How long can you live without eating?

Summary

• The human body survives without food by using its reserves: first glucose, then fats, and finally muscles after one week.
• The duration of survival depends on factors such as sex, age, initial weight, and water consumption.
• Complications include muscle weakness, fatigue, bone loss, hair loss, and metabolic disorders.
• Hydration plays a key role in prolonging survival in the absence of food.

Facing extreme situations or in the context of practices such as fasting, a question often arises: how long can one live without eating? The remarkable functioning of the human body allows it to draw on its own reserves to survive, but this capacity varies depending on several factors.

Age, weight, sex, and hydration all play a key role in the duration of survival without food. Understanding these mechanisms can both shed light on and warn about the risks associated with such deprivation.

The role of the body's reserves

When we do not eat, the body quickly activates its survival mechanisms. In the first few hours after the last meal, it draws its energy from the glucose reserves circulating in the blood. This glucose, which primarily feeds the brain, is then produced by the liver from glycogen. This process generally lasts 1 to 2 days.

But what happens next? After 48 to 72 hours, the body changes its strategy and begins to draw on its fat reserves. This phase, called ketogenesis, produces fatty acids and ketones, molecules capable of temporarily nourishing muscles and the brain. This mechanism is essential for prolonging survival while conserving muscles.

When the body attacks muscles

If fasting or starvation continues beyond 7 days, the body no longer has enough fats to use. It then attacks muscle tissue to produce energy. These muscles, broken down into proteins, provide the last fuels needed for vital organs.

This phase, even more critical, can lead to major risks. For example, the heart muscles can weaken, as can the kidneys or liver. Excessive muscle degradation directly jeopardizes vital functions.

Factors influencing the duration of survival

Not everyone reacts the same way to the absence of food. Several parameters influence the duration of survival:

• Sex: Women, thanks to often larger fat reserves, can sometimes survive longer.
• Age: Children and the elderly are generally more vulnerable, as their reserves are limited.
• Initial weight: An obese person has more fat to fuel their body, but these reserves do not replace the need for essential nutrients.
• Hydration: Drinking water remains essential. Without hydration, organs stop functioning in just a few days.

Complications of food deprivation

Stopping eating has consequences for the body, even in the short term. In the prolonged absence of food intake, collateral effects appear:

• Muscle weakness and bone loss that decrease mobility.
• Intense fatigue, feeling cold, or hair loss.
• In women, loss of menstruation may occur, indicating a significant hormonal imbalance.
• Metabolic disorders such as constipation, shortness of breath, or pronounced paleness.

These complications make it difficult, or even dangerous, to abruptly resume eating after a period of prolonged fasting.

A fragile balance

The human body has an extraordinary capacity to survive in the temporary absence of food. It mobilizes its reserves of glucose, then fats, and finally muscles to continue functioning. However, prolonged deprivation carries significant risks, and the role of hydration remains crucial in prolonging this resistance to food deprivation.