It may sound like weird science, but "energy density" is nothing more than the calories in a portion of food. Fruits, vegetables, legumes, and cooked grains are examples of low-energy-density ...

For example, Mumbai is one of the most densely populated cities on earth with roughly 29,650 people/km 2. London, on the other hand, has a population density of around 5,100 people/km 2 ...