keto flu
/ˈkiː.toʊ fluː/
CommonThe wave of fatigue, headaches, and brain fog that hits during the first week of a ketogenic diet.
Not an actual flu. It is a normal metabolic transition that passes in a few days, but it is unpleasant enough that many people quit keto during it.
Real-world examples4 examples
| # | Example | What it means | Source |
|---|---|---|---|
| 01 | day 3 of keto and the keto flu is destroying me rn | Currently experiencing the worst of the adjustment symptoms. | x, 2024 |
| 02 | push through the keto flu, it goes away after like day 5 | Encouraging someone to not quit because the symptoms are temporary. | |
| 03 | nobody told me about keto flu. i thought i was actually sick | The person was caught off guard by the symptoms. | tiktok, 2023 |
| 04 | drink electrolytes or the keto flu will eat you alive | Electrolyte supplementation helps reduce keto flu severity. |
Use it when
- Describing the initial rough adjustment when starting a ketogenic diet.
- Warning someone who is about to start keto what to expect.
- Explaining why you feel terrible even though you started eating 'healthy'.
Do not use it when
- You mean an actual viral illness that coincides with starting keto.
- You mean general fatigue from any diet change.
Origin and context
Coined within low-carb and ketogenic diet communities online, likely emerging in the early 2010s as keto became popular on Reddit and diet forums.
- First seen
- early-2010s
- Confidence
- medium
Cite this page
Use this stable URL to reference the entry.
https://slang.fyi/keto-fluUpdated: 2026-08-28License: CC BY 4.0