Regular and Long-Term Effects of a Commercial Diet on Bone Mineral Density

(1) Background: Although the effects of diets used worldwide, such as the Mediterranean diet, have been repeatedly studied, the effects of diet plans developed by national nutritionists are unknown. Our cross-sectional study aimed to assess the effects of the commercial Fitlap diet plan, widely used among Estonians, on bone mineral density (BMD), while considering other influential factors (physical activity, body composition, and macro- and micro-nutrients). (2) Methods: A total of 68 women participated (followers of Fitlap diet—FDF, n = 34; age-matched controls, n = 34). Body composition, bone mineral density (BMD), including the whole body (WB) and areal BMD from the femoral neck (FN) and lumbar spine (LS), and blood micro-nutrient levels were measured. The menu analysis was based on dietary recalls. (3) Results: The Fitlap diet contains significantly more calcium (p < 0.001) and magnesium (p = 0.007). FDF consume more fiber (coef. 6.49; p < 0.001) and protein (coef. 20.12; p < 0.001), which influences fat-free mass (coef. 3674.8; p = 0.008) and vitamin B12 blood values (coef. 184.98; p < 0.001). The only influencing factor of WB BMD, LS, and FN aBMD was fat-free mass (coef. in all locations 0.000009; and p = 0.015; p = 0.015; p = 0.01, respectively). (4) Conclusions: Fitlap is an example of a commercial diet plan that has no negative effects on bones.