**Core Concept**
The World Health Organization (WHO) recommends dietary guidelines to promote public health. One of these guidelines involves the optimal percentage of fat in the diet to prevent chronic diseases such as heart disease, diabetes, and obesity.

**Why the Correct Answer is Right**
The WHO recommends a maximum of 30% of total energy intake from fats to prevent excessive energy intake and subsequent weight gain. This recommendation is based on the understanding that high-fat diets can lead to increased energy intake, which can contribute to obesity and related health problems. The WHO also emphasizes the importance of choosing healthier fats, such as unsaturated fats, over saturated and trans fats.

**Why Each Wrong Option is Incorrect**
**Option A:** 20% - This is lower than the recommended percentage, which may not provide sufficient energy from fats for optimal health.
**Option B:** 40% - This exceeds the recommended percentage, which may increase the risk of excessive energy intake and related health problems.
**Option C:** 50% - This is significantly higher than the recommended percentage and may lead to serious health consequences.

**Clinical Pearl / High-Yield Fact**
When counseling patients about dietary fat intake, it's essential to emphasize the importance of choosing healthier fats, such as those found in nuts, seeds, avocados, and olive oil, over saturated and trans fats.

**Correct Answer:** B. 30%