**Core Concept**
The calculation of Body Mass Index (BMI) is a widely used method to assess an individual's weight status. BMI is a dimensionless value obtained by dividing a person's weight in kilograms by the square of their height in meters (kg/m^2). This measurement helps categorize individuals into various weight categories such as underweight, normal weight, overweight, and obesity.

**Why the Correct Answer is Right**
In the context of obesity, BMI is a useful tool to determine if an individual has a high body fat percentage. The World Health Organization (WHO) defines obesity as a BMI of 30 or higher, which indicates a high risk of developing various health conditions such as diabetes, cardiovascular disease, and certain types of cancer. BMI takes into account both weight and height, providing a more accurate assessment of body fat distribution compared to other measurements.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify a correct BMI category for obesity. BMI values range from underweight (less than 18.5) to obesity (30 or higher), with normal weight falling between 18.5 and 24.9.
**Option B:** This option is incorrect because it does not accurately represent the BMI threshold for obesity. While a BMI of 25 may indicate overweight, it does not necessarily indicate obesity.
**Option C:** This option is incorrect because it does not correctly identify the BMI threshold for obesity. A BMI of 29 may indicate overweight, but it is not the threshold for obesity.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that BMI is only an estimate of body fat and may not accurately reflect muscle mass or body composition. However, it remains a widely used tool for assessing weight status and identifying individuals at risk for obesity-related health conditions.

**Correct Answer:** D. 30 or higher.