And how many carbs per day?
The benefits of a low-carb diet is the body producing an abundance of ketones that will convert fatty lipids as energy. One other benefit would be the "flat" look since carbohydrates (especially those that are more water soluble) retain more water inside and give the body a "fuller" look.
Scientifically, the body doesn't NEED carbohydrates, it can survive without them. The only macronutrients the body needs in order to survive are proteins and fats - one to preserve and create muscle tissue and the second to stabilize hormone levels and promote healthy glycerin/insulin levels.
So how many carbs a day? As many as you wish. Generally, the macronutrient guidelines for the 'average' untrained person is:
1g protein/lb. 1g carb/lb. .3g fat/lb.
Someone who is physically active like say bodybuilders or competitive athletes use higher numbers such as:
1-2g protein/lb. 2-3g carb/lb. .3-1g fat/lb.
There is no correct number or range to be in when it comes to any nutrient, you have to just listen to your body. If you feel like you're retaining lots of water, then cut the carbs a bit, if you're putting fat on too fast, cut the calories not the fat. Also, you can ideally eat all carbs from fibrous sources like green vegetables and brown rice since the majority of these are fibrous.
Play around and see what works for you. In the year and a few months of serious training, I went from 400g+ of carbs and 300g+ protein with 50g fat, to now at 270g+ protein with 260-80g carbs and 90-110g fat. For me, the higher fat helps me maintain better vascularity without looking too bloated or fat.
Burning ketones is not a good state for the body to be in. Our muscles can run on fat (aerobic) or glycogen (combination aerobic and anaerobic) but as Danielle points out, our brain can not run on fat. When we are starving (or eating a radically low carb diet) our body reacts by first burning most of its glycogen then by breaking down muscle. Muscle can be converted to glucose though the process is inefficient. Obviously if this was allowed to continue long our muscles would waste away. This is where ketones come in. Our brain can burn ketones so the body produces ketones so it won't have to break down too much muscle. Ketosis is a very handy thing when we face famines and don't have reliable nutrition. Ketosis should be a temporary state until food is available again. Part of the "flatness" you observe when on a ketogenic diet is from dehydration. You see every gram of glycogen binds to several grams of water. This is why people on Atkin's can gain 10 lbs in one high carb meal. They didn't eat 35,000 calories in one meal; that would be impossible! What they did was replenish their muscle and liver stores of glycogen which also bound a lot of water.
Well first off i want to say that any diet that restricts some sort of needed nutrition often ends in failure and results in weight gain once the diet is complete. Also on a low carb diet you can't consume alot of fruits and vegetables as well as grains so you aren't getting enough fiber your body needs. You can experience, nausea, and irritability. The best diet is to eat about as much protein as you do carbs. Since i am an active runner i need to consume about 75grams of protein a day so i would suggest you get at least 50grams worth of protein and maybe 50 or 60 grams of carbs. It gets your body in a perfect zone for burning fat without any real side effects. If you are trying to loose weight restrict the amount of calories you eat a day by about 500 and get at least an hour of exercise in a day and you should start to loose weight slowly
Actually, your body really really does need carbohydrates. Glucose, the simplest of carbohydrates is essential for your brain. In fact, it is the only form of fuel your brain uses, and lack of it can cause permanent brain damage. On a low-carb eating plane, you utilise the carbohydrates your body has stored as fat.
opps, meant to say plan, not plane...