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.

A large percentage of children that suffer from PEM also have other co-morbid conditions. The most common co-morbidities are diarrhea (72.2% of a sample of 66 subjects) and malaria (43.3%). However, a variety of other conditions have been observed with PEM, including sepsis, severe anaemia, bronchopneumonia, HIV, tuberculosis, scabies, chronic suppurative otitis media, rickets, and keratomalacia. These co-morbidities tax already malnourished children and may prolong hospital stays initially for PEM and may increase the likelihood of death.

Although protein energy malnutrition is more common in low-income countries, children from higher-income countries are also affected, including children from large urban areas in low socioeconomic neighborhoods. This may also occur in children with chronic diseases, and children who are institutionalized or hospitalized for a different diagnosis. Risk factors include a primary diagnosis of intellectual disability, cystic fibrosis, malignancy, cardiovascular disease, end stage renal disease, oncologic disease, genetic disease, neurological disease, multiple diagnoses, or prolonged hospitalization. In these conditions, the challenging nutritional management may get overlooked and underestimated, resulting in an impairment of the chances for recovery and the worsening of the situation.

PEM is fairly common worldwide in both children and adults and accounts for 6 million deaths annually. In the industrialized world, PEM is predominantly seen in hospitals, is associated with disease, or is often found in the elderly.

In almost all countries, the poorest quintile of children has the highest rate of malnutrition. However, inequalities in malnutrition between children of poor and rich families vary from country to country, with studies finding large gaps in Peru and very small gaps in Egypt. In 2000, rates of child malnutrition were much higher in low income countries (36 percent) compared to middle income countries (12 percent) and the United States (1 percent).

Studies in Bangladesh in 2009 found that the mother’s literacy, low household income, higher number of siblings, less access to mass media, less supplementation of diets, unhygienic water and sanitation are associated with chronic and severe malnutrition in children.

The World Health Organisation estimated in 2008 that globally, half of all cases of undernutrition in children under five were caused by unsafe water, inadequate sanitation or insufficient hygiene. This link is often due to repeated diarrhoea and intestinal worm infections as a result of inadequate sanitation. However, the relative contribution of diarrhea to undernutrition and in turn stunting remains controversial.

Poor maternal nutrition during pregnancy and breastfeeding can lead to stunted growth of their children. Women who are underweight or anemic during pregnancy, are more likely to have stunted children which perpetuates the inter-generational transmission of stunting.

Inadequate complementary child feeding and a general lack of vital nutrients beside pure caloric intake is one cause for stunted growth. Children need to be fed diets which meet the minimum requirements in terms of frequency and diversity in order to prevent undernutrition.

Persons in prisons, concentration camps, and refugee camps tend to suffer from marasmus, due to poor nutrition.

Vitamin poisoning is the condition of overly high storage levels of vitamins, which can lead to toxic symptoms. The medical names of the different conditions are derived from the vitamin involved: an excess of vitamin A, for example, is called "hypervitaminosis A".

Iron overload disorders are diseases caused by the overaccumulation of iron in the body. Organs commonly affected are the liver, heart and endocrine glands in the mouth.

Not only the causes, but also the complications of the disorder must be treated, including infections, dehydration, and circulation disorders, which are frequently lethal and lead to high mortality if ignored. Initially, the child is given dried skim milk powder mixed with boiled water which is then followed by mixing it with vegetable oils and finally sugar. Once children start to recover, they should have more balanced diets which meet their nutritional needs. Infections are also common in children with marasmus. So, they are also treated with antibiotics. Ultimately, marasmus can progress to the point of no return when the body's ability for protein synthesis is lost. At this point, attempts to correct the disorder by giving food or protein are futile.

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.

Obesity increases health risks, including diabetes, cancer, cardiovascular disease, high blood pressure, and non-alcoholic fatty liver disease, to name a few. Reduction of obesity lowers those risks.

A 1-kg loss of body weight has been associated with an approximate 1-mm Hg drop in blood pressure.

Obesity is caused by eating too many calories compared to the amount of exercise the individual is performing, causing a distorted energy balance. It can lead to diseases such as cardiovascular disease and diabetes. Obesity is a condition in which the natural energy reserve, stored in the fatty tissue of humans and other mammals, is increased to a point where it is associated with certain health conditions or increased mortality.

The low-cost food that is generally affordable to the poor in affluent nations is low in nutritional value and high in fats, sugars and additives. In rich countries, therefore, obesity is often a sign of poverty and malnutrition while in poorer countries obesity is more associated with wealth and good nutrition. Other non-nutritional causes for obesity included: sleep deprivation, stress, lack of exercise, and heredity.

Acute overeating can also be a symptom of an eating disorder.

Goitrogenic foods can cause goitres by interfering with iodine uptake.

Social conditions such as poverty, social isolation and inability to get or prepare preferred foods can cause unintentional weight loss, and this may be particularly common in older people. Nutrient intake can also be affected by culture, family and belief systems. Ill-fitting dentures and other dental or oral health problems can also affect adequacy of nutrition.

Loss of hope, status or social contact and spiritual distress can cause depression, which may be associated with reduced nutrition, as can fatigue.

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.

In order to avoid problems, the person must be rehabilitated with small but frequent rations, given every two to four hours. During one week, the diet, hyperglucidic, is gradually enriched in protein as well as essential elements: sweet milk with mineral salts and vitamins. The diet may include lactases - so that children who have developed lactose intolerance can ingest dairy products - and antibiotics - to compensate for immunodeficiency. After two to three weeks, the milk is replaced by boiled cereals fortified with minerals and vitamins until its mass is at least 80% of normal weight. Traditional food can then be reintroduced. The child is considered healed when his mass reaches 85% of normal.

Though heart disease is not exclusive to the poor, there are aspects of a life of poverty that contribute to its development. This category includes coronary heart disease, stroke and heart attack. Heart disease is the leading cause of death worldwide and there are disparities of morbidity between the rich and poor. Studies from around the world link heart disease to poverty. Low neighborhood income and education were associated with higher risk factors. Poor diet, lack of exercise and limited (or no) access to a specialist were all factors related to poverty, though to contribute to heart disease.

Both low income and low education were predictors of coronary heart disease, a subset of cardiovascular disease. Of those admitted to hospital in the United States for heart failure, women and African Americans were more likely to reside in lower income neighborhoods. In the developing world, there is a 10 fold increase in cardiac events in the black and urban populations.

More than 300 million people worldwide have asthma. The rate of asthma increases as countries become more urbanized and in many parts of the world those who develop asthma do not have access to medication and medical care. Within the United States, African Americans and Latinos are four times more likely to suffer from severe asthma than whites. The disease is closely tied to poverty and poor living conditions. Asthma is also prevalent in children in low income countries. Homes with roaches and mice, as well as mold and mildew put children at risk for developing asthma as well as exposure to cigarette smoke.

Unlike many other Western countries, the mortality rate for asthma has steadily risen in the United States over the last two decades. Mortality rates for African American children due to asthma are also far higher than that of other racial groups. For African Americans, the rate of visits to the emergency room is 330 percent higher than their white counterparts. The hospitalization rate is 220 percent higher and the death rate is 190 percent higher. Among Hispanics, Puerto Ricans are disporpotionatly affected by asthma with a disease rate that is 113 percent higher than non-Hispanic Whites and 50 percent higher than non-Hispanic Blacks. Studies have shown that asthma morbidity and mortality are concentrated in inner city neighborhoods characterized by poverty and large minority populations and this affects both genders at all ages. Asthma continues to have an adverse effects on the health of the poor and school attendance rates among poor children. 10.5 million days of school are missed each year due to asthma.

The exact mechanism in which these diseases cause cachexia is poorly understood, but there is probably a role for inflammatory cytokines, such as tumor necrosis factor-alpha (which is also nicknamed 'cachexin' or 'cachectin'), interferon gamma and interleukin 6, as well as the tumor-secreted proteolysis-inducing factor.

Related syndromes include kwashiorkor and marasmus, although these do not always have an underlying causative illness and are most often symptomatic of severe malnutrition.

Those suffering from the eating disorder anorexia nervosa appear to have high plasma levels of ghrelin. Ghrelin levels are also high in patients who have cancer-induced cachexia.

According to the 2007 AHRQ National Inpatient Sample, in a projected 129,164 hospital encounters in the United States, cachexia was listed as at least one of up to 14 recorded diagnosis codes based on a sample of 26,325 unweighted encounters. A sample of 32,778 unweighted US outpatient visits collected by the CDC's National Ambulatory Medical Care Survey did not list any visits where cachexia was one of up to three recorded diagnoses treated during the visit.

Given the lack of scientific data on the effects of high-protein diets, the US Food and Nutrition Board does not set a tolerable upper intake level nor upper acceptable macronutrient distribution range for protein.

Antiretrovirals and anabolic steroids have been used to treat HIV wasting syndrome. Additionally, an increase in protein-rich foods such as peanut butter, eggs, and cheese can assist in controlling the loss of muscle mass.

Malnutrition is an important health concern in Tibet. According to a study conducted in 1994/1995 in eleven districts of Tibet, malnutrition affected more than half of the children from 1–7 years old. The major cause was poverty.