Almost every time you open a magazine or turn on a television, you're likely to be reminded to eat less fat. Fifty years ago, scientists involved with the Framingham Heart Study determined that a high blood cholesterol level increased a person's risk for coronary heart disease. Soon thereafter, the connection between dietary fat and cholesterol was established, and Americans were exhorted to adopt low-fat diets. According to a 2008 review in "Journal of the History of Medicine and Allied Sciences," this message has continued unabated, despite new evidence that some fats are not only essential for normal cellular function, but they might even protect you from heart disease.
Dietary Fat and Cholesterol
"The Merck Manual of Diagnosis and Therapy" states that over 95 percent of dietary fat is in the form of triglycerides. Dietary triglycerides are broken into fatty acids in your intestine; the fatty acids are absorbed into your bloodstream; and your liver uses the fatty acids to reconstruct triglycerides and to synthesize cholesterol. Ostensibly, the more fat there is in your diet, the more cholesterol your liver can make.
Different Fats, Different Risks
One discovery that has emerged from ongoing studies of human cardiovascular disease is that not all fatty acids are the same. Saturated fatty acids and trans fats, for example, have been implicated as instigators of atherosclerosis, or hardening of the arteries. Conversely, monounsaturated fats -- such as those found in olive oil and canola oil -- are believed to be protective, as are some polyunsaturated fatty acids, such as those found in fish oil.
An Evolving Understanding of Fats
A January 2011 review in "The American Journal of Clinical Nutrition" confirms that your risk for coronary heart disease is reduced when you replace dietary saturated fats with polyunsaturated fats. In fact, if you replace 1 percent of your daily saturated fat intake with polyunsaturated fats, you will decrease your risk for coronary heart disease by at least 2 percent. Surprisingly, even though people who consume monounsaturated fat-rich diets -- such as the Mediterranean diet -- have less heart disease, the evidence to support replacing saturated fats with monounsaturated fats is less convincing. Notably, elimination of all saturated fats may be an unrealistic goal, for some foods that contain saturated fats may confer health benefits of their own.
Current Recommendations
The scientific fervor that spawned draconian, ultralow-fat diets is gradually moderating in favor of diets that allow the consumption of fats that appear to be beneficial, particularly those that reduce your risk for heart disease. The American Heart Association currently recommends that you limit your fat intake to about 30 percent of your total daily energy consumption. You should keep your saturated fat intake to 7 percent or less of your total caloric intake, and trans fats should constitute less than 1 percent of your daily energy consumption. Hence, the majority of your fat intake should consist of polyunsaturated and monounsaturated fats.
References
- Framingham Heart Study: Research Milestones
- "Journal of the History of Medicine and Allied Sciences"; How the Ideology of Low Fat Conquered America; Ann F. LaBerge; Feb 2008
- "The Merck Manual of Diagnosis and Therapy, 18th Edition"; Lipid Disorders; Mark H. Beers, M.D., Editor-In-Chief; 2006
- "The American Journal of Clinical Nutrition"; The Role of Reducing Intakes of Saturated Fat in the Prevention of Cardiovascular Disease: Where Does the Evidence Stand in 2010?; A. Astrup, et al.; January 2011
- American Heart Association; Knowing Your Fats; Sept 2010
