Why is there fat in our bones?

An illustration from the Nature Communications study showing the presence of MAT in a bone cross-section.
An illustration from the Nature Communications study showing the presence of MAT in a bone cross-section.

“Every woman wants to look better, to feel better in the year ahead. Slenderness is the way to health, beauty and fitness,” the advertisement reads, the print reminiscent of a mother’s handwriting on a lunchbox note. The face of a pretty woman, hair coiled neatly behind her ears, her lips curled in a slightly seductive smile. “Stay fit and slim by taking amphetamines.”

Obetrol Pharmaceuticals aggressively marketed its premier drug, obetrol, as a diet pill in the 1960s. Available from 1960 until 1973, when it was pulled from the market for safety reasons, obetrol contained four different mixtures of amphetamine salts, two of which were meathamphetamines. Before long, it wasn’t just slightly chubby housewives looking for the drug– because of its psychotropic effects, it was Andy Warhol’s drug of choice.

Obetrol is an extreme example but nonetheless characteristic of the wild diet tactics promoted over the decades in the U.S. and worldwide. From the Beyonce maple syrup diet to the infamous lemonade-cayenne pepper diet, people have fainted, become malnourished, yo-yo dieted and suffered serious mental issues because of the intensity of the desire to lose weight quickly. Needless to say, our emphasis on fat and relationship to food in the U.S. is sometimes unhealthy. When people read “fat” on a product in the grocery store, they’re less likely to buy it because it’s seen as unhealthy.

However, fat is a natural substance. And everywhere you look in our bodies, there is a trace of it, even in our bones.

Scientists have known for some time that bone marrow is composed partially of fatty tissue, called marrow adipose tissue (MAT). However, its precise function and effect on health is still being studied. One study published last year in Cell Metabolism garnered a fair amount of attention for showing that MAT expanded during periods of caloric restriction, unlike other adipose tissue, but still, little is known about it, other than it contributes to systemic metabolism.

A new study published in the journal Nature Communications has taken a deeper look into this tissue for more basic facts. So basic, in fact, that the researchers were able to differentiate two types of MAT for the first time. The researchers, based at the University of Michigan, found that the two different types of tissue performed different functions: one was regulated, and the other was constitutive. The regulated tissue forms later than the constitutive tissue… and that’s really all the researchers were willing to say confidently. The evidence shows that the tissues differ, but the scientists did not want to cast a definitive conclusion on how this affects the body.

However, it’s still a reasonably important finding. MAT has been shown to be inversely linked to osteoporosis, and some have posited that reducing the amount of MAT in an individual’s bones could aid in delaying osteoporosis. It could also reveal more about the somatic controls of metabolism, a complex process that is remarkably intrinsic to each person’s daily life but still baffles most.

Metabolism is an inexplicably complicated process because it involves communication between millions of cells. It is different in each organism, and while it obeys certain laws (i.e. which enzymes a species will find nutritious or toxic, cellular respiration, the combination of enzymes, etc.) it is a complex network of reactions, not an equation. That is why our bodies depend on a balance of nutrients and tissues to work properly, including vitamins, proteins, carbohydrates and yes, even fat.

Fat is demonized in our culture, often, but it is a necessary part of our bodies. Given too much of it, our hearts will fail to work and we become too heavy for our joints, but without enough of it, our metabolisms will not work properly and we cannot generate our own heat to make our bodies warm. As with most things, it is a misunderstood tissue. But if work like that at the University of Michigan continues, perhaps we can develop a healthier relationship with it and ourselves.

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