**Core Concept**
Colorectal cancer is a leading cause of cancer-related deaths worldwide, and identifying effective preventive strategies is crucial. Epidemiological studies have investigated various lifestyle and dietary factors to determine their association with the risk of developing colon cancer.

**Why the Correct Answer is Right**
High dietary fiber intake, particularly from plant-based sources, has been consistently associated with a reduced risk of colon cancer. This protective effect is thought to be mediated by the increased production of short-chain fatty acids (SCFAs) in the colon, which help to maintain a healthy gut microbiome. SCFAs also promote the growth of beneficial bacteria, improve colonic motility, and reduce the availability of carcinogens. Additionally, high-fiber diets tend to be rich in antioxidants, phytochemicals, and other nutrients that may contribute to their cancer-preventive effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Although physical activity has been linked to a reduced risk of various cancers, its association with colon cancer is less clear, and more research is needed to establish a causal relationship.
**Option B:** Red meat consumption has been identified as a potential risk factor for colon cancer, although the evidence is not as strong as it is for high-fiber diets.
**Option C:** While there is some evidence to suggest that calcium and vitamin D may have a protective effect against colon cancer, the relationship is complex, and more research is needed to confirm these findings.

**Clinical Pearl / High-Yield Fact**
A high-fiber diet should be a cornerstone of colon cancer prevention, with a daily intake of at least 25-30 grams of fiber from sources such as whole grains, fruits, vegetables, and legumes.

**Correct Answer:** C. Fiber-rich diet.