(This post is directed to detractors of a low carb - high fat approach.)

"A calorie is a calorie" lie. Our body burns, uses, and reacts to different forms of energy differently, and to view each calorie equal is not an optimal strategy for weight loss.

Your body is a furnace. Everything which facilitates and defines your existence as a living organism, from the cooperation of your bodies muscles resulting in a vigorous sprint, to something as basic as your heart beating while you sleep all require fuel. Your body has two types of fuel, glucose and lipids/ketone bodies. Carbohydrates and protein are broken down into glucose, fats are broken down into ketones.

Carbohydrates come from many different sources. Unlike fats and proteins, carbohydrates can be very different on a molecular level from one another. For example, stripped and refined white sugar or white bread on a molecular level much more closely resembles pure glucose than does unprocessed and unrefined fresh strawberries. How closely a carbohydrate resembles pure glucose is tracked in a system called the glycemic index (or glycemic load, which considers average portion size). The more molecularly close to glucose a food item is, the easier it is for your body to break it down into glucose. Eating high glycemic carbohydrates as a dietary staple are bad for three reasons:

1) They are easy to break down to usable fuel, which means your body expends very little energy doing so. Since your body requires less energy to create energy from these types of carbs, you cannot eat that many calories before you have "overeaten". Though overeating fat is worse than overeating carbohydrate, it is in practice much easier to overeat on carb than overeat fat.

2) Because simple and processed carbs are so easy to break down for fuel, you are met with a "fuel rush" into your bloodstream once ingested. You feel elated, satisfied, lethargic and tired. This is known as a blood sugar high, or hyperglycemia. This rush of fuel is quickly met with an equally large rush of insulin, brining your b:s low again, known as hypoglycemia. You feel irritable, shaky, weak, and ravenous. The cycle repeats itself. Unstable blood sugars are ultimately behind the epidemic of overeating.

3) The perils of excessive carb intake does not stop there, though. As i said, after blood sugar rises very high from eating, say, a huge bowl of pasta, your body produces an equally large dose of insulin to attempt to balance your blood sugar. Now, insulin is a hormone which encourages your body to store food it has taken in as fat on your body, and it will sacrifice biological function to a degree so it can.

There is an evolutionary reason for this. In an evolutionary response to environmental factors, nature (the network of all species on earth) works together in cycles of youth (summer), old age (fall), death (winter), and then rebirth (spring). The way your body reacts to different food sources is an evolutionary response to this "seasonal" natural environment. Lipids are the fuel source for the hard times, carbs and protein are fuel sources for the good times. Your body evolved to react a certain way to the presence of very high blood glucose levels. It thinks, "wow, fruit stuff must be really plentiful, lets store as much of it as we can for the winter!". Thing is, most human cultures have defied nature. "Rough winters" are no longer a reality for people, and that carbohydrate induced stored fat is fairly useless. Living in an eternal period of biological prosperity means the fat is never burned off, so the cycle just keeps repeating as we eat more high gi carbs, and more fat is added on.

This is why low carb works so well. Though i will not argue, it is important to watch calories, it is also important to watch what kind of food we eat. Since we are members of a prosperous species, unless we wish to suffer a lifetime of crippling obesity we must restrict the % of calories which comes from our "prosperity fuel source" intake. We no longer need to store food for the winter, which is what carbohydrates (and protein, to a lesser degree) does, as it is always a figurative summer.

Since in our natural environment, your body will actually elect to use dietary or stored fat as fuel only during times of hardship, fat is broken down slowly and does not cause b:s spikes.
The minimizing or elimination of b:s spikes eliminates hypo/hyperglycemia, which encourages healthy caloric intake. The minimizing or elimination of high insulin levels discourages the conversion of dietary food intake to physical fat stores on the body. Your body sees the lack of "prosperity fuel" and reacts appropriately: "gosh, times must be hard, don't be a pig, take and use just what you need, nothing more".

A low carb - high fat diet is the key to weight management.