drawn-out gym classes.
SIT = 20 seconds of all-out sprint effort, followed by 60–90 seconds of full recovery. Repeat for 3–5 rounds. This style fires up your metabolism, improves fat oxidation, and builds power by recruiting fast-twitch muscle fibres.
HIIT = 30–60 seconds of hard work with 15–30 seconds of rest between rounds. It improves cardiovascular fitness, endurance, and metabolic health.
Dr. Sims highlights that SIT, in particular, is highly effective for women by helping retain lean muscle, improve metabolic flexibility, and burn fat more efficiently than steady-state cardio. Just a couple of sessions per week can deliver powerful results.
👉How do I do it? I like to do 20 seconds on the AirDyne bike followed by 90 seconds recovery, five times only twice a week during the first half of my cycle.
How to Fuel for Exercise That Promotes Adaption and Fat-Loss:
As you have hopefully learnt by now, female physiology thrives on fuel, especially during workouts. Here is your guide to nourished training:
👉For weightlifting: Aim for 15g of protein before you work out. It fuels your body and boosts post-exercise oxygen consumption (i.e. calorie burn), helping to elevate your metabolism for better recovery. Here are some examples of 15g protein snacks:
- 2 hard boiled eggs
- 30g of almonds
- 1 cup of Greek yoghurt
- 1/2 a serve of a standard whey protein shake
- 50g turkey slices
👉For cardio or cardio + weights: Add around 30g of carbs to that protein before you work out. This combo helps maintain blood sugar and signals the hypothalamus that nutrition is incoming, reducing the stress response often triggered by fasting/ training. Here are some examples of 30g of complex carbs:
- 1 medium banana
- 1 slice sourdough
- 1 apple with peanut butter
- 1 cup mixed berries
🍽️Always aim to have your post-workout meal within 45 minutes of training to optimise recovery and preserve lean muscle mass.
For more on how to fuel before and after exercise to maximise results (lean muscle mass, nourished fat loss), check out this post
Pulling it all together
Need help working WITH your female body, not against it?
My Pillars of Health Guide will help you:
Balance blood sugar to support steady energy & metabolism
Reduce cortisol spikes that drive fat storage
Optimise nutrition, movement, and stress management for sustainable fat loss and metabolic health
👉No more battling cravings—just science-backed strategies for thriving.
Amy is a degree-qualified naturopath dedicated to helping busy, tired clients regain their energy and vitality.
She combines evidence-based naturopathic medicine, nutrition, and lifestyle interventions to empower clients on their journey to optimal health. Whether it’s reclaiming energy, balancing hormones, resolving digestive issues, or enhancing overall well-being and longevity, her personalised approach focuses on identifying and addressing the root cause of health concerns. With a Bachelor of Health Science, ongoing studies in a Master of Advanced Practice, and full membership in the Naturopaths and Herbalists Association of Australia, Amy offers a unique blend of traditional wisdom and science to support individuals and families at every stage of life.
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