Can Our Bones Be Fat?

Bone Fat?

Spot losing fat has been busted, but recommendations still persist that we can beat everything from belly fat to back fat with exercise.

Now, we can possibly beat bone fat with exercise? Wait, our bones can be fat?

We have already seen that our tongues can be fat, so maybe bone fat is a possibility. At first glance, it might appear that too much bone fat is related to the “big bone” myth, but this is a bit different, and is not a cosmetic or body image issue.

Marrow Adipose Tissue

What is actually being referred to is marrow adipose tissue, or the fat deposited in the yellow bone marrow. This yellow marrow fat is different than other fat in our body, and is not to be confused with the original smooth mello yello.

We already know that, “Higher levels of marrow fat are known to occur in humans in conditions of starvation, alcoholism, spinal cord injury, and prolonged bed rest, conditions that are also associated with reduced bone density.”² There are subsequent effects on bone formation, osteoporosis, and fracture risk.

Magnetic Resonance Spectroscopy can be used to show us how much fat we have deposited in our bones. Using this technology to examine the lumbar spine, this study found that, as visceral fat increased – or the fat inside, around the organs – so did fat content in the bone.¹ However, this relationship was fairly weak.

Subsequently, “...the effect of localized ‘obesity’ within bone, as represented by marrow adipose tissue (MAT), on bone health is controversial.”³

Exercise, Bone Fat, and Mice

Okay, so what about exercise? This well done study is the root of the media attention.³ After a 3-month dietary lead-in, 16-week-old mice did an exercise intervention of running for 6 weeks.

Weighing in at around 25 grams, they ended up running about 0.4 kilometers per gram each day, totaling 10 kilometers or around 6 miles per day. For a 150 pound human, that would be nearly 17,000 miles per day.

The mice were assigned to one of four groups. Sedentary mice fed with a low-fat diet (LFD), exercising mice fed a low-fat diet (LFD-E), sedentary mice fed with a high-fat diet (DIO), and exercising mice fed with a high-fat diet (DIO-E).

As you would imagine the sedentary mice fed the high-fat diet (DIO) gained the most fat in the 6 weeks – about 14% more than the low-fat diet. The two exercise groups stayed the leanest.

As shown in these scans of their femur bones, the two exercise groups had less fat, as illustrated by less blue to purple coloration.

For percentage of fat in the marrow, there was a significant main effect of exercise, being lower in the exercise groups – about 0.3% less than the low-fat sedentary group, and 1% lower than the high-fat sedentary group.

The authors conclude, “Exercise appears to drive a more organized form of bone remodeling as a strategic means to accommodate the changes brought on by obesity.”³

Conclusion

So, yes, our bones can hold more or less fat in the marrow, and exercise appears to help reduce it in an animal model. However, it took a lot of exercise – by body weight, the equivalent of a human running from New York to Los Angeles, six times per day for 6 weeks.

In conclusion, this one is a clarify, because there are many unanswered questions for both exercise and diet for future research. The good thing is that it can bring about more attention to the importance of maintaining our bone health.

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References

1. Bredella, M. A., Torriani, M., Ghomi, R. H., Thomas, B. J., Brick, D. J., Gerweck, A. V., ... & Miller, K. K. (2011). Vertebral bone marrow fat is positively associated with visceral fat and inversely associated with IGF‐1 in obese women.Obesity, 19(1), 49-53.
2. Schwartz, A. V. (2015). Marrow fat and bone: Review of clinical findings.Frontiers in Endocrinology, 6.
3. Styner, M., Pagnotti, G. M., McGrath, C., Wu, X., Sen, B., Uzer, G., ... & Rubin, J. (2017). Exercise Decreases Marrow Adipose Tissue Through ß‐Oxidation in Obese Running Mice.Journal of Bone and Mineral Research.