Lipids – or fat – types and functions

Lipids concept mapLipids – or fat as most people call them – have a bad rep and people who diet try to stick to “fat free” diets. It may work in the short term, but we do need some fats. Fat is needed to store energy and also to digest fat soluble vitamins. So, which ones should we eat and which ones should we avoid?

The difference between lipids and fat
Lipids and fat are a bit different, and also different depending on who you ask. A chemist would say lipds there are 4 types of lipids: Fatty acids, Triglycerides, Phospholipids and Sterols. Chemist also further separate lipids into fats and oils like this:

  • Fats are solid at room temperature
  • Oils are liquid at room temperature

From a nutritional perspective, lipids are the same, but fat are Fatty Acids, Triglycerides and Phospholipids that contain 9 kcal / g.

Take olive oil as an example. A chemist call it an oil. because it is fluid at room temperature and a nutritionist call it a fat because it contains 9 kcal / g.

Lipid 1: Fatty acids
The fatty acids that have methyl in one end called omega acid, which is where the naming “acid” comes from.

Fatty acids in nature that we eat differ from each other in three ways:

  1. Carbon chain length (they could have for example 6 carbons or 18 carbons)
  2. Saturation: They can be saturated or unsaturated.
  3. Double bonds. None or several double bonds.

The fatty acids have carbon chains from 4 to 24 in length. They also contain hydrogen and some oxygen.
Classification depend on the number of carbons: They chain length is dependent on the number of carbons, and the names too:

  • Short-Chain Fatty Acid < 6 carbons
  • Medium-Chain Fatty Acid 6-10 carbons
  • Long-Chain Fatty Acid ≥12 carbons

This is important, because carbon chain length impacts the melting point. A shorter chain fatty acid, like an oil, is more likely to be liquid, and a longer chain fatty acid, like butter, is more likely to be solid at room temperature.

Monounsaturated fats have lost 2 hydrogen atoms an have instead ONE double bond. Fatty acids with more than one double bond are called polyunsaturated acids. This is important, because it is how we define saturated and unsaturated fats.

Saturation
Fatty acids are grouped by how saturated they are:
Saturated fatty acid have no double bonds at all.
Monounsaturated fatty acids (abbreviated MUFA) have one double bond.
Polyunsaturated fatty acids (abbreviated PUFA) have two or more double bonds.

A more saturated fat will be more solid – like butter. A less saturated is often fluid at room temperature – like oil. The less saturated fats are more prone to oxidation and becoming rancid which is why oil is sometimes processed into trans-fats, this will also give them a harder texture. The structure of the unsaturated fat changes during the process and if the oils are completely hardened the unsaturated fatty acids will turn into saturated fatty acids. Most of the time some unsaturated fatty acids are left, and the rest turn into trans fats called “partly hardened fats”, one example is margarine. Trans fats are often used in biscuits and deep fried food. Over consumption of transfats is thought to be bad for your health and especially your heart.

Non essential fatty acids
Saturated and Monosaturated (for example omega 9) are not essential since we can make them in the body.

Essential fatty acids
Essential fatty acids are acids the body can’t synthesize – or make – and need to be included in the diet – they have to be eaten. Omega 3 (Alpha-linolenic Acid) and Omega 6 (Linoleic Acid) are essential.

Omega 3
Why is it called omega 3? It’s not only the number of double bonds that determine what kind of fat it is, but also where in the chain the first carbon atom is placed. Counting from one end until you come across the first double bond, you’ll know the name of the fatty acid. If the first double bond starts with the third carbon atom, the fatty acid is called omega-3. If it start with the 6th it’s called omega-6.

Omega 3 has been credited with a lot of health benefits, for example to:

  • Prevent inflammatory and autoimmune diseases
  • Prevent cardiovascular disease
  • Prevent metabolic syndrome
  • Maintaining eye health
  • Prevent cancer

As a vegetarian it is important to try to get enough omega 3 and 6. The plant based omega 3 is unfortunately not as good as the omega 3 that comes from fatty fish such as salmon. But, there are sources for omega 3 even for vegetarians: Flax seeds, walnuts, canola oil and egg. Good sources for omega 6 for vegetarians are vegetable oils, nuts and seeds.

Lipid 2: Triglycerides
Triglycerides are a good source of energy. They contain 9 calories per g making them an effective source of energy. An over intake will be stored in the body and too much will of course lead to being overweight.

Lipid 3: Phospholipids
One of the phospholipids contains Lecithin, which helps building up the membranes of cells, making the membranes easer to transport. Phospholipids also store fatty acids, such as EPA, important for the immune system, blood pressure and a lot of other stuff. Fish and meat contains AA, EPA and DHA, but a vegetarian diet is very low in these. It’s not a problem since the body can make them from omega 3 and omega 6 – so again, make sure you get omega 3 and omega 6 in your diet. Rapeseed oil contains both omega 3 and 6 and the ratio between them is good, making it a good choice for vegetarians.

Lipid 4: Sterols
Cholesterol is probably something most people have heard of and it is a sterol. So how does good and bad cholesterol work?

Lipids have hydrophobic (fear of water) properties. If you put oil in a glass of water it will float on the surface, that is because fatty acids are not water soluble, so to transport them in the blood a substance called lipoprotein is needed.

LDLLow Density Lipoprotein – carry cholesterol molecules from the liver to the cells. It is often called bad cholesterol because an excess can build up plaque in the system, clogging the arteries, and if an artery gets blocked it can cause heart disease. The easy way to remembember is that the L=lethal.

HDLHigh Density Lipoprotein – is usually called good cholesterol because it takes unused cholesterol back from the cells to the liver. The way to remember this is that H=healthy.

The ratio of LDL and HDL is important. It’s not good to have too much LDL. A 5/1 ratio is often recommended. Stone age diets are thought to contain a ratio as low as 2/1. Western diets are often of a ratio of 10/1.
It is important to replace the saturated fatty acids and monosaturated fatty acids with Omega 3, not add that as well. Then the fat content of the diet will be too high.

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