Blood lipids are fats in the blood. They can be tested for with a blood test. A blood lipid test typically gives levels for triglycerides, HDL-cholesterol, LDL-cholesterol, and total cholesterol. It is only triglycerides and HDL-cholesterol that can give an indication of insulin resistance.
What is it?
Triglycerides are a type of fat in the blood. They are essential for the body and are a main source of fuel.
Triglycerides come directly from food, and they are also made in our body, especially by our liver. The liver turns any excess sugar into triglycerides.
The main storage location of triglycerides is in our fat (adipose) tissue.
There should only be a small amount of triglyceride in our blood. The vast majority of triglycerides should be kept in storage in our fat tissue.
It is normal for the amount of triglyceride in the blood to increase after eating fat. So, when measuring blood triglycerides to assess for insulin resistance it is important to fast prior to the test.
What is the healthy range?
A lower triglyceride level indicates a healthier and less insulin resistant state. This low level of triglycerides means the liver is not making excessive amounts of triglycerides, and the body is easily able to remove triglycerides from the blood.
A triglyceride level of less than 1.7mmol/L is considered normal, and less than 1.3mmol/L is ideal.
Why does it increase with insulin resistance?
The fasting blood triglyceride level increases with insulin resistance because:
- The liver is creating and releasing more triglycerides into the blood.
- The fat stores struggle to remove triglycerides from the blood.
- The fat stores constantly ‘leak’ fat into the blood.
- A fasting triglyceride level of more than 5.6 is considered very high. This should be discussed routinely with an appropriate healthcare professional.
- Blood triglycerides can be high for reasons other than insulin resistance. These include individual genetic profile, alcohol, and pancreatitis (inflammation of the pancreas).
What is it?
HDL-cholesterol is cholesterol that is part of a HDL particle in the blood. HDL stands for High Density Lipoprotein. HDL-cholesterol goes down with insulin resistance.
(A lipoprotein can be thought of as a transporter in the blood. There are many different types of these lipoprotein transporters, with HDL being just one type. Lipoprotein transporters carry molecules including cholesterol.)
What is the healthy range?
A higher HDL-cholesterol level is an indicator of better health. For males the HDL-cholesterol should be 1mmol/L or greater, and for females it should be 1.3mmol/L or greater.
Why does it decrease with insulin resistance?
Insulin resistance, and the associated high insulin level in the blood, decreases the amount of HDL-cholesterol in the blood by:
- An increased insulin level reduces the production of HDL-cholesterol in the liver.
- Insulin resistance in the body reduces HDL-cholesterol.
Total cholesterol and LDL-cholesterol
When testing for HDL-cholesterol and triglycerides the test may also provide a result for total cholesterol and for LDL-cholesterol. Total cholesterol and LDL-cholesterol are not useful for the assessment of insulin resistance.
Current medical guidelines (NICE Guideline CG71, Familial hypercholesterolaemia: identification and management.) advise a total cholesterol level of more than 7.5 mmol/L may indicate a condition called familial hypercholesterolaemia and recommend a routine medical assessment to be sought.
Total cholesterol is also occasionally found to be high in people that follow a very low carbohydrate (ketogenic) diet. A high total cholesterol with a very low carbohydrate diet is more commonly seen in people who are lean without other indicators of insulin resistance. What the high total cholesterol level means for health in this particular circumstance is currently unknown and more scientific research is needed.