Loss of bone density during weight loss
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Bone density loss during weight loss means a reduction in the amount of bone-building minerals that can occur during body weight reduction, especially when it is rapid, substantial, or achieved at the expense of muscle and proper nutrition. The phenomenon primarily affects bone mineral density (BMD), but may also include the deterioration of the microarchitecture and mechanical strength of the skeleton. Not every body weight reduction leads to clinically significant bone weakening. The risk depends on age, hormonal status, baseline bone mass, the rate of weight loss, intake of protein, calcium, and vitamin D, physical activity, and comorbidities. Older adults, postmenopausal women, bariatric surgery patients, and people following very restrictive diets require special protection.
Loss of bone density during weight loss - why bones also lose weight
Bone is a living, constantly remodeling tissue. Its mass depends on the balance between resorption, which is the removal of old tissue by osteoclasts, and the formation of new bone by osteoblasts. An energy deficit can shift this balance toward resorption.
The most important mechanisms include:
- reduced mechanical loading of the skeleton: lower body weight means a weaker stimulus prompting bones to adaptive remodeling;
- muscle loss: lower muscle strength limits the strain transferred through tendons to the bones, while simultaneously increasing the risk of falls;
- hormonal changes: during energy restriction, levels of estrogens, testosterone, insulin-like growth factor IGF-1, and leptin may decrease, while the activity of the stress axis may increase;
- insufficient intake of calcium, protein, and vitamin D, especially with elimination or very low-calorie diets;
- secondary hyperparathyroidism, which can develop with calcium or vitamin D deficiency and intensify the mobilization of calcium from bones;
- increased bone turnover: the resorption marker CTX can increase even during a short-term low-energy diet.
The greatest changes are usually observed in the hip and femoral neck. However, it should be noted that a significant change in the amount of adipose tissue can affect the accuracy of DXA measurements. A decrease in the score after weight loss does not always entirely correspond to actual bone tissue loss, although the biological mechanisms of its loss are well documented. In interventional studies, combining weight loss with appropriately planned exercise protected bones better than weight loss without exercise or pharmacological treatment without concurrent physical activity.
Loss of bone density during weight loss - who is most at risk
The risk does not depend solely on the number of kilograms lost. What matters most is the baseline bone reserve and the way the weight reduction is conducted.
Higher-risk groups include:
- postmenopausal women, especially those with early menopause or untreated hypogonadism;
- menstruating women who have developed irregular periods or amenorrhea as a result of an energy deficit;
- men with testosterone deficiency;
- people over 65 years of age, in whom weight loss is often accompanied by sarcopenia, i.e., a decrease in muscle mass and function;
- people with osteopenia, osteoporosis, or a history of low-energy fractures;
- patients losing weight rapidly, repeatedly following reduction diets, or using very low-calorie diets;
- people who are underweight, have eating disorders, or have low peak bone mass;
- patients after bariatric surgery, especially procedures that limit nutrient absorption;
- people with celiac disease, inflammatory bowel diseases, chronic kidney disease, hyperthyroidism, hyperparathyroidism, or liver diseases;
- people on long-term treatment with glucocorticosteroids, certain antiepileptic drugs, aromatase inhibitors, or antiandrogen therapy;
- people who smoke, abuse alcohol, and avoid weight-bearing physical activity.
Anti-obesity medications, including GLP-1 receptor agonists, should not be automatically considered a direct cause of osteoporosis. However, significant weight loss and a lack of exercise may play a role. In a randomized trial on liraglutide, combining pharmacotherapy with exercise protected BMD more effectively than using the drug without an exercise program. This result should not be directly generalized to every medication or to all patients.
Bone density loss during weight loss - how to test it
The primary examination is DXA densitometry, most commonly covering the lumbar spine and proximal femur. In selected patients, the forearm is also examined. DXA measures areal bone mineral density in g/cm².
The result is presented as:
- T-score: comparison with the average peak bone mass of young adults; used primarily in postmenopausal women and men over 50 years of age;
- Z-score: comparison with individuals of the same sex and similar age; more important in younger adults. A Z-score value ≤ –2.0 is defined as bone mass below the expected range for age.
According to densitometric criteria, a T-score from –1.0 to –2.5 corresponds to low bone mass, whereas a result ≤ –2.5 may meet the criterion for osteoporosis. However, diagnosis and therapeutic decisions require taking into account age, previous fractures, and total clinical risk.
If accelerated bone loss is suspected, the doctor may order:
- complete blood count, creatinine, calcium, phosphorus, albumin, and alkaline phosphatase;
- 25-hydroxyvitamin D, parathyroid hormone, and TSH;
- tests for hypogonadism, celiac disease, or other causes of secondary osteoporosis;
- bone turnover markers, especially CTX and P1NP, mainly to monitor treatment;
- fracture risk assessment using the FRAX tool;
- vertebral imaging in case of back pain, height loss, or suspected compression fracture.
Follow-up examinations are best performed in the same facility and on the same machine. A change is reliable only when it exceeds the least significant change (LSC) determined for the facility. The timing of the next DXA should be determined individually, when its result may affect management.
Bone density loss during weight loss - how to protect bones during reduction
Skeletal protection should be part of an overweight or obesity treatment program from the beginning, rather than only after osteopenia is diagnosed. The most important factors include:
- Moderate, controlled energy deficit. Self-directed, chronic use of extremely low-energy diets should be avoided. The rate of weight loss should be tailored to age, nutritional status, comorbidities, and the risk of sarcopenia.
- Resistance training and bodyweight exercises. Strength training engaging major muscle groups, typically 2–3 times a week, as well as safe weight-bearing activities are recommended. Walking alone is beneficial for overall health, but may provide an insufficient stimulus to maintain BMD. In cases of osteoporosis or fractures, the program should be developed by a physiotherapist. Current guidelines confirm the importance of combining resistance training and weight-bearing exercises.
- Muscle mass protection. An adequate intake of complete protein, distributed across meals, is essential. In older adults, approximately 1.0–1.2 g of protein/kg of body weight per day is often considered, and sometimes more during intensive training. The amount requires individualization, especially in chronic kidney disease.
- Calcium and vitamin D. Calcium requirements should primarily be met through diet. For many adults, it is approximately 1000 mg/day, and in older groups usually 1200 mg/day. Supplementation should address an actual deficiency rather than replace proper nutrition. Polish guidelines most often recommend 1000–2000 IU of cholecalciferol daily for healthy adults during periods of insufficient cutaneous synthesis, taking into account body weight and dietary intake. Treatment of a diagnosed deficiency requires separate dosing under medical supervision.
- Treatment of secondary causes. Menstrual disorders, hormonal deficiencies, bowel diseases, vitamin D deficiency, and drug side effects require diagnostics. Diagnosed osteoporosis may be an indication for antiresorptive or osteoanabolic treatment, regardless of the weight reduction program.
Body contouring treatments available at Ambasada Urody, such as CoolTech cryolipolysis, VelaShape, and acoustic wave therapy, act locally on subcutaneous tissue, skin appearance, or cellulite. They do not increase bone mineral density, do not treat osteopenia or osteoporosis, and do not replace resistance training, nutrition, and medical care. They may support local body shaping and improve skin quality; however, they do not exert a therapeutic effect on bone metabolism. Reducing the circumference of a selected body part does not mean treating obesity as a metabolic disease, nor does it provide protection against osteopenia and osteoporosis.
