## Calipers and Science

Just for kicks I dug up the original Jackson/Pollock paper for skinfold measurements for determining body fat percentage. Turns out there's also a 7-point equation that also takes circumference of waist and forearm into account.

Here's a snapshot of the equations for men from the paper ("Generalized equations for predicting body density of men" by A.S. Jackson and M.L. Pollock, 1978. I couldn't find the PDF for the women paper online).

Important notes: skinfolds are in millimeters, circumferences are in meters, and log is the natural log (ln in most computer languages). I plugged my values from two weeks back into a spreadsheet and got the following results:

JP Equation | Density | %BF |
---|---|---|

Sum of seven skinfolds | ||

S, S^2, age | 1.0518 | 20.62% |

S, S^2, age,C | 1.0476 | 22.51% |

log S, age | 1.0506 | 21.15% |

log S, age, C | 1.0482 | 22.25% |

Sum of three skinfolds | ||

S, S^2, age (5) | 1.0607 | 16.69% |

S, S^2, age,C (6) | 1.0549 | 19.24% |

log S, age (7) | 1.0578 | 17.95% |

log S, age, C (8) | 1.0574 | 18.14% |

The most interesting thing here is that there's a large difference between 7 and 3 site measurements, and the 3 site range is significantly larger. Also very interesting to note is that the one-site (suprailiac) AccuMeasure chart is, for me, in line with the 7-site measurement (22.1%). Given other measurements I've taken and just general guesswork based on what I see in the mirror, I think that is a decent estimate.

It's also curious that there are two sets of equations given, one using logs and one using squares.

Moral of the story: more data is better, sometimes not-enough more data is worse than a simpler estimate, and interesting things can be learned when you go to the original source. (This is just a quick note, but the paper is very interesting and reading it will be an interesting exercise that sets proper expectations for, and understanding of, the JP7 skinfold method).

## Crema

Joe Pastry's post on Crema Fresca got me curious. He says,

In fact crema fresca is closer to crème fraîche than sour cream. Its fat

content is usually a bit higher, about 25% compared to sour cream which

clocks in around 20%. Both are still lightweights compared to crème fraîche,

though, which weighs in at a chubby 35-48%.

Well if that's true, then why is sour cream thicker than crema fresca? Or are

we not talking about the same thing. Maybe it's related to what happens in

yogurt. The next time I ended up at the grocery store I was armed with pen and

paper.

Product | Fat / Serving | Fat Content |
---|---|---|

Buttermilk (1%) | 3g / 240ml | 1% |

Whole Milk | 8g / 240ml | 3% |

Half and Half | 3g / 30ml | 10% |

Crema Mexicana ("Mexican Table Cream") | 2.5g / 15ml | 17% |

Sour Cream | 5g / 30g | 17% |

Crema Mexicana Agria ("Mexican Sour Cream") | 8g / 30g | 27% |

Whipping Cream | 6g / 15ml | 30% |

Heavy Whipping Cream | 6g / 15ml | 40% |

I used the rule of thumb that 1ml = 1g. (A pint's a pound the world around

except in England and where people don't use pints or pounds, which is pretty

much everywhere but the USA) Though it's technically not true it's precise

enough for the level of accuracy we need (rounded to the nearest percent). (See

this fact sheet

for more about density of dairy.)

I should note that none of the Mexican cream products in my grocery were

labeled as crema fresca, though that's what I was referring to when I asked

Joe about crema fresca. I don't remember where I picked up the term, or whether

it's entirely accurate. Apparently Joe is thinking about the Agria kind, which

does indeed have more fat than sour cream. Or maybe this brand's table cream is

particularly lean. Anyway, the Crema Mexicana in my grocery is on par with sour

cream for fat content, but it's pourable and not nearly as thick as sour cream.

I imagine we have some kind of yogurt effect going on in the sour cream. I

don't know whether the agria stuff is less pourable, but I suspect it is just

as pourable since it comes in a tall narrow container.

To make crema fresca, based on these numbers, I'd go for 1

cup whole milk and 1/2 cup cream (heavy or light, depending on your level of

decadence), and a tablespoon of sour cream or buttermilk to inoculate.

I can only take his word for the fat content of crème fraîche, as I have never

seen or tasted it.

If you like sour cream on your rice and beans (or burritos or chimichangas or …) then you'll like crema fresca even better. Give it a try!

## Use a balloon to estimate RV

So it's been awhile since I estimated my residual lung volume (RV), and I figured it was time to do it again.

I'm a big guy, so my lungs hold a lot of air. When you're blowing all your air into containers in the bathtub, and you're ⅔ or more exhaled, is not the best time for pausing to move your straw to another container—or worse, refilling the container. This time I decided to use a balloon.

I took a deep breath, exhaled maxmially into the balloon, then blew the rest into the container through a straw. (Wait, did he just say "the rest" after "maximally exhaled"?) I heard that. Yes, you can't exhale all of your air because the pressure in the balloon is higher than atmospheric pressure. In my case, I had another 400ml of air.

Then I emptied the air out of the balloon into the container. This is easy and leisurely once you figure out the trick, but it can seem next to impossible at first. Hint: don't try to submerge the balloon. If you grab the lip of the balloon mouth only, and avoid pinching the neck, you can control the air flow very well. There, I had measured my vital lung capacity (VC).

It worked great, and compared with the last circus event when I measured VC it was much easier.

Now I had to figure out how to get from VC to RV. The clown who wrote http://hans.fugal.net/density kind of left this step vague. I've remedied that and added a page to my spreadsheet. For the curious, my RV is up from 2.0 liters to 2.2 liters, and a total lung capacity of 8.2 liters.

## %BF Nomogram

Remember that system I came up with for calculating body fat percentage using a gallon jug in a swimming pool? I always let the computer do the calculations for me—I have a little script that I run that updates my weight graph. But not everyone is as geeky as that, and formula is not *that* simple, and when you add units conversion in it gets downright hairy.

I finally figured out how to generate a nomogram. Now you have no excuses.

## Fat Loss Progress

Back in October I talked about my fat loss plan, which boiled down to this: exercise 30 minutes a week and live a 1.5 lb-per-week feedback diet.

Here's a snapshot of the graph on the sidebar: