However this recommended diet may not be of the optimal composition in preventing the progressive increase in obesity and lifestyle diseases. The traditional dietary recommendation has been challenged by the epidemiologist Walter Willett, Harvard Medical School in Boston. He claims that dietary fat is less important for the development of obesity, and that the fat content of the diet can be 40-45% of the energy providing from mainly mono- and polyunsaturated fatty acids. Based on mainly large-scale observational studies ('Nurses Health Study') he has developed new dietary guidelines, expressed as a new diet pyramid. In contrast to the current guidelines, more plant oils and plant foods, limited animal products, such as meat and dairy products (even lean products), and increased intake of olive oil, nuts, etc., e.g. guidelines closer to the "Mediterranean Diet".