Heat damage has detrimental impacts on food and its nutrients when they are cooked or processed at temperatures above 46°C (115°F), which is enough heat to damage human skin as well as the heat-sensitive nutrients in food.
Cooking can result in the following health damaging issues:
- Carcinogenic or potentially carcinogenic compounds: High-temperature cooking can produce heterocyclic amines (HCAs) and polycyclic aromatic hydrocarbons (PAHs), particularly when meat is grilled, charred, or exposed to smoke.
- Acrylamide can form when carbohydrate-rich foods such as potatoes, bread, and cereals are heated at high temperatures, especially during frying, roasting, and baking.
- Advanced glycation end products (AGEs): High temperature Dry-heat cooking methods such as frying, grilling, and roasting tend to produce more AGEs than moist-heat cooking methods.
- Loss of nutrients: Heat can destroy or reduce some heat-sensitive nutrients including:
The extent of the nutrient loss depends heavily on the food and cooking method.
- Oxidation of fats: High temperatures—particularly prolonged heating or repeatedly heating oil—can cause fats to oxidize and form various degradation products.
- Loss of beneficial compounds: Some antioxidants and phytochemicals can decrease with cooking.
- Formation of smoke/irritants: Burning food, fat, or cooking oil can produce irritating compounds and particulate matter that are undesirable to inhale.
- Formation of undesirable compounds from processed foods: Certain cooking conditions can promote formation of compounds such as nitrosamines, particularly in foods containing nitrites/nitrates.
- Production of health damaging substances including tumorigens, mutagens and antinutrients.
Factors that affect the degree of heat damage caused by cooking include:
- Temperature
Higher temperatures generally increase thermal degradation and oxidation.
- Time
Longer exposure generally increases degradation.
- Water exposure
Increases leaching of water-soluble compounds.
- Oxygen exposure
Promotes oxidation.
- Surface area
Cutting food into smaller pieces increases the area exposed to heat, water and oxygen.
- Water-to-food ratio
More cooking water can increase the opportunity for nutrient leaching.
- Oil/fat temperature
Higher temperatures accelerate oxidation and thermal degradation of fats.
- Type of food
Different nutrients have very different sensitivities to heat, water and oxygen.
- Type of nutrient
When heated, vitamin C behaves very differently from minerals, protein, starch, etc.
- Degree of browning
Increasingly intense browning indicates increasingly severe thermal reactions.
- Charring
Represents particularly intense heating and should be distinguished from less strong browning.
- Repeated heating/reheating
Can compound some degradation and oxidation processes.
- Whether cooking liquid is consumed
Determines whether leached nutrients are also lost from the meal.
- Whether the food is subsequently cooled
Particularly important for starch and resistant starch formation.