On BMI and carbs

▼ Last week at OHM2013, Bert Hubert had an interesting talk: What you need to know about what you eat: health & weight. He started with a slightly simpler version of this graph that show how we all started getting a lot fatter since the mid-1980s:

Source: Prevalence of overweight, obesity and extreme obesity among adults: United States, trends 1960-62 through 2005-2006.

I have a big problem with these kinds of statistics. Basically what they do here is count how many people go from a BMI of 24.9 to 25.1 (normal weight to overweight) and 29.9 to 30.1 (overweight to obese). And obviously a BMI of 24.9 is perfectly healthy while 25.1 is problematic </sarcasm>.

Still, it's interesting and somewhat alarming to see how the obese line started going up around 30 years ago. But Bert's graph didn't include the overweight line, which curiously has been quite stable over the past 50 years.

Another issue with these statistics is that the BMI itself is a very flawed measure. The idea is that if you're twice as tall, you get to weigh four times as much: BMI = kg/m². But we live in a three-dimensional world. If you make an object twice as big, its volume gets eight times larger. So all else being equal, it should be eight times heavier: kg/m³. However, that's not exactly how things work with humans. Using a power of 2.3 to 2.7 would be more appropriate, and not "punish" tall people like the current BMI does. As the population grows taller, this could be an issue.

But after crunching some numbers collected by the US National Center for Health Statistics, it turns out that the effect of people getting taller isn't very significant. According to the 1960-1962 numbers, males in the US age 20-74 had a mean BMI of 25.1 and females 24.8. Nearly 40 years later in the 1999-2002 figures this was 28 and 28.3. The mean height of men 20-74 had increased from 173.4 to 176.2 cm, women from 160.2 to 162.5 cm. (Curiously, younger people are actually smaller than they used to be; in the 1999-2002 figures the age group 40-49 is the tallest.)

So the mean BMI for men increased by 11.2% and for women by 14%. 1.2% of that increase in BMI can be explained by the increase in height and goes away if we use kg/m^2.7. A 10 - 13 % increase in height-adjusted BMI is still very significant, but not quite a "graph of doom".

So now that we have a better idea of the size of the problem, what's the cause?

Bert argues that we've been given some very bad advice the past 30 years, and that eating less fat (like meat) and more carbohydrates (bread, pasta, potatoes, rice) has made us all fatter. The reason to reduce our fat intake was to avoid cardiovascular disease, a major cause of death. But it turns out that many fats aren't really bad for you (saturated animal fat) or even good for you (in oily fish, olive oil). You may still want to avoid processed vegetable oils (margarine), especially trans fats, though. But an overdose of carbohydrates is quite problematic.

However, it seems to me that the pendulum is now swinging too far in the opposite direction. Yes, eating too much sugar or carbs in general makes you fat and will likely give you diabetes. But eating too much of anything makes you fat and increases your risk of various diseases.

Grains and potatoes have been a staple of our diets for thousands of years, and we managed to get a lot of things done eating them. The fact that people got smaller and didn't live as long when we switched from hunting/gathering to agriculture is fairly meaningless: when something new comes around, it's almost always inferior to the old thing that it'll be replacing soon—at first.

So for thousands of years we managed to have a healthy weight eating lots of grains and potatoes. This suggests to me that carbohydrates can be part of a healthy, balanced diet. However, there are many people who swear by a low-carb diet. Good for them. It's just that what works for them isn't necessarily the best thing for everyone.

If anyone is interested in my advice, here it is. Don't drink your calories (or joules). Stick to water if you can, but if you need something sweet to drink, find something using an artificial sweetener that you like. Eat bread, pasta, rice, potatoes in moderation, and combine them with foods that have proteins and fats. Minimize candy and snack food. These are optimized to taste good and be cheap to make, so they have lots of sugar, flour and processed vegetable oils that you don't need, and it's sooo easy to overeat this stuff. Eat fruit instead and don't worry about the sugar it contains. Even Bert says 120 grams of carbohydrates a day is ok. That's 10 apples.

Permalink - posted 2013-08-07

Having fun with invisible ink

▼ A month ago, I got a message from the OHM2013 speakerdesk:

Since you you'll be giving a presentation, lecture or workshop at OHM2013 (for grownups), we'd like to ask you; do you feel like giving a little talk about your subject for kids?

Thinking that my talk (about federation of online services, where you can have a choice of service providers or even run your own server rather than be beholden to big companies like Google, Facebook and Twitter (PDF of the slides, explanation in Dutch) might be a tad too abstract for kids age 6 - 10, I proposed something else instead: writing secret messages in invisible ink.

So I got to experimenting a bit. A well-known type of invisible ink is lemon juice or sugar water. After writing with it, you heat the paper, the ink turns brown and the message appears. Another option is to write with something that is acidic or basic, and then use red cabbage juice to bring out the message. This has the advantage of not requiring a heat source. So I got a cabbage, cut it into small pieces and cooked it with only a little water to obtain the dark purple juice. You can then easily create your own litmus paper by soaking up some juice in coffee filters.

About 25 kids age 6 - 10 participated. They really do seem to get younger every year... they're so small! I wanted to get them involved, so I brought several kinds of fruit and let them squeeze out juice to be used as ink. The onion wasn't a success, it's almost impossible to get juice out of it and it's not very acidic so it doesn't make for very good ink anyway. Apples are also hard to juice by hand, but are supposed to be quite acidic if you get the right kind. The juice we got was definitely weaker than the lemon juice, though. Grapes are fairly easy to juice, but it helps to have a coffee filter. Use white/green grapes or the ink is too visible... But lemons give you the most bang for your buck by far: just cut them up and squeeze, and you get plenty of juice without much pulp and it's nice and acidic.

The kids were completely unfazed by the fact that cabbage juice turns different colors when exposed to fruit juice and soap, by the way. They also had no problem drawing pictures using the "invisible" ink. (I guess drawing is more fun than writing.) In practice, the ink is not that invisible, because you can see where the paper is wet. I brought a bunch of small brushes to use for this, and that seemed to work well.

After finishing, we let the drawings dry in the sun. Then finally we got all the kids back inside and put all the drawings on a table, and applied the cabbage juice. I put the juice in a spray container, but this didn't work all that well: the juice doesn't get everywhere evenly, and a lot gets into the air, not smelling all that great. Using a big brush to paint it over the drawings worked better.

It takes a minute or two for the reaction to happen, turning the cabbage juice blue on unpainted parts of the paper, and red/purple where there's fruit juice on the paper. Putting cabbage juice on a drawing takes half a minute, so having all the kids come back inside before we started doing this was not the best approach with just one big brush. Having them come in as their drawing had dried would have been better.

If I'm going to do that again, I want to investigate some alkaline materials and see if we can get additional colors. Cabbage juice can be red, purple, blue, green or yellow, so there should be lots more possibilities than just the red/purple/blue that we got with fruit juices as ink. Also, it's easy enough to manufacture the cabbage juice on the spot, it doesn't have to cook long and you can just rip the leaves by hand if you don't want to use a knife. You can also buy prepared canned red cabbage and squeeze the juice out. I don't think the stains are too hard to get out, but you may not want to wear anything too new or too white.

Permalink - posted 2013-08-05