Harold is 72 years old. Recently he has been feeling tired and forgetful. Then he began having tingling in his hands and feet, difficulty walking, and diarrhea. Laboratory tests indicated that he had low levels of vitamin B12. A diet history revealed that he eats lots of grains, fruits, and vegetables but very little meat or dairy products. The doctor explained that Harold's symptoms were due to a vitamin B12 deficiency.
Why might Harold's diet increase his risk for vitamin B12 deficiency and what are dietary changes Harold must make in order to increase his vitamin B12 consumption?
