Brent Cornell

    
Types of Fats

Whilst all types of fats consumed as part of dietary intake will cause adverse health effects if taken in excessive amounts, some types of fats are associated with increased health risks

The mix of fats in the diet influences the level of cholesterol in the bloodstream

Saturated fats and trans fats raise blood cholesterol levels, while (cis) unsaturated fats lower blood cholesterol levels

Comparison of Main Types of Fatty Acids

Regulating Blood Cholesterol Levels

Fats and cholesterol cannot dissolve in blood and are consequently packaged with proteins (to form lipoproteins) for transport

• Low density lipoproteins (LDL) carry cholesterol from the liver to the rest of the body
• High density lipoproteins (HDL) scavenge excess cholesterol and carry it back to the liver for disposal

Hence LDLs raise blood cholesterol levels (‘bad’) while HDLs lower blood cholesterol levels (‘good’)

High intakes of certain types of fats will differentially affect cholesterol levels in the blood

• Saturated fats increase LDL levels within the body, raising blood cholesterol levels
• Trans fats increase LDL levels and decrease HDL levels within the body, significantly raising blood cholesterol levels
• Unsaturated (cis) fats increase HDL levels within the body, lowering blood cholesterol levels

Effect of Different Types of Fats on Cholesterol Levels

Health Risks of High Cholesterol

High cholesterol levels in the bloodstream lead to the hardening and narrowing of arteries (atherosclerosis)

When there are high levels of LDL in the bloodstream, the LDL particles will form deposits in the walls of the arteries

The accumulation of fat within the arterial walls lead to the development of plaques which restrict blood flow

If coronary arteries become blocked, coronary heart disease (CHD) will result – this includes heart attacks and strokes  

Role of Lipoproteins in the Development of Atherosclerosis

    
Lipid Health Claims

There are two main health claims made about lipids in the diet:

• Diets rich in saturated fats and trans fats increase the risk of CHD
• Diets rich in monounsaturated and polyunsaturated (cis) fats decrease the risk of CHD

These health claims are made based on evidence collected in a number of ways:

• Epidemiological studies comparing different population groups
• Intervention studies that monitor cohorts following dietary modifications
• Experimental designs utilising animal models or data based on autopsies

Evidence Supporting Health Claims

A positive correlation has been found between the intake of saturated fats and the incidence of CHD in human populations

• Counter: Certain populations do not fit this trend (e.g. the Maasai tribe in Africa have a fat-rich diet but very low rates of CHD)

Intervention studies have shown that lowering dietary intakes of saturated fats reduces factors associated with the development of CHD (e.g. blood cholesterol levels, blood pressure, etc.)

• Counter: Validity of intervention studies is dependent on size and composition of cohort, as well as the duration of the study

In patients who died from CHD, fatty deposits in diseased arteries were found to contain high concentrations of trans fats

• Counter: Genetic factors may play a role (e.g. blood cholesterol levels only show a weak association to dietary levels)

Evidence Against Health Claims

Proportion of saturated and trans fats in Western diets has decreased over the last 50 years, but incidence of CHD has risen

• Counter: Increased carbohydrate intake may cause detrimental health effects associated with CHD (e.g. diabetes, obesity)
• Counter: Incidence of CHD dependent on a myriad of factors besides dietary intake (e.g. exercise, access to health care, etc.) 

Summary of Types of Dietary Fats