Rapidly losing fat neither benefits nor harms bones.
Is fat good or bad for our bones? Researchers have long wrestled with this question, but now they seem to have part of the answer.
A new study of mice by researchers in Sweden shows that rapid fat loss has no adverse effects on bone.
The process does not make the bones stronger or more brittle.
The results are another piece of the puzzle for understanding what might happen to the human body following acute weight loss, such as in connection with bariatric surgery.
“The results would probably have been more interesting if we could demonstrate that losing fat tissue either benefits or harms bones, but we found no difference. Perhaps this is because various factors relating to increased fat mass either benefit or harm bones. We need to elucidate this in the future,” explains a researcher behind the study, Louise Grahnemo, Department of Internal Medicine and Clinical Nutrition, University of Gothenburg, Sweden.
The research has been published in Scientific Reports.
Fat is both good and bad for bones
The study is based on previous studies indicating that fat can have varying effects on bones.
Some studies and theories suggest that fat tissue negatively affects bone mass because it increases inflammation, which is generally bad for the bones and the body. The hypothesis therefore states that shedding a lot of fat will make the bones stronger because the inflammation decreases.
The second possibility is that fat tissue makes the bones stronger, because higher body mass increases the biomechanical load on the bones, and this activates bone-building mechanisms that make the bones stronger. This hypothesis therefore claims that shedding a lot of fat will lead to weaker bones.
“Excessive fat tissue harms metabolism and increases the risk of cardiovascular diseases, but it’s not fully understood how it affects our bones,” says Louise Grahnemo.
Mice lost more than 50% of their body fat in 2 weeks
Louise Grahnemo and colleagues studied how acute fat loss affects mice that have been artificially genetically modified to include a foreign sequence called a transgene (transgenic mice).
The genetic engineering enabled the researchers to inject a substance that almost instantly eliminated all the fat cells so that they could measure bone mass before and after a very rapid loss of adipose tissue.
The researchers used dual-energy X-ray absorptiometry to measure bone mineral content and bone density while the mice were alive and X-rayed the bones after death.
“We aimed to solely investigate the effect of fat loss. People who lose weight can also lose muscle tissue, and since muscle helps to make the bones stronger, loss of muscle can negatively affect bone mass. Bariatric surgery can also affect bone mass in ways other than through fat loss, because it affects various gut hormones. We therefore ensured that the mice lost fat very rapidly to specifically affect the fat tissue and minimise the effect on other organs,” explains Louise Grahnemo.
No difference before and after acute fat loss
The results showed that bone mass did not differ before and after acute fat loss.
The researchers started to measure the loss of fat tissue after 2–3 days, and the mice lost half their body fat within 2 weeks. However, the bones remained just as strong.
Louise Grahnemo speculates that the reason for this may be the two opposing influences on bone mass: inflammation and biomechanical loading, both of which decline in mice subjected to acute fat loss.
“In addition, we only examined the effect of losing fat tissue surrounding the body and not losing bone marrow fat tissue. This warrants further investigation in future studies,” concludes Louise Grahnemo.
