What the texts say
Vagbhata lists reheated food with food that has grass or hair in it, meals made mostly of vegetables and poor grains, and food too hot or too salty. Sushruta's reason is taste: food cooked long before, gone hard and cold, then heated again, does not taste as it should.[1][2]
The modern view
We have not found a study that tests the rule itself. One adjacent controlled trial gave 32 people with type 1 diabetes white rice freshly cooked on one day, and rice cooled for 24 hours at 4 C and then reheated on another. The cooled rice raised blood sugar less, because cooling turns some starch into a form the gut does not absorb (resistant starch). Using a standard insulin dose, 12 of the 32 had low blood sugar afterwards, against 3 after fresh rice. That is an effect of cooling on starch, not evidence that reheating harms food. If you take insulin, it is worth mentioning to your doctor.[3]
From the classical texts
Questions people ask
Does this mean food heated in a microwave?
Vagbhata's phrase is ushnikritam punah, 'made hot again', so it is the second heating that he counts.[1]
Related
Stale makoy (kakamachi)
Charaka lists makoy (kakamachi) kept overnight among incompatible foods. Vagbhata also bars it cooked in a pot used for fish or ginger.
FoodBurnt food (jala hua khana)
Charaka lists burnt food as incompatible in cooking (paka viruddha), in the same line as undercooked rice and food cooked over poor fuel.
FoodUndercooked rice
Charaka counts undercooked rice, like overcooked or burnt food, as wrongly cooked: paka viruddha, incompatible by cooking.
Sources
- Ashtanga Hridaya, Sutra Sthana 8.39, GRETIL e-text.
- Sushruta Samhita, Sutra Sthana 46.477-478 (Annapanavidhi Adhyaya), NIIMH e-Sushruta edition.
- Strozyk S, Rogowicz-Frontczak A, Pilacinski S, LeThanh-Blicharz J, Koperska A, Zozulinska-Ziolkiewicz D. Influence of resistant starch resulting from the cooling of rice on postprandial glycemia in type 1 diabetes. Nutrition & Diabetes. 2022;12:21. PMID 35429987.
Updated 4 November 2026