Restricted cubic splines

I am using linear regression to evaluate the association between body fat percentage and HbA1c; however, I am uncertain whether this relationship is truly linear.I am therefore considering whether restricted cubic splines (RCS) may provide a more appropriate approach for modeling this association.Regression models are widely used to estimate relationships between predictors and outcomes.A key challenge arises when modeling continuous predictors, for which the true functional form is often unknown.Analysts must balance model simplicity with the need to accurately capture potentially complex relationships.Traditional approaches include categorizing continuous variables or applying polynomial transformations, although other methods such as fractional polynomials, generalized additive models, and piecewise regression are also available.