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Leptin’s Role in Obesity
The story of how the hormone leptin went from ‘cure for obesity’ to afterthought
How the human body stores energy (calories)
The human body stores energy in two main forms –
1. Glucose (sugar)
2. Fat (body fat).
Glucose is stored in the liver in long chains known as glycogen. Once the glycogen storage system is full, the body can turn excess glucose into fat in the process known as de novo lipogenesis. The body can also use two main forms of stored energy when food is not available — glucose and fat. This makes sense because it corresponds exactly to the way it’s stored.
Notice that glucose and fat comprise two of the three macronutrients — carbs, fat and protein. Protein is not primarily used as a fuel. Instead, it’s main role is as a building block for other proteins — muscles, connective tissue, skin, tendon etc. As a last resort, the body can use protein as a fuel, but it doesn’t want to.
The two forms of energy storage are complementary. Stored sugar (glycogen) is easily available because t’s right there in the liver. But the downside is that there is a limited capacity.
Body fat is a little harder to get to. Most of our body can use fat directly. Muscles, kidney, liver can all burn fat (triglycerides) directly for energy. But it’s a little harder, and the brain can’t use it directly — it needs to be converted to ketones first to cross the blood brain barrier. The upside of the fat storage system is that there is virtually unlimited storage capacity.
So, this makes sense. We have an easily accessible system with limited storage, and a harder to access system with unlimited storage. This is the same as our wallet and our bank. The money in our wallet is easy to put in and take out, but can only hold a small amount of money. The money in the bank is harder to put in and take out, but you can hold unlimited amounts.
Or like our refrigerator and basement freezer. We can easily put food in and take it out of the fridge, but can only hold so much. The freezer is harder to get food, because it’s in the basement, but it holds a lot of stuff.
