What is the main dependent variable and main operational definition of this experiment?

Title: Reversal of Type 2 Diabetes Mellitus and Improvements in Cardiovascular Risk Factors After Surgical Weight Loss in Adolescents
We hypothesized that gastric bypass would improve parameters of metabolic dysfunction and cardiovascular risk in adolescents with type 2 diabetes mellitus... After surgery there was evidence of remission of type 2 diabetes mellitus in all but 1 patient. Significant improvements in BMI (–34%), fasting blood glucose (–41%), fasting insulin concentrations (–81%), hemoglobin A1c levels (7.3%–5.6%), and insulin sensitivity were also seen. There were significant improvements in serum lipid levels and blood pressure.

Body mass index (BMI) is a measure body fat through a height and weight ratio. The index applies to children, teens, men and women. BMI categories include

underweight- less than 18.5,
normal ranging from 18.5 to 24.9;
overweight ranging from 25 to 29.9
obese with a BMI of 30 or greater.

This is the dependent variable, as its value depends on weight loss surgery.

and main operational definition of this experiment?

Gastric bypass, a weightloss surgery, would improve parameters of metabolic dysfunction and cardiovascular risk in adolescents with type 2 diabetes mellitus.

Diabetes is an autoimmune disease, where immune cells attack cells within the pancreas which produce insulin. It lessens the insulin available, which is essential to sugar metabolism in cells.