The science of starvation: how your body reacts to food deprivation

Understanding the Science of Starvation

Hunger exists on a spectrum, ranging from mild food insecurity to severe starvation. Food insecurity occurs when individuals have to reduce their meal frequency or portion sizes due to limited access to food. As food becomes scarcer, the body begins to rely on its internal energy reserves. This process starts with a drop in energy levels, followed by the breakdown of fat stores and eventually muscle tissue. In the most extreme cases, critical organs begin to fail, leading to life-threatening conditions.

Acute malnutrition is a severe form of undernourishment that can lead to starvation. Today, thousands of children under five and pregnant or lactating women in Gaza are experiencing acute malnutrition. Similarly, in Sudan, conflict and restricted humanitarian access have pushed millions to the brink of starvation, with famine warnings becoming increasingly urgent.

To understand the science behind starvation, we consulted nutritionists Ola Anabtawi and Berta Valente. They provided insights into what the human body needs to survive and how it reacts when deprived of food.

Minimum Nutrition Required for Survival

Survival requires more than just clean water and safety. Access to food that meets daily energy, macronutrient, and micronutrient requirements is essential for maintaining health, supporting recovery, and preventing malnutrition.

According to the World Health Organization (WHO), adults need varying amounts of energy depending on factors such as age, sex, and level of physical activity. A kilocalorie (kcal) is a measure of energy, indicating how much energy a person gets from food or how much energy the body needs to function. The body uses this energy for breathing, digestion, maintaining body temperature, and growth in children.

Energy needs come from three main sources:

• Resting Energy Expenditure: The energy used by the body at rest to maintain vital functions like breathing and circulation.
• Physical Activity: Varies during emergencies based on factors such as displacement, caregiving, or survival tasks.
• Thermogenesis: The energy used to digest and process food.

Resting energy expenditure typically accounts for the largest portion of energy needs, especially when physical activity is limited. Other factors including age, sex, body size, health status, pregnancy, or cold environments also influence energy requirements.

Energy Requirements Across Different Life Stages

Energy needs vary throughout life. Infants require approximately 95 to 108 kcal per kilogram of body weight per day during the first six months and between 84 to 98 kcal per kilogram from six to 12 months. For children under ten years old, energy needs are based on normal growth patterns without distinction between boys and girls.

For example, a two-year-old child typically requires about 1,000 to 1,200 kcal daily. A five-year-old needs around 1,300 to 1,500 kcal, while a ten-year-old generally requires between 1,800 and 2,000 kcal per day. From age ten onward, energy requirements begin to differ between boys and girls due to variations in growth and activity levels.

For adults with light to moderate physical activity, the average daily energy requirement for men aged 19 to 50 is about 2,900 kcal, while women in the same age group require roughly 2,200 kcal per day. These values include a range of plus or minus 20% to account for individual differences in metabolism and activity. For adults over 50 years, energy needs decrease slightly, with men requiring about 2,300 kcal and women around 1,900 kcal daily.

In humanitarian emergencies, food aid must guarantee the minimum energy intake to maintain basic health and function, which was set to 2,100 kcal per person per day. This level aims to meet fundamental physiological needs and prevent malnutrition when food supply is limited.

Nutritional Balance and Essential Micronutrients

This energy must come from a balance of macronutrients, with carbohydrates supplying 50%-60% (such as rice or bread), proteins 10%-35% (like beans or lean meat), and fats 20%-35% (for example, cooking oil or nuts). Fat requirements are higher for young children (30%-40%) and for pregnant and breastfeeding women (at least 20%).

In addition to energy, the body requires vitamins and minerals, such as iron, vitamin A, iodine, and zinc, which are critical for immune function, growth, and brain development. Iron is found in foods like red meat, beans, and fortified cereals. Vitamin A comes from carrots, sweet potatoes, and dark leafy greens. Iodine is commonly obtained from iodized salt and seafood. Zinc is present in meat, nuts, and whole grains.

When food systems collapse, this balance is lost, leading to widespread malnutrition.

Physical Effects of Starvation

Physiologically, the effects of starvation on the human body unfold in three overlapping stages. Each reflects the body’s effort to survive without food, but these adaptations come at great physiological cost.

In the first stage, which lasts up to 48 hours after food intake stops, the body draws on glycogen stored in the liver to keep blood sugar levels stable. This process, called glycogenolysis, is a short-term solution. When glycogen runs out, the second stage begins.

The body shifts to gluconeogenesis, producing glucose from non-carbohydrate sources like amino acids (from muscle), glycerol (from fat), and lactate. This process fuels vital organs but results in muscle breakdown and increased nitrogen loss, especially from skeletal muscle.

By day three, ketogenesis becomes the dominant process. The liver starts converting fatty acids into ketone bodies—molecules derived from fat that serve as an alternative fuel source when glucose is scarce. These ketones are used by the brain and other organs for energy. This shift helps spare muscle tissue but also signals a deeper metabolic crisis.

Hormonal changes—including reduced insulin, thyroid hormone (T3), and nervous system activity—slow the metabolic rate to conserve energy. Over time, fat becomes the main energy source. But once fat stores are exhausted, the body is forced to break down its own proteins for energy. This accelerates muscle wasting, weakens the immune system, and increases the risk of deadly infections.

Death, often from pneumonia or other complications, typically occurs after 60 to 70 days without food in an otherwise healthy adult.

Psychological and Long-Term Effects

As the body enters prolonged nutrient deprivation, the visible and invisible signs of starvation intensify. Physically, individuals lose substantial weight, experience muscle wasting, fatigue, slowed heart rate, dry skin, hair loss, and compromised wound healing. Immune defenses weaken, increasing vulnerability to infections, particularly pneumonia—a frequent cause of death in starvation.

Psychologically, starvation creates profound distress. People report apathy, irritability, anxiety, and a constant preoccupation with food. Cognitive abilities decline, and emotional regulation deteriorates, sometimes leading to depression or withdrawal.

In children, long-term effects include stunted growth and impaired brain development. Both can become irreversible.

Breaking the Cycle of Starvation

After a period of starvation, the body is in a fragile metabolic state. Sudden reintroduction of food, especially carbohydrates, causes a spike in insulin and a rapid shift of electrolytes like phosphate, potassium, and magnesium into cells. This can overwhelm the body, leading to what’s known as refeeding syndrome, which may result in serious complications such as heart failure, respiratory distress, or even death if not carefully managed.

Standard protocols begin with therapeutic milks called F-75, specially designed to stabilize patients during the initial phase of treatment for severe acute malnutrition, followed by ready-to-use therapeutic food, a specially formulated peanut-butter paste or biscuit with the power to bring a malnourished child from the brink of death to full nutritional recovery in just four to eight weeks, oral rehydration salts, and micronutrient powders.

These must be delivered safely. Consistent humanitarian access is essential. Airdrops are not part of food security. Survival requires sustained, coordinated efforts that restore food systems, protect civilians, and uphold humanitarian law. Anything less risks repeating cycles of hunger and harm.