Excess energy in the body is converted into fat through metabolic processes, which serve to store energy for later needs. When we consume more calories than our body uses for current functions (e.g. physical activity, basal metabolism), the excess energy is stored as fat tissue. This process takes place mainly in the liver and adipose tissues.
How does the process of converting energy into fat work
- Excess calorie consumption: Energy is supplied to the body in the form of carbohydrates, fats, and proteins. Each of these macronutrients provides calories that the body uses to function or, if not needed, stores.
- Carbohydrate metabolism: Carbohydrates are broken down into glucose (a simple sugar) that enters the bloodstream. Glucose is the primary source of energy for cells. When the body does not need immediate energy, some glucose is stored as glycogen in the muscles and liver. When glycogen stores are full, the excess glucose is converted into fatty acids and stored in adipose tissue. This process is called lipogenesis.
- Lipogenesis (fat synthesis): When excess glucose or carbohydrates are not used immediately, the body converts them into triglycerides (the main form of fat in the body). The triglycerides are then stored in fat cells (adipocytes) in adipose tissue. Lipogenesis is a biochemical process in which excess glucose and other compounds (such as amino acids from proteins) are converted into fats.
- Dietary fats: Dietary fats are directly stored as triglycerides. Once consumed, the fats are broken down into fatty acids and glycerol and then transferred to the bloodstream, where they are delivered to fat cells. Fats provide a large amount of energy (9 kcal per 1 g of fat), making them an efficient energy store.
- Protein metabolism: Proteins are not the body’s primary source of energy, but in the case of excess calories, they can also be converted into fat. Once consumed, proteins are broken down into amino acids, which are used to build and repair tissues. Excess amino acids, once the body’s needs have been met, can be converted into glucose in a process called gluconeogenesis, or into fatty acids, which are stored as fat.
- Storage in adipose tissue: Triglycerides are stored in adipocytes (fat cells), which can expand to store more fat. Adipose tissue acts as an energy reserve. In situations where the body needs energy (e.g. during fasting or intense physical activity), triglycerides are broken down by lipolysis, and the released fatty acids are used as fuel.
Key processes
- Lipogenesis: The conversion of excess carbohydrates into fat.
- Triglyceride synthesis: The conversion of fatty acids and glycerol into triglycerides, which are stored in adipose tissue.
- Fat storage: Triglycerides are stored in adipocytes (fat cells) as an energy source for later use.
When fat storage occurs
Fat is a very efficient form of energy storage, as 1 gram of fat provides more calories (9 kcal) than carbohydrates (4 kcal) or proteins (4 kcal). Fat also plays other roles:
- Thermal insulation: Protects the body from losing heat.
- Organ protection: Adipose tissue cushions internal organs.
- Energy supply: During periods of food shortage, the body can draw energy from fat stores.
Excess energy from food, especially carbohydrates and fats, is converted to fat by lipogenesis and stored in adipose tissue. This is an evolutionarily advantageous mechanism that allows the body to store energy for later times when access to food may be limited. In today’s world, with easy access to calories and often limited physical activity, this process can lead to overweight and obesity.