There are many different types of fats and they can be conveniently divided into four main categories: saturated fats, monounsaturated fats, polyunsaturated fats, and trans fatty acids.
The term "saturation" simply refers to the number of hydrogens a fatty acid chain is holding. Thus, in the case of saturated fatty acids, every available carbon bond is holding onto a hydrogen.
Interestingly enough, saturated fatty acids yield more energy than unsaturated fatty acids. The source of saturated fatty acids is mainly animal products. They have a negative reputation because they tend to raise your total serum cholesterol.
Since there is a well established relationship between total cholesterol concentrations and heart disease, eating diets high in saturated fats may increase your risk for the complications of heart disease such as heart attacks and strokes1.
The most potent saturated fatty acids at increasing serum cholesterol are myristic (14 carbons in length) and palmitic (16 carbons in length) acids. They are mainly found in dairy products and red meats.
Stearic acid (18 carbons in length), on the other hand, is relatively less potent at increasing serum cholesterol and can be found in beef and cocoa butter.
The second category of fats is the monounsaturated fatty acids or MUFA (for those who love acronyms). MUFA's have one point where the hydrogens are missing and so they have one point of unsaturation. Many studies have shown that switching from a diet high in saturated fatty acids to monounsaturated fatty acids can help reduce LDL (bad cholesterol) and maintain HDL (good cholesterol).
Furthermore, studies show that patients with Type II Diabetes who switch from polyunsaturated fatty acids to monounsaturated fatty acids can help reduce their insulin resistance and restore their endothelium-dependent vasodilation (which decreases their risk for atherosclerosis)2. Good vegetable sources of MUFA's include the famous olive oil and canola oil.
The third category of fats is polyunsaturated fatty acids or PUFA. PUFA's have two or more points of unsaturation. They include the omega-6 family (linoleic acid) and the omega-3 family (alpha-linoleic acid) of fatty acids. The main sources of omega-6 fatty acids are safflower oil, sunflower oil, corn oil and cereal grains.
The omega-6 fatty acids are used by the body to make hormone-like substances called eicosanoids. These eicosanoids are involved in a number of functions including muscle contraction/relaxation, blood vessel constriction/relaxation, immune response to injury and infection, producing fever, pain and inflammation3.
In general, omega-6 fatty acids tend to lower both serum LDL and HDL cholesterol. Some studies suggest that increased intake of linoleic acid may INCREASE platelet aggregation, which is associated with an elevated risk of heart attacks4.
Furthermore, some animal studies also suggest that high amounts of omega-6 polyunsaturated fatty acids may be carcinogenic5.
The main sources of omega-3 fatty acids include fish oils, vegetable leaves, and a modest amount in soybean oil. Omega-3 fatty acids are thought to be required for the brain's cerebral cortex development and retinal development for vision6.
Some of their beneficial effects include the prevention of ventricular fibrillation (heart rhythm irregularity)7 and a DECREASED platelet response to aggregation8 (so less risk for clots).
Lately there has been a lot of talk about the ratio between omega-6/omega-3 fatty acids. A few studies have shown very promising results with decreasing this ratio to 4:1 or even 2:1. The Lyon Heart Study looked at the effects of a Mediterranean alpha-linolenic acid-rich diet to the usual diet given to patients after heart attacks.
After a first heart attack, the patients were randomly assigned to either the experimental group (n=302) or control group (n=303). The patients were seen at the end of the first 8 weeks and then annually for the next five years. The experimental group ate significantly less lipids, saturated fat, cholesterol, and linoleic acid but more oleic and alpha-linolenic acids (omega-3).
After a mean follow up of 27 months, the results were quite remarkable. There were 16 cardiac related deaths in the control group but only 3 in the experimental group (high omega-3). There were 17 non-fatal heart attacks in the control group but only 5 in the experimental groups.9
Another interesting study was the Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto miocardico (GISSI) Prevenzione Trial in which participants were on a traditional Italian diet versus a traditional Italian diet plus 850-882 mg of omega-3 fatty acids.
The group supplemented with omega-3 fatty acids showed a decrease in sudden cardiac death by 45%.10
In a review article, A. P. Simopoulos concluded, based on the numerous literature available, that "many of the chronic conditions, cardiovascular disease, diabetes, cancer, obesity, autoimmune diseases, rheumatoid arthritis, asthma and depression, are associated with increased production of thromboxane A2 (TXA2), leukotriene B4 (LTB4), IL-1 , IL-6, tumor necrosis factor (TNF), and C-reactive protein.
All these factors increase by increases in omega-6 fatty acid intake and decrease by increases in omega-3 fatty acid intake, either ALA or EPA and DHA. EPA and DHA are more potent, and most studies have been carried out using EPA and DHA".11
The bottom line on the omega-6/omega-3 ratio is that maintaining a low omega-6/omega-3 ratio is an important part of maintaining a healthy diet.
Trans Fatty Acids
The last category of fatty acids is the trans fatty acids. Most trans fatty acids are the result of industrial hydrogenation of polyunsaturated fatty acids. Basically manufacturers partially hydrogenate to get fats that are easier to cook with and spoil less than naturally occurring oils.
The problem with trans fatty acids, unlike saturated fats, is that they cause reductions in your HDL (high density lipoprotein) cholesterol. Recall that HDL cholesterol is known as the "good" cholesterol because high levels of it seem to protect against heart attack.12
A second problem with trans fatty acids is that they interfere with the desaturation and elongation of omega-3 fatty acids, which are also important in preventing heart disease.
As a side note I thought I might mention about the effects of a low fat vs. low carbohydrate diet. The individuals on low-fat, high carbohydrate diets as compared to low carbohydrate diets utilize the fatty acid synthetic pathway extensively.
Basically, this pathway results in citrate leaving the mitochondria to generate high concentrations of malonyl-CoA. Malonyl-CoA inhibits the activity of fatty acid breakdown.13 Thus people on high carbohydrate diets burn less fat than those on low carbohydrate diets.
- The Expert Panel. Second Report of the Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults. NIH Publication No. 93-3095. US Government Printing Office, Washington, DC, 1993.
- Ros E.Dietary cis-monounsaturated fatty acids and metabolic control in type 2 diabetes. Am J Clin Nutr. 2003 Sep;78(3 Suppl):617S-625S.
- Sizer F, Whitney E. Nutrition Concepts and Controversies, 9th ed., Copyright 2003 Thomas Learning Inc. pp. 138-157.
- Renaud S. Linol-eic acid, platelet aggregation and myocardial infarction. Atherosclerosis 1990;80:255-6.
- Noguchi M, Rose DP, Earashi M et al. The role of fatty acids and eicosanoid synthesis inhibitors in breast carcinoma. Oncology 1995; 52: 265-271.
- Uauy R, Mena P. Lipids and Neurodevelopment, Nutrition Reviews 2001;59:S34-48.
- Singh RB, Niaz MA, Sharma JP, Kumar R, Rastogi V, Moshiri M. Randomized, double-blind, placebo-controlled trial of fish oil and mustard oil in patients with suspected acute myocardial infarction: the Indian experiment of infarct survival-4. Cardiovasc Drugs Ther 1997;11:485-91.
- Freese R, Mutanen M, Valsta LM, Salminen I. Comparison of the effects of two diets rich in monounsaturated fatty acids differing in their linoleic/alpha-linolenic acid ratio on platelet aggregation. Thromb Haemost 1994;71:73-7.
- Lorgeril M. De, Renaud S., Mamelle N., Salen P., Martin JL., Monjaud I., Guidollet J., Touboul P. and Delaye J., Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease. Lancet 343 (1994), pp. 1454-1459.
- GISSI-Prevenzione Investigators: dietary supplementation with n-3 polyunsaturated fatty acids and vitamin E after myocardial infarction: results of the GISSI-Prevenzione trial. Lancet 354 (1999), pp. 447-455.
- Simopoulos, A. P. The importance of the ratio of omega-6/omega-3 essential fatty acids. Biomed Pharmacother. 2002 Oct;56(8):365-79.
- Lichtenstein, AH, Ausman, LM, Jalbert, SM, Schaefer, EJ. Effects of different forms of dietary hydrogenated fats on serum lipoprotein on cholesterol levels. N Engl J Med. 1999; 340:1933.
- Pizzorno. Textbook of Natural Medicine, 2nd ed., Copyright 1999 Churchill Livingstone, Inc. pp. 723-731.