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If you have hypothyroidism or Hashimoto's, you've been strict on carnivore for six or eight weeks, and the scale has barely moved, here's the short answer: you probably didn't fail the diet. Your body is running on a slower thermostat, and a slower thermostat means slower loss. Most women I've talked to in this spot are also eating too little, which makes the problem worse rather than better.
Weight loss on carnivore with a treated thyroid usually still happens. It just tends to show up later, in smaller weekly amounts, and often in inches before pounds. So before you decide meat and eggs don't work for you, it's worth checking three things: whether your thyroid is actually well treated right now, whether you're eating enough to let your body spend energy, and whether the scale is even the right thing to watch.
Why a hypothyroid body loses slower
Thyroid hormone sets the pace for how much energy your body burns at rest. When thyroid function drops, resting energy expenditure drops with it. Treatment brings that back up, and research on treated hypothyroidism shows resting energy use rising as hormone levels normalize.
Here's the part that frustrates people. Your TSH can sit in the normal range while you still feel cold, tired, and puffy. Normal on paper and optimal for you aren't always the same number, and that gap is a conversation for your doctor, not a forum. Research shows general patterns. Your body may respond differently based on your own history and how long you were undertreated.
Add menopause on top, which is where a lot of our readers are, and you've got two things at once: less estrogen changing where fat sits, and a thyroid that needs steady management. That combination isn't a personal failing. It's just a slower runway.
What happens to T3 when you undereat for months
Most of what your thyroid makes is T4, which is mostly inactive. Your body converts T4 into T3, the form that actually does the work in your cells. That conversion isn't fixed. It responds to how much energy you're taking in.
When you eat well below what you need for a long stretch, your body reads that as scarcity and dials conversion down. Less T4 becomes T3, and more of it becomes reverse T3, which is basically an inactive placeholder. This is a normal, protective response. Your body isn't broken, it's being careful.
So the woman who's eating one small meal a day, skipping fat because she's afraid of it, and doing an hour of cardio, ends up in the worst spot. She's given her body every reason to conserve. Then when nothing moves, the instinct is to eat even less. That's the loop I'd most like to break.
Eating enough is the lever most people won't pull
Here's what I've seen work. Eat protein to satisfaction at every meal, don't fear the fat that comes attached to it, and stop stacking long fasts on top of an already low intake. Give it twelve weeks, not two.
That doesn't mean eating without limits. It means hitting a real protein target and letting appetite regulate the rest, instead of white-knuckling a number you picked out of the air. If you have no idea what "enough" looks like for your height, age, and activity, the free macro calculator at /calculator.html gives you a starting point to check yourself against. Some women find it reassuring to see they've been eating far less than they assumed.
One more piece worth knowing: levothyroxine absorbs best on an empty stomach, and calcium, iron, and coffee can interfere with it. If your routine on carnivore changed when you started, say you moved your first meal earlier or added a supplement, that's worth mentioning at your next appointment.
The labs to ask for before blaming the diet
A lone TSH doesn't tell you much when you feel awful. Here's what's reasonable to ask for:
- TSH, free T4, and free T3. Free T3 is the one that often gets skipped, and it's the one that tells you about conversion.
- TPO and thyroglobulin antibodies. If nobody's ever checked, this tells you whether Hashimoto's is in the picture at all.
- Ferritin, B12, and vitamin D. Low iron is very common in women over 45 and causes the exact fatigue people blame on thyroid.
- Fasting insulin and A1c. Insulin resistance and thyroid problems travel together more often than people realize.
Two practical notes. Get labs drawn fasted, at a similar time of day each time, and before you take that morning's dose, since taking it first can push free T4 up temporarily. And use the same lab when you can, because reference ranges vary between them.
Reverse T3 gets talked about a lot online. It's real, but most endocrinologists don't use it to guide dosing, so don't be surprised or offended if yours declines to run it.
About medication, iodine, and the internet
If you lose a meaningful amount of weight, your levothyroxine dose may genuinely need adjusting, because dosing partly tracks body weight. That's a good problem. It's also entirely your doctor's call, based on your labs and your symptoms, not something to work out from a comment thread.
Same goes for iodine. Carnivore eaters often drop both dairy and iodized salt without noticing, and those were two common sources. But high-dose iodine can make autoimmune thyroid disease worse, so this is a question to raise with your doctor, not a supplement to grab on your own.
Measure something other than the scale
Scale weight in perimenopause and menopause bounces for reasons that have nothing to do with fat. Water shifts, sodium, sleep, and stress can hide four to six weeks of real progress.
Track your waist at the navel once a month. Notice how your rings and waistbands feel. Watch whether joint stiffness eased, whether you stopped needing an afternoon nap, whether your blood pressure came down. Those changes are usually the first honest signal that things are working, and they show up well before the scale agrees.
If twelve weeks of eating enough, sleeping decently, and walking most days still shows nothing anywhere, that's your cue to go back for labs. Not your cue to eat less.
I'm not a doctor. I've researched this deeply and worked with many people, but I'm not your doctor. Thyroid medication dosing is a medical decision that belongs to you and your physician, based on your labs and your symptoms. Never change, split, skip, or stop a dose based on something you read online, including this. If you take medication or have a diagnosed condition like Hashimoto's, any dietary change deserves your doctor's input, and your situation might be different from what's described here.