Malnutrition is an imbalance between the nutrients your body needs to function and the nutrients it gets. It can mean undernutrition or overnutrition. You can be malnourished from an overall lack of calories, or you might have a protein, vitamin or mineral deficiency. You might also have more excess calories than your body knows what to do with.
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.
Cleveland Clinic is a non-profit academic medical center. Advertising on our site helps support our mission. We do not endorse non-Cleveland Clinic products or services. Policy
Malnutrition can mean undernutrition or overnutrition. It can also mean an imbalance of macronutrients (proteins, carbohydrates, fats) or micronutrients (vitamins and minerals).
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.
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.
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.
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.
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.
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.
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.
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.
Undernutrition may look like:
Overnutrition might look like:
Undernutrition is usually caused by not eating enough nutrients. It can also be caused by certain medical conditions that prevent your body from absorbing nutrients.
You might have trouble getting enough nutrients if you have:
Overnutrition is caused by consuming more nutrients than you need. You might do this if you have:
Physical observation and a history of your diet and health conditions are often enough to diagnose protein-energy undernutrition or overnutrition. Healthcare providers may measure your BMI or measure a child’s arm circumference to help understand the extent of the problem. If possible, they will take a blood sample to test for specific micronutrient imbalances. Micronutrient undernutrition often accompanies macronutrient undernutrition, and it can accompany macronutrient overnutrition too. A blood test will also diagnose the rare case of micronutrient overnutrition if you have those symptoms.
Undernutrition is treated with nutritional supplements. This might mean individual micronutrients, or it might mean refeeding with a custom, high-calorie nutritional formula designed to restore everything your body is missing. Severe undernutrition can take weeks of refeeding to correct. But refeeding can be dangerous, especially in the first few days. Your body changes in many ways to adapt to undernutrition. Refeeding asks it to change back to its old way of operating, and sometimes that change is more than it's prepared to handle. It’s best to begin refeeding under close medical observation to prevent and manage the complications of refeeding syndrome, which can be serious and even life-threatening.
Overnutrition is generally treated with weight loss, diet and lifestyle changes. Losing extra weight can help reduce your risk of developing secondary conditions such as diabetes and heart disease. Weight loss treatment may include diet and exercise plans, medications or medical procedures. You may also need to treat an underlying condition, such as thyroid disease, or a mental health disorder. Weight loss can be rapid or it can be long and gradual, depending on the path you take. But after you lose weight, it’s the lifestyle changes you stick with that will help keep it off. This may involve long-term support systems such as counseling, behavioral therapy, support groups and education in nutrition.
Malnutrition is a global problem. In both the developed world and the developing world, poverty and a lack of understanding of nutrition are the leading causes. We can help control the disease of malnutrition with better worldwide education and support for the disadvantaged, including access to clean water, nutritious whole foods and medicine. Children and elders who may not be able to advocate for themselves are especially at risk and may need closer attention paid to their diet and health condition.
The best way to prevent malnutrition is to eat a well-balanced diet with a variety of nutritious whole foods in it. If you have enough of all the nutrients your body needs, you will be less likely to overeat trying to satisfy those needs. Some micronutrient deficiencies are common even with a fairly standard diet. A blood test is one way to find out if you could benefit from micronutrient supplements. Your healthcare provider can help you determine the correct dose to take.
Malnutrition is treatable, but some effects can linger. Effects of severe undernutrition, such as blindness from vitamin A deficiency, soft bones from vitamin D deficiency and stunted growth from protein-energy undernutrition in children may not be reversible, even after rehabilitation. Secondary effects of long-term overnutrition, such as insulin resistance and carotid artery disease, may last even after weight loss. However, with earlier intervention and good follow-up support, people can make full recoveries.
Contact your healthcare provider if:
A note from Cleveland Clinic
Most people think of malnutrition as undernutrition — a deficiency of overall calories or of certain nutrients that the body requires. Undernutrition is one face of malnutrition, but overnutrition can also be detrimental to your health. Nutritionists now define malnutrition as a mismatch between the nutrients you need and the nutrients you get. By this definition, malnutrition is quite common. It’s also a significant contributor to disease, disablement and death worldwide. Malnutrition needs to be fought on many fronts, including education, infrastructure and policy measures. At home, you can help prevent malnutrition by eating a well-balanced diet.
Last reviewed by a Cleveland Clinic medical professional on 05/04/2022.
Learn more about our editorial process.