Healthful and Unhealthful Fats 
Healthful and Unhealthful Fats

Gabe Mirkin, M.D.
Fat is classified into saturated fats, polyunsaturated fats, and 
monounsaturated fats. Saturated fats appear to increase your risk 
for heart attacks when you take in more calories than you burn. 

Monounsaturated fats are considered healthful because they form LDL 
cholesterol that is resistant to oxidation; plaques are formed by 
oxidized LDL. Good sources include olive oil and avocados. 

We used to think that all polyunsaturated fats help to prevent heart 
attacks when they replace saturated fats, but now we have different 
information. Polyunsaturated fats are classified by their structures 
into omega-3s and omega-6s, and you need both types; these are 
called the essential fatty acids because you cannot make them in 
your body and must get them from your food. 

For most of the time humans have been on earth we have eaten foods 
that contain omega-6's and omega-3's in a ratio of about 2:1. 
However, over the last 50 years in North America, the ratio has 
changed; it now ranges from 10:1 to 20:1. Today our diet includes 
huge amounts of oils that are extracted from plants and used for 
cooking or in prepared foods. These oils (such as corn oil, 
safflower oil, cottonseed oil, peanut oil, soybean oil) are 
primarily omega-6s. We have decreased our intake of omega-3's, 
found primarily in whole grains, beans and other seeds, and seafood. 
Eating too much omega-6 and too little omega-3 causes clots and 
constricts arteries to increase risk for heart attacks, increases 
swelling to worsen arthritis, and aggravates a skin disease called 
psoriasis. It may block a person’s ability to respond to insulin, 
causing high insulin and blood sugar levels and obesity. It 
increases hormone levels of insulin like growth factor-1 that causes 
certain cancers. To get your ratio on omega-6s to omega-3s back to a 
more healthful 2:1, eat seafood, whole grains, beans and other 
seeds, and reduce your intake of foods made with or cooked in 
vegetable oils.

The most unhealthful fats are the polyunsaturated oils that have 
been processed to form trans fats (partially hydrogenated vegetable 
oils); see reports #N198 and #N185. 

Checked 12/8/07