Obesity in Elephants: Body Size Is Beside the Point

Some people still object to the idea that obesity is a chronic disease. They express concerns that body size is a poor marker for health. But that argument confuses obesity with body size. For insight, consider the case of obesity in elephants. These are all large animals. Some have obesity and some do not.

A new study of elephants in Obesity offers fresh insight into the difference between body size and adiposity. In this regard, elephants and humans are alike. If you want to understand the impact of obesity on health, you must consider body composition, not just size. It’s all about the fat tissue.

Visible and Invisible Signs of Obesity

Until now, studies of obesity in elephants have used Body Condition Scores (BCS). Those scores don’t come from direct measures of fat tissue. They are based on a visual assessment.

For the first time in this new study, Daniella Chusyd and colleagues actually quantified the body composition of elephants. To do so, they used deuterated (heavy) water. By measuring how that deuterated water was diluted in each elephant’s body, they could calculate body fat percentages.

Chusyd showed that BCS is not so accurate for assessing body composition and adiposity. Although it correlated with age, weight, and fat-free mass, it was not a reliable indicator of percent body fat.

BCS Is a Poor Proxy for Obesity

It turns out that these animals can have a high BCS without having excessively high relative body fat.

The practical importance of this for elephants has to do with fertility. Prior studies in zoo elephants suggested that fertility problems might be due to obesity, based on BCS. But this new study suggests it’s more likely a function of age. That’s because BCS is more closely related to age than it is to adiposity.

Bottom line, in elephants, as in humans, you can’t diagnose obesity just by looks. It’s all about the fat tissue. Seeing is believing. But sometimes it’s deceptive.

Click here for the study and here for further perspective.

Elephant, photograph © aotaro / flickr

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December 27, 2017

2 Responses to “Obesity in Elephants: Body Size Is Beside the Point”

  1. December 31, 2017 at 4:12 pm, David Stone said:

    Obesity is messy. How do you even define it? BMI of 30+? Some upper cut-off for % body fat? Should “over-fat” [minimal musculature, but filled out with adipose to normal proportions w/ a BMI well under 30] be considered obesity? Is it always a “whole-body” thing? What about “abdominal/central obesity” which is not necessarily accompanied by excess adiposity elsewhere or an obese BMI? And maybe a stretch, but can obesity be defined by the production of inflammatory biomarkers from damaged/inflamed fat cells?

    Re the cited paper, it looks like obesity is far easier to eyeball in people than it is in elephants. Those fellows turned out to be rather lean by our standards in terms of % fat by weight.

    • December 31, 2017 at 6:20 pm, Ted said:

      David, ultimately obesity must be diagnosed by clinical status. BMI is a crude, though helpful screen. But it’s only a screen. Epidemiologists rely on it because it’s all they’ve got.