Exploring the sense and nonsense of food and health

The Low-Fat Diet – What the Research Says?

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Mediterranean diet (close up)

Mediterranean diet (close up) (Photo credit: grobery)

Is it time to redirect our attention away from the low-fat “craze”?  Low fat claims on new product food labels indicate that low-fat, and low trans fat claims dropped off in 2011.  The number of products featuring low/no-reduced saturated fat claims grew from 186 in 2010 to 207 in 2011, although this number still represents a very small percentage (1%) of new products introductions overall.  How did the low-fat diet hold up in research studies when assessed about its effectiveness in weight loss and prevention of chronic disease?

Large Major Nutrition Interventions

In the Women’s Health Initiative Dietary Modification Trial (WHI) there was little difference in heart disease and cancer rates between those who were counseled to follow a low fat diet vs. those who followed a usual diet (no change or counseling).  One major limitation of this intervention was that the most women in low fat group never achieved the goal of reducing their fat intake to less than 20% of total calories so that their 29% was not much different than those in the usual group with 38% of total calories.

In the Nurses Health Study at long-term follow-up, there were no differences in the relationships between percent calories from fat and risk of breast cancer, colon cancer or heart disease.  One major limitation of this study was that all participants completed a self-reported food intake questionnaire, so there was doubt as to its validity of what these women actually consumed.

In the area of weight loss, Dariush Mozaffarain, codirector of the cardiovascular epidemiology program at Brigham and Women’s Hospital and Harvard Medical School and assistant professor at the Harvard School of Public Health says:  “No randomized trial looking at weight changes has shown that people did better on a low-fat diet.”

Case-Control Studies

This type of study compares patients who have a disease (cases) with patients who do not have the disease.  It looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.  Results from 25 studies that looked at the effect of total fat intake on breast cancer risk are inconsistent.  Only two of these studies reported that a high fat intake was significantly associated with an increased risk of breast cancer.

Cohort Studies

In this type of study one or more samples (called cohorts) are followed prospectively and evaluations with respect to a disease or outcome are conducted to determine which risk factors are associated with it. Healthy women were asked about their usual dietary intake and then contacted later to see how many developed breast cancer.  None of the available studies reported a significant increase in the risk of breast cancer associated with a high fat intake.

Animal Studies

More than 95 animal studies reported that dietary fat increased the development of breast tumors.  This effect appeared to be dependent on the type of fat in the diet, not just the amount.  Therefore, more recent research on fats have shifted to the type of fat involved and not just the percent from calories as in earlier studies.

Olive Oil

Olive oil primarily contains a predominance of monounsaturated fat. In three out of five studies conducted in the Mediterranean area where women may have a total fat intake of 42%, far higher than in the U.S., the consumption of olive oil was associated with a significant decrease in the risk of breast cancer.  Of the two remaining studies, one reported that the consumption of olive oil was associated with a lower incidence of breast cancer and the other reported no association between olive oil consumption and breast cancer.

Fish Oil

From animal studies it was observed that fish oils slow the development and decrease breast tumor growth. Human studies are inconsistent with about half of the studies reporting a decrease in the risk associated with a high intake of fish.  Varied results may be due to the ratios of omega-3 fats to omega-6 fats (plentiful in vegetable oils).

Men who ate a low fat diet with fish oil supplements for four to six weeks before having their prostate removed had slower cancer-cell growth in their prostate tissue than men who ate a traditional high-fat Western diet, according to a recent study at UCLA’s Jonsson Comprehensive Cancer Center. The low fat diet was only 15% of the calories from fat and the men additionally took five grams of fish oil per day.  The key to this study was that the meals were prepared and delivered to the study participants which resulted in a very high rate of compliance, making the study very well controlled.  This is contrast to the earlier interventions that have compliance or recall problems.  The study was short-term and the sample size was small; a more extensive study is planned.

William J. Aronson, et al. Phase II Prospective Randomized Trial of a Low-Fat Diet with Fish Oil Supplementation in Men Undergoing Radical Prostatectomy, in Cancer Prevention Research, Published online Oct. 25, 2011.


In spite of the disappointing research, the low-fat diet should not be put to rest, in my opinion

It appears from the research that large intervention studies may not be the best approach to assess the relationship between dietary fat and disease due to some serious design limitations.   Perhaps smaller and carefully controlled studies will tell us more about any association.

One thing that has been consistently established is that trans fats raise bad cholesterol, lower good cholesterol, increase triglycerides, promote inflammation and insulin resistance.  It’s ironical that the low-fat “fad” initially resulted in the demonization of “natural” fats to remove saturated fats and promoted the widespread use of unnatural fats from hydrogenated oils in the form of margarine and other products.

The concept of “good” and “bad” foods has entered the mindset of consumers.  No wonder consumers throw up their hands, and give up on trying to eat a healthy diet. The advice is totally confusing – margarine yesterday, butter today?  One concept that Americans know but often ignore is moderation.  Another concept often ignored is nutrient density – choosing foods high in healthy nutrients and low in calories.

What can be done about our current dilemma – low fat, low carb, high protein, high fat, high fiber, good and bad foods?    If you go to your doctor or dietitian, they more than likely will prescribe a low fat or low carb diet?  Research has shown that the traditional Mediterranean diet reduces the risk of heart disease. In fact, a recent analysis of more than 1.5 million healthy adults demonstrated that following a Mediterranean diet was associated with a reduced risk of overall and cardiovascular mortality, a reduced incidence of cancer and cancer mortality, and a reduced incidence of Parkinson’s and Alzheimer’s diseases.  Health professionals should be emphasizing the foods and principles of Mediterranean-types of diets and instructing consumers on how to easily and practically incorporate them into their daily diets.

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