This is a VERY vast field and really cannot be summarised into a few sentences, but a brief introduction/ categorization of food may be into:
- 5 Flavours: sweet, acrid, salty, sour, bitter; each flavour has a certain function within the body
- 4 Qi (energetic movements): upwards, downwards, inwards, outwards
- 5 Thermal Natures: Cold, cool, neutral, warm, hot; attention: this is not the physical temperature, but the energetic temperature
- Meridian Affiliation: each food is linked to one or several acupuncture channels; Spleen, Stomach, Lungs, Liver etc
So, for example:
Green onions: Acrid, upwards, warm, Lungs/ Stomach => beneficial for head colds and abdominal pain from Cold
Lemon: Sour, downwards, cold, Stomach/ Liver/ Lungs => Beneficial for nausea/ belching, agitation, sinusitis