Monday, July 15, 2013

Bigger goes along with better

kw: book reviews, nonfiction, history, economics, sociology

I remember my father telling me, when I was a pre-teen or early teen, his theory of "why kids are getting bigger" and in particular, why new Olympic records were still being set, after generations of competition. "Better food and better medicine. When kids don't get sick as much, they can get bigger and stronger and faster and smarter."

Another memory. Valley Forge, maybe five years later. A park guide said, "General Washington was like Goliath to the British. The average 'redcoat' was about 5-foot-2, and Washington was 6-4. He rode the biggest horse he could find, and it scared the crap out of the British." He exaggerated a little—Washington was 6'-2" (187 cm), and as the chart below shows, British recruits just prior to 1800 were about 5'-6" (167 cm)—but the point is accurate. He was the tallest man most of them had ever seen. Of course, most of his own men were similar in stature to the British, and he scared the crap out of them also.

This chart illustrates a "Waaler Surface". It is from page 60 of The Changing Body: Health, Nutrition, and Human Development in the Western World Since 1700 by Drs. Roderick Floud, Robert W. Fogel, Bernard Harris, and Sok Chul Hong. The chart is rather complex, so take a moment to peruse it, and then I'll explain.
For Americans, refer to these tables:

160 cm = 63.0" ≈ 5'-3"
170 cm = 66.9" ≈ 5'-7"
180 cm = 70.9" = 5'-11"
190 cm = 74.8" = 6'-3"
(to convert cm to inches, divide by 2.54)

40 kg = 88 lbs
60 kg = 132
80 kg = 176 lbs
100 kg = 220 lbs
(to convert kg to lbs, multiply by 2.2046)

The Iso-BMI curves—the dashed lines—set a foundation. The heavy curve shows minimum risk of dying in the next ten years. To the left is underweight, and to the right is overweight. Now, the iso-mortality-risk curves—the thin solid lines—show relative risk of dying within ten years, gleaned from a study of middle and late middle aged Norwegian men, and correlated with the sketchier records of the past 300 years throughout Europe. The curve labeled 1.0 passes through the minimum-risk curve at 1.675m (66") height. At that point, the healthiest weight is 72 kg (168 lbs). But a person taller than 1.84m (72.4"), weighing about 80 kg (176 lbs) has a 30% lower mortality risk!

Hmm. I am 6'-0" and 207 lbs (1.83m and 94 kg). That puts my relative mortality risk at 0.9. That is 15-20% worse than the optimum for my height. More properly, among a group of men just my size, 20% more of them are likely to die in the next ten years, compared to those at optimum weight/BMI. That is according to this Waaler surface.

But the little circled × and + signs mark the important historical message of this chart. Throughout most of the past 300 years, the French were shorter than the British, and less healthy. However, the trend through time has brought the two populations to near parity, with average heights of about 1.77m (just under 5'-10"), and though the British tend to be heavier, their mortality risk is the same (they are on the same iso-mortality-risk curve).

A little further along in the book, Table 2.5 on page 67 lists the average height for men in six European countries, as it has changed since 1750. I converted the data into this chart:

A quarter-century marked 18-IV, for example, refers to the years 1875-1899. That is the range of dates during which men in a particular cohort reached physical maturity.

I am not sure what happened in Denmark since 1975, but for three of the other five countries the height scoops up toward the 1.8m range, then slows down approaching the year 2000. The last data point is missing for Hungary, and we see that France is apparently a little behind England and the Scandinavian countries, perhaps lagging by 25 years (It is tempting to speculate that the different lines will converge on some optimal average height, but only time will tell).

This is something the authors remark upon, that in the richer western countries the trend of increasing height seems to be slowing down. Perhaps there is a genetically-determined maximum height for each family, and as barriers are removed, through better nutrition, better medical care and less need for very heavy labor, that maximum is being reached by a larger and larger number in each generation.

The book is a textbook for a socio-economics course. Thus it is very dense with figures and tables and discussions of the sources and assumptions and calculations needed to reach the authors' conclusions. In a way, the plethora of illustrative material shortens the reading substantially. Reading a text-only book of this density, of 374 pages, would have taken somewhat longer than the 12 days it took me! I can swallow up a page-size table quicker than I can read a page of scientific text. I would say that the first 80% of the book is devoted to "confidence building": presentation of the facts and sources and so forth, so that the later conclusions will be more readily accepted. If the authors choose to write a more popularized version, I'd expect something quite a bit more brief.

But this book is quite valuable as it is, for those willing to slog through it. All that data on size and weight and purported health are fine, but what has caused it? And are we really healthier? Not all agree that we are. Much of the work discussed, work done by the authors and many colleagues, and by others, including those who may draw different conclusions, is intended to tease out mortality and morbidity as they have progressed through time. Prior to about 1930, when the first effective antibiotics were developed, we see that average size and health were already increasing. The "Third World" is presently living an 18th-Century life, nutritionally and medically, and it shows; average adult male heights for most groups are near 1.65m, plus or minus 5 cm or so.

However, the discussions do not dwell only on averages. One large section deals with distributions of caloric intake, compared to the basal metabolic requirement plus "maintenance", which is necessary to stave off long-term starvation. Throughout the 1700s and into the early 1800s, 15-30% of the poorest didn't have enough to eat, and were starving. Even those just a little better off had little energy to work. Did you ever wonder why the beggars in poor countries (and poor areas of richer ones) do little more than sit around begging? I am not talking about panhandlers on American city streets, but the truly destitute. It is because they eat so little they have no energy left for any kind of work.

For example, if a man of a certain size could sleep all day, his basal metabolism might require 1,600 calories (AKA kcal). Yet he needs to awake from time to time to, at least, eat and eliminate. Also, his body uses some energy replacing worn out tissues. These maintenance activities bring his caloric requirement to 2,030 (an added 27%, or 430 kcal). Just walking around takes about 3 times as much energy as sitting still (2x for the walking and 1x for basal). This factor of 3 is a Physical Activity Ratio, or PAR; a 24-hour walk would require 4,800 kcal (the exercise plus the basic) plus 430 (maintenance) for a total of 5,230. Of course, a full-time panhandler won't walk 24 hours, but may walk a few hours a day. If we assume 4, the total caloric requirement is 2,030 plus about 530, or 2,560 kcal. If this person does anything else except lie around quietly, more calories are needed.

At the high end of the scale, assuming a farmer can eat all he needs to, the PAL for most farm labor is about 5. Farmers work long days; 10 hours or more is quite common, 7 days per week. Then many around-the home activities have a PAL around 2. A farmer's energy budget may resemble this:
  • sleep 8 hr: 530
  • labor 10 hr: 3,330
  • family interaction 3 hr: 400
  • read, talk, etc. 3 hr: 300
  • body maintenance: 430
That all adds up to 4,990 kcal that he needs to eat. The next time you are at a café that farmers or farm hands frequent, don't be surprised by their enormous breakfasts! However, for those without such ready access to abundant food, such as the lower classes in 18th Century Europe, undernourishment was the norm. Dad was underfed and couldn't work hard enough to earn much, Mom was underfed and so had undersized babies; she had a scant milk supply and after being weaned the youngsters frequently went hungry. They grew up short and scrawny. Then, being undernourished made them all less able to fight off disease, which also takes energy. Their lives were short and hard, and other charts in the book show how size correlates with social class. Simply put, the aristocrats were taller because they could afford sufficient food, and being better nourished means they were less often ill.

The epigenetic effects of such a history can't be shrugged off in a single generation. The 300-year chart above shows how gradual the change was. Increasing food supplies came first, and it took a few generations for size changes to follow. 300 years represents 12-15 generations.

Now we can consider life expectancy. At this point, data for women was also available. This chart, from page 148, shows the increase just through the 20th Century. The bars represent average remaining life expectancy. Thus, for 65-year-olds, only a dozen or so years remain, meaning that on average they can expect to live to age 80 (men) or 85 (women; for the 2000-2002 figures).

From the bottom, note that at age 0 compared to age 1, there is quite a difference in 1900, but very little in 2000, though for both there are great increases from 1900 to 2000. Infant mortality was so great in 1900, that a 1-year-old, who had already survived a few "childhood diseases", could expect on average 5-6 years more life than a newborn.

As an aside, two years ago we visited a cemetery in Missouri, where some of my ancestors are buried. I was sobered by the large number of tiny gravestones for infants and children under 5, who had died between about 1830 and 1930. The gravestones for those who survived to ages in the range 70 and up were very few. I think my great-grandfather was the only 90-year-old buried there. When he was 65, in 1935, his average life expectation was to live to about 77. He beat that, but most didn't. My father, who was 88 when we went there, had given me a list of men to look for, in the nearby town, men he had known as a child. I reported later that I found them all—in the cemetery. Dad is the last survivor of his generation from that town.

Today, it is considered unusually tragic to have a child die. Prior to 1900 it was tragically common. So perhaps the age-15 figures tell the best story. At age 15, in 1900 a young man might expect to live another 48 years, to 63. By 1950, it was 53 or 54, to almost 70, but by 2000, a 15-year-old has an average remaining expected lifetime of 62 years, to age 77. For young women, add 3-4 years to all these figures.

Now we come to the last figure I wish to show, Figure 6.8 from page 341:

The squares on the dotted lines are for Union soldiers who'd survived the American Civil War, measured and weighed at ages 40-59, and their dates of death from military pension records. The circles on solid lines are from modern non-Hispanic Americans, measured and weighed at ages 40-59 in the 1980s (61,000 of them). In both data sets, the relative mortality risk is for the succeeding decade. The simple message is clear. Being shorter is riskier, and being too skinny is also riskier. The "sweet spot" for the Civil War veterans is about 1.9m tall and BMI near 24 (87 kg: 6'-3" and 192 lbs). For the recent cohort, it is about the same height, but optimum BMI is nearer 26 (94 kg or 207 lbs).

Both BMI charts show that risk rises gradually upwards of 26, and picks up faster after 30, the criterion for "obese". However, a Waaler chart such as the one above is needed to ferret out whether being short and heavy is better or worse than being tall and heavy. Look at the Waaler surface above: at any BMI between 19 and 31 or 32, being over 1.8m tall is better than being 1.6m tall at any weight!

But this introduces a new and sobering realization. In the west we have gone from being undernourished to overnourished. In America 30-40% are now obese, and the European nations are following closely behind. Mortality and morbidity (chronic debilitation from illness) are increasing again. The number of morbidly obese (BMI more than 40) is the most rapidly increasing segment of American society. I'd be morbidly obese at 295 lbs, or 134 kg. These days I know lots of folks over 300 lbs, and a few in the 400-plus category.

As the authors of Changing Body show, there has been an amazing run of three centuries, with improving nutrition, public health, medical care, that have led to taller and heavier and stronger and even smarter people throughout the west. But we are going over the top. Now we spend about as much for weight loss programs and products as we do for food. How long will it be, until, if nothing else, those who most easily grow exceedingly obese are culled from the gene pool?

1 comment:

Anonymous said...

Nice post. I learn something totally new and challenging on websites
I stumbleupon everyday. It's always helpful to read content from other writers and
practice a little something from their sites.

Look at my website: vertical jump increase Workout