Dietary phosphorus overload is an underinvestigated cancer risk factor in public health nutrition. An excessive intake of dietary phosphorus can prevent the kidneys from removing the excess phosphorus from the blood, causing dysregulation of phosphorus metabolism and tissue accumulation of inorganic phosphate, which has been associated with phosphate toxicity and tumorigenesis. Low amounts of dietary phosphorus in ketogenic and fasting-mimicking diets have been associated with the regression of tumors in adults. The level of phosphorus in these diets is consistent with the adult estimated average requirement from the US Institute of Medicine’s dietary reference intakes for phosphorus. Nevertheless, few adult members of the public follow the Institute of Medicine’s recommended dietary allowance of 700 mg phosphorus per day, consuming approximately two to three times as much dietary phosphorus. Furthermore, the MyPlate Plan of the US Department of Agriculture recommends high levels of dietary phosphorus—amounts which have been associated with increased all-cause mortality and increased risk of breast cancer incidence. Grains, protein, and dairy food groups are the highest sources of phosphorus in the MyPlate Plan. Suggestions to improve the MyPlate Plan include increasing intake of fruits and vegetables and lowering current intake of grains, protein, and dairy to modulate dietary phosphorus and reduce cancer risk.