The carbs are major fuel source and are in 2 groups: simple and complex. The simple are simple sugars and are refined sugar and fruits. Complex carbs are starches or beans, grains, root veggies, grain pasta, brown rice and grain breads. When the complex carbs become refined they are starchy and those are white bread and flour, additive cereals, baked goods, white rice and white pasta. Carbs are fuel and needed but we must eat healthy carbs.
Low carb diet
The low carb diets are mostly for better health, lower body weight and treating issues like diabetes, fatigue, epilepsy and polycystic ovaries. High carb foods must be replaced with fats and proteins. The carbs allowed daily varies for every person. Examples of such a diet is Atkins, Zone, Primal Blueprint and South Beach. As to Mayo Clinic the long term after effects of this diet are still not certain and have to be studied. Talk to a doctor before trying these diets.
The obvious effect of this diet is weight loss. When carbs are limited or removed, you lose weight and glucose is lower too. Glucose is linked to blood sugar and weight and we typically burn the glucose from carbs and use it as fuel. When carbs are lowered, the body gets other fuels in shape of fat deposits and burns them instead. Thus you lose fat and water retention too.
This is a bad side effect of removing carbs. Veggies, fruits and grains give you fiber for a healthier colon. The soluble fiber adds water to the waste material or stool and it passes easy in the colon. But insoluble fiber adds bulk for another easy passing in the gut. Mayo Clinic said that long term fiber deficit can make diverticulitis and increase the cancer risks.
Damage of kidneys
The long term diets rich in proteins might damage the kidneys. Such low carb diets must be carefully chosen by those with kidney issues. Mayo Clinic says that such diets must NOT exceed 4 months. Those with kidney diseases, liver issues or diabetes must be really cautious here and talk with a doctor before starting the diets.