Question 42 - Biological and Biochemical Foundations of Living Systems Practice Test for the MCAT

Water and the energy-yielding nutrients are also referred to as macronutrients because the body needs them in large amounts. In contrast, micronutrients are vitamins and minerals. These elements and compounds participate in many essential chemical reactions and processes, such as nerve impulses, and some, such as calcium, also contribute to the body’s structure. Your body can store some of the micronutrients in its tissues, and draw on those reserves if you fail to consume them in your diet for a few days or weeks. Some other micronutrients, such as vitamin C and most of the B vitamins, are water-soluble and cannot be stored, so you need to consume them every day or two.

Vitamin \(B_{12}\) is a co-enzyme involved in a wide variety of cellular processes. Synthesis of vitamin \(B_{12}\) occurs only in bacteria; in animals, these bacteria populate anaerobic environments in the gut. Consequently, vegan diets in developing nations and diets common to developing nations provide no source of \(B_{12}\). Researchers (Ghosh et al. http://dx.doi.org/10.3389/fnut.2016.00001) found that rats whose diets contained limited (L) and no (N) \(B_{12}\) displayed symptoms that were not observed in the control group (C) whose diet included \(B_{12}\) and was otherwise identical. Chemical analysis of adipocytokines in the plasma after feeding periods of 4 and 12 weeks are shown in the following table. Over the 12 weeks of feeding, the weights of all three groups were equivalent, while the percent of body fat increased relative to the control for the rats fed a diet of limited and no \(B_{12}\): 40% (N) and 20% (L), respectively.