“Your microbiome—that is, the composition of the bacteria in your gut—also influences how many calories certain foods actually deliver. It is often claimed that our gut contains about 300,000 billion bacteria, about ten times as many bacteria as there are cells in our body. However, a recent study estimates the number of gut bacteria to be about 40,000 billion, by and large the same amount as the number of human cells that make up our body. Anyhow, the composition of the gut microbiome can determine how much food (calories) we absorb. Some Japanese people have bacteria in their intestines that are specialized in breaking down seaweed. Thus, the seaweed is better absorbed and will deliver more energy in the form of calories than it would for Europeans who do not have this type of bacteria in their gut.”