What are fats?

This subpage on fats belongs to Biotech Academy’s primary school project The Body and the Diet

 

 

Triglyceride

Triglycerides are the most common fats. They consist of one glycerol molecule and three fatty acids (Figure 1).

Figure

1
. A triglyceride consists of a glycerol molecule and three fatty acids

The fatty acids on the glycerol molecule can have different structures and depending on their structure, the fatty acids are divided into:

• Saturated fatty acids
• Monounsaturated fatty acids
• Polyunsaturated fatty acid

Figure 2. Fatty acids can be divided into saturated and unsaturated fatty acids. Unsaturated is further divided into monounsaturated and polyunsaturated fatty acids.

A fatty acid consists of a carbon chain to which an acid group is attached at the end. These groups can vary in length, and the smallest have three carbon atoms, while the longest have 22 carbon atoms. Fatty acids with between four and seven carbon atoms are called short-chain fatty acids. Carbon chains containing between eight and ten carbon atoms are called medium-chain fatty acids, while chains containing ten or more carbon atoms are referred to as long-chain fatty acids.

Fatty acids

Saturated fatty acids

A saturated fatty acid contains no double bonds between the carbon atoms. The magnifying glass in Figure 3 shows what “a thank you” looks like in a saturated fatty acid.

If a fat contains a large amount of saturated fatty acids, the fat will be solid at room temperature. Butter is an example of a fat high in saturated fatty acids. Studies have shown that a high intake of saturated fatty acids can increase the risk of developing diabetes and cardiovascular disease.

Cis / Trans fatty acids

Fatty acids may contain double bonds in their chemical structure. Depending on how the double bond sits, either cis or trans fatty acids are referred to.

Trans fats belong to unsaturated fatty acids as they contain one or more double bonds, but due to the location of the double bonds, the trans fatty acids are both physically and chemically similar to saturated fatty acids. They are firmer at room temperature and have a longer shelf life. Cis fatty acids have a lower melting point than trans fatty acids, so they are more often in liquid form at room temperature. Studies have shown that trans fats can increase the risk of developing cardiovascular disease as much as 10 times.

Trans fats are found naturally in, for example, beef, but the content is very low and therefore does not harm the body. They can also be formed industrially, for example by heating oils at very high temperatures over a long period of time.

Monounsaturated fatty acids

As the name suggests, monounsaturated fatty acids contain one double bond between two carbon atoms, as Figure 4 shows.

 

Figure 4. Monounsaturated fatty acids contain one double bond. The magnifying glass shows what the carbon chain looks like with a double bond. The side chain (R) varies depending on where on the fatty acid the sample is taken from. Monounsaturated fatty acids originate primarily from plants and are found, among other things, in avocados.

Figure 5. Polyunsaturated fatty acids contain two or more double bonds. Fatty fish such as mackerel and salmon are rich in polyunsaturated fatty acids.

At room temperature, fats with monounsaturated fatty acids are liquid and only become more solid when they get just below the freezing point of water. Foods containing monounsaturated fatty acids may help prevent diabetes and cardiovascular disease.

Polyunsaturated fatty acids

If fatty acids contain two or more double bonds, they are referred to as polyunsaturated fatty acids. An example of a polyunsaturated fatty acid is shown in Figure 5.

Cholesterol

As mentioned, the cell membrane is made up of lipids, and cholesterol is part of them.

The body itself is able to form cholesterol from fatty acids and glucose, among other things, but it is a complicated process that is not discussed here. Cholesterol also ensures that vitamin D and various hormones are formed. Cholesterol is obtained through the food you eat, but makes up only a small part. Some people have problems with their cholesterol levels and they need to think about their eating habits. As mentioned earlier, an elevated cholesterol level can cause cardiovascular diseases.

 

Digestion and absorption of fats

In order for the body to benefit from the fats, they must first be broken down. But the breakdown is more complicated than with the other nutrients. Fat cannot be dissolved in water, and this is a problem, as the blood’s largest component is water. The blood contains approximately 55% plasma, which is the fluid that contains water. If you have tried mixing oil and water, you will see that it cannot be done. Fat must therefore go through several processes before the blood can absorb it. Figure 6 shows the digestion of fat.

The liver produces bile, which is transported to the gallbladder. The gallbladder secretes bile acid and bile salts, which via the bile duct enter the duodenum. The bile salts emulsify the fat, that is, the fat splits into even smaller fat droplets. In the small intestine, the intestinal contents are mixed with the enzyme, lipase. The pancreas produces this enzyme that breaks down the triglycerides into glycerol and three free fatty acids.

Because glycerol and short-chain fatty acids are soluble in water, it is no problem to absorb these. However, the long-chain fatty acids need the help of bile acid. When bile acid surrounds the long-chain fatty acids, they are converted into micelles. Micelles are very small and water-soluble particles and this means that they can be transported more easily across the intestinal mucosa.

The intestinal mucosa contains intestinal cells. Inside the intestinal cells, glycerol and fatty acids are again bound together to form triglycerides. But, as mentioned, triglycerides are fat-soluble. This means that the body once again needs help in order to absorb triglycerides. The helpers are called kylomicrons. Before entering the bloodstream, they must first pass through so-called lymphatic vessels. The release of kylomicrons into the bloodstream can occur as long as 14 hours after a high-fat meal.

Unlike glucose and amino acids, triglycerides do not pass through the liver before they are released into the blood.

How much fat you should eat

According to the Nordic Nutrient Recommendations (published in 2012), 25-40% of your energy needs should be covered by fat. In addition, it is recommended:

• Cis-monounsaturated fatty acids should make up 10-20% of your energy intake.
• Cis polyunsaturated fatty acids should make up 5-10% of your energy intake, of which omega-3 fatty acids should make up at least 1%. Omega-6 fatty acids should make up at least 3%.
• Saturated fatty acids should make up no more than 10% of your energy intake.
• The intake of trans fatty acids should be kept as low as possible.

Like carbohydrates and proteins, fats also provide energy. However, you get over twice as much energy out of fat, as 1 gram provides 38 kJ (9.08 kcal).

 

Foods with fats

• Saturated fats are mainly found in animal fats, e.g. beef, butter and cheese.
• Monounsaturated fatty acids are found in, among other things, olive and rapeseed oil.
• Polyunsaturated fatty acids are found especially in fatty fish (salmon, mackerel, etc.).

 

 

Question:
Does beef or chicken contain the most saturated fat?

You can find the answer by clicking here!

Figure 6. The breakdown of fats (triglycerides) starts with an emulsification using bile salts. It splits the fat into smaller droplets. This means that lipase can break down triglyceride to glycerol as well as free fatty acid. In the intestinal cell are kylomicrons, which take care of capturing the glycerol molecule as well as the free fatty acids and restoring them to triglycerides. The kylomicrons are first transported into the lymph, from where the fat is released into the bloodstream when the body needs it.