Nutrition

The Skinny on Fat

By June 29, 2015 No Comments

Saturated fat.  Oh what a long and sorted history we have! What do you think of when you think of saturated fat? Butter? Beef? Heart disease? Avoidance? Standard nutritional advice and the dietary guidelines support a low saturated diet intake (<10%).  Because saturated fat causes heart disease, right? Right?! Here’s the thing, the supposed evidence backing this claim is, well, from my estimations and research, a bit shaky.  Some of you may have seen some of the more recent articles like this one and this one, in which medical minds have come forward and suggested the so-called evidence our current diet recommendations are based upon are not as solid as we have been led to believe.  Some are saying these are new findings, and we have to have many years of research before we can consider making changes, etc., etc., but in truth, the studies are decades old – erroneous conclusions were just drawn.

Now, I’m not telling you to walk away from this thinking every government agency is out to get you; I simply want you to have all the facts, not just the more convenient or mainstream ones.  I’ve spent days and days reading through research articles and trying to get a firm handle on what the saturated fat research really says.  So, here it is, to the best of my ability, the “other side” of the saturated fat story.

Groundwork
Ok, let’s set some groundwork:

Saturated fat – tends to come from animal sources, especially red meat and dairy.  Coconut oil and butter are also good sources of saturated fat.

Polyunsaturated fat – mostly plant oils; the best ones are the ones that occur naturally like in nuts, avocado, seeds, fish

Cholesterol – is a type of fat that comes both from the diet and is produced in the body itself.  Cholesterol gets a really bad rap, but it is ESSENTIAL for health.  Cholesterol is necessary for the formation of steroids (like testosterone and estrogen), to form vitamin D, and for bile formation so you can digest fats.  Total Cholesterol is a sum of LDL and HDL cholesterol. Remember that last bit; this means that if HDL (the definitely good stuff) increases and LDL remains the same, TOTAL CHOLESTEROL WILL INCREASE (making total cholesterol a poor indicator of actual health/disease risk)

LDL – the “bad” cholesterol. Truthfully, LDL stands for low-density-lipoproteins.  Essentially, LDL is a little “taxi” for cholesterol. Cholesterol is carried around in LDLs and deposited into tissues. As noted above, cholesterol is ABSOLUTELY NECESSARY, i.e. LDLs are ABSOLUTELY  NECESSARY.  No LDL = no cholesterol to tissues = bad effects on health.

HDL – the “good” cholesterol.  So, if we think of LDLs as chickens walking around a farm (our body) and laying eggs (cholesterol) around the farm, we can think of HDL as the farmer, walking around the farm and picking up the eggs. HDL picks up the excess cholesterol, the cholesterol the body doesn’t need, and returns it to the liver for disposal.  If there’s not enough farmers (HDL), the chicken eggs start running rampant (cholesterol).

Ok, so the prevailing story is that saturated fat raises the risk of heart disease.  The “equation” looks something like this:

Increased Saturated Fat Intake leads to Increased LDL
Increased LDL leads to Increased Heart Disease Risk
So….
Increased Saturated Fat Intake leads to Increased Heart Disease Risk

I argue that correlation does not equal causation.  Another way to put it (analogy thanks to my brother…)

Fires cause Firemen to show up
Fireman cause Women to swoon
But…
Fires don’t cause Women to swoon

The problem with the Saturated Fat assumption is that it doesn’t take all the facts about saturated fat’s effects on the body into consideration.  Let’s take a look at the research.  So that this post doesn’t get too long, I’ve given a brief snippet of each article with a citation at the end of the summary to allow you to read even further.  Text in italics is my comments/additions to the summary.

1) In an analysis of many, many studies on the relationship between saturated fat intake and heart disease risk, intake of saturated fat was NOT associated with an increased risk of  coronary heart disease (CHD), stroke, or cardiovascular disease (CVD).  Age, sex, and study quality did NOT change the results.  Prospective epidemiologic (study over time of a group of people) studies showed NO significant evidence to conclude dietary saturated fat increases risk of CHD or CVD (1)

2) This was a GREAT article.  It examined three major reports by important U.S. and European advisory committees comparing the findings in scientific literature and the actual dietary advice relating saturated fat to CVD (USDA/USDHHS report, the Institute of Medicine (IOM) report, and the European Food Safety Authority report).
-Saturated fat intake increases LDL; Carbohydrates do not increase LDL
-Saturated fat increases HDL (the GOOD stuff!); Carbohydrates do not
-HDL and LDL are INDEPENDENT risk predictors of heart disease (i.e. HDL is a NEGATIVE risk factor). In other words,     the higher your HDL level, the lower your risk of heart disease
– AND ratio of total cholesterol to HDL was the STRONGEST predictor of heart disease mortality.  So, again, the higher your HDL, the lower your risk of heart disease.  (This is super important because much/most of the medical world’s emphasis is on LDL levels, but HDL has the GREATEST impact on heart disease risk.  Remember, saturated fats INCREASE HDL, while carbohydrates do not and may even lower it.)
-Polyunsaturated (PUFA) vs Saturated fat, or eating more polyunsaturated fats in place of saturated fats: protective effect against CVD risk was found, but NO significant association with CVD mortality; no significant effect when just looking at PUFA veggie oils; researchers did NOT conclude that saturated fat would change CVD risk (That was a lot, I know. Essentially, the study found that saturated fat and PUFAs had little difference on heart disease risk and no effect on death from heart disease)
– analyzing 20+ cohort studies (following a group of people through time to see an effect) looking at saturated fat intake and CVD risk, only ONE small cohort found an association and the effect was only in men (in other words, out of 20+ studies, only ONE found that saturated fat intake increased heart disease risk)
– none of the investigators from the systematic reviews or pooled analyses concluded that changes in saturated fat intake would change CVD risk (i.e. none of the researchers/authors found that reducing saturated fat intake had a beneficial effect on heart disease)
– the USDA/IOM, etc reports that wrote actual dietary recommendations based on research, used a limited number of studies, picking and choosing what they wanted to discuss.  (the authors of the reports basically used only pieces of the studies or chose studies to include that supported what they wanted to say instead of disclosing and using all of the available evidence and research)
*Saturated fat increases LDL; LDL increases CVD risk… Saturated fat also increases HDL; HDL reduces CVD riskmost significantly (2)

3) Article looking at the TYPE of LDL that saturated fat intake produces.  There are two major type of LDL — big, fluffy LDL particles (type A), and small, dense LDL particles (type B).
-Dietary saturated fat –> larger LDL particles (type A) 
-Small, dense LDL particles (type B) –> increased risk of heart disease
-Some studies have shown small LDL (type B) to be more atherogenic (causing blockage of blood vessels and leading to increased heart disease risk) than larger LDL (type A) secondary to increased susceptibility to oxidation (oxidation = inflammation = bad) and increased promotion of intracellular cholesterol accumulation (cholesterol is more likely to get stuck in the blood vessels and accumulate, blocking blood flow and increasing heart disease risk)
– Reduction in small LDL (but not larger) associated w/ decreased heart disease progression  (Saturated fat causes increase in LARGE LDL particles; SMALL LDL particles are the dangerous, heart disease-promoting form of LDL; saturated fat leads to more LARGE particles, not SMALL (disease-causing) LDL particles) (3)

4) Another brief study looking at the TYPE of LDL particles caused by saturated fat intake
– LDL bigger –> less atherogenic; what some lipid-controlling meds (like HMG-CoA reductase inhibitors) do (so, drugs aimed at reducing heart disease risk “work” by reducing the number of small LDLs and increasing the number of LARGE LDLs; saturated fat does this too)(4)

5) Trading PUFAS for saturated fat in the diet.
– PUFA for Saturated fat supported by a few studies, but not in others
– PUFA in place of saturated fat lowers LDL AND HDL (remember, HDL = good)
– Carbohydrate in place of saturated fats (especially refined carbs), increase triglycerids (fats in the blood), increase small LDL (the disease-causing type), and decreased HDL (the really good stuff) (5)

In summary, saturated fats do increase LDL – no disagreement there – but they increase the large, type A, “healthier” version of LDL and reduce the small, dense, type B disease-causing type of LDL.  LDL is necessary for cholesterol to make its way around the body to the needy tissues and cholesterol is essential for good health.  Saturated fats also increase HDL, one of the most significant modifiers of heart disease risk.  The higher your HDL, the better.  PUFAs and carbohydrates do NOT positively affect HDL levels.

This is just a truly brief summary on all the information out there, but I hope it’s enough to get you thinking and asking questions.  I hope to hear from you and encourage you to read a bit more about this complex and really fascinating subject.  I’ve never been a proponent of the saturated fat vilifying.  As a nutrition blog I enjoy puts it, blaming old foods (like butter, beef, milk) on new problems (like metabolic syndrome, obesity, and type 2 diabetes) just doesn’t make sense.  Eat real foods, whole foods; save the processing for your toys and clothes. 🙂

(1) Siri – Siri-Tarino, PW, Qi S, Hu FB, & Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010 Jan 13. doi: 10.3945/ajcn.2009.27725
(2)  Hoenselarr, R. Saturated fat and cardiovascular disease: the discrepancy between the scientific literature and dietary advice. Nutrition. 2012 Feb; 28(2): 118-123
(3) Dreon DM, Fernstrom HA, Blanche P, Williams PT, & Krauss RM. Change in dietary saturated fat intake is correlated with change in mass of large low-density-lipoprotein particles in men. Am J Clin Nutr. 1998 May; 67(5): 828-836
(4) Packard C, Caslake M, & Shepherd J. The role of small, dense low density lipoprotein (LDL): a new look. International Journal of Cardiology. 2000 June 30; 74(suppl. 1): S17-S22
(5) Siri-Tarino PW, Qi S, Hu FB, & Krauss RM. Saturated fat, carbohydrate, and cardiovascular disease. Am J Clin Nutr. 2010 March; 91(3): 502-509

 

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