Metabolic Syndrome and Fat Metabolism

This post is basically what it says in the title: an overview of metabolic syndrome and fat metabolism!

Metabolic Syndrome

1. What is metabolic syndrome?

Metabolic syndrome is a group of conditions associated with the development of cardiovascular disease and diabetes.

2. What are the risk factors used to define metabolic syndome?

Metabolic syndrome is defined as having central obesity, as well as at least two of the following four factors:

1. Raised triglyceride level or specific treatment for this abnormality
2. Reduced HDL levels or specific treatment for this abnormality
3. Raised blood pressure or previously diagnosed hypertension
4. Raised fasting plasma glucose (FPG) or previously diagnosed type 2 diabetes

3. What are the key lifestyle diseases associated with metabolic syndrome?

The key lifestyle diseases associated with metabolic syndrome are type 2 diabetes and atherosclerosis (as well as diseases that often result from atherosclerosis, such as coronary heart disease, heart attack and stroke).

4. Which groups are likely to have metabolic syndrome?

People with obesity, insulin resistance or reduced physical activity are the most likely to have metabolic syndrome.

Dietary Fat

1. Why is fat required in the diet?

Fat is required in the diet in order to make cell and organelle membranes, steroid hormones, bile salts and so on. They are also required in order to transport fat-soluble vitamins (A, D, E and K) as well as carotenoids. Aside from these functions, fatty acids are a good source of energy. Our body can manufacture many fatty acids, but there are two that we must take in our diet (and are thus known as "essential fatty acids"). These are linoleic acid and α-linolenic acid.

2. How are fatty acids metabolised?

There are several different metabolic pathways for fatty acids in the liver:

1. Can be stored as fat
2. Can be broken down to Acetyl-CoA via the process of beta-oxidation (see here for more details). Acetyl-CoA can then help out in two main ways:
1. Conversion into cholesterol, which can become incorporated in cell membranes. Cholesterol can also be broken down to form bile salts or steroid hormones.
2. Entrance into the citric acid cycle, which ultimately results in the production of ATP.

3. What are the different types of fats?

The different types of fats include:

• saturated fats (SFA), which contain only single C-C bonds;
• monounsaturated fats (MUFA), which contain one double C=C bond (all other C-C bonds are single);
• polyunsaturated fats (PUFA), which contain multiple double C=C bonds;
• trans fats, which are essentially MUFAs or PUFAs in which the double bonds are in the trans- (rather than cis-) conformation); and
• cholesterol, which has a characteristic four-ring structure

4. Describe the terminology for fatty acids.

The terminology for fatty acids was discussed in a post for CHEM1004. (Yup, first-year stuff is still relevant.)

5. Describe the differences in quality between different fats. What are the benefits of unsaturated fatty acids?

Not all fats are created equal. The different fats have different effects on our health:

• Saturated fatty acids (SFA), found in animal fats, coconut oil, palm oil and other places, tend to be cholesterol-raising. They also form solids more easily (as I'll explain in a bit), allowing them to clog up arteries and so forth. It is generally advised that you keep your saturated fat intake to 10% of your total calories or less.
• Monounsaturated fatty acids (MUFA), such as oleic acid, decrease blood cholesterol levels.
• Polyunsaturated fats (PUFA) include linoleic acid and α-linolenic acid which, as I said above, are essential fatty acids (i.e. they can't be made by the body). Polyunsaturated fats also include omega-6 and omega-3 fatty acids, which weren't covered in any more detail in this lecture, but are often touted as being beneficial to your health.
• Trans fats, as I'll explain below, are somewhat similar to saturated fats in that they can easily form solids. The advantage of this is that solids are easier to transport and are more resistant to spoilage, but the obvious disadvantages lie in what they do to your arteries.
• Cholesterol is an essential part of cell membranes, as well as a precursor for steroid hormones and bile acids. There is no evidence for a particular dietary requirement surrounding cholesterol, as our body makes quite a bit of it anyway. In the past, people were advised to avoid dietary cholesterol; however, now we know that dietary cholesterol is really a drop in the bucket compared to the cholesterol that our bodies make. As such, you don't need to be too concerned about overconsumption.

6. Why are saturated fats solid at room temperature?

Saturated fatty acids tend to be more linear (as opposed to cis-unsaturated fatty acids, which have "kinks" in them due to the double bond). This linear conformation allows the molecules to get closer together, which helps them solidify.

Note that trans fats, despite having double bonds, are also somewhat linear (the trans configuration doesn't create a "kink"). This means that trans fats often have somewhat similar properties to saturated fats.