Both forms of malnutrition—undernutrition and obesity—have substantial negative impact on bone health mediated by nutritional deficiencies (protein, calcium, vitamin D, phosphate, magnesium, zinc, and vitamin K), hormonal imbalances, chronic inflammation, and reduced physical activity and muscle mass. Children, adolescents, and elderly are especially vulnerable to adverse impact of malnutrition on bone health due to growth and bone modelling in children/adolescents and reduced physical activity and osteoporosis in elderly. Additionally, the diagnostic ability of markers of bone health may be compromised in the presence of undernutrition. Public health strategies to combat malnutrition and improve bone health include promotion of balanced diet ensuring adequate consumption of proteins, calcium, vitamin D and micronutrients, supplementation in high-risk groups (e.g., universal vitamin D supplementation during infancy for prevention of rickets, calcium and vitamin D supplementation in elderly with osteoporosis for prevention of fractures), promotion of healthy lifestyle and physical activity, and legislation (e.g., food labeling and taxation strategies for reducing consumption of unhealthy foods for prevention of obesity). Public health programs to combat malnutrition should also take in account local values, available resources, suitable delivery platforms, behavior change communication channels, and existing practices to design suitable and locally acceptable strategies.