Let's take a look at UK nutritional guidelines, from the back of a pack of ASDA Mackerel fillets :-
Guideline daily amounts
Calories 2000 2500
Protein 45g 55g
Carbohydrate 230g 300g
of which sugars 90g 120g
Fat 70g 95g
of which saturates 20g 30g
Fibre 24g 24g
In the early stages of my low carb diet I was limiting my carbohydrate intake to below 20g per day. This means I was eating 280g less than the guidelines, a saving of 1120 calories per day ! That is enough to drop my calories to 1380 per day if nothing else changes.
1120 calories per day is equivalent to about 124g of fat from my ample deposits, so a loss rate of 124g per day relative to the standard guidelines looked to be on offer. At 871g per week that's 1.9 pounds (lbs) per week and close to 50 lbs or 3.5 stones in 6 months. Perhaps a bit more if you include the water weight that is also stored with the fat on your body.
I did actually lose 3 stones in 6 months, from just over 16 stone in April 2010 to just under 13 stone in October 2010. So the reduction in carbohydrate compared to the standard food guidelines seems to equate to my weight loss, more or less.
In practice I eat more protein than the guidelines, probably 90-100g say 50g more which is 200 calories more. My fat intake is probably around the 95g mark, so my calories are approximately :-
Carbohydrates 20g 80 calories
Protein 100g 400 calories
Fat 95g 855 calories
Total 1335 calories, 64% of which from fat.
Am I losing out by having a low carbohydrate intake ? Not in my opinion. There are essential minerals and vitamins we have to eat, and essential fatty acids. "Essential" means we have to have it and we can't make our own, so we have to eat it. There are no essential carbohydrates !
Low carb dieters adapt to use fat as a muscle and brain fuel, to replace the glucose that would otherwise be used. The whole blood stream only contains about 5g of glucose so it is continually being used and replaced with glucose from food or from previously stored glycogen. When the supply of glucose isn't enough then fat is broken down and ends up as ketones to fuel muscles and the brain. Some parts of the body can only use glucose, but there's enough for them from conversion of protein ie Gluconeogenesis.
Once adapted to low carb eating my blood sugar became stable, I didn't feel hungry and sugar highs and lows were a thing of the past. My metabolism has adapted to my diet which is no longer based around fast absorbed carbohydrates as recommended in the Guideline Daily Amounts.