Ageing leads to the lower secretion of certain digestive enzymes. Seniors also tend to be deficient in the micronutrient vitamin B12 unless on a supplement. Vitamin B12 requires acid in the stomach for absorption. And with age, the acid secretion decreases due to the withering of the acid-secreting cells. B12 is required to convert fat stores to energy, which is what helps one lose weight. Experts claim that lack of B12 leads to "stubborn fat".