Jamie is a 16-year-old tennis player who has recently embarked on a vegan diet. Because of her food choices (mostly fruit smoothies made with almond milk and salads with a mix of richly-colored vegetables, fat-free dressing and nuts sprinkled on the top for protein), she is having difficulty meeting her caloric and protein requirements. She has lost 10 pounds in the two months she's been vegan. A week ago, Jamie tripped on the court and skinned her knee. Her injury is inflamed and is slow in healing. What might be a reason for this?