Question

A person is undergoing prolonged fasting. His urine wold contain abnormal quantities of (a) fats (b) amino acids (c) glucose (d) ketones.

Short answer

During prolonged fasting, a person's urine would contain abnormal quantities of (d) ketones due to the body entering ketosis and excreting excess ketone bodies.

Step-by-step solution

Understanding Prolonged Fasting

Prolonged fasting leads to the body using stored fats as a source of energy because the glycogen stores get depleted. The liver breaks down fats into fatty acids and glycerol, which are further converted into ketone bodies.

Identifying Metabolic Changes

As the process of ketogenesis takes place, the level of ketone bodies like beta-hydroxybutyrate and acetoacetate in the blood increases. This condition is known as ketosis.

Analyzing Urine Composition

When ketone bodies reach a high concentration in the blood, they start to get excreted through urine, a condition known as ketonuria.

Elimination of Substances

Normally, the urine does not contain large amounts of fats, amino acids, or glucose because these substances are reabsorbed. However, during prolonged fasting, ketones are found in the urine due to ketosis.

Key concepts

Prolonged Fasting

When an individual hasn't eaten for an extended period, the body enters a state of prolonged fasting. This is not merely skipping a meal or two; we're talking about several hours to days without food intake. During this time, the body initiates several metabolic changes to sustain life. Initially, it burns the glucose reserves stored in the form of glycogen, primarily found in the liver and muscles.

Once these stores are depleted, the body turns to stored fat as its next energy source. Fat breakdown is a complex process involving lipolysis, where triglycerides are split into glycerol and fatty acids. The fatty acids can be directly used by many tissues for energy, while glycerol can serve as a substrate for gluconeogenesis, the production of glucose from non-carbohydrate sources. Prolonged fasting is effectively a trigger for these metabolic pathways to ensure that even in the absence of food, the body can function.

Ketone Bodies

Ketone bodies are three water-soluble molecules — acetoacetate, beta-hydroxybutyrate, and acetone— that are produced by the liver from fatty acids during periods of low food intake, carbohydrate restrictive diets, starvation, prolonged intense exercise, or in untreated type 1 diabetes mellitus. They are used as an alternative energy source when glucose is not readily available.

During prolonged fasting, as fatty acids are broken down, the liver converts them into these ketone bodies. This mechanism allows the brain, which normally relies on glucose, to receive a steady supply of energy as it can use ketone bodies as well. This is a prime example of the body's adaptability in managing energy reserves and ensuring survival when food supply is scarce.

Ketosis

Ketosis is a metabolic state characterized by elevated levels of ketone bodies in the bloodstream. It's often associated with a ketogenic diet but is also a natural response to prolonged fasting. When the body switches from using glucose to using ketones for energy, you enter a state of ketosis.

This transition can come with various effects, some being beneficial—like weight loss and improved metabolic profile—and others potentially uncomfortable, often referred to as the 'keto flu'. The presence of ketones is detectable not only in blood but also in the breath and urine, which can be useful for those tracking their state of ketosis. Understanding the nuances of this metabolic state helps individuals stay informed about their body's condition and adjust their diet and lifestyle accordingly.

Metabolism

Metabolism comprises all the biochemical reactions in your body that keep you alive, with energy metabolism being the process of generating energy from nutrients. It's usually divided into two categories: catabolism, the breakdown of molecules to produce energy, and anabolism, the synthesis of all compounds needed by the cells.

During prolonged fasting, catabolism ramps up as stored fats and proteins are broken down into substances that can be used to produce energy. The increase in catabolic activity leads to the generation of ketone bodies, putting the body into a ketogenic state. Metabolism is highly adaptive, and its regulation is complex, often contingent on various hormones and signaling pathways such as insulin and glucagon. Understanding your metabolism is crucial, as it affects body weight, energy levels, and overall health.