I have always known trans fats are bad, unsaturated fats are good, and saturated fats somewhere in-between. But I never knew exactly why. It has to do with their different effects on cholesterol and lipoprotein molecules. Different fats have complex actions on various lipoprotein levels and it is the levels and ratios of these lipoproteins that can affect health risks, particularly cardiac health risks.
LDLs are low density lipoproteins and are considered the bad cholesterol because they carry cholesterol to parts of the body including to injured arterial walls where the cholesterol forms artery blocking plaque. HDLs are high density lipoproteins which are considered the good cholesterol because they pick up cholesterol and return it to the liver where it is processed and removed. High levels of LDLs and cholesterol as well as low levels of LDLs are risk factors for cardia disease. Unsaturated fats, particularly mono unsaturated fats tend to lower LDL levels and there for decrease cardiac risk. Saturated fats, found in dairy and red meats, are considered bad since they are found to increase LDL levels. Trans fats are the worst as they both increase LDL levels and decrease HDL levels. Trans fats are only found in very tiny insignificant amounts in plants and animal food sources but are produced in food processing and used to increase longevity of packaged foods. They are so bad that there is no listed dietary amount that is considered safe and many countries and local governments have banned their use completely. While this is the basic explanation of how these fats affect HDL and LDL levels, it is actually a bit more complicated. For example it is known that if in a particular diet saturated fats are reduced but replaced with carbohydrates, the results are a worse LDL to HDL ratio. But overall it is healthiest to eat mostly unsaturated fats (olive oil, avocados, almonds), limit saturated fats ( dairy and meats), and completely avoid all trans fats (packaged baked goods, frozen pizza, and microwave popcorn). Something to note is that there is various data on the effects of red meat, and it is not always consistent because the groups that are being studied have different diets/lifestyle and are well controlled. One meta analysis showed some benefits in regards to lipids versus combined animal protein, carbohydrates, or usual diet, and had mixed effects when red mead was compared to fish or poultry. With this, it is important to note that lifestyle and other foods consumed need to be taken into account when performing studies on the effects of certain foods on diet.
Harvard School of Public Health: https://www.hsph.harvard.edu/
Guasch-Ferré, M., Satija, A., Blondin, S. A., Janiszewski, M., Emlen, E., O’Connor, L. E., Campbell, W. W., Hu, F. B., Willett, W. C., & Stampfer, M. J. (2019). Meta-analysis of randomized controlled trials of red meat consumption in comparison with various comparison diets on cardiovascular risk factors. Circulation, 139(15), 1828–1845. https://doi.org/10.1161/circulationaha.118.035225
Mensink, R.P., et al., Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am J Clin Nutr, 2003. 77(5): p. 1146-55.
I have always known trans fats are bad, unsaturated fats are good, and saturated fats somewhere in-between. But I never knew exactly why. It has to do with their different effects on cholesterol and lipoprotein molecules. Different fats have complex actions on various lipoprotein levels and it is the levels and ratios of these lipoproteins that can affect health risks, particularly cardiac health risks.
LDLs are low density lipoproteins and are considered the bad cholesterol because they carry cholesterol to parts of the body including to injured arterial walls where the cholesterol forms artery blocking plaque. HDLs are high density lipoproteins which are considered the good cholesterol because they pick up cholesterol and return it to the liver where it is processed and removed. High levels of LDLs and cholesterol as well as low levels of LDLs are risk factors for cardia disease. Unsaturated fats, particularly mono unsaturated fats tend to lower LDL levels and there for decrease cardiac risk. Saturated fats, found in dairy and red meats, are considered bad since they are found to increase LDL levels. Trans fats are the worst as they both increase LDL levels and decrease HDL levels. Trans fats are only found in very tiny insignificant amounts in plants and animal food sources but are produced in food processing and used to increase longevity of packaged foods. They are so bad that there is no listed dietary amount that is considered safe and many countries and local governments have banned their use completely. While this is the basic explanation of how these fats affect HDL and LDL levels, it is actually a bit more complicated. For example it is known that if in a particular diet saturated fats are reduced but replaced with carbohydrates, the results are a worse LDL to HDL ratio. But overall it is healthiest to eat mostly unsaturated fats (olive oil, avocados, almonds), limit saturated fats ( dairy and meats), and completely avoid all trans fats (packaged baked goods, frozen pizza, and microwave popcorn). Something to note is that there is various data on the effects of red meat, and it is not always consistent because the groups that are being studied have different diets/lifestyle and are well controlled. One meta analysis showed some benefits in regards to lipids versus combined animal protein, carbohydrates, or usual diet, and had mixed effects when red mead was compared to fish or poultry. With this, it is important to note that lifestyle and other foods consumed need to be taken into account when performing studies on the effects of certain foods on diet.
Harvard School of Public Health: https://www.hsph.harvard.edu/
Guasch-Ferré, M., Satija, A., Blondin, S. A., Janiszewski, M., Emlen, E., O’Connor, L. E., Campbell, W. W., Hu, F. B., Willett, W. C., & Stampfer, M. J. (2019). Meta-analysis of randomized controlled trials of red meat consumption in comparison with various comparison diets on cardiovascular risk factors. Circulation, 139(15), 1828–1845. https://doi.org/10.1161/circulationaha.118.035225
Mensink, R.P., et al., Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am J Clin Nutr, 2003. 77(5): p. 1146-55.
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