How Fat Animals Regulate Their Fat: and What This Implies About the Study of Human Obesity

Fat animals who gain weight in preparation for hibernation and then lose it during the winter (or other off-season) abound in nature. When we discuss healthy diets and nutrition in humans, however, we often ignore evidence from animal research and focus exclusively on therapies that manipulate behavior. Why?

Fat animals get fat in preparation for hibernation. They fatten in specific areas of their bodies, such as their tails, backs, guts, and wings. This fattening is clearly modulated by physiological factors. But we typically don't think about physiology or hormones when discussing human weight gain and loss. Instead, we focus on calories. Why this disconnect? And what can evidence from the animal kingdom teach about healthy diets?

The Caloric Balance tells us that "Calories In" and "Calories Out" control our fat tissue. Eat too much and don't exercise enough, and you'll gain fat. Eat less and exercise more, and you'll lose fat.

The Lipophilia Hypothesis tells us that our fat tissue regulates appetite and metabolism to maintain itself, just like the body strives to maintain an internal temperature of 98.6 degrees. When something causes a change in that homeostasis – for instance, if we "overeat" calories - the fat tissue drives a countermanding force to "maintain its stock."

When you look at evidence of fat animals in the animal kingdom -- particularly when you consider hibernation -- Lipophilia seems to be by far the better hypothesis:

1. Per Gary Taubes: "The world is full of species that do fatten regularly, always to serve a purpose."[1] He mentions that migration and reproductive needs (among other factors) compel animals to store fat deposits during certain seasons and to shed those deposits in other times. For instance, ground squirrels have been shown to gain weight in the summer -- whether they are out in the wild or locked in a lab. And these squirrels will shed weight in the winter, whether they are in the lab being fed or out in the wild, living off the fat they stored. Taubes quotes one of the main researches in animat fat metabolism, Mrosovsky, as saying that it is very hard to prevent squirrels from gaining/losing fat according to schedule. Even when researchers cut out sizable amounts of fat from these animals, they automatically restored the missing fat within months.

Taubes also points out that fat storage is an evolutionary adaptation. Thus, the fat tissue tends to be exquisitely bio-engineered to maximize benefits and minimize risks for fat animals.

2. Here's a confirmatory argument from a paper published in the American Journal of Physiology: "Adipose tissue dynamic during cyclic weight loss and weight gain of ground squirrels."[2]

The researchers concluded that "total lipid mass .... is regulated during the annual body mass cycle."

When they say "regulated," they are clearly talking about hormones and other physiological factors -- not calories in/calories out.

3. Just in case the point about fat animals hasn't been driven home hard enough, consider this article: "The regulation of body weight" published in 1986.[3]

The authors write:

"Body weight, like blood pressure or temperature, is physiologically regulated... Not only by the control of food intake, as often assumed, but also by complementary adjustments in energy utilization and expenditure. Such a proposal has broad implications for understanding... such disturbances as obesity."

This tells us that "Calories In" and "Calories Out" are dependent variables. But in order for the Caloric Balance Hypothesis to make any sense at all, "Calories In" and "Calories Out" must be independent variables. You need to be able to manipulate "Calories In" and "Calories Out" separately, or else the entire Caloric Balance theory collapses.

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1. Taubes, Gary. "Good Calories, Bad Calories." pp 249 New York: Knopf (2007).

2. J. Dark, J. S. Stern and I. Zucker. "Adipose tissue dynamic during cyclic weight loss and weight gain of ground squirrels." Am J Physiol Regul Integr Comp Physiol 256: R1286-R1292, 1989.

3. Eric Jéquier and Luc Tappy. "The regulation of body weight" Physiological Reviews, Vol. 79, No. 2, April 1999, pp. 451-480.

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