9.4: Storing Excess Calories
- Page ID
- 55517
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What happens when we take in more energy-providing nutrients than we need? In other words, what happens to those excess calories when we over-eat? As we know from personal experience, the excess is stored as body fat. The body does this by using some of the same reactions that break down carbohydrates, protein, and fat.
As shown in Figure 9.2, all the energy-providing nutrients can be broken down to acetate, and most of the energy from these nutrients comes from the breakdown of acetate. If the energy isn’t needed just then, the cell doesn’t break down acetate. There’s also no need to break down dietary fatty acids to acetate. When you eat more calories than you need, acetate and fatty acids are diverted from energy production to energy storage as fat.
It’s clear from Figure 9.3 that we can become fat from excess calories, whether from over-eating carbohydrate, protein, or fat. But note how much easier it is to make body fat from dietary fat. In contrast, protein and carbohydrate first have to be broken down to acetate before they can be made into fatty acids (an energy-requiring process). This is thought to be one reason why it’s easier to become fat on a high-fat diet.
