Final answer:
Mr. Mathis should increase his intake of calcium-rich foods such as dairy products, leafy greens, and calcium-fortified foods, alongside regular weight-bearing and resistance exercises to prevent a decrease in bone density.
Step-by-step explanation:
To prevent a decrease in bone density, Mr. Mathis should increase his intake of foods rich in calcium and vitamin D. Good sources of calcium include dairy products like milk, yogurt, and cheese. Additionally, there are non-dairy sources such as Chinese cabbage, kale, broccoli, and calcium-fortified products like some fruit juices, tofu, and cereals. The recommended daily intake of calcium for teenagers is 1300 mg. Besides dietary intake, regular exercise, including weight-bearing and resistance exercises, plays a crucial role in maintaining and increasing bone mineral density. For instance, weight training, dancing, and stair climbing are excellent for bone health. It is also recommended to avoid smoking, excessive alcohol consumption, and carbonated beverages, which can negatively affect bone density.