Phat Fat?
July 9, 2008 9:19 AM   Subscribe

Fat: What is it good for? How does body fat, and fat in your diet help you? Why is a really low body fat percentage unsafe?

I'm having a debate with someone who usually follows rational, logical arguments, but while his math and physics is sound, his biology is less informed and he believes that dangerously low body fat levels (ie 5% on a guy, 12% on a woman) are practical and reasonable. Help me explain in clear phrasing, with as much reliable scientific backing as possible, what good things human body fat does for the diet and how fats are something that you need in your diet, not an indulgent extra?

Bonus points if you can find me a scientific article that explains how body fat has a genetic component to how much and where you put it down, as he seems to operate under the idea that food in -exercise = what you get out, for all humans, no mater what the state of their thyroid or whatever.
posted by Phalene to Health & Fitness (23 answers total) 4 users marked this as a favorite
Fat provides cushioning around organs, protecting them from damage. It also functions as an energy reserve, obviously.
posted by nasreddin at 9:21 AM on July 9, 2008

Fat stores energy. Evolution has shaped some people's fat content and placement, for others it's health related. Lance Armstrong has single digit fat, he also has a enormous heart muscle... some of that is good genes, some of it is training.

There really is no fast and sure explanation. You could have a similar discussion over height.
posted by wfrgms at 9:24 AM on July 9, 2008

Response by poster: References = good, btw. I know obvious things like needing it for fat-soluble vitamins, but I lack sources beyond books I read when I was eight. Also ‘It’s genetic’ as an argument tends to lead to the response that ‘Well, they should eat less to work with what they've got, then!’
posted by Phalene at 9:27 AM on July 9, 2008

Check out "Don't You Realize Fat is Unhealthy?" over at Shapely Prose.
posted by ferociouskitty at 9:32 AM on July 9, 2008

Check out the Dietary Reference Intake Macronutrient Publication by the Institute of Medicine . Good primer on fat.

Clinical effects of inadequate intakes, requirements at different life stages, etc.
posted by tiburon at 9:34 AM on July 9, 2008

And here is a review paper that would be a good starting point regarding genetic and nongenetic determinants of regional fat deposition
posted by tiburon at 9:37 AM on July 9, 2008

"Why is a really low body fat percentage unsafe?"

This is a tricky question because it often isn't the low body fat that it is unsafe, but rather a confounding factor that is related to both a deleterious health factor and the low body fat itself. For example it could be protein-energy malnutrition, an underlying disease, the female athlete triad, sarcopenia, substance abuse, intentional weight loss in response to a medical diagnosis, etc etc etc
posted by tiburon at 9:47 AM on July 9, 2008

posted by goo at 9:50 AM on July 9, 2008

"he believes that dangerously low body fat levels (ie 5% on a guy, 12% on a woman) are practical and reasonable."

It is perhaps also worth noting that these "dangerously low levels" are often seen in healthy, well-conditioned athletes such as boxers and sprinters.
posted by tiburon at 9:52 AM on July 9, 2008 [1 favorite]

Response by poster: @kalessin

The 'fat is okay' websites are what I'm trying to avoid. Between the 'Diet Pillz!$$$' and 'I'm a fat woman, deal with it!' blogs, there seems to be very little sound information that doesn't have a strong bias attached.
posted by Phalene at 10:05 AM on July 9, 2008 [1 favorite]

Response by poster: @tiburon Olympic athletes are known for their own health problems. For example the obsession with trying to get into the right weight class in combat sports leads to yo-yo weight gain and loss, same as for body building, where people who compete will briefly lower their body fat levels below safe levels to look good on stage.
posted by Phalene at 10:12 AM on July 9, 2008

How does ... fat in your diet help you?

Cholesterol is important for cell membranes and the production of various hormones.
posted by CKmtl at 10:20 AM on July 9, 2008

Dr. Weil points out that the loss of menstrual cycles in women with very low body fat has other consequences, particularly that we need estrogen to deposit calcium in our bones. Thus very low body fat may cause osteoporosis (in addition to temporary infertility, which is so obvious I almost didn't mention it).

Many of your organs, particularly your kidneys, are cushioned by body fat. This keeps them from getting damaged as you move around.

One symptom of anorexia is the growth of very fine hair all over the body. This seems to be a response to the body's difficulty maintaining its appropriate temperature - there is not enough fat to insulate the body, so hair is another attempt to serve that purpose. So obviously we need fat to help regulate our internal body temperature.

According to The Diabetes Institutes Foundation:
The fats we eat provide us with essential fatty acids, which the body cannot produce, and are necessary for cell structure; kidney, liver, and reproductive function; growth; skin, hair; and wound healing. Fats in the diet provide calories for energy, transport fat soluble vitamins (A, D, E, K), regulate body temperature, and cushion internal organs. Fat also provides satiety and can add to the taste of food.
posted by vytae at 10:21 AM on July 9, 2008

In terms of fat in your diet you need it because certain vitamins (A,D,E,K) and 'fat soluble', without fat in your diet you can't absorb them.

There was also a study done recently but unfortunately I can't find the link right now, that showed that higher levels of subcutaneous fat (as opposed to the stuff coating your organs) was actually good for you and reduced the risks of diabetes and heart disease, ofcourse how you get your fat to only go under your skin and not to coat your organs I don't know ;) There are other more obvious benefits - cushioning/protection for organs and insulation to keep you warm.
posted by missmagenta at 10:34 AM on July 9, 2008

Cholesterol is important for cell membranes and the production of various hormones.

But cholesterol is (as noted in your first link) produced by the human body; there's no need to include it in your diet.
posted by mr_roboto at 10:40 AM on July 9, 2008

The intake of fats and the presence of fat in the body are actually two separate things. Eating fats doesn't make you fat. The fat you eat is broken down in digestion, and your body only converts the sugars back into fat if you have enough of an energy surplus to store. So you've really asked two very different questions here.

I'm not an expert, but I know on the intake side that there are fats that are considered essential. Meaning... a deficiency in these fats would lead to health problems.
posted by knave at 10:45 AM on July 9, 2008

Also be sure to check out the very instructional Shangri-La Diet book (official site, WP entry), which offers an alternative but proven theory around fat, set point, hunger and their social interactions.
posted by meso at 10:51 AM on July 9, 2008

mr_roboto: Hm. So it does. Serves me right for only skimming. Disregard that then.
posted by CKmtl at 10:54 AM on July 9, 2008

There are actually many different kinds of fat, and we still don't understand everything there is to know about which we need and which we don't. For some background on what and how little we know, i would check out this book. I haven't read the whole thing yet, but it details some of the myths about fat being bad and low-fat items being good that were driven, in part, by the dairy industry. It's more the ratio of certain fats (omega-3) to others (omega-6) that is important in a diet, rather than total fat intake.

Also, personally, 12% seems way too low for a woman. I imagine that a female would have more body fat than that just by virtue of internal fat, breasts, and hips alone. I am a very thin woman (5'6 107 pounds) and my body fat is around 18% (I think? it's hard to measure). If work out too much my period will stop, which I'm sure causes many problems besides just pregnancy scares. But it's different for everyone I suppose.
posted by speef at 11:09 AM on July 9, 2008

@knave: FYI ingested fat isn't necessarily converted to sugars and then back to fat for storage. It is broken into free fatty acids to cross through the gut wall, then back into fat for packaging and transport in the blood. Adipose tissue can then store it, without significant further chemical processing.
posted by Good Brain at 12:35 PM on July 9, 2008

Interesting, thanks for the correction.
posted by knave at 12:52 PM on July 9, 2008

Don't have time to dredge of specific links, but here are a few blogs that stress that fat-soluble vitamins and cholesterol are important
Whole Health Source
Modern Forager
Mark's Daily Apple
Plus good ol' fat pushers Weston A. Price Foundation
And a book I read that was all about the important of fatty acids is The Queen of Fats

All advocate getting a significant portion of your calories from good fat and they have some good articles about problems athletes like marathoners with low body fat experience.

For example here is a post on low cholesterol being associated with colorectal cancer and here is one on the important of fat soluble vitamin K2 and one on Omega-3 deficiency and depression.

I wish I could find it, but look up visceral fat. It's the "bad" kind of fat you accumulate in your belly. A study I read found that other types of fat, on the hips for example, are not associated with health problems (they may even be good), but visceral fat definitely is. Aha here is the post. And here is why subcutaneous fat is good and visceral fat isn't
posted by melissam at 12:58 PM on July 9, 2008

Cholesterol is important for cell membranes and the production of various hormones

This is true. It's also worth mentioning that animal cell membranes are made of fat. That's why even extremely lean people (or cuts of meat, for that matter) will never be 0% fat.
posted by Sublimity at 2:16 PM on July 9, 2008

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