Low Fat Diets: Not Always the Cure All.

The information on this page has been compiled and edited from previously published articles, by Dr. Connie Guttersen.  The articles are not intended as health advice, nor do they necessarily reflect the views and opinions of the California Olive Committee. Always consult your physician on matters of health and wellness.

by Connie Guttersen, RD PhD.

It is interesting that in the 1960's Ancel Keys' Seven Countries Studies provided us with the initial insight that a low fat diet is not always the answer to a healthier heart. His studies also showed that when it comes to health, the type of fat plays a more important role than the amount of fat (such as the monounsaturated fats found in olives, nuts and olive oil or the omega 3 oils found in seafood, as compared to saturated fats or hydrogenated oils).

Well as I write this in 2006, one of the largest and most expensive studies in our time, The Women's Health Initiative Dietary Modification Trial, indicates that low fat diets do not better prevent disease or improve weight loss. The eight year trial, published in the Journal of the American Medical Association, followed almost 50,000 women between the ages of 50 and 70 years who were randomly assigned to follow a low fat diet (20% of total calories) and then compared them to another group of women who continued with their usual diet. After eight years, the researchers looked at how many women in each group developed health problems. The results show that the women assigned to the low fat diet did not appear to gain protection against breast cancer, colorectal cancer, cardiovascular disease, and their body weights where similar to those women following their usual diets. The debate will most likely continue since some of the proposed limitations include that the level of fat in the diet was not low enough and should have been below 20% of total calories. (A dietary restriction that has been regarded  as difficult to follow for long periods of time.)  The other limitations being mentioned include that the women studied were not at an ideal age range, or perhaps the study should have continued for a longer period of time. Regardless, there will still be some discussion among the medical community as to how to apply these results to key messages for the American public.

These results may come as a surprise for many who have been hearing for years that reducing dietary fat in the diet is important for long term health and weight loss.  Yet, numerous studies have been proving this concept inaccurate. Studies such as the Nurses Health Study have consistently found little relation between the percentage of calories from fat and risks of breast cancer, colon cancer, or coronary heart disease. These studies, amongst others, have strongly influenced positive changes in dietary recommendations made by the USDA, US Dietary Guidelines Committee, and the US Institute of Medicine to advocate a greater emphasis on the type of fat consumed rather than the low fat approach.

Replacing saturated fat and trans unsaturated fats with monounsaturated and polyunsaturated fats is more effective in preventing coronary heart disease in women than reducing overall fat intake.

The following three sections on Heart Disease, Cancer and Obesity contain important studies, which substantiate key messages for why low fat diets are not always the cure all for these conditions. These studies can help health professionals emphasize the importance of choosing nutrient rich foods in a balanced diet and to communicate that the type of fat we eat is a more effective message than just focusing on the phrase, “low fat” as healthy. 

Heart Disease

The conventional low fat diets have not been shown to be the best heart healthy approach. While they tend to reduce cholesterol, it is at the expense of a decreased level of high-density lipoproteins, and an increased level of triglycerides. On the other hand, a diet which contains a moderate amount of fat, primarily from the monounsaturated type, will decrease an elevated blood cholesterol and low density lipoproteins, and will also maintain the level of high density lipoproteins and lower the elevated triglyceride levels.

A recent study conducted by Harvard School of Public Health used a regression analysis of data from the Nurses Health Study (80,000 women for 14 years) suggests that replacing saturated fat and trans unsaturated fats with monounsaturated and polyunsaturated fats is more effective in preventing coronary heart disease in women than reducing overall fat intake. More recent information compares different sources of monounsaturated fats (olive oil, peanut oil, peanuts, peanut butter) to the American Heart Association: Step II cholesterol lowering diet (low fat, high carbohydrate). In this study, Etherton, et al. proposes that diets moderate in dietary fat, (35% of total calories) and primarily comprised of monounsaturated fat will lower total and low-density lipoprotein cholesterol to a degree similar to that of the Step II diet. Moreover, the monounsaturated studies had the added benefit of not decreasing high-density lipoprotein or increasing triglycerides, as the Step II diet did.  In this particular study, all the different monounsaturated sources contained similar amounts of oleic acid (77%).  Despite this, differences were seen in their individual ability to decrease cardiovascular risk. These differences in cardiovascular risk reduction among the different types of monounsaturated foods may be attributed to additional components such as antioxidants and phytochemicals which were present prior to refinement.

Further review of the research finds protective qualities, such as antioxidants naturally found in olives, nuts, and olive oil.

 

REFERENCES:

• Prentice RL, Caan B, Chlebowski RT, et al. Low-fat dietary pattern and risk of invasive breast cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006; 295:629-42.
• Beresford SA, Johnson KC, Ritenbaugh C, et al. Low-fat dietary pattern and risk of colorectal cancer: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006; 295:643-54.
• Howard BV, Van Horn L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease: the Women's Health Initiative Randomized Controlled Dietary Modification Trial. JAMA 2006; 295:655-66.
• Howard BV, Manson JE, Stefanick ML, et al. Low-fat dietary pattern and weight change over 7 years: the Women's Health Initiative Dietary Modification Trial. JAMA 2006; 295:39-49.
• Etherton, P, et al High monounsaturated fatty acid diets lower both plasma cholesterol and triacylglycerol concentrations Am J Clin Nutr 1999;70:1009-15
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