The Myth of Calories In = Calories Out
The math ain’t mathin’ and it’s time to move on.
January 16, 2025
The fairy tale of weight loss
How many times have you heard “calories in = calories out”? This tidy formula claims to hold the secret to weight loss: eat less, move more, and you’ll shed pounds. But real life (and actual research) tells a very different story. For moms battling postpartum exhaustion, hormone chaos, and trying to figure out why their jeans are still tight even though they’ve been eating like a bird, this outdated concept is especially useless. Let’s blow this myth up with some data.
Overfeeding studies: the results are… confusing
Here’s what happens when researchers purposely overfeed humans (yes, this is a real thing): They calculate how many calories a person needs at rest and then make them eat an extra 1,000 calories a day. (Think Thanksgiving dinner, every day, forever.) The participants don’t get to cheat by running marathons or lying on the couch all day. Everything is tightly controlled, in these fascinating, albeit very small studies.
What happens? Some people gain a couple of pounds. Others gain 9 pounds in six weeks. And a few? They lose weight, including body fat. Like… what?
What does this mean? This wide range shows that the human body is not a math problem, and our bodies don’t follow a one-size-fits-all rule. Factors like genetics, gut health, hormones, and even stress can drastically influence how our bodies respond to extra calories.
But most of us aren’t over here trying to pack on the pounds so what about weight loss studies?
Underfeeding studies: does eating less guarantee weight loss?
Ok so here we have the same idea as overfeeding as far as calculating what someone needs at rest - but the subjects are all underfed by about the same; generally 1000 calories a day. According to the weight loss bible, everyone should lose the same amount of weight. Right. RIGHT??
What happens? After these strict calorie deficits, the outcomes were just as varied. Some people lost weight (as expected). Others barely budged. A few somehow lost nothing.
What does this mean? Calorie restriction works for some, not everyone. Weight loss does not follow a consistent math formula.
I know so many of you have experienced this. I have heard countless stories that go something like “My husband stopped using creamer in his coffee for 30 days and lost 10 pounds. I stopped eating all carbs and gained 2.”
Seriously WTF right? If this math doesn’t even work in the most controlled lab settings let alone our own lived experiences, why the hell are we still selling it as gospel?
Read Next:
For moms, this equation fails even more spectacularly
If you’re a postpartum mom (postpartum = 2 to 3 years after birth. I KNOW RIGHT?), the extra weight you’re carrying is like the kid in your freshman class that always fell asleep during algebra. AKA not paying attention to math.
Your postpartum body isn’t a word problem—it’s a symphony of hormones, nutrients, and stress. Slashing calories while trying to recover from creating and sustaining human life? At best this can leave you further nutrient, energy, and hormone depleted. At worst it can do all that PLUS make you gain weight. I’ve seen it!
For moms past the postpartum stage, but dealing with chronic stress and burnout, or super fun perimenopause - then restricting calories can also backfire due to…. you guess it. Hormones like cortisol, insulin, and estrogen.
Case study: Jenn the marathoner
Jenn, a client of mine, was 11 months postpartum, breastfeeding, half marathon training, and eating a low-calorie diet. Despite all this effort, her weight was going up. Why? Her metabolism was in the gutter, cortisol levels were sky-high, and inflammation was rampant. When we adjusted her diet to include more food and addressed her underlying inflammation and hormonal issues, her weight began to shift and she lost 10 pounds in 6 weeks without even trying.
That my friends, is the goal. Recalibrating your body so it releases weight, not trying to muscle it off with dieting.
The Dangers of long-term caloric deficits
or honestly even medium or short term!
Here’s where it gets dark. For some reason, the world thinks moms surviving on 1,300 calories a day, skipping breakfast à la Huberman podcast is inspirational. Spoiler: It’s not. And it’s going to bite you in the butt sooner or later.
Here’s what happens when you live in a calorie deficit for too long:
Hormone Drama: Prolonged calorie deficits disrupt hormones like cortisol, thyroid hormones, and sex hormones. The result? More PMS, worse mood swings, and stalled weight loss.
Nutrient Deficiencies: Low calories mean low nutrients, which leads to exhaustion, brain fog, insomnia, and even hair loss. No fun.
Metabolic Slowdown: Chronic under-eating tells your body to slow down your metabolism and thyroid, burn muscle for fuel, and hold onto fat for dear life. This, my friends is the recipe for even harder weight management.
How hormones impact weight loss
hormones are the bossy toddlers running the show. You can’t out-diet cortisol, insulin, or thyroid dysfunction. Here’s a quick rundown of what’s messing with your weight:
Cortisol (Stress Hormone)
High and too-low levels can lead to fat storage, especially around the midsection.
Thyroid Hormones
Essential for metabolism, they often take a hit during hormonal transitions like postpartum and perimenopause, or even chronic stress.
Insulin
Balancing blood sugar is critical for weight loss and energy levels, and also impacts estrogen and testosterone levels.
Progesterone, Testosterone and Estrogen
These fluctuate after baby and during perimenopause, influencing everything from sleep to glucose control to fat storage.
Read Next:Testosterone: The Vitality hormone you didn’t know was missing
Why eating more might be the answer
If you’ve been stuck in calorie-cutting hell (or considering starting a restrictive new diet), here’s your permission to stop. Instead of eating less, let’s focus on eating for what your body needs in this season:
Balance Your Plate: Start with equal portions of protein, starch, and vegetables at meals. This helps stabilize blood sugar and provides the nutrients your body needs to function optimally.
Increase Meal Sizes: Larger, more nutrient-dense meals can actually rev up your metabolism. This isn’t about overeating—it’s about eating enough to fuel your body.
Address the Root Causes: Look at your hormones, stress levels, and nutrient deficiencies. These often matter far more than calorie counting. Some testing is going to be helpful here.
Moms, you’ve been sold a lie about weight loss. It’s time to focus less on numbers and more on nourishing your body. Trust the process, eat enough, and address the deeper causes behind weight struggles. You’re not alone in this journey, and you don’t have to fight against your body to feel good again.
What’s next?
I’m hosting a free workshop about hormones, weight, and moms. Come join us!
xo
Alison
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