Why Do I Feel Weak on the Ketogenic Diet?

The Mayo Clinic's R.M. Wilder, M.D., developed the ketogenic diet in the 1920s as a cure for epileptic seizures in children. While conventional medicine now is used to control most cases of epilepsy, the ketogenic diet still is used as an alternative treatment when conventional medicines do not have the intended effect. As the ketogenic diet consists of high amounts of fat, it can deprive the body of essential vitamins and minerals and also can give rise to mood disorders and weight loss.

frail woman out of breath hunched with one hand to knee the other pressed to the forehead (Image: 4774344sean/iStock/Getty Images)

The Ketogenic Diet

The ketogenic diet consists in extremely low levels of carbohydrates, adequate amounts of protein and high levels of fat. As carbohydrates are the main source of blood sugar, or glucose, this composition of food lowers blood sugar levels significantly. Most cells in the body do not need glucose to thrive. Muscle cells, for example, can use fat or protein. Brain cells, however, cannot use fat or protein as an energy source. When glucose levels are low, it switches to ketone bodies, a byproduct of fat metabolism in the liver. As ketone bodies are an efficient fuel source, their metabolism requires additional mitochondria, or cell engines. These additional mitrochondria stabilize neurons and prevent overexcitement of the kind that can lead to seizures.

Vitamin and Mineral Deficiency

Vitamins and minerals are essential for body growth, cell repair and metabolism. The main source of vitamins and minerals is vegetables, fruits and legumes. As vegetables, fruits and legumes are moderately high in carbohydrates, you can eat them only in small amounts if you follow the ketogenic diet. Without a vitamin and mineral supplement, the body quickly gets deprived of vitamins and minerals. This can lead to fatigue and muscle weakness.

Mood Changes

According to Judith Wurtman, director of the Adara Weight Loss Center in Boston, when carbohydrates are severely restricted, the brain stops regulating the neurotransmitter serotonin. This neurotransmitter plays a central role in regulating mood. The main medications currently prescribed for depression block the serotonin transporter, a molecule that transports serotonin back into the neurons. This increases the extra-cellular levels of serotonin and in many cases controls depression. Since the ketogenic diet severely restricts carbohydrates, it might be affecting the brain's ability regulate to serotonin. This, in turn, could lead to depression and an accompanying feeling of weakness.

Not Enough Calories

The ketogenic diet is not intended as a weight loss diet. While it restricts carbohydrates and protein, it supplies the full amount of calories required to maintain body weight. For some people following the ketogenic diet, it can be difficult to get enough calories because the choices of foods are very limited. When the body does not get enough calories, it lowers its metabolism to avoid using up all of its stored sources of fat and glucose. A slow metabolism can give rise to fatigue and a feeling of weakness.