Heart disease, diabetes, and stroke are health complications often associated with carrying excess body weight, but there’s a link between osteoporosis and obesity that shouldn’t be ignored.

Osteoporosis is a bone disease characterized by decreases in bone strength and mineral density. It affects more than 200 million people worldwide and is more common in people assigned female at birth.

While osteoporosis is often seen as a condition that mainly affects the aging population, it’s not a natural part of aging, and anyone of any age can be diagnosed with osteoporosis.

Traditionally, low body mass index (BMI) has been associated with a higher risk of osteoporosis, but research suggests this may be true at the opposite end of the spectrum may as well.

Currently, there’s no evidence that shows obesity directly causes osteoporosis. Carrying excess weight may have both protective and harmful effects on bone health.

Once upon a time, obesity was thought to be mainly protective against osteoporosis. The theory —supported by research — was that the more weight your skeletal frame had to carry, the stronger and denser your bones became.

Now research is suggesting the mechanical loading benefits of weight on the body may not be enough when it comes to other characteristics of obesity.

Obesity does more within your body than just add weight — it affects numerous biological processes and can lead to chronic diseases that can compromise bone health.

What’s the correlation between BMI and osteoporosis?

Your BMI is a calculation of your weight in kilograms divided by your height in meters. It provides a general idea about where your body fat level is on a clinical scale.

Low BMI has historically been a risk factor for osteoporosis, as being underweight can mean you have less bone to lose overall.

BMI isn’t always an accurate depiction of your body fat. It can overestimate body fat if you have a muscular build, and it can underestimate body fat if you’ve lost muscle mass.

A 2018 study looking at BMI versus percentage of body fat (PBF) as indicators of bone density found PBF was a more accurate indicator of bone health.

Your bones aren’t inactive. They’re made from living tissue that remodels and reshapes itself through metabolic processes over the course of your lifetime.

Like endocrine organs, bones secrete hormones. These hormones are essential to maintaining bone health and function. When bone metabolic balance is disrupted, their strength and density can be affected.

Research ndicates adipose tissue (body fat) secretes its own hormones and substances. Too-high amounts of body fat can cause changes in your body’s biology that indirectly affect bone.

For example, adiponectin is a hormone associated with glucose regulation, bone formation, and anti-inflammation in your body. People living with obesity often have lower levels of adiponectin.

When adiponectin levels are low, levels of certain pro-inflammatory cytokines become high. This creates a cascade of reactions in your body that ultimately create the resorption of bone tissue back into the body.

Other factors

An imbalance of hormones is just one part of the obesity-osteoporosis puzzle. According to a 2020 review, a handful of other factors co-occurring in obesity may come into play, including:

All of these may create a microenvironment in your body that compromises bone health.

Visceral abdominal fat, such as the fat deposits around organs and deep into the abdomen, may be more metabolically active compared with fat just beneath the skin (subcutaneous fat).

This means visceral fat may be more disruptive to your body’s processes than subcutaneous fat.

Osteosarcopenic obesity

Osteosarcopenic obesity is a relatively new term used to describe when progressive loss of muscle mass and strength (sarcopenia) and conditions of impaired bone health (such as osteoporosis) occur alongside obesity.

Not everyone living with obesity who experiences bone loss has osteosarcopenic obesity.

This condition must also meet the criteria for sarcopenia, a musculoskeletal disease where physical performance, muscle strength, and muscle quality or quantity progressively decline.

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The saying “if you don’t use it, you lose it,” is true when it comes to osteoporosis risk.

Your bones respond to physical activity just like other tissues in your body. Exercising not only helps you reach peak bone mass and strength, but it can also help prevent bone loss as you age while reducing your risk of falls and fractures.

Being less physically active is linked to a higher risk of osteoporosis. Prolonged inactivity reduces the demand on your musculoskeletal system, which includes your bones, muscles, tendons, ligaments, and soft tissue. When your body has no demands to meet, it has no need to increase bone strength or density.

Can osteoporosis be caused by a poor diet?

Nutritional imbalances and deficiencies can also increase your risk of osteoporosis. Bone loss has been linked to:

  • low calcium
  • vitamin D deficiency
  • low protein intake
  • excessive dieting

Research suggests a high fat diet may create a state of systemic inflammation in the body that increases bone resorption and promotes fat accumulation in bone marrow.

Limited research exists on the benefits of weight loss in obesity for osteoporosis.

Some evidence indicates losing weight might help change metabolic factors that negatively affect bone health. For example, weight loss and fat reduction can increase adiponectin concentrations that help improve bone mass density.

Losing weight when you’ve been diagnosed with osteoporosis, though, should be done slowly and under professional guidance, especially if you’re an older adult.

Rapid weight loss can increase bone loss by depleting micronutrients such as calcium and vitamin D. The sudden reduction of mechanical stress may also lead to bone loss as the demands on your musculoskeletal system decrease.

Osteoporosis and obesity were once thought to have a positive relationship — the more weight your musculoskeletal system carried, the more likely your bones would be strong and dense.

While the mechanical benefits of carrying excess weight do still exist, they may not override the numerous metabolic challenges from obesity that can compromise bone health.

Obesity-related hormonal imbalances, visceral and bone marrow fat deposits, and systemic inflammation can indirectly cause bones to weaken and become brittle.

While weight loss may improve metabolic factors, losing too much weight too quickly can also increase your risk for osteoporosis.