"Low carb diets often work because they serve as a simple way to reduce overall calories."

Yes, low carb diets reduce overall calories, but the mechanism is not simple. When carbohydrates are reduced and adequate proteins and fats are introduced hormonal changes take place such that people are satisfied with their meals and do not tend to overeat.

"If we take our average male carbohydrate intake of 252g as above and we reduce it to 100g, we have reduced our carb intake by 152g per day. There are four calories (kcal) in a gram of carbohydrate, so we have effectively created a daily overall calorie deficit of 608kcal, which is certainly enough to elicit significant fat loss, especially if we are exercising."

What is overlooked here is that, in most low carbohydrate diets, carbohydrate calories are not simply reduced but are replaced by dietary fats, and sometimes protein. The reduction of insulin that results from reduction in carbohydrates, with addition of appetite satisfying fats and protein, lead people to eat less food overall.

Carbohydrates make people and animals hungry. Studies of meat pigs show the less satisfying the meal, the more fat they gain. The ideal commercial mix for meat pigs to promote the greatest fat gain is skim milk mixed with grains. This formula is sadly reminiscent of the American Food Pyramid of 1992 (6-11 servings of grain per day plus non-fat dairy and other low-fat foods).

"It is worth noting however that we could have just as easily done this (added back calories lost when carbohydrates are removed from the diet--AC) with protein, given that the calorie load per gram is the same for protein as it is for carbohydrates, and that it is not necessarily the cutting of carbs per se that has caused us to lose weight, but rather the reduction of overall calories."

It's really about insulin. Insulin is a storage hormone. Foods that provoke the production of insulin provokes fat storage. You see, insulin helps convert excess blood sugars to fat to prevent sugar toxicity. When circulating insulin is high, excess carbohydrate energy is locked away as fat and cannot used as energy. With energy continuously locked away, hunger strikes every few hours and people gain weight. We don't get fat because we eat more; we eat more because we're getting fat. In this way a high carbohydrate dietary strategy leads to excess food intake and weight gain. The only way to lose weight on a high carbohydrate diet is to restrict calories. But when calories are restricted on a high carbohydrate diet people most often become exhausted, depressed and irritable, making it nearly impossible to do.

Starch and sugar, especially refined starch and sugar, provoke insulin to the highest degree. Protein comes in second (protein provokes the production of insulin via gluconeogenesis, the production of the blood sugar glucose from protein). Fat is least able to provoke insulin. Replace carbohydrate calories with fat (making sure high quality protein is about 23% of the diet for an average adult) and you are most likely to lose weight or maintain a more normal weight as a result of reduced appetite. Meal satisfaction is one reason people eat less on a low carbohydrate diet. It is how many obese people eat "all they want" on a low carbohydrate diet and lose weight; the trick is they want to eat less, as much as 1000 Cal less each day because they feel satisfied. Eating excess protein provokes gluconeogenesis, thereby adding carbohydrate back into the system.  In this way excess protein can sabotage a weight loss plan. 

In America 49% of adults over age 20 are either diabetic or pre-diabetic. Our research team (Feinman, et. al. Nutrition, Elsevier 2014) demonstrates a low carbohydrate diet is an essential first step for treating Type I and Type II diabetes. I would add that those of us who are pre-diabetic or prone to become overweight (carbohydrate sensitive) can also benefit. Partner with your doctor if you will consider this or any diet. Cheers! --Ann