During pregnancy and breastfeeding, women must ingest enough nutrients for themselves and their child, so they need significantly more protein and calories during these periods, as well as more vitamins and minerals (especially iron, iodine, calcium, folic acid, and vitamins A, C, and K). In 2001 the FAO of the UN reported that iron deficiency afflicted 43 percent of women in developing countries and increased the risk of death during childbirth. A 2008 review of interventions estimated that universal supplementation with calcium, iron, and folic acid during pregnancy could prevent 105,000 maternal deaths (23.6 percent of all maternal deaths).

Frequent pregnancies with short intervals between them and long periods of breastfeeding add an additional nutritional burden.

Women have unique nutritional requirements, and in some cases need more nutrients than men; for example, women need twice as much calcium as men.

For the individual, prevention consists of ensuring they eat plenty of food, varied enough to provide a nutritionally complete diet.

Starvation can be caused by factors, other than illness, outside of the control of the individual. The Rome Declaration on World Food Security outlines several policies aimed at increasing food security and, consequently, preventing starvation. These include:

- Poverty reduction

- Prevention of wars and political instability

- Food aid

- Agricultural sustainability

- Reduction of economic inequality

Supporting farmers in areas of food insecurity through such measures as free or subsidized fertilizers and seeds increases food harvest and reduces food prices.

Under normal metabolic conditions, the human body relies on free blood glucose as its primary energy source. The level of blood sugar is tightly regulated; as blood glucose is consumed, the pancreas releases glucagon, a hormone that stimulates the liver to convert stored glycogen into glucose. The glycogen stores are ordinarily replenished after every meal, but if the store is depleted before it can be replenished, the body enters hypoglycemia, and begins the starvation response.

After the exhaustion of the glycogen reserve, and for the next 2–3 days, fatty acids become the principal metabolic fuel. At first, the brain continues to use glucose, because, if a non-brain tissue is using fatty acids as its metabolic fuel, the use of glucose in the same tissue is switched off. Thus, when fatty acids are being broken down for energy, all of the remaining glucose is made available for use by the brain. Basically the body will use up stored fat cells first, then move on to muscles.

After 2 or 3 days of fasting, the liver begins to synthesize ketone bodies from precursors obtained from fatty acid breakdown. The brain uses these ketone bodies as fuel, thus cutting its requirement for glucose. After fasting for 3 days, the brain gets 30% of its energy from ketone bodies. After 4 days, this goes up to 75%. Thus, the production of ketone bodies cuts the brain's glucose requirement from 80 g per day to about 30 g per day. Of the remaining 30 g requirement, 20 g per day can be produced by the liver from glycerol (itself a product of fat breakdown). But this still leaves a deficit of about 10 g of glucose per day that must be supplied from some other source. This other source will be the body's own proteins.

After several days of fasting, all cells in the body begin to break down protein. This releases alanine and lactate produced from pyruvate into the bloodstream, which can be converted into glucose by the liver. Since much of human muscle mass is protein, this phenomenon is responsible for the wasting away of muscle mass seen in starvation. However, the body is able to selectively decide which cells will break down protein and which will not. About 2–3 g of protein has to be broken down to synthesize 1 g of glucose; about 20–30 g of protein is broken down each day to make 10 g of glucose to keep the brain alive. However, this number may decrease the longer the fasting period is continued in order to conserve protein.

Starvation ensues when the fat reserves are completely exhausted and protein is the only fuel source available to the body. Thus, after periods of starvation, the loss of body protein affects the function of important organs, and death results, even if there are still fat reserves left unused. (In a leaner person, the fat reserves are depleted earlier, the protein depletion occurs sooner, and therefore death occurs sooner.) The ultimate cause of death is, in general, cardiac arrhythmia or cardiac arrest brought on by tissue degradation and electrolyte imbalances.

Disorders usually resolve after early treatment. If the treatment is delayed, the overall health of the child is improved but physical (reduced) and intellectual (mental disabilities) sequelae are feared. Without treatment or if treatment occurs too late, death is inevitable.

A high risk of death is identified by a brachial perimeter < 11 cm or by a weight-to-height threshold < -3 SD. In practice, malnourished children with edema are suffering from potentially life-threatening severe malnutrition.

Kwashiorkor is a form of severe protein–energy malnutrition characterized by edema, irritability, ulcerating dermatoses, and an enlarged liver with fatty infiltrates. Sufficient calorie intake, but with insufficient protein consumption, distinguishes it from marasmus. Kwashiorkor cases occur in areas of famine or poor food supply. Cases in the developed world are rare.

Jamaican pediatrician Cicely Williams introduced the name into the medical community in a 1935 "Lancet" article, two years after she published the disease's first formal description in the Western medical literature. The name is derived from the Ga language of coastal Ghana, translated as "the sickness the baby gets when the new baby comes" or "the disease of the deposed child", and reflecting the development of the condition in an older child who has been weaned from the breast when a younger sibling comes. Breast milk contains proteins and amino acids vital to a child's growth. In at-risk populations, kwashiorkor may develop after a mother weans her child from breast milk, replacing it with a diet high in carbohydrates, especially sugar.

Until the late 20th century, dietary issues in Mexico were solely a question of undernutrition or malnutrition, generally because of poverty and distribution issues. For this reason, obesity was associated with wealth and health, the latter especially in children. Despite changes in the Mexican diet and food distribution, malnutrition still remains problematic in various parts of the country.

Obesity in Mexico is a relatively recent phenomenon, having been widespread since the 1980s with the introduction of processed food into much of the Mexican food market. Prior to that, dietary issues were limited to under and malnutrition, which is still a problem in various parts of the country. Following trends already ongoing in other parts of the world, Mexicans have been foregoing traditional whole grains and vegetables in favor of a diet with more animal products, more fat, and more sugar much of which is a consequence of processed food. It has seen dietary energy intake and rates of overweight and obese people rise with seven out of ten at least overweight and a third clinically obese.