Saturated Fat Bad For Bones?

by (0) Updated October 15, 2013 at 2:43 AM Created October 12, 2013 at 10:28 PM

I like a lot of what the paleo movement reccomends but I think its too early to conclude that saturated fat is some miracle superfood when there are too many conflicting studies for any one to reccomend we start eating these fats with reckless abandon.

Moderation seems to go out the window with people.

But anyway I'm primarily interested in this study which says that too much saturated fat could be linked to lower bone mineral density:


I was curious about peoples opinions on this study and the trend of thinking its healthy to eat LARGE AND UNLIMITED AMOUNTS of something just because we now understand that there are benefits.

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4 Replies

278 · October 15, 2013 at 2:43 AM

ABSOLUTELY, people go overboard trying to follow what they believe is healthy... if some is good, more is always better, right?

But, I think that aside from the correlation =/= causation point (which is absolutely an important one to highlight) and the point that any conclusions based on US nutritional recall data are usually pretty sketchy, we need to be aware of the difference between statistical significance and clinical significance. Just because there's a statistically significant change in BMD (that may or may not be attributable to just SFA intake) doesn't mean that you're going to see a higher number of fractures or breaks in the highest SFA population.... (I'm aware that in the discussion section they talk about an estimated 12% increase in fracture risk, but I still think people tend to focus on numbers rather than real-world effects of... everything.)

"The fact that effects were strongest in the younger cohort of men is of particular concern and may reflect reduced dietary quality in that segment of the population." --> There ya go.

This part in particular made me laugh: "The contribution of saturated fat to overall variability in the present study was modest (<1%); however, it was at about the same level, and in some cases stronger than dietary calcium intake in these models. Although modest reductions in bone density are associated with individual factors in isolation, their combined effects are potentially profound. Therefore, any factors that can affect bone density are worthy of attention, especially those that are modifiable (such as diet and lifestyle)." (We know that these results don't really show that much, but things combine to cause problems so you should probably avoid SFA because it'll for sure cause problems in combination with other stuff.) Then they go on to say, "Although not demonstrating a cause/effect relation, the data presented here corroborate evidence from animal and in vitro studies, indicating that dietary fats can have potent effects on bone health." Potent effects?

Also, with respect to the paleo community in particular: we know that exercise (particularly the weight-bearing stuff) is good for improving bone density, and I think that weight-bearing exercise is kind of a cornerstone of the paleo lifestyle, so if anybody would be more "protected" against bone-dissolving saturated fat, it would be people like us. Add to that our generally more nutrient-dense diet, and I think it becomes difficult to apply a study like this to the paleo community.

962 · October 13, 2013 at 6:07 PM

Maria's post highlights one fundamental concept for me: The SAD is so skewed, that very little can be learned by US studies. The bulk of solid facts, on which one can build an understanding of human nutrition, comes from comparative anthropological studies of ancestral (and more modern) diets. At best, US studies can be used to confirm concepts developed from anthropology. Examples are the various Omega 3 studies, the relatively recent set of studies on intestinal flora, and the many studies encouraging people to eat more fruits and vegetables.

992 · October 13, 2013 at 1:12 AM

It looks like they just asked people to guess / recall what they ate for the week and report their own nutrition data based on some "USDA nutrient database." Then they divided them up into a sort of "Guys who claim to eat lots of saturated fat but not as much MUFAs or Omegas" vs "Guys who claim to eat lots of MUFAs and Omegas but say they don't eat as much saturated fats."

Then they threw out the results of anyone with too low of an intake to be telling the probable truth, and threw out the results of anyone with too high of an intake to be telling the probable truth. Then they threw out some other results they didn't like for pregnant women and such. It looks like they adjusted the numbers for those who were eating more calcium. They also adjusted for race, and how much someone reported they exercised. Also smoking and age and some other factors.

After they messed with the sample, divided it up, and altered the numbers, it appears as though the guys that were concerned with eating less saturated fat tended to have better bone density. It could very well be that those guys ate more fat-soluble nutrients like vitamin k2, where the guys eating homogenized SFAs didn't.

There's also this from the study:

The present results are not in agreement with results reported in a smaller epidemiologic study (24). In that study, no effect of saturated fat on forearm BMD was found in either men or women.

They explain the conflicting results by saying those people from that study were Greek and ate a different diet on top of the SFAs or that their alterations to the raw data or inaccuracies in reporting accounts for the difference.

I'm not that impressed with either study.

To me, this just says that if you ask a guy what he eats on average. And he tends to eat things with a ton of saturated fat and not much MUFAs or Omegas. That even if he claims to exercise a lot, he's probably not and eating junk food, and thus, has poor bone density if you actually get in there and scan it.

4247 · October 13, 2013 at 12:30 AM

OK I will admit: I didn't read the whole study. HOWEVER, just from the abstract I can tell you one key thing:

The title has the dread words: "associated with."

In other words, this is not evidence that saturated fat causes low BMD. It is simply associated with BMD. Correlation =/= causation. People who eat a lot of saturated fat primarily get it from junk food (look up the 2010 dietary guidelines and take a gander at the "sources of dietary saturated fat" chart; iirc the first category is "grain-based desserts"). So "saturated fat is associated with" ALSO means "junk food is associated with" and "not giving a fuck about your health is associated with." It does not prove that saturated fat per se is responsible for any of this.

If you look a little further, you can see that they controlled for "age, sex, weight, height, race, total energy and calcium intakes, smoking, and weight-bearing exercise" - so in other words, there are still a lot of uncontrolled variables that might be skewing the results. Vitamin D and K2 intake, overall dietary quality, time spent in the sun (=Vitamin D synthesis), and magnesium intake come to mind.

Basically in the US, people who care about their health by and large avoid saturated fat. This means that saturated fat is a marker for the "I don't give a fuck" lifestyle. It's not surprising that "I don't give a fuck" lifestyle is associated with low bone mineral density, but it doesn't prove anything about saturated fat specifically.

That said, I agree with your point that there's no reason to go overboard on the saturated fat just because we know it isn't the devil. But this study does not give you reason to fear your bones crumbling into dust because you ate some butter that one time.

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