Fats, otherwise known as lipids, are insoluble of poorly-soluble substances. They can be classified into many different categories, many of which fit under the umbrella term “dietary fats”. The great majority (over 9 in 10) of these fats are either triacylglycerols or triglycerides. The remaining 10% include cholesterol.
Triacylglycerols are lipids containing three fatty acids connected to a glycerol molecule. Fatty acids vary in length, which is a hydrocarbon chain, and in the number of double bonds between carbon molecules. These variations are responsible for specific physical characteristics as well as their function. All triacylglycerols provide 9 kcal per gram, which makes fat the most concentrated source of energy. Fats should not be responsible for more than 35% of energy in the diet – no more than 70g daily for women or 90g for men.
Some of the foods that contain a lot of fat are cooking oils, fatty meats, and fried products. As such, they should be consumed in moderation. Whenever possible, food should be grilled instead of fried, so as to allow the fat to drip out, also, lean meats and low-fat dairy products should be chosen.
That said, some fatty acids are essential parts of good nutrition. fats have many functions:
1. They form cell membranes
2. They are important for the structure of many essential compounds, such as hormones, agents associated with blood clotting, and with immune/inflammatory responses.
3. Fats play an essential role in transporting fat soluble vitamins and antioxidants.
4. Fats provide insulation and protective layers for organs.
5. Fats take part in the construction of the nervous system and the brain.
6. Fats create a reserve energy supply – adipose tissue (a.k.a body fat).
Saturated fatty acids
Saturated fatty acids are called that because each carbon atom has the maximum number of hydrogen atoms linked to it (except the end carboxyl group). In saturated fatty acids carbon atoms have no double bonds. Since the molecules are straight, they can be very close to each other, and can thus be tightly packed – they are therefore solid at normal temperatures and have a high melting point.
Saturated fatty acids increase the cholesterol level, including the kind known as “bad cholesterol” (low-density lipoprotein). High levels of “bad cholesterol” lead to health problems, particularly cardiovascular disease. This happens because LDL cholesterol transports excess cholesterol through blood and it gathers on the walls of artheries and reduces the flow of blood to organs. In this condition a blood clot can cause a heart attack, and saturated fatty acids can be partially blamed for that as well – they increase the stickiness of blood, thus increasing it’s tendency to clot.
The recommended daily amount of saturated fatty acids is 22g for women and 28g for men, or 10% energy.
Monounsaturated fatty acids
Due to their structure, monounsaturated fatty acids (molecules are loosely placed), they are liquid at room temperature. The most concentrated sources of monosaturated fatty acids are olive oil and rapeseed oil, but can also be found in other products, such as eggs, meat fat, and nuts.
Monounsaturated fatty acids reduce the level of “bad cholesterol” and maintains the level of “good cholesterol” (high-density lipoprotein), which transfers cholesterol to body tissues where it is used to create hormons and other necessary substances. Approximately 15% energy should be gained from monounsaturated fatty acids.
Polyunsaturated fatty acids
Like monounsaturated fatty acids, due to their structure polyunsaturated fatty acids take the form of liquid at room temperature. Because they are susceptible to chemical changes, they lead to cell damage in the body. Polyunsaturated fatty acids have one fatty acid from which all other fatty acids can be made in the human body – these are not made by the body and are thus a necessary part of the diet. Of the essential fatty acids, 1% dietary energy should be obtained from linoleic acid and 0.2% from alpha-linoleic acid. They create longer chains of fatty acids, which are important in the making of hormones and other necessary substances. There is one essential fatty acid in each of these groups from which all other fatty acids can be made in the human body. These essential fatty acids cannot be made by the body and must be obtained from the diet. They are a necessary component of the diet; without them deficiency symptoms and poor health would result. Linoleic acid (omega-6) and alpha-linolenic acid (omega-3) are the essential fatty acids.
Linoleic acid can be found in vegetable oils, nuts, seeds, fruit, vegetables, and cereals. Alpha-linoleic acid is found in flaxseed or linseed oil, walnut oil, canola oil, and rapeseed oil. The best sources of long chain omega-3s are fish and fish oil.
Trans fatty acids
Due to their structure, trans fatty acids are semi-solid at room temperature. They are rarely found in nature, and are primarily the consequence of a food manufacture process called hydrogenation. There are significant health risks associated to the consumption of trans fatty acids, namely the fact that they raise levels of “bad cholesterol” and lower the levels of “good cholesterol. Trans fatty acids also increase blood triglyceride levels. This combination of effects is the perfect formula for cardiovascular disease. With that in mind, no more than 1% of dietary energy (2.5 grams a day) should be obtained from trans fatty acids.