(The Conversation) — At Thanksgiving dinner, lucky families will avoid heated discussions about religion and politics. But another argument is almost inevitable: white meat versus dark meat.
Light meat lovers claim that dark meat is fatty; dark meat lovers complain that the light meat is dry and lacks flavor. Few meat eaters are ambivalent on the issue.
But why do these different types of meat exist and what underlies these differences? As a muscle physiologist, I can tell you that it comes down to the metabolic and functional differences between different types of muscle.
Consider how turkeys move. Have you ever seen a flock of turkeys go by? Of course not! If a turkey is threatened, it may run for brief periods in an attempt to escape. But these birds spend most of their time standing and walking.
These activities – walking and standing versus a brief, panicked flight – are quite different. They are supported by different types of muscles suited to these different functions, and you can see these differences in your plate.
What makes dark meat black?
First consider the dark meat, which is largely found in the thighs. This type of meat comes from muscles that are heavily used because turkeys spend their time walking around like turkeys.
Muscle physiologists call these types of slow-twitch muscles or type I muscles. They are also called oxidative muscles, which refers to the way they produce adenosine triphosphate, abbreviated as ATP. Think of ATP as a cell’s energy currency to perform a given function. The cells do not need a job to earn this money; they just produce it.
The metabolism of the muscles must be able to support them throughout their long and sustained activities. In this case, since large amounts of ATP must be produced over long periods of time, muscle cells depend on their organelles called mitochondria. Mitochondria are like factories that make ATP.
It’s the mitochondria that give dark meat one of its distinguishing (disgusting?) characteristics. They can use fat to produce ATP. Due to its higher muscle fat content, some people may perceive dark muscle as fatty, while others find it delicious.
Mitochondria also need oxygen to function. They rely on an iron-containing protein called myoglobin, which carries oxygen from the blood to the mitochondria present inside the muscle. Due to the large amount of myoglobin, these muscles appear dark.
What makes white meat light?
How about that drier white meat? Again, it is useful to first consider its function.
Much of the white meat is found in the chest muscles, which are used to create the explosive force needed for flight. But keep in mind that for turkeys, this flight is very short: just enough time to escape a predator. This work is ideal for what physiologists call type II or fast-twitch muscle.
This type of activity is supported by another means of ATP production – one that does not rely heavily on mitochondria or require oxygen. White muscle uses a process called glycolysis, which requires carbohydrates to create ATP. They are light in color due to their poor ability to use oxygen during exercise; there is simply no need for a great abundance of the iron-rich oxygen shuttle, myoglobin.
White muscle is low in fat because it does not need or have a large amount of mitochondria needed to make ATP from fat. This is why some people find this meat to be dry.
Different species of animals perform different tasks with their muscles. For example, duck breast muscles have to withstand very long flights and, like turkey thighs, are dark in color and loaded with fat.
In case you were wondering, people’s muscles are a little more complicated than just light or dark. Most human muscles are what physiologists consider to be mixed, with a variety of oxidative and slow muscle fibers. People who possess proportionally more than another can excel in different activities – think sprinters versus marathon runners.
The next time you sit down to enjoy your holiday meal, rest assured that you know why your choice of meat is delicious. Now can you believe what these DC politicians are up to?
This story was originally published by The Conversation on November 21, 2019.
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