Ketogenic diets restrict carbohydrate consumption. Dieters employ ketogenic diets for rapid weight loss. When subjected to a ketogenic diet, your body enters ketosis. Carbohydrates serve as the primary source of energy for the human body. Fat acts as a secondary source of energy. Because ketogenic diets restrict carbohydrate intake, energy needed for exercise comes from other sources. Scientists differ in opinion on the safety of exercise during a ketogenic diet.
During ketosis, keto-acids build up in the blood, and are eliminated from your body through your kidneys. If keto-acids in the blood build up beyond the ability of the kidneys to eliminate the acid, fatigue, irregular heartbeat or dizziness may occur. Avoid exercise if you experience dizziness or irregular heartbeat while on a ketogenic diet. Both may represent serious conditions like dehydration or electrolyte imbalance.
The aim of a ketogenic diet is to burn fat instead of carbohydrates. The human body uses fat as the primary source of energy during extended ketosis. Initially the body will use stored carbohydrates for energy. After depleting carbohydrates, the body switches to fat for fuel. Keto-acids or ketones, the end-product of incomplete fat metabolism, serve as a source of energy. While on a ketogenic diet, ketones provide energy for brain function. In their book "The Treament of Epilespy," Dr. Eric Kossoff and Dr. Eileen Vining note that ketones maintain 65 percent of brain energy when in ketosis.
Inuit populations in the Arctic survived on low carbohydrate diets prior to the introduction of modern carbohydrate-based nutrition. Dr. Stephen D. Phinney, professor of Medicine Emeritus at University of California at Davis, suggests the carbohydrate-restricted diets of the Inuit population prove that ketogenic diets provide enough energy to sustain body function. The Inuit population primarily hunted for food, eating a diet based upon animal consumption and little agriculture. Hunting requires prolonged energy exertion, further suggesting that ketogenic diets allow for sustained energy levels.
Any exercise lasting more than three minutes is aerobic. Under normal conditions, the body uses fat as a primary source of energy during low-intensity aerobic exercise and carbohydrates for high-intensity exercise. Without carbohydrates as an energy source, ketogenic dieters use fat as a primary source of energy during high-intensity aerobic exercise. According to certified strength and conditioning specialist Lyle McDonald, performance during high-intensity exercise decreases for people on ketogenic diets. However, with adequate time to adapt to carbohydrate restriction -- two to three weeks -- near maximum performance is possible.
A day of carbohydrate-loading in a ketogenic diet increases your performance during anaerobic exercise, such as weight training. Anaerobic exercise requires carbohydrates as a primary fuel source; fat will not provide adequate energy for this type of exercise. To maintain performance during weight training, ketogenic dieters require a carbohydrate-loading phase. Eat whole grains, fruits or beans as a source of carbohydrates for carbohydrate loading.