MyPyramid: Steps to a...more confused you?
The 2010 Dietary Guidelines suggest lowering our saturated fat intake even more. For the past 15 years, Americans have done a tremendous job of nearly achieving the current goal of no more than 10% of their calories coming from saturated fats. However, due to the less than satisfactory reduction in heart disease rates, the new guidelines suggest we should eat even less:
given that in the US population 11-12 percent of energy from SFA [saturated fatty acids] intake has remained unchanged for over 15 years, a reduction of this amount resulting in the goal of less than 7 percent energy from SFA should, if attained, have a significant public health impact.
For a 2,000 calorie diet, this means eating about 15 grams of saturated fat a day, a value that seems unattainable for the omnivore. The equivalent of a glass of milk and two 6 ounce pieces of chicken breast; or one 9 ounce piece of steak:
9 ounce ribeye
Given these rather strict limitations on saturated fat, it seems logical to assume that the clinical trials supporting this relationship are clear-cut and abundant. However, this is not the case.
Since the 1950s, there have been a relatively small number of large, long-term clinical trials examining the potential benefits of decreased saturated fats in the diet as a primary focus. All major trials (along with a study description and link to the original article) since 1966 are listed here. Some took place in mental institutions, some were not randomized, and some also involved major cocontaminant interventions such as weight loss, exercise, or increased fruit and vegetable consumption. Many show benefits to replacing saturated fats with polyunsaturated fats, while others do not.
It is therefore very difficult to come up with a straight answer, and very simple to cherry-pick research that best fits your hypothesis. If there is a benefit to decreasing saturated fat intake, increasing polyunsaturated fats, or both, the evidence is mixed at best. The larger trials seem to suggest no major effect, while others do show significant benefits.
If we were to focus on the largest (i.e. > 100 subjects), randomized, most famous trials ever done lasting longer than 1 year, we are left with very few to assess that meet the following 2 criteria:
1) The only significant intervention involved a reduction in fat and saturated fat and an increase in polyunsaturated fats
2) They ask the question: does this diet reduce heart disease? (defined as heart attacks or death from heart disease)
Listed in reverse chronological order:
Women’s Health initiative (2006) – 48,835 women, 8 years, no significant difference between intervention and control.
Diet and Reinfarction trial (1989) – 2,033 men, 2 years, no significant difference between the groups given and not given fat and fiber advice. No significant differences in ischaemic heart disease between intervention and control (intervention was only advice in this trial)
Minnesota Coronary Survey* (1989) – 4,393 men and 4,664 women, double-blind, mean 1 year, no significant reduction in cardiovascular events or total deaths from the treatment diet
Finnish Mental Hospital (1972) – 12 years, physicians not blinded, significant decrease in coronary heart disease (CHD)death in men ( 5.7 deaths /1000 person-years vs 13 deaths /1000 person-years in the control. Non-significant decrease in CHD in women. (Not randomized, although included here because this is main experiment cited in support of diet-heart hypothesis)
Los Angeles Veteran’s Trial* (1969) – 846 subjects, up to 8 years, non significant difference in primary endpoints – sudden cardiac death or myocardial infarction. When cerebral infarcts were added, it reached significance. More non-cardiac deaths in experimental group
Oslo Heart Study (1968) – 412 men, 5 year, significant decrease in CHD with intervention. When stratified by age, the results were significant only in subjects younger than 60.
* Double blind
A full list of all the trials done supporting and refuting the saturated fat-heart-disease relationship, and a more in depth description of each can be found here . There are many others that did not meet the criteria I defined above.
Extra weight loss in high saturated fat groups adds complexity
To further complicate things, the diets that are typically characterized by high amounts of saturated fats seem to result in the most weight loss. When researchers compare a calorie unlimited, low-carb, high saturated fat diet to a traditional low calorie, low-fat diet, the low carb group generally — but not always — loses more weight. With few exceptions, their good cholesterol levels go up and their triglycerides go down. Despite having an unlimited calorie budget and often consuming 3x the amount recommended saturated fats, the subjects tend to lose more weight and rarely increase their bad cholesterol levels. ( For more on this and a list of all major clinical trials, see Low Carb Diets.)
Recommending such low levels of saturated fat, primarily found in meats, may have indirect consequences. Since saturated fats are mainly found in protein-dense animal products, decreasing saturated fat intake to very low levels by definition encourages low-protein diets, which seem to be less effective for weight loss and satiety (feeling full). Given our seemingly unyielding obesity epidemic, this may not be the best approach. Such a drastic decrease in one nutrient of our diets can lead to a large increase in another. This is exactly what has happened the past 30 years with carbohydrates. Especially refined ones:
Gross et al. 2004. American Journal of Clinical Nutrition
For a more in depth analysis of this relationship, see our page on saturated fats and heart disease in our new research library, Data Driven Dining.
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Dietary Research, Nutrition and Weight Loss, Policy