"Synthesis" implies that fats are deposited directly and your body converts other food types to body fat by some different process.
To be clear, whether protein, carbohydrates, fiber or fat, your body digests the food and it is burned for energy. 300 calories of carbohydrates will have the exact same effect as 300 calories of fat. From a weight perspective, the big difference is one gram of fat has twice the calories of one gram of protein or carbs in addition to the negative effect fats have on your circulatory system.
Regardless of what the above commercial is trying to sell, the U.S. Department of Agriculture did an extensive study of weight loss programs and found that weight gain/loss simply depends on whether you consume more calories than you burn or burn more than you consume.