According to a major study conducted by the Center for Disease Control and Prevention (CDC), Mississippi is the fattest state in the United States. The study used the Behavioral Risk Factor Surveillance System database with the diet and exercise information of 300,000 American adults from the years 2003 to 2005. The study found that over two thirds of Mississippi's population is either overweight or obese. Being overweight is defined as having a body mass index (BMI) between about 25 and 29.9, while a BMI of 30 or higher is considered obese. A normal BMI is often considered to be within the 18.5 to 24.9 range with anything below 18 considered underweight.

As BMI is calculated using only a person's height and weight measurements, some say it is not an accurate indicator of fitness. No considerations are given for muscle mass weighing more than fat. Athletes, for example, have more lean muscle than fat, but may still come out with a higher BMI than someone who is actually somewhat overweight. Others say the fattest state study is controversial as research has shown a definite correlation between obesity and poverty levels. Poor people do not have the same access to healthier foods and gym memberships as richer people.

The fattest county in the fattest state is definitely one of the poorest areas in the United States. Jefferson County, in Fayette, Mississippi in the Delta region has the highest concentration of overweight and obese people in the fattest state. Jefferson County, population 7,000, has very low average incomes and high unemployment rates. The tiny Mississippi town does have a nutrition center and weight loss classes, but many who live there see being heavy as normal and not unhealthy.

Many people think the history of slavery plays a part in Jefferson's distinction as the fattest county in America's fattest state. Slaves worked hard all day in the Mississippi Delta in the 1850s and existed on low quality, but rich and filling foods such as calorie-laden gumbos and cornbreads. The same types of satisfying food remain a part of culture of the fattest state today. Biscuits and gravy, and many fried foods are eaten regularly in the Mississippi Delta region of the fattest state. Fried foods such as chicken fried steak, shrimp, catfish, pecans, sweet potatoes, and even dill pickles are common fare here.

Although the origin of Mississippi mud pie is disputed, the rich, densely chocolate pie is at least named for the dark thick mud banks along the Mississippi river. The pie is widely sold in the fattest state. Since the study labeling Mississippi as America's fattest state, government park-building and nutrition intervention programs have been launched in Mississippi.