Question

How does digestion affect metabolism?

Answer 1

Hint: Metabolism is the essence of what nutrition is all about. It is the sum of all of the physiological and chemical processes by which our bodies break down and rebuild foods we eat. Digestion is the chemical and mechanical breaking down of food into smaller components which can be absorbed into a blood stream.

Complete answer:
Digestion that happens in gastrointestinal systems is one of the most important components of a digestive system, the second being the correlated organs such as the pancreas, is the process by which food particles are broken into small and important components, such as the glucose molecules.
Metabolism is an internal-process that controls several important body parameters, like energy, which implies in macro-states such as body weight.
Our metabolism increases whenever we eat, digest, and store food, a process called the thermic effect of food. Protein has a higher thermic effect compared to carbohydrates and fats because it takes longer for our body to burn the protein and absorb it.
Digestion affects metabolism in two ways: input of energy, control of important hormones such as insulin. When we eat food containing carbohydrates, the digestive system breaks down digestible ones into sugar, which enters blood. As blood sugar level rises, the pancreas produces insulin which is a hormone that prompts the cells to absorb blood sugar for storage or energy. Liver converts glucose into the glycogen and stores; it can be reconverted whenever the blood sugar level becomes low. This function is mediated by the hormones glucagon and insulin; both are produced by the pancreas but have opposite effects.

Note: The rate of metabolism is measured in terms of the calories or energy expended over a specified period of time, to conduct all of the body's necessary functions while at rest. The metabolic rate is similarly governed by many factors. Height, weight, body composition (amount of fat mass v/s muscle mass), age, sex, presence of fever, and levels of various hormone levels—including stress hormones and thyroid —are all factors in determining resting metabolic rate.