Fatty acids, which derive from the saturated fat that we eat, are never stored as adipose tissue in the body. Thus, they do not make you fat; glucose does. Fatty acids are first broken down into ketone bodies (aceto-acetate, beta-hydroxybutyrate, and acetona) before being used by the mitochondria in the Krebs cycle. The primitive hunter's cellular mitochondria used ketone bodies (fatty acids) as cells' fuel instead of glucose because he simply did not eat carbohydrates-containing food, for agriculture had not been developed yet. To sum up, excess glucose makes you fat, fatty acids never.
High levels of glucose make you fat because it induces the pancreas to pump up insulin into your blood stream. Insulin, in turn, makes your body tissues stores it as adipose tissue, that is to say, fat. That's how you become obese. Glucose is obtained from the starchy and sugar-containing foods we eat. Starch and sugar are called carbohydrates, which are broken down into glucose in the body by the pancreas enzymes. Thus, too much starchy and sugary foods means high levels of glucose in your blood stream, which are converted into bodily fat by insulin.