Malnutrition: Definition, Causes, Symptoms & Treatment (2024)

What is malnutrition?

Your body needs a variety of nutrients, and in certain amounts, to maintain its tissues and its many functions. Malnutrition happens when the nutrients it gets don’t meet these needs. You can be malnourished from an overall lack of nutrients, or you may have an abundance of some kinds of nutrients but lack other kinds. Even the lack of a single vitamin or mineral can have serious health consequences for your body. On the other hand, having an excess of nutrients can also cause problems.

What are the 4 types of malnutrition?

Malnutrition can mean undernutrition or overnutrition. It can also mean an imbalance of macronutrients (proteins, carbohydrates, fats) or micronutrients (vitamins and minerals).

Undernutrition

Undernutrition is what most people think of when they think of malnutrition. Undernutrition is a deficiency of nutrients. You may be undernourished if you don’t have an adequate diet, or if your body has trouble absorbing enough nutrients from your food. Undernutrition can cause visible wasting of fat and muscle, but it can also be invisible. You can be overweight and undernourished.

Macronutrient undernutrition

Also called protein-energy undernutrition, this is a deficiency of macronutrients: proteins, carbohydrates and fats. Macronutrients are the main building blocks of your diet, the nutrients that your body relies on to produce energy to maintain itself. Without them — or even just one of them — your body soon begins to fall apart, breaking down tissues and shutting down nonessential functions to conserve its low energy.

Micronutrient undernutrition

Micronutrients are vitamins and minerals. Your body needs these in smaller amounts, but it does need them, for all types of functions. Many people are mildly deficient in certain vitamins and minerals from a lack of variety in their diet. You might not notice a mild vitamin deficiency affecting you, but as micronutrient undernutrition becomes more severe, it can begin to have serious and lasting effects.

Overnutrition

The World Health Organization has recently added overnutrition to its definition of malnutrition to recognize the detrimental health effects that can be caused by excessive consumption of nutrients. This includes the effects of overweight and obesity, which are strongly associated with a list of noncommunicable diseases (NCDs). It also includes the toxicity that can result from overdosing specific micronutrients.

Macronutrient overnutrition

When your body has an excess of protein, carbohydrate and/or fat calories to use, it stores them away as fat cells in your adipose tissue. But when your body runs out of tissue for storage, the fat cells themselves have to grow. Enlarged fat cells are associated with chronic inflammation and with a host of metabolic disorders that follow. These can lead to NCDs such as diabetes mellitus, coronary artery disease and stroke.

Micronutrient overnutrition

You can actually overdose on vitamin and mineral supplements. More research is needed to explain how this happens and how much is too much of a certain vitamin or mineral. In general, micronutrient overnutrition is uncommon and doesn’t occur from diet alone. But if you take mega doses of certain supplements, it can have toxic effects. It’s a good idea to check with your healthcare provider first.

Who does malnutrition affect?

In its broadest sense, malnutrition can affect anyone. Lack of knowledge of nutrition, lack of access to a variety of foods, sedentary modern lifestyles and economic disadvantages are all common contributors to malnutrition. Certain populations are more at risk of certain types of malnutrition.

Populations more at risk of undernutrition include:

• Poor and low income. Whether in a developed country like the U.S. or in developing countries with fewer resources overall, poorer communities have less access to adequate nutrition.
• Children. Children have greater nutritional needs than adults in order to grow and develop. Disadvantaged children are especially at risk of undernutrition and its consequences.
• Chronically ill. Many chronic illnesses can directly affect appetite and/or calorie absorption. Some increase your caloric needs. Spending time in the hospital is also a risk factor for undernutrition.
• Elderly. As adults advance in age, their nutrition can deteriorate for several reasons, including reduced mobility, institutionalization, reduced appetite and reduced absorption of nutrients.

Populations more at risk of overnutrition include:

• Poor and low income. In developed countries, poorer communities often have easier access to fast foods, which are high in calories but low in nutritional value, than they have to nutritious whole foods. This can lead to macronutrient overnutrition with micronutrient undernutrition.
• Sedentary. Desk jobs, family obligations, health and social factors that keep people sitting all day instead of out and moving about can lead to significant weight gain.

What happens to the body during malnutrition?

Macronutrient undernutrition (protein-energy undernutrition) deprives your body of energy to sustain itself. To compensate, it begins breaking down its own tissues and shutting down its functions. This begins with its body fat stores and then proceeds to muscle, skin, hair and nails. People with protein-energy undernutrition are often visibly emaciated. Children may have stunted growth and development.

One of the first systems to begin to shut down is the immune system. This makes undernourished people highly prone to illness and infection and slower to recover. Wounds take longer to heal. Cardiac activity also slows down, leading to low heart rate, low blood pressure and low body temperature. People may feel faint, weak and apathetic about life. They may lose appetite, and parts of their digestive system can atrophy.

People who have macronutrient undernutrition are likely to also have micronutrient undernutrition. When overall calories are lacking, that affects vitamin and mineral levels too. Some of the complications of severe undernutrition conditions, such as marasmus and kwashiorkor, result from particular vitamin deficiencies. For example, vitamin A deficiency can cause vision problems, and vitamin D deficiency can cause soft bones.

Some people may consume a lot of calories, but not enough vitamins and minerals. In these cases, the effects of malnutrition may be less obvious. People may be overweight from macronutrient overnutrition but may have symptoms of anemia — weakness, faintness and fatigue — due to the lack of minerals or vitamins. People who have overnutrition may show symptoms of metabolic syndrome, such as insulin resistance and high blood pressure.