Salt, water, and why week one feels rough

15 October 2026 · lifestyle, not a protocol

Plenty of people start carnivore or a long fast, feel flat and headachy by day three, and quit before the good part. A lot of that early drag is likely salt and water, not willpower.

What's going on

When insulin drops, from eating very low carb or from fasting, the kidneys let go of more sodium and water. That's long-described physiology. It's strongest in the first days and tends to settle over roughly the first couple of weeks. The common complaints (headache, tiredness, dizziness, cramps) fit that picture.

What the research is starting to show

A 2025 scoping review of "keto flu" literature found the studies are mixed in quality and mostly observational. It pointed to sodium and fluid shifts as the likely mechanism, but it also noted that no clinical trials have proven electrolyte supplements prevent the symptoms, and no trial-proven daily salt number exists. The 3 to 5 grams you see quoted online is a practice habit, not a tested standard.

So there's no magic electrolyte mix. Salted food and broth are a reasonable, low-cost thing to try first.

Where exercise fits

Belly fat responds best to steady movement over weeks, so the goal in week one is staying able to walk. If you're lightheaded or achy, a short walk after a cup of salted broth beats skipping movement for days. Keep it easy until the first week or two passes, then build.

A simple way to try it

• Salt your food to taste. Most people want more than they used to.
• Sip warm salted bone broth on fasting days or when you stand up and feel woozy.
• Zero-sugar ferments like kraut, pickles, and olives add a little sodium too.
• Food first for potassium and magnesium, and skip megadoses.

If you take blood pressure meds, a diuretic, or have heart or kidney issues, salt and fluid changes matter more for you. Talk with your prescriber before changing either. And get checked quickly for fainting, a racing or uneven heartbeat, or confusion.

Sources

• 2025 scoping review on keto-induction symptoms (PMC)
• Diet Doctor, starting low carb with high blood pressure