Summer is a time when the universe is living at its furthest extremities; furthest reaches. In the tradition of understanding life as a reflection of the universe (i.e. living in harmony with our natural environment), our energy, qi, is most active at our surface during summer's warmth. This is not the time to introduce ice cold substances to the body: creating an imbalance of cold inside and hot outside. Only if the surrounding environment is off-balance, such as an Heat Advisory, do cold foods and substances have a place (cold in temperature and nature of foods). See Henry Lu and Paul Pitchford for more detail on thermal nature of foods.