Which of the following statement(s) is/are true concerning various energy sources?

b. Endogenous fat is the major source of energy during starvation

c. The respiratory quotient of carbohydrate is greater than either fat or protein

d. Ketones can be used as a source of energy during starvation

The major sources of energy are carbohydrates and fats. Carbohydrates are a major source of energy during normal, nonstarving existence. The brain, the red cells, and some other organs are obligate glucose users. The brain and red cells can develop the capacity to use ketones as an energy source, a process known as starvation adaptation. Fat is the most efficient source of energy. Fat produces 9 calories of energy per gram of substrate metabolized while carbohydrate produces only 4 calories. The respiratory quotient represents the number of molecules of carbon dioxide for each molecule of oxygen consumed. For carbohydrates it is 1.0, whereas for fat, this respiratory quotient is 0.7. Endogenous fat is the major source of energy during starvation. The glycogen storage is basically depleted after a day of fasting and fat becomes a major energy source with protein breakdown supplying glucose through the process of gluconeogenesis.