"Typically, the body's main source of energy comes from glucose, which is a sugar that is metabolized from the digestion of carbohydrates," said Lorraine Kearney, holistic nutritionist. Glucose is the main source of fuel for the brain, nervous system, red blood cells, and certain bodily tissues — and carbohydrates are a key source of glucose.
"Without adequate glucose sources in the diet, the body must change the way it burns energy so that it can function. Low-carb, high-fat, and hihg-protein diets cause a shift in glucose metabolism and the body begins to rely on partially broken down products of fat, called ketone bodies, as fuel," Kearney explained. "If just the right amount of calories from carbohydrates are consumed, the body prevents the breaking down of protein into amino acids for energy (i.e., ketones) to maintain optimum functioning of vital organs, such as the liver and kidneys."
However, people on the keto diet run the risk of not having enough glucose in their bodies due to the diet's restriction of carbohydrates. When this happens, Kearney said that the body will begin to take protein from the muscles. "This will decrease the building, repair, and functioning of the body and its vital organs, such as the heart, lungs, liver, and kidneys," she explained.