Few nutrients are as important as protein.
Protein is the building block of your muscles, skin, enzymes and hormones, and it plays an essential role in all body tissues.
Most foods contain some protein. As a result, true protein deficiency is rare in developed countries. However, some people may still be at risk.
Deficiency leads to various health problems, while low protein intake may also be a concern, as it can cause subtle changes in your body over time.
This article lists 8 symptoms of low protein intake or deficiency.
What Is Protein Deficiency?
Protein deficiency is when your intake is unable to meet your body’s requirements.
An estimated one billion people worldwide suffer from inadequate protein intake ().
The problem is especially severe in Central Africa and South Asia, where up to 30% of children get too little protein from their diet ().
Certain people in developed countries are also at risk. This includes vegetarians and vegans who follow an imbalanced diet, as well as institutionalized older people and hospitalized patients (, ).
While true protein deficiency is uncommon in the Western world, some people get very low amounts from their diet.
Too little protein may cause changes in body composition that develop over a long period of time, such as muscle wasting.
The most severe form of protein deficiency is known as kwashiorkor. It most often occurs in children in developing countries where famine and imbalanced diets are common.
Protein deficiency can affect almost all aspects of body function. As a result, it is associated with many symptoms.
Some of these symptoms may start to occur even when protein deficiency is marginal. They are listed below, along with some typical symptoms of kwashiorkor.
Summary: Protein deficiency is when people do not get adequate amounts of protein from their diet. Kwashiorkor, its most severe form, is most commonly seen in children in developing countries.
Edema, which is characterized by swollen and puffy skin, is a classic symptom of kwashiorkor.
Scientists believe it is caused by low amounts of human serum albumin, which is the most abundant protein in the liquid part of blood, or blood plasma ().
One of albumin’s main functions is to maintain oncotic pressure — a force that draws fluid into the blood circulation. In this way, albumin prevents excessive amounts of fluid from accumulating in tissues or other body compartments.
Because of reduced human serum albumin levels, severe protein deficiency leads to lower oncotic pressure. As a result, fluid accumulates in tissues, causing swelling.
For the same reason, protein deficiency may lead to fluid buildup inside the abdominal cavity. A bloated belly is a characteristic sign of kwashiorkor.
Keep in mind that edema is a symptom of severe protein deficiency, which is unlikely to happen in developed countries.
Summary: Key symptoms of kwashiorkor are edema and a swollen abdomen.
2. Fatty Liver
Another common symptom of kwashiorkor is a fatty liver, or fat accumulation in liver cells ().
Left untreated, the condition may develop into fatty liver disease, causing inflammation, liver scarring and potentially liver failure.
Fatty liver is a common condition in obese people, as well as those who consume a lot of alcohol (, ).
Why it occurs in cases of protein deficiency is unclear, but studies suggest that an impaired synthesis of fat-transporting proteins, known as lipoproteins, may contribute to the condition ().
Summary: Fatty liver is one of the symptoms of kwashiorkor in children. In worst case scenarios, it may lead to liver failure.
3. Skin, Hair and Nail Problems
Protein deficiency often leaves its mark on the skin, hair and nails, which are largely made of protein.
For instance, kwashiorkor in children is distinguished by flaky or splitting skin, redness and patches of depigmented skin (, ).
Hair thinning, faded hair color, hair loss (alopecia) and brittle nails are also common symptoms (, ).
However, these symptoms are unlikely to appear unless you have a severe protein deficiency.
Summary: Severe protein deficiency may affect your skin, causing redness, flaky skin and depigmentation. It may also cause brittle nails and hair loss.
4. Loss of Muscle Mass
Your muscles are your body’s largest reservoir of protein.
When dietary protein is in short supply, the body tends to take protein from skeletal muscles to preserve more important tissues and body functions. As a result, lack of protein leads to muscle wasting over time.
Even moderate protein insufficiency may cause muscle wasting, especially in elderly people.
One study in elderly men and women found that muscle loss was greater among those who consumed the lowest amounts of protein ().
This has been confirmed by other studies that show that an increased protein intake may slow the muscle degeneration that comes with old age ().
Summary: Protein is essential for muscle growth and maintenance. Loss of muscle mass is one of the first signs of inadequate protein intake.
5. Greater Risk of Bone Fractures
Muscles are not the only tissues affected by low protein intake.
Your bones are also at risk. Not consuming enough protein may weaken your bones and increase the risk of fractures (, , ).
One study in postmenopausal women found that a higher protein intake was associated with a lower risk of hip fractures. The highest intake was linked to a 69% reduced risk, and animal-source protein appeared to have the greatest benefits ().
Another study in postmenopausal women with recent hip fractures showed that taking 20 grams of protein supplements per day for half a year slowed bone loss by 2.3% ().
Summary: Protein helps maintain the strength and density of bones. Insufficient protein intake has been linked to a lower bone mineral density and an increased risk of fractures.
6. Stunted Growth in Children
Protein not only helps maintain muscle and bone mass, but it’s also essential for body growth.
Thus, deficiency or insufficiency is especially harmful to children whose growing bodies require a steady supply.
In fact, stunting is the most common sign of childhood malnutrition. In 2013, an estimated 161 million children suffered from stunted growth ().
Observational studies show a strong association between low protein intake and impaired growth (, ).
Stunted growth is also one of the main characteristics of kwashiorkor in children ().
Summary: Insufficient protein intake may delay or prevent growth in children.
7. Increased Severity of Infections
A protein deficit can also take its toll on the immune system.
Impaired immune function may increase the risk or severity of infections, a common symptom of severe protein deficiency (, ).
For instance, one study in mice showed that following a diet consisting of only 2% protein was associated with a more severe influenza infection, compared to a diet providing 18% protein ().
Even marginally low protein intake may impair immune function. One small study in older women showed following a low-protein diet for nine weeks significantly reduced their immune response ().
Summary: Eating too little protein may impair your body’s ability to fight infections, such as the common cold.
8. Greater Appetite and Calorie Intake
Although poor appetite is one of the symptoms of severe protein deficiency, the opposite seems to be true for milder forms of deficiency.
When your protein intake is inadequate, your body attempts to restore your protein status by increasing your appetite, encouraging you to find something to eat (, ).
But a protein deficit doesn’t aimlessly drive the urge to eat, at least not for everyone. It may selectively increase people’s appetite for savory foods, which tend to be high in protein ().
While this may certainly help in times of food shortage, the problem is that modern society offers unlimited access to savory, high-calorie foods.
Many of these convenience foods contain some protein. However, the amount of protein in these foods is often considerably low compared to the number of calories they provide.
As a result, poor protein intake may lead to weight gain and obesity, an idea known as the protein leverage hypothesis ().
Not all studies support the hypothesis, but protein is clearly more satiating than carbs and fat (, ).
This is part of the reason why increased protein intake can reduce overall calorie intake and promote weight loss (, ).
If you are feeling hungry all the time and have difficulties keeping your calorie intake in check, try adding some lean protein to every meal.
Summary: Low protein intake may increase appetite. While a greater appetite is beneficial in times of food shortage, it may promote weight gain and obesity when food is plentiful.
How Much Protein Do You Need?
Not everyone has the same protein requirement. It depends on many factors, including body weight, muscle mass, physical activity and age.
Arguably, body weight is the most important determinant of protein requirements. As a result, recommendations are usually presented as grams for each pound or kilogram of body weight.
The recommended daily allowance (RDA) is 0.4 grams of protein for each pound of body weight (0.8 grams per kg). Scientist estimate this should be enough for most people.
This translates to 66 grams of protein per day for an adult weighing 165 pounds (75 kg).
For athletes, the American College of Sports Medicine recommends a daily protein intake ranging from 0.5 to 0.6 grams for each pound of body weight (1.2–1.4 grams per kg), which should be enough for muscle maintenance and training recovery ().
However, scientists don’t agree how much is enough. The International Society of Sports Nutrition’s daily recommendation is 0.9 grams of protein per pound of body weight (2 grams per kg) for athletes ().
Just like athletes, older adults also seem to have higher protein requirements.
While the RDA is currently the same for old and young adults, studies indicate it is underestimated and should be raised to 0.5 to 0.7 grams per pound of body weight (1.2–1.5 grams per kg) for older people (, ).
Simply put, if you are older or physically active, your daily protein requirements are probably higher than the current RDA of 0.4 grams per pound of body weight (0.8 grams per kg).
The richest sources of protein include fish, meat, eggs, dairy products and legumes.
Summary: The RDA for protein is 0.4 grams per pound (0.8 grams per kg). However, studies show the requirements may be greater for athletes and older adults. Exactly how much greater is a matter of debate.
The Bottom Line
Protein is found everywhere in your body. Your muscles, skin, hair, bones and blood are largely made of protein.
For this reason, protein deficiency has a wide range of symptoms.
Serious protein deficiency can cause swelling, fatty liver, skin degeneration, increase the severity of infections and stunt growth in children.
While true deficiency is rare in developed countries, low intake may cause muscle wasting and increase the risk of bone fractures.
Some evidence even suggests that getting too little protein may increase appetite and promote overeating and obesity.
For optimal health, make sure to include protein-rich foods in every meal.