What does that even mean, not eating vitamins for a day? They’re kinda hard to avoid. Are you talking about skipping a multivitamin or something?

I haven’t heard that such direct vitamin sensing is a thing. At most I’ve heard of people getting appropriate cravings when they lack a vitamin, and I’m not even sure whether that’s just anecdotal or an actual effect. Which vitamin do you think you’re sensing after just one day?

I would bet that whatever you’re experiencing is either

• due to different food choices altogether, like eating less fruit and vegetables or more junk food. That can definitely be noticeble to the GI-tract, due to different fiber and fat content.
• essentially an example of the placebo effect, and would fail to appear if you didn’t know that you took placebos instead of your vitamin supplements.