John may need to eliminate foods containing lactose (milk, cheese, yogurt, ice cream, etc.), citrus fruits (oranges, lemons, limes, etc.), and gluten (wheat, barley, rye, etc.) from his diet.
If John eliminates these foods from his diet, he may lack calcium, vitamin D, vitamin C, fiber, and B vitamins. Milk and dairy products are good sources of calcium and vitamin D, citrus fruits are high in vitamin C, and grains containing gluten are often fortified with B vitamins and are a good source of fiber.
Due to a lack of calcium and vitamin D, John may experience weak bones and teeth, as well as an increased risk of osteoporosis later in life. Without vitamin C, he may have weakened immunity and may be more prone to infections. A lack of fiber may lead to constipation, while a lack of B vitamins may cause fatigue, weakness, and nerve problems. Some deficiency symptoms may appear immediately, while others may take longer to appear, depending on the nutrient and the extent of the deficiency.
Foods that are nutrient-dense and could be served in place of the eliminated foods include:
Non-dairy sources of calcium, such as leafy greens (kale, collard greens, spinach), tofu, almonds, and fortified plant milks (soy, almond, etc.)
Foods high in vitamin C, such as strawberries, kiwi, papaya, bell peppers, broccoli, and kale
Gluten-free whole grains, such as rice, quinoa, amaranth, and buckwheat, as well as gluten-free bread, pasta, and crackers made from these grains
Foods high in B vitamins, such as legumes (beans, lentils, peas), nuts, seeds, whole grains, and fortified plant milks