While all fats, when consumed in excess, will contribute to weight gain, unsaturated varieties, when taken in moderation, help lower blood cholesterol levels as they replace harmful saturated fats.
Unsaturated fats stay liquid at room temperature. Some examples of food where these are found in high concentrations are olive, peanut, and canola oils, avocados, nuts like almonds, hazelnuts, and pumpkin and sesame seeds. These are examples of foods rich in a monounsaturated variety of these molecules.
The sources of polyunsaturated fatty acids in high concentration include sunflower, corn, soybean, flaxseed oils, walnuts, fish, and canola oil (this has both mono and polyunsaturated fatty acids). Omega 3 is unsaturated fat. While fish is a good source of this type of fatty acid it is also found in flax seeds, walnuts, canola oil, and soybean oil.
The American Heart Association suggests 8 to 10% of daily calories should come from polyunsaturated fats. The Mediterranean diet comprises an abundance of plant foods, fresh fruit, and olive oil as the principal source of fat, dairy products, fish, and poultry, and low in saturated fats (7-8%). The total fat of this food ranges between 25 to 35%. It is an example of healthy food (Willet et al., 1995).
A good diet should decrease saturated fat and reduce blood cholesterol by consuming more fruits, vegetables, whole grains, fish, and poultry and less red meat. This diet will protect the body from cardiovascular diseases (Krish-Etherton et al., 2001; Hu., 2003).
Monounsaturated fatty acids in plant oils like rapeseed or olive oil positively impact the blood lipid profile. These favorably influence the metabolism of diabetics too. Suppose the fatty acid composition of the diet is optimized. In that case, even a total dietary fat content of 35% of total energy intake (at the top end of the recommended energy intake from these molecules) continues to have a protective effect. In such cases, a higher level of physical activity is recommended. This diet is largely plant-based (Wahrburg, 2004).
When choosing the type of fat that we should consume in our diet, it is best to avoid trans-fatty acids or trans fats. Heating liquid vegetable oils make the trans variety in the presence of hydrogen gas and a catalyst. This process is called hydrogenation. Partial hydrogenation makes the oil more stable and less likely to turn rancid. Oil is converted into a solid and functions more like margarine or shortening.
Partially hydrogenated oils can withstand repeated heating. These do not break down and so are ideal for frying fast foods. Trans fats are also found naturally in beef fat and dairy fat. Trans fats raise bad cholesterol and lower good cholesterol. These are particularly bad for the heart and blood vessels and generally are bad for our health.