A low-carb diet, whether it's Atkins, ketogenic or a Paleo plan, promises weight loss and vitality. Not everyone thrives on such a diet, however. Carbohydrates are the body's primary source of fuel -- too few can mean your energy levels plummet. In addition to possible side effects such as constipation, headaches and weakness, you may also experience tiredness and fatigue.
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What Counts as Low-Carb?
The publication "Dietary Guidelines for Americans, 2010" recommends you get between 45 percent and 65 percent of daily calories from carbohydrates, including those found in breads, pasta, vegetables and fruit. Although many diet plans reduce your intake of carbohydrates, a true low-carb diet limits your intake of carbs to fewer than 150 grams per day, according to a 2007 paper published in the "American Journal of Clinical Nutrition." Ketogenic diets, which are ultra-low-carb plans that may be followed during certain phases in bodybuilding or to treat specific medical conditions, may restrict you to just 30 to 40 grams per day. Cut out most grains, breads, pizza, fruit and sugar to reduce your carb intake to low levels.
Your body uses carbohydrates as an immediate source of fuel. Carbohydrates raise your blood sugar and, in turn, stimulate certain brain chemicals that blunt your appetite and make you feel good. Many athletes, especially endurance athletes, need carbohydrates to perform at their best. When you limit carbohydrates, your body may feel weak and lack energy. You'll switch from burning carbohydrates for fuel to burning fat, a process called ketosis, which requires extra energy from your body. The resulting ketones can cause side effects, such as nausea, lightheadedness and tiredness. Athletes who stick to low-carb plans may feel exhausted by their workouts and require longer recoveries between them. Low-carb diets can also make your brain tired, inhibiting your ability to concentrate and do well on memory-based tasks.
Many low-carb diets are also low in calories. When you restrict calories below what you need for daily function, your body sends signals to your brain to slow down and use less energy. If you choose to follow a low-carb diet, make sure you get at least 1,200 calories per day to prevent this fatigue.
Thyroid and Adrenal Effects
Low thyroid hormones usually cause an overwhelming sense of fatigue. A low carbohydrate intake negatively affects your thyroid function. When you eat carbs, your body releases the hormone insulin. Insulin helps stimulate production of thyroid hormones. On a very-low-carbohydrate diet, you may not produce enough insulin to adequately assist your thyroid, and the result could be too little thyroid hormone and extreme tiredness.
Low-carb dieting also puts stress on your body. The adrenal gland, which pumps out stress hormones, may be called upon to produce even more cortisol, a stress hormone, when you go low-carb. This can overwhelm a bodily system already inundated with stress from life circumstances. A low-carb diet can contribute to a problem known as adrenal fatigue, with side effects including mood swings and tiredness.