Energy on a Low Carb Diet

For the body, food is all about energy. Energy comes in the form of calories consumed. Calories come from different types of macronutrients---fat, carbohydrate or protein. Even though each kind of macronutrient supplies energy, the way your body uses this fuel varies. When you make a giant shift in the type of fuel you use, it takes time for the body to adjust. Until it does, you may feel tired, listless, foggy, or generally bad. But, if this feeling continues or gets worse, be sure to see your physician.

Typical Diet

The typcial modern American diet usually features a preponderance of carbohydrates. The American Council on Exercise suggests that with a 2,000 calorie-per-day-diet, a healthy person should eat about 225 to 325 grams of carbohydrates. Carbohydrates are the most easily accessible form of energy. This energy source is simply what we're used to using for fuel, and our bodies are extremely good at it.

Low-Carb Diets

Many people have reduced the number of carbs in the diet in an effort to lose weight or build lean muscle mass. There is a plethora of low-carb diets, and each has its own percentage of the day's food should come from carbs. The Atkins Plan, one low-carb example, restricts dieters to 25 grams of carbs in phase one. That's about 10 percent of the amount of carbs most people are used to eating.

Metabolic Changes

If you tried to switch from fueling your car with premium gasoline to natural gas, the car just wouldn't work. Unlike your car engine, human metabolism can change types of fuel, but not without a few coughs and spurts along the way. One complication is that although most systems in the body can use fuel from fat and protein just fine, the brain and liver need a particular kind of fuel. To meet this need without carbs, your body produces ketones.

Ketosis

Low-carb dieters are actually trying to provoke a state called ketosis. When in ketosis, the body is breaking down fat in order to convert protein into sugar for the brain, liver and muscles to use. The Mayo Clinic explains that ketosis can cause weakness, nausea, dehydration, dizziness and irritability. For many people, this goal state of ketosis actually makes them feel generally bad.

Duration

Most people adapt to dietary changes over the course of a few weeks if they choose to stick with the plan. For many, the lack of energy eventually dissipates as their bodies become more efficient at metabolizing protein and fat. If the low-energy feeling continues, or if you notice a sustained decrease in endurance during training, it may be time to gradually add a few more carbs back into the diet. Don't carb-load, but have a healthy whole-grain snack a few hours before working out. If that doesn't help, talk to a physician or registered dietitian to get specific advice for your situation.