Ans. is 'a' i.e., CarbohydratesMetabolic alteration during fasting-starvationo he metabolic changes observed in fasting are generally opposite to those described for absorptive (fed) state. In the absence of food, plasma levels of glucose, amino acids, and TGs fall, triggering a decline in insulin secretion and an increase in glucagon release. This results in decreased insulin: glucagon ratio. Which is responsible for most of the metabolic changes.o The primary role of altered metabolism during fasting is to maintain blood glucose through the synthesis (gluconeogenesis) and utilization of alternate substrates. Fasting-starvation is divided in three broad categories:-Initial stage :- Lasts upto 2-3 daysIntermediate stage Lasts upto 24 daysAdvanced stage:- begins after 24 days.Initial stage (first stage):- Liver glycogen is the first main provider of energy. But due to limited storage it can not last longe (16-18 hrs.). Further glucose is provided by gluconeogenesis by non- carbohydrate sources (muscle protein breakdown is increased which provides amino acids alanine and glutamine for gluconeogenesis). Utilization of alternate substrates (other than glucose) starts increasing interminal period of this stage. Free fatty acids and ketone bodies start rising in this stage. Glycogenis completely depleted by the end of this stage. Blood glucose is slightly decreased.Intermediate stage (Second stage):- Free fatty acids are the major substrates for energy production. They are derived from hydrolysis of fat (triglycerides) in adipose tissue. Ketone bodies serve as additional source of energy. As glycogen source is already depleted, the only source of glucose is increased gluconeogenesis. After sometimes muscle breakdown decreases due to decreased need of glucose as a fuel for brain which has began using ketone bodies as a source of energy.Advanced stage (Third stage):- When fat stores are almost exhaused, energy requirment is obtained from breakdown of tissue proteins and protein stores once again enter in stage of rapid depletion.