Why do we need fat and how does fat not make me more fat?

In 2007 Scientific Journalist Gary Taubes wrote a book titled "Good calories, Bad calories: Fats, carbs and the controversial science of diet and health". Taubes argued that the last few decades of dietary advice promoting low fat diets has been incorrect and Taubes goes on to say that carbohydrates, specifically refined carbohydrates like white flour, sugar and starches contribute to obesity, diabetes, heart disease and other ailments.Taubes also suggests that there is a link between certain cancers and carbohydrates as well. Taubes asserts that the human body secretes insulin in response to the consumption of carbohydrates in order to regulate blood sugar, this process, in turn drives the human body to store fat. Taubes elaborates by examining the evidence of the effects of carbohydrates on tribes with a traditional diets high in meat or fats and low in carbohydrates. He found that the introduction of refined carbohydrates in diets of these cultures resulted in increased prominence of diseases like obesity and heart desease. A no carbohydrate diet excludes all dietary consumption of carbohydrates and suggests fat as the main source of energy with a sufficient intake of protein. No carbohydrate diets are called Ketogenic diets which basically means it causes the body to go into a state of ketosis converting dietary fat and body fat into ketone bodies, using them to fuel the body and up to 95% of the brain while the remaining 5% still runs on glucose. This is achieved via glucogenesis or by converting glycerol from the break down of fat. Many people including medical authorities, confuse ketosis (a natural energy burning process used by the body) with ketoacidosis, which is a dangerous medical condition which is more likely to be caused by excessive carbohydrate consumption.