You see the same obsession with weight in vets: a common cat lives on average 2 years if feral, 4-5 years if outside pet, 12-18 years as an indoor pet. As recently as 20 years ago, the life expectancy for a cat was only 6 years as an indoor pet. Clearly, we have no idea what the optimum weight or body composition of cats is, there is literally no precedent.

1. “Low lean mass was associated with greater impairment in symptoms [and] activity” among “patients with obstructive airways disease.”

2. Among elderly women in one study, “a one-unit gain in lean mass:fat mass ratio reduced [self-reported functional] limitation.”

3. In another study, “changes in body composition, as a consequence of dietary and exercise modification, contribute to 12% of the ‘observed’ improvement noted in weight-adjusted peak aerobic capacity following cardiac rehabilitation and exercise training.”

4. “High BMI [hemodialysis] patients with inferred high body fat have increased and not decreased mortality, [with] the protective effect conferred by high BMI … limited to those patients with normal or high muscle mass.”

5. In a study of premenopausal women, “Fat and lean mass both independently predicted poor performance on postural stability, [indicating] that greater fat mass may compromise stability and, thus, increase fall risk in heavier individuals.”

So in sum, body composition is kind of a big deal for individual health outcomes. Still, as I understand it, the data is insufficient to show the effects of changing body comp over time on the health of the general population.

Ask yourself this: what is “true health” anyway? Is it a chronic but manageable condition? Is it trying to avoid diseases with a high genetic component? Is it feeling able to do whatever you want to?

As for body composition, my assumption isn’t that it is stable from a century ago. My assumption is that it doesn’t matter. And so far, no one has successfully proved that it does.

I also agree that as Americans’ life expectancy has been hitting record highs, our understanding of the effects of increased BMI on populations’ health remains incomplete. While obese Americans have been more likely to self-report ill health, and, as zoelouise wrote above, be diagnosed with various maladies, these are noisy, perhaps biased, indicators of true health.

Finally, on historical changes in body comp: no one has data on percentage bodyfat in representative samples from a century ago. Anecdotally, it is a common assertion that people have been getting fatter, not just bigger. (See, e.g., the discussion here). So while your skepticism is on point, it does not mean that we should default to the assumption that body composition has remained stable over time.

Yes, the CDC has data going back to 1971. But the NHANES data were not standardized. Most notably, prior to 2000, actual heights and weights were reported, rather than the more recent and meaningless BMI. (For more on this, no significant trends between 1999 and 2006. So, not accelerating, not increasing.

There is no evidence whatsoever to support your contention that increases in weight, along with height, are exclusively fat. What’s more important perhaps, is, so what? Americans are also living longer than ever. Since most of humanity has never had the advantage of plentiful food, and since much of humanity still doesn’t, we have no idea what being taller, and heavier, and healthier will mean for us.

My point on how Americans have been affected by nutritional changes over time is this: we have been able to get more calories, and more cheaply, from just about every conceivable source. Yet as the population has gotten taller, it has gained fat, not lean mass, suggesting that some factor is channeling the effect of improved nutrition into an increase in the prevalence of obesity. I do concede that neither of us can back up our (opposing) assumptions on this point with data.

At the end of the day, I fear you will not get far denying that Americans have been getting heavier (and, strictly speaking, fatter). That “small shift” of the normal curve of the BMI distribution you mentioned in your first post doesn’t seem to exist. What seems to be going on is that at any point in time, some people are fat and others aren’t (assuming plentiful food); and, over time, more Americans have become fat, and fat Americans have become fatter.

@P:

I specifically did not say that Americans were getting fatter, as I do not think there is reliable evidence of any change in percent body fat, as you say, and feel we should not make assumptions about it. We do not know the composition of the small amount of weight that the American population gained, nor does the assumption that we gained body fat account for the height gain as well.

Childhood obesity is a harder question because much less (and much less history of) data is available to understand the trends. “Obesity” and “overweight” have only recently been defined for children, and the information we have on this is only in the last decade or so. During the first part of that time, children gained a small amount of both weight and height, and have since leveled off.

The increase in children’s weights and heights can be attributed to the same factors as those for adults:

1. Increased nutrition and health play a role, and are as likely to affect children as adults. Perhaps more so, as the period of time when non-genetic factors play a role in determining adult height (and likely weight, although I know of little research) is concentrated in infancy and childhood.

2. It is possible for the age of the population as a whole to have an effect on heights and weights of children. People are having children at later ages and I do remember seeing a population study which correlated higher-weight babies with older mothers.

3. Second-hand smoke has a stimulatory effect on children.

4. There is also another reason I thought of since I last posted that might be considered as an explanation of increase in height and weight for the populations as a whole, including children, which is the increasing prevalence of non-white people in the US. Current statistics show that according to the arbitrary definitions, minorities are more likely to be “overweight” or “obese”.

The question as to why we grew both taller and heavier at the same time confuses me a bit. The answer seems self-explanatory to me. To the small extent that height and weight are influenced by factors other than genetics (and twin studies show they are influenced by genetics by about the same amount), adequate nutrients and general good health in childhood both seem to influence those numbers higher. It seems as if you believe that growing both heavier and taller due to the same causes is somehow a contradiction.

@Lyndsay:

Why are people getting diabetes at a younger age?

I will assume you mean type II diabetes. We don’t know that people _are_ getting type II diabetes at younger ages. First, there has been a change over time of diagnostic criteria from symptoms (which children do not, as a rule, exhibit) to serum blood sugar, and then to ever-lower blood sugar numbers. Second, there has been an increase in blood-sugar testing of the population as a whole, and the beginning of testing blood-sugar in children at all, a previously unknown practice except in very, very rare cases. Finally, children naturally go through periods of high blood sugar before a growth spurt, so even those cases that are found are suspect.

All of these can cause diagnosed cases to go up, without an actual increase in incidence.

Are there any articles or studies that you know of that show the correlation of increasing age of the population and increasing obesity?

During the time that information has been collected on height and weight in the U.S., both the average age of the American population and the average BMI have gone up. Strictly speaking, this constitutes a statistical coincidence and does not prove diddly and/or squat, but we don’t need anyone else to do the comparing for us.

A more interesting comparison for these purposes would be to see if there exists a correlation between individual age and increasing weight, which has been done.

During the time we increased in height, BMI wouldn’t have increased that much, right?

No, actually. Remember that BMI is computed with the _square_ of height, so, e.g., a 10% increase in height will only decrease BMI by 1%, whereas a 10% increase in weight increases BMI by a full 10%.

Hope this helps,
pocket_owl

* 2.9 times more likely to have been diagnosed as diabetics (26% vs. 9%).

* 2.6 times more likely to have been diagnosed as having a sleep disorder

(21% vs. 8%).

* Twice as likely to have been diagnosed as suffering from depression

(32% vs. 16%).

* Twice as likely to have been diagnosed as suffering from back problems

(26% vs. 13%).

* Twice as likely to have been diagnosed with anxiety disorder

(20% vs. 10%).

* 1.9 times more likely to have been diagnosed as hypertensives

(41% vs. 22%).

* 1.8 times more likely to have been diagnosed with digestive disorder

(18% vs. 10%).

* 1.7 times more likely to have been diagnosed as having arthritis

(40% vs. 23%).

* 1.7 times more likely to have been diagnosed as having high cholesterol

(38% vs. 22%).

* 1.7 times more likely to have been diagnosed with migraine

(20% vs. 12%).

* 1.3 times more likely to have been diagnosed with allergies

(48% vs. 37%).

Overall, adults diagnosed as obese report that they have been diagnosed with an average of 6.4 chronic conditions, compared to an average of 3.1 conditions for those among the general adult population

Colorado is one of the skinniest states in the US. According to newsy.com, one of the reasons is because they have a health conscious society. http://www.newsy.com/videos/the_obesity_epidemic As a citizen originally from Arkansas, part of the reason for the health crisis is how people are raised to eat food. Fried food is a common diet there and it stems from times such as the Great Depression when food was scarce. People fried food to add more calories to their every day diet. Now it’s a part of the culture.

Why are people getting diabetes at younger ages?
Are there any articles or studies you know of that show the correlation of the increasing age of the population and increasing obesity? This explanation makes sense but I’d love to read more.
During the time we increased in height, BMI wouldn’t have increased that much, right?

You both write that Americans have gotten fatter because the population has gotten older, and weight increases with age. It would be more precise to say that, with a few exceptions, people gain fat as they get older. This, on its face, is a reasonable explanation for the trend: if people gain fat steadily throughout their lives, the longer they live, the fatter their population will be.

However, it does not explain why the prevalence of childhood obesity has also increased.* By definition, children don’t get older from one cohort to the next. (To the best of my knowledge, they also aren’t big on smoking.) So even though children were omitted from the dataset I initially cited, changes in the population’s age and smoking habits don’t account for all of the change in the prevalence of obesity.

I think pocket_owl makes a great point in noting that nutrition and health have improved drastically over the past century. As a small example, the physiques of old-time elite athletes are now attainable for millions of average Americans. Cheap food and the decline of infectious disease are undoubtedly important. But – bringing it back to definitions – it is equally important that what Americans have been gaining is largely fat, not lean mass.** We grew taller, but also wider. Why is that?

It would be interesting to see if BMI trends did settle into a pattern of logistical growth: this might happen if populations genetically couldn’t get fatter beyond a certain point, or if society were unable to accommodate large numbers of people over a certain BMI.

* http://www.cdc.gov/obesity/childhood/prevalence.html
** There is little (no?) reliable historical data on body composition, but this seems a reasonable premise.