eli5: Why are the effects of eating 100g chicken and 100g cake different on the body?


One example being variation in weight gain despite consuming 100g food in both the cases.

I’ve not studied the subject after HS, so the premise and analogy may not be entirely correct.

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Different nutrients and components breakdown and are stored in various rates and ability. Carbs (sugars) are easily broken down and store in various organs. Proteins are much larger and break down into amino acids, if not used within their appropriate time frame, you poop it out. Similar with fats.

As a simple explanation: how much of each of those is retained by the body for more than 24 hours?

I think you’ll find that a lot more of the mass of the cake is converted into substances the body retains.

First off, different items have different caloric densities. For example, sugar vs salt. 100g of sugar is 387 calories, and 100g of salt is 0 calories. That’s because sugar has chemical bonds that the body can break apart to gain a net positive energy balance; salt doesn’t give off any energy if you split it into individual ions.

100g of chicken also contains fewer carbs and a higher amount of protein compared to the cake, so you’re also getting different chemical structures (nutrients) from each of those foods. Carbs can’t be made into proteins — the body isn’t an assembly machine. The digestive system can construct *some* compounds from what you eat, but a lot of it has to be obtained from your diet… take paint as an example. If I want to paint a sunflower, no amount of red paint is going to give me yellow. I can mix red with other colors to get orange or brown or purple, but it won’t give me yellow. The body’s kinda like that.

There are many compounds that we can get through multivitamins without actually having to eat them in our food (vitamin B, ascorbic acid/vitamin C, etc), but those multivitamins are limited/less nuanced in what they provide. For paint, it’s like having one big tube of yellow paint vs many small containers of yellow paint in different shades. I can mix the big tube to get the colors I want, but it takes a bit more work than just getting the exact shade I want straight from the tube.

Being healthy generally involves a painting of many different colors, which lets your body get what it needs at any given moment. Our brains, however, might have a favorite color that we already have a lot of…. and so you might want get more of a paint that you already have a lot of, even if what you need is a completely different shade (like getting more green when what you really need is more blue). That gets into historical resource scarcity, since certain foods and ingredients used to be difficult to get.

So, from that health perspective, eating 100g of cake gets you different colors than eating 100g of chicken. Cake also has a different energy density, and so provides a different amount of chemical energy (calories) when your digestive system processes those chemical bonds. The number of calories a food provides is different than the amount of nutrients (useful chemicals) inside of it. Like water or salt, not all chemicals have chemical energy to give us, but we need them anyways. Even if we have paint, we still need a brush and a canvas if we want to do anything with those colors.

100 gram cake is mostly carbs, which you digest quickly to give you energy. You might end up storing some of it in your body (say you need 20g carbs only, 80g is stored) hence you’ve gained 80g carbs worth of calories

100 gram chicken is converted into energy by an entirely different pathway. It takes more time. Meanwhile, if you need 20g carbs right now, body will take it from your stores. Hence you’ve lost calories from body.

It’s been 3 months since I gave up all forms of added carbs, and increased protein intake (100g chicken daily) and my clothes no longer fit, they are loose now