For several years, populations of developing countries including Mexico and Latin America have been undergoing changes in dietary habits [1]. The nutrition transition comprising changes in food patterns and dietary intake is linked to increased energy-dense sources, such as sugars, edible oils, and processed foods, whereas consumption of complex carbohydrates, fiber, and micronutrient-rich foods including fruits and vegetables is often low. These facts, coupled with reduced physical activity, increase obesity, bone density problems and the risk of non-communicable chronic diseases among the population [2,3].
Micronutrients such as Ca, P, Mg, Sr, vitamin D and vitamin K play an important role in bone health [4,5] and are required for bone mineralization and growth. An adequate intake of calcium during childhood and adolescence is necessary to achieve the peak bone mass (PBM), which is related to the adolescent growth spurt. A low PBM is a contributing factor for determining risk of fractures in children and osteoporosis in adulthood [6]. In North America and Europe, the main dietary sources of calcium are milk and dairy products. In contrast, in Mexico and Central America the major calcium supplies within the diet are nixtamalized corn products (foodstuffs derived from the thermo-alkaline treatment of corn grains) and vegetables as a result of their low cost compared with animal products [7]. In Mexico, micronutrient deficiencies (vitamin A, folate, zinc, iron and calcium) are important public health problems, affecting the most vulnerable age groups including children between 5 and 11 years of age [8].
In plant foods, calcium bioavailability decreases due to the presence of oxalic, phytic and uronic acids. These compounds bind to calcium, forming insoluble complexes which cannot be absorbed in the intestine [9]. Opuntia ficus indica cladodes (modified flattened stems in cacti) are part of the usual diet of the Mexican population and represent a potential source of calcium in the human diet [10]. It has been demonstrated that calcium content in cladodes increases with maturity, while the concentration of oxalates shows a cyclic tendency [11,12]; consequently, we hypothesized that calcium bioavailability of O. ficus indica cladodes depends on the growth stage of the plant. This topic has not been previously investigated. Considering the above mentioned, the objective of this study was to evaluate the effect of O. ficus indica at different maturity stages as a calcium source within the diet on mechanical, microstructural properties, bone mineral density and mineral content of the femur in growing rats.
The results in this study show evidence that O. ficus indica at different maturity stages have different effects on bone properties of rats in growing stage. Cladodes at early maturity stage do not provide an adequate source of dietary calcium, as was demonstrated by the detrimental effects in the femur properties in rats fed with O ficus indica cladodes with 60 and 200 g weight. In contrast, cladodes with 400 and 600 g weight showed the greatest potential as a calcium source within their diet, supported by the physical, mechanical, and microstructural properties, mineral content and bone mineral density in the femurs of rats fed with cladodes at the late maturity stage. The results supported by this research demonstrate, for the first time, that the calcium contained in O. ficus indica cladodes is actually bioavailable and capable of improving the mineral density and mechanical and microstructural properties of bones in rats. These findings suggest that the consumption of cladodes at the late maturity stage in the diet might have a beneficial impact on bone health. The effects of consumption of O. ficus indica on human bone health need to be further evaluated.