Here’s the physiological reason fasting or under eating on a zero carb carnivore diet can actually cause belly fat gain, even though it sounds counterintuitive. This effect is most noticeable in women, especially over 40, but it can happen to anyone on a strict carnivore diet.
This isn’t “bro science”, it’s how the stress, cortisol, and fuel management systems work when protein is removed from an already zero carb metabolism.
On a zero carb carnivore diet:
- insulin stays very low
- glucagon stays high
- you burn fat all day
- blood sugar stays stable
- cortisol stays regulated
- your body gets consistent protein for repair
This is already a fasting-mimicking metabolic state.
Your body loves this state. It’s safe, fed, stable, and hormonally calm.
But when you remove food, especially protein, you flip a switch.
Fasting Removes the ONE Fuel Zero Carb Eaters Still Need: PROTEIN
In strict ketosis (zero carb diet), your body gets:
- glucose needs from gluconeogenesis (protein → glucose)
- structural repair from dietary amino acids
- hormone production from protein and fat
- enzyme turnover from protein
When you fast:
Protein intake goes to zero.
But protein requirements do not go to zero!
So where does the body get protein?
From lean tissue and organ proteins!
(muscle, connective tissue, digestive enzymes, immune proteins)
This triggers a stress response… and here’s where belly fat enters the picture.
Fasting Raises Cortisol Significantly, Even in Deep Ketosis
Cortisol rises during fasting for several reasons:
- to mobilize glucose
- to liberate amino acids
- to maintain blood pressure
- to keep the brain energized
- to help the liver produce glucose from tissue
This cortisol increase is NORMAL during fasting.
But for zero carb people, it’s amplified because:
- they have no glycogen
- no dietary protein
- no carb buffer
- the body must break down tissue faster
- stress signals rise sooner
High cortisol tells the body:
“We’re in a scarcity situation.”
This activates belly fat storage.
Cortisol Shifts Body Composition Toward BELLY FAT
Cortisol doesn’t just increase fat breakdown, it also increases fat storage, especially in the visceral (“belly”) region.
Evolutionarily:
- belly fat is the most metabolically active
- easiest to mobilize
- safest for storing emergency energy
So during intense metabolic stress the body stores emergency fuel around the organs even while losing muscle from protein shortage.
This is why women who under eat, restrict protein, or fast too long often say:
- “I’m losing weight but my belly looks worse”
- “I’m getting softer around the middle”
- “My stomach looks puffy even though I’m eating less”
This is cortisol-driven redistribution.
On zero carb, you rely heavily on daily protein.
When fasting:
- you lose lean mass
- your basal metabolic rate drops
- your mitochondria downshift (you NEVER want to make your mitochondria unhappy!)
- your body becomes more conservative with energy
Lower metabolism means your body prefers storing fat in the easiest place:
The belly area (visceral fat)!
So even though you’re eating zero carb the rest of the time, the cycle becomes:
Fasting → muscle loss → slowed metabolism → belly fat accumulation
This happens EVEN without carbs!
Fasting Raises Blood Sugar (Cortisol Effect)
This is the sneaky part.
Cortisol:
- raises blood glucose
- increases gluconeogenesis
- reduces insulin sensitivity in muscles
- reroutes energy to central fat stores
This means:
Fasting can cause higher glucose and lower insulin sensitivity…
despite eating a zero carb carnivore diet.
This cortisol-driven glucose instability tells the body again:
“Store more fat around the organs.”
For Women, This Is Magnified 2-5×
Especially during perimenopause/menopause, when:
- estrogen is lower (estrogen buffers cortisol)
- progesterone is lower (progesterone is calming)
- thyroid is more fragile
- muscle loss accelerates
- stress response is stronger
So fasting produces:
- bigger cortisol spikes
- faster thyroid suppression
- more muscle loss
- more visceral fat deposition
- worse blood sugar in the morning
This is why many zero carb carnivore women over 40 say:
“I gained weight or can’t lose fat on the Carnivore Diet.”
This isn’t fat from food, it’s stress induced fat storage and muscle loss caused by under eating, restricting protein and or fasting.
Why Fasting on Zero Carb Leads to Belly Fat Storage
– Zero carb metabolism already mimics fasting
– Removing protein triggers muscle breakdown
– Muscle breakdown triggers high cortisol
– High cortisol = increased visceral/belly fat storage
– Stress hormones raise blood sugar
– Slowed metabolism shifts body composition toward belly fat
– Women are far more sensitive to this pattern, especially 40+
Bottom Line
For people eating a zero carb carnivore diet:
Fasting isn’t a stronger version of the diet, it’s a stressor that cancels out many benefits.
In zero carb adapted metabolism, fasting and restriction often leads directly to belly fat storage through cortisol and muscle loss.
You can LOSE weight but GAIN belly fat because the composition shifts.
For more information about the Zero Carb Carnivore Diet join us in our Facebook Groups : Zero Carb Health and Zeroing in on Health.
