Final answer:
Regular exercise is the factor that can increase basal metabolism because it builds muscle mass, which in turn raises BMR. Aging, fasting, and low thyroid hormone levels all contribute to a decreased BMR.
Step-by-step explanation:
The factors that can increase basal metabolism (BMR) are important to understand when studying human physiology. One such factor is regular exercise; this increases muscle mass, which in turn requires more energy for maintenance, thus raising BMR. In contrast, aging generally causes a decrease in BMR as the thyroid gland produces less of the thyroid hormones. Similarly, fasting is not associated with increasing BMR; it might initially raise it due to stress on the body but long-term fasting will decrease BMR as the body conserves energy. Lastly, low levels of thyroid hormones, as seen in hypothyroidism, will reduce BMR, not increase it. Therefore, regular exercise is the correct answer that would increase basal metabolism.