Too few carbohydrates in the diet causes an energy deficit that forces the body to break down stored energy and seek energy from less desirable foods, which can trigger unwanted side effects. According to MedlinePlus, carbohydrates are the body's predominant source of glucose, which provides the fuel required by all of the body's cells.
MedlinePlus states that when low carbohydrate intake results in low calorie intake, the condition is considered a form of malnutrition. Some people with inadequate carbohydrate intake are able to maintain their calorie intake, but they often seek out fat-laden foods to sustain energy levels. Consuming too many high-fat, low-calorie foods is associated with weight gain and obesity. MedlinePlus recommends that individuals receive 40 to 60 percent of their total caloric intake from carbohydrates.
According to the Mayo Clinic, regularly limiting carbohydrates in the diet leads to undesirable side effects, including headache, fatigue, weakness and dizziness. Over time, it may also lead to nutritional deficiencies, since carbohydrates provide most of the body's essential vitamins and minerals. The Mayo Clinic warns that eating fewer than 20 grams of carbohydrates a day triggers ketosis, a condition in which stored fats are broken down to provide glucose. Ketones are a by-product of fat breakdown and buildup in the body that result in mental fatigue and bad breath.
A diet that provides fewer than 50 grams of carbohydrates per day is often called a ketogenic diet. Individuals on ketogenic diets consume a lot of vegetables, a lot of fat and moderate levels of protein. They avoid carbohydrate-rich foods, such as grains, starchy vegetables and sweet fruits.