With Covid testing in England (not sure about Wales, Scotland and Northern Ireland) the free lateral flow kits have been in 2 forms.
The first DHSC kits
DHSC (Department of Health and Social Care) home lateral flow testing kits require both throat and nasal swabbing (see this instruction booklet PDF).
The new kits
For a while now, they changed the free kits to ACON Flowflex.
These only require nasal swabbing (see this instruction booklet PDF)
Both sets of instructions state that you must not eat or drink 30 minutes prior to conducting the test (Page 3 of both instruction booklets).
I can understand the possibility that eating or drinking before or during the test could affect the results if throat swabbing, but I can't find anything online why it would affect nasal swabbing.
How would eating or drinking affect the new nasal swab only testing?