Hemoglobin is the protein that transports oxygen in red blood cells. Myoglobin is a similar protein in the striated muscles that captures oxygen to be used there.

Both proteins are a good source of heme iron, which is the form of iron that is more readily absorbed by the body. Iron in plants is not as useful, which explains why many vegans develop anemia - there is not enough iron in their diet to make red blood cells.

So, there is an easy way to define red meat: look how much myoglobin it contains. Some fast-swimming fish have dark meat because it contains a lot of myoglobin. In Spain we call it “pescado azul” - blue fish. It is also rich in omega fatty acids. Sardines, mackerel, anchovies, herring… Americans are not fond of this small fish.