The discussion on oils and health can be relatively confusing.

Trans-fats, unsaturated, poly-unsaturated, saturated, smoking points all have aspects that are linked to in the use of oils and the health debate. Trans-fats are currently seen as an unhealthy fat.  They increase the risk of coronary heart disease by raising the levels of LDL and lowering HDL cholesterol. This proportion of HDL/LDL cholesterol is an indicator of risk, The higher the ratio the lower the risk.

The next part of the issue is that related to unsaturated fats and saturated fats. Specific cooking or edible oils fit into this classification. Oils with lower amounts of saturated fats seem to be healthier than those oils high in saturated fats.  Coconut oil and Palm oil are high in saturated fats. Olive oil, peanut oil, canola oil, avocado, safflower, corn, sunflower, soy, mustard and cottonseed oils are lower in saturated fats and higher in unsaturated fats, so are believed to be healthier but only when they have not been used for cooking.

Deep frying with oils.

When oils are heated the unsaturated fats can become oxidised and this leads to a risk of heart disease and artherosclerosis. It's also understood that oils with higher smoking points are safer for cooking and the smoking point is related to the ease of oxidation.

It is recommended to use a quality thermometer to measure the temperature of hot oils. Other methods are simply not accurate.

The oils which have higher smoke points and are believed to be safer for cooking at high heats above 230 °C/446 °F
  • Avocado oil
  • Corn oil
  • Mustard oil
  • Palm oil
  • Peanut oil (marketed as "groundnut oil" in the UK)
  • Rice bran oil
  • Safflower oil
  • Sesame oil (semi-refined)
  • Soybean oil
  • Sunflower oil

And these are oils that are suitable for cooking when used at temperatures of around 190ºC(374F).
  • Almond oil
  • Rapeseed oil (marketed Canola oil or, sometimes, simply "vegetable oil" in the UK)
  • Ghee, Clarified butter
  • Cottonseed oil
  • Grape seed oil
  • Lard
  • Diacylglycerol (DAG) oil
  • Olive oil (Virgin, and refined)
  • Walnut oil
  • Mustard oil

Unrefined cooking oils should not be used for frying.

Keeping oils for the kitchen.

All cooking oils are sensitive to heat, light and air(oxygen).  An easy way to protect oils from light is to store them in a cupboard and preferably refrigerated.  Purchase only a couple of months supply at a time.  Some oils have longer safe shelf lives than others, Olive Oil and EVOO have safe storage times of 9 months after opening .

Disposing of "spent" oils

This can be a little bit of a problem for people in various communities. Firstly don't dispose of the oils in sinks and toilets as this can cause havoc by blocking the systems. Don't discard it into storm drains as the oil can cover vast areas of water and prevent oxygen absorption into the water.

It should be discarded in your garbage collection sealed in bottles or recycled in oil bins if supplied within your community. There is a market for recycled oils being bio-fuels and soaps.