If to gain 1 pound (450 grams) you need to eat 3500 calories over your maintenance, how does it make sense that eating 400 grams of straight oil (which is 3536 calories) leads to a 450g gain which is more than the weight of excess food Where does the roughly 50 extra grams come from?
In: Biology
The underlying assumption is false. Eating 3500 excess calories of food does not mean you gain a pound. Conversely, burning off 3500 more calories than you take in does not mean you lose a pound. The best you can say is that a pound of fat when burned can be shown to contain about 3,500 calories of energy. But the biological processes of digestion and nutrient absorption and metabolism and hormonal regulation are far too complex to be accurately captured an a “number of calories equals amount of weight” formula. It’s a convenient shorthand for dieters, and the underlying idea that fewer calories taken in can lead to weight loss is sound, but the devil is in the details, and is highly particular for each individual. There are plenty of people who have a caloric surplus in excess of 3,500 calories each week, yet they’re not gaining a pound each week. And there are also many examples of individuals in a caloric deficit of 3500 calories a week, yet they don’t lose a pound a week, week in and week out. I wouldn’t get too hung up on a rigid formulaic approach when it comes to intake and weight gain or weight loss.
You have other energy sources in your body, that would normally be used to fuel you, that it stores away when given fuel like this. As well as most likely salty oils would make you retain more water throughout the day. In a vacuum this wouldn’t happen, but there are so many other things happening in and to your body that you can’t just look at the weight of the oil and expect it not to effect other things.
Water
The fats you eat (lipids) are basically straight oils which makes them very dense. When your body goes to pack them away in adipose tissue(fat cells) it stores them in a matrix with some water which is how you can gain more weight than just the raw grams of food that you eat.
Fats and oils are virtually all just carbon and hydrogen atoms with a few oxygens. When they are digested, other atoms, chiefly more oxygen, will be incorporated. The first stage to break down a fat molecule is to split off separate fatty acids from the glycerol molecule that holds them together. The net difference is the addition of three extra molecules of water so the products are heavier than the starting material.
(Very simplified chemistry for ELI5)
Others have directly answered your question but I want to give you some more context as well. The stat that eating 3500 calories over your maintenance level will add 1 pound to your body is just an *average*.
The individual, their diet, their exercise, their metabolism, what time of day the food was eaten, rather their body is in a caloric surplus or deficit, and of course the type of food that is eaten, all effect the true amount of weight a person will gain.
3500 calories = 1 pound is an averaged guideline, not an absolute rule.
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