Health, with a Grain of Salt

Explaining the science and debunking the myths of nutrition, metabolism, and health.

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Better than Butter? Not Sugar

The battle against saturated fat continues.  In the past, it was considered nutritional dogma that saturated fats should be limited in order to preserve or restore cardiovascular health.  However, in recent years, this has been called into question as some studies have found no association between intake and risk for coronary heart disease (CHD) (1).

Recent work out of the Harvard School of Public Health may bring some more clarity to this question (2).  An important issue when considering how we limit certain nutrients is with what we are replacing said nutrient.  This is important because people typically don’t just stop eating a lot of calories of one nutrient without replacing it with something different.  Many studies are unable or do not consider this in their analysis or study design.

Using data from over 120,000 adults enrolled in the Health Professional’s Follow-up Study and the Nurse’s Health Study, Li, et al. evaluated diet over time.  After 24-30 years of follow-up, over 7,000 cases of CHD (defined as death from CHD or heart attack) were reported.  Interestingly, those who had the highest intake of polyunsaturated fatty acids (PUFAs; think: vegetable oils, fish, nuts, seeds) or high quality carbohydrates (think: whole grains, quinoa, beans) had a significantly reduced risk of developing CHD compared to those who had the lowest intake.

But regarding saturated fat, when 5% of intake was replaced with either PUFAs, whole grains, or monounsaturated fatty acids (think: olive oil, avocados, nuts), risk for developing CHD dropped by 9-25%, with PUFAs being the most beneficial.  However, if saturated fats were replaced with trans fats or refined carbohydrates (think: sugar, white bread/rice/pasta/crackers, etc.), there was no change in risk for CHD.

This analysis is unique because the study was able to determine nutrient intake over time. Many studies simply have dietary data at one time point and correlate that with some outcome years and maybe even decades down the line.  This is an issue because diet may change over time and, because of that, these analyses may be subject to drawing false conclusions.  However, because this study was able to evaluate diet over time, it could determine the effect of changes in diet (i.e. replacing 5% of saturated fat with another nutrient).

Furthermore, it tells us why previous studies may not have been able to detect a role of saturated fat on CHD risk.  Hypothetically, consider this scenario: two people have heart attacks. Person 1 ate less saturated fat than person 2, but he/she ate more refined carbs/trans fats than person 2.  A general analysis would tell us that saturated fats aren’t necessarily the problem.  This study by Yi, et al. takes that a step further and shows us that refined carbohydrates, saturated fat, and trans fats are all associated with relatively equal risk of CHD.  However, calorie for calorie, if you replace the butter or cheese with vegetable oils, nuts, beans, quinoa (or a host of other healthy fats and carbohydrates!) you could be saving yourself from some heart trouble down the line.

Read about the study by Li, et al. here.

References
1. Chowdhury R, et al. Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Ann Intern Med 2014;160: 398–406

2. Li Y, et al. Saturated fats compared with unsaturated fats and sources of carbohydrate in relation to risk of coronary heart disease: a prospective cohort study.  J Am Coll Cardiol 2015;66(14):1538-48.

 

Image from unsplash.com by Juan Jose Valencia Antia.

cardiovascular diseasecoronary heart diseasefatnutritionscience

caitlindowphd • November 4, 2015


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