Saturated Fats and Heart Disease: Prospective Studies

1.The majority of prospective cohort studies found no correlation between saturated fat and heart disease

2. Poor dietary assessment methods and large potential for bias create strong limitations to this data

3. Focus should be placed on improving dietary patterns and not incriminating one specific nutrient

Summary:

Since the 1950s, saturated fat has been incriminated as the major dietary contributor to heart disease, attributed mainly to the fact that saturated fats have the ability to raise blood cholesterol. This temporary physiologic response to dietary fats led to the logical hypothesis that replacing saturated fats with polyunsaturated fats, which lower blood cholesterol, may also lower coronary heart disease (CHD) rates, cardiovascular mortality, or both. This biological response to saturated fats has been the main reason diets high in meats carry such a stigma. The best way to determine if this hypothesis is true is through randomized, clinical trials. As discussed on our Saturated Fats & Heart disease – Clinical trials page, the evidence from the past 60 years has been inconclusive.

Yet conducting a large, long term trial is tremendously expensive and burdensome. For these reasons, prospective cohort studies offer a viable alternative, although no causation can be determined. Subjects can be followed for a very long time and associations between their diets and disease can be illuminated. However, prospective cohorts have many short comings as well.

When researchers study the possible negative effects of saturated fats in prospective cohorts, they perform a baseline dietary intake measurement (usually a Food Frequency Questionnaire (FFQ), 24-hour recall, or 7 day food record), then follow subjects for up to ~25 years. The majority of them do not assess the diet anywhere in between. Just day one (or week one), and year 25. Of course the likelihood that the baseline assessment is representative of their diet for the next 25 years is low. The best baseline assessments were 7-day food records, where subjects meticulously weigh and record everything they ate. These were rare.

To complicate matters further, a large percentage of these cohorts used an FFQ to assess the baseline intake. Dr. Walter Willet, from the Harvard School of Public Health has demonstrated that FFQs can be quite inaccurate. In one validation study, the foods most accurately reported were tea and beer, while things like meat, fish, bacon, and hamburgers were at best 25% accurate. The subjects filling them out also had a tendency to under-report foods deemed unhealthy while over reporting fruits and vegetables. From the screen shot below of an FFQ, it becomes apparent why it can be so inaccurate and subject to bias.

Never the less, researchers’ attempts to to find a link between saturated fats and heart disease have been unsuccessful for the most part. Some studies have found a correlation, usually of borderline significance, while many have not.

Trying to isolate one nutrient, saturated fats, in the sea of nutrients, vitamins, and calories a subject’s diet consists of is difficult if not impossible, and leads to many correlations that may be misleading. For these reasons, it is likely more beneficial to focus on making more practical and tangible changes to the diet, such as eliminating processed foods and sugar or increasing your daily servings of fruits and vegetables.

Bibliography:

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Meta-analyses and reviews
Prospective cohorts showing no correlation between saturated fat and heart disease
Prospective cohorts showing a correlation between saturated fat and heart disease

Meta-analyses and Reviews

Siri-Tarino et al 2010 Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease

  • Overview: Meta-analysis of 21 prospective cohort studies examining the evidence that saturated fat is associated with cardiovascular disease
  • Outcome: During 5-23 year follow up ofr 347,747 subjects, 11,006 developed Cardiovascular disease or stroke. Intake of saturated fat was not associated with increased risk of cardiovascular disease or stroke. The pooled relative risk (RR) estimates comparing the highest intake of saturated fat to lowest, found that those who ate the most had a RR=1.07 (95%CI=0.96-1.19) for Coronary heart disease, 0.81(95% CI=0.62-1.05) for stroke, and 1.00 (95% CI=0.89-1.11) for CVD
  • Comments: The most recent meta-analysis, finding no association between saturated fats and heart disease. Researchers also found a non-significant reduced risk of stroke for those consuming the most saturated fat.

Jakobsen et al. 2009 Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies

  • Overview: Investigated the association between various types of fats and carbohydrates and heart disease in 11 prospective cohorts.
  • Outcome: During 4-10 year follow up, 5,249 coronary events and 2,155 corohary deaths occured among 344,696 persons. For a 5% lower intake from SFAs and a cocomitant higher energy intake from polyunsaturated fats, there was a significant inverse association between PUFAs and coronary events: Hazard Ratio: 0.87, (95% CI=0.77, 0.97); for coronary deaths the hazard ratio was 0.74 (95% CI=0.61, 0.89). When replacing 5% saturated fats with carbohydrates, there was a slightly significant association between carbs and coronary events: HR=1.07, (95% CI = 1.01, 1.14); Monounsaturated fats were not associated with CHD
  • Comments:Many of the 11 cohorts chosen did not publish their dietary intake data. The researchers also mentioned that “Dietary intake was determined by using food-frequency questionaire or a dietary history interview…Only baseline information regarding dietary habits was available.”

Cohorts that found no association between saturated fat and heart disease:

Study Sample Size Sex & Age Average time to follow up Diet Assessment # of diet assessments after baseline Saturated Fat
associated with CHD?
Comments
Yamagishi et al 2010 58,453 Men & Women 40-79 14.1 years FFQ None NO SFAs were inversely associated with stroke
Leosdottir et al 2007 28,098 Men & Women 8.4 years 7 day food record, FFQ, interview None NO
Xu et al. Strong Heart Study 2006 2,938 47-79 7.2 years 24-hr Recall None NO. When stratified by age, Yes for those 47-59
Jakobsen et al. 2004 78,778 Women 16 years 7 day weighed food record; FFQ for a subset 4 times NO. Only benefit seen when stratified by age: Women <60 showed benefit: HR=2.48 (95% CI=1.3-4.77)
Ascherio et al 1996 43,757 Men 40-75 14 years FFQ 3 times NO
Pietinen ATBC study 1997 21,930 Men 50-69 6.1 years FFQ None NO
Fehily et al. Caerphilly study 1993 2,512 Men 45-59 5 years FFQ, 30% received 7 day food records None NO
Posner et al. Framingham 1991 859, further divided by age Men 45-55 and Men 56-65 16 years 24-Hr Recall None NO
Farchi et al. 1989 1,536 Men 45-64 20 years FFQ None NO Higher saturated Fat consumption in the lower risk group
Khaw et al. 1987 859 Men & Women 50-79 12 years 24-Hr Recall None NO
Kromhout et al. Zutphen Study 1984 871 Men 40-59 10 years FFQ and interview None NO
Gordon et al. 1981 16,349 Men 45-64 6 years 24-Hr Recall None NO
Garcia-Palmieri et al. Puerto Rico Study 1980 8,218 Men 45-64 6 years 24-Hr Recall None NO
Yano et al. Japanese in Hawaii 1978 7,705 Men 45-64 6 years FFQ, 24-Hr Recall, validation in subset with 7-day food record None NO
Morris et al. 1977 337 Men 30-67 20 years 7 day weighted food record None NO
Paul et al. 1963 5,397 Men 40-55 4 years Interview with Dietitian None NO


Prospective evidence that saturated fat intake is in fact associated with heart disease:


Study Sample Size Sex & Age Average time to follow up Diet Assessment # of diet assessments after baseline Saturated Fat
associated with CHD?
Comments
Tanasescu et al. 2004 5,672 Women 18 years FFQ 3 times YES for age adjusted model; RR=1.29; NO for multivariate model or after adjusting for other fats
Oh et al. 2005 78,778 Women 20 years FFQ 4 times YES for age adjusted model in 2 highest quintiles; No for multivariate RR
Hu et al. 1997 80,082 Women 34-59 14 years FFQ 3 times YES for age adjusted model: RR = 1.38; NO for multivariate model or after adjusting for other fats
Esrey et al. Lipid Research Clinic 1996 4,546 Men & Women 30-79 12 years 24-Hr Recall None YES. RR= 1.11(95% CI= 1.04-1.18) Difference in CHD deaths vs. No Deaths was 3 grams of Saturated fat
Kromhout et al. 1995 12,673 Men 40-59 25 years Food record in small sub sample None YES
Keys et al. 7 Country study 1986 11,579 Men 40-59 15 years 7 day food record None YES
Kushi et al. Ireland-Boston study 1985 1,001 Men YES
McGee et al. Honolulu study 1984 8,000 Men 45-68 10 years 24-Hr Recall None YES

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