Heating honey to high temperatures (above 60°C or 140°F) can lead to the formation of 5-Hydroxymethylfurfural (HMF), nutritionist Dr Priyanka Shukla told Indian Express. In large amounts, HMF may have toxic effects, and heating also destroys the beneficial enzymes, antioxidants, and bioactive compounds in honey, she said. However, she added that gentle warming, below 40°C, is safe.