During commercial food processing, fats sometimes undergo the process of hydrogenation, where the structure of the fat becomes “hardened.” Almost all margarines and all products, that list fats or oils in their ingredient list contain hydrogenated fats.

 Hydrogenation allows manufacturers to start with cheap, low-quality oils, and to

 turn these into products that compete with butter in texture. The low cost of raw

 materials allows margarine to be sold at a much lower price than butter.

 Hydrogenation turns fats into trans-fats. Trans- fatty acids have been shown to increase cholesterol, decrease beneficial

 high-density lipoprotein (HDL), interfere with the liver's detoxification system,

 and interfere with Essential Fatty Acid function.

     Hydrogenation is the most common way of drastically changing natural

 oils. This process has major effects on health. Industry's reason for using the

 process is to provide cheap spreadable products for consumers, or to provide shelf

 stability at the expense of nutritional value.

    Hydrogenation changes the unsaturated and essential fatty acids present in a

 natural oil. In this process, oils are reacted under pressure with hydrogen gas at

 high temperature (248 to 410 F) in the presence of a metal catalyst

 (usually nickel, a confirmed carcinogen,) but sometimes platinum or even copper)

 for 6 to 8 hours. A "nickel" catalyst often used in hydrogenation, called "Rayney's

 Nickel", is actually 50% nickel and 50% aluminum. Remnants of both metals

 remain in products containing hydrogenated or partially hydrogenated oils, and 

are eaten by people. The presence of aluminum is particularly worrisome, because

 its presence in the human body is associated with Alzheimer's disease and

 osteoporosis, and can contribute to cancer.

   The problem is that many oils begin to oxidize and therefore turn into trans-fats even before they are put into the commercial fryer to make French fries. Refined vegetable oils, sold in clear bottles, react with light and begin to turn rancid already on the shelf of your supermarket. Using butter, coconut oil and pure extra virgin organic olive oil and sesame oil, sold in dark bottles will help you to limit your trans-fat intake. Avoiding all processed foods will help you even more. The following is a table of smoke point of different oils.Once a fat starts to smoke, it usually will emit a harsh smell and fill the air with smoke. Fats that have gone past their smoke points contain a large quantity of free radicals and become carcinogenic, so it's a good idea to cook with oils, which have a high smoke point.

Fat	Smoke Point °F	Smoke Point °C
Unrefined canola oil	225°F	107°C
Unrefined flaxseed oil	225°F	107°C
Unrefined safflower oil	225°F	107°C
Unrefined sunflower oil	225°F	107°C
Unrefined corn oil	320°F	160°C
Unrefined high-oleic sunflower oil	320°F	160°C
Extra virgin olive oil	320°F	160°C
Unrefined peanut oil	320°F	160°C
Semirefined safflower oil	320°F	160°C
Unrefined soy oil	320°F	160°C
Unrefined walnut oil	320°F	160°C
Hemp seed oil	330°F	165°C
Butter	350°F	177°C
Semirefined canola oil	350°F	177°C
Coconut oil	350°F	177°C
Unrefined sesame oil	350°F	177°C
Semirefined soy oil	350°F	177°C
Vegetable shortening	360°F	182°C
Lard	370°F	182°C
Macadamia nut oil	390°F	199°C
Refined canola oil	400°F	204°C
Semirefined walnut oil	400°F	204°C
High quality (low acidity) extra virgin olive oil	405°F	207°C
Sesame oil	410°F	210°C
Cottonseed oil	420°F	216°C
Grapeseed oil	420°F	216°C
Virgin olive oil	420°F	216°C
Almond oil	420°F	216°C
Hazelnut oil	430°F	221°C
Peanut oil	440°F	227°C
Sunflower oil	440°F	227°C
Refined corn oil	450°F	232°C