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Comment by bgentry | Hacker News Reader

At the pure physical level, yes: calories remaining = calories in - calories out

However, the "calories out" portion of that equation is actually quite complicated. In recent years many studies have indicated that the body does not process all calories in the same way. So "calories out" depends on a lot of things, including:

- metabolism, which can be increased by exercise and muscle mass

- what specific kind of "calories in" you're getting, and how your body processes these

- calories burned directly by exercise

To highlight one specific example of this, a calorie of fructose may be processed by the body very differently than a calorie of, say, vegetable fat: https://www.youtube.com/watch?v=dBnniua6-oM

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> However, the "calories out" portion of that equation is actually quite complicated

The "calories in" part is more complicated than people like to admit too, and probably more important for weight loss. The way our body handles hunger and its relative primacy in our mental state makes it unnecessarily difficult to calorie restrict and then maintain, when eating certain diets. It's like telling an alcoholic "just stop drinking, duh" or an insomniac "just relax and sleep, simple as that". Just because something is in our brain doesn't mean we have full control over it, and I'm not sure why food is treated like something that everyone magically has complete self-control over, in contrast to _literally everything else_.

I'm really really fortunate to have grown up in a good food culture, and worked on it a little more in college. Meeting CICO goals and losing weight when I want to is really not that difficult for me, but I don't think this has much to do with self-control or my genetics. The way I eat just makes hunger less of a factor in my life: I rarely get hungry, skipping meals is never a problem, I get satiated quickly, etc etc.

>However, the "calories out" portion of that equation is actually quite complicated. In recent years many studies have indicated that the body does not process all calories in the same way.

I think of this as the "calories in" portion. There was never any reason to assume the means by which we measure the caloric content of food truly represented the caloric energy available to the body.

It's the phlogiston fallacy that all heat is equally the same chemical energy, and that all chemical reactions "just" produce or consume heat. The body is not an ideal furnace, and food is not an ideal fuel.

The process for storing fat as fat is paradoxically very difficult for the body chemically. The easiest way for the body to add stores of fat reserves is through sugar and the more refined (HFCS comes to mind) it is the easiest it is for the body.

Can you source that? Because as far as I can tell, de novo lipogenesis is a relatively rare process, exactly because our body prefers to just store the fat in the blood as fat. Sugar is burned preferentially, and only when your carb intake exceeds your total daily energy expenditure, it will start converting it to fat: https://www.ncbi.nlm.nih.gov/pubmed/10365981

I'm not sure what chemically needs to happen, fat is transported from the bowel to the bloodstream in a relatively complex process, but once it's in the blood, it's in the same form as in storage, as triglycerides.

In fact, the triglyceride content of a person's fat stores will reflect their diet, which is a strong indication it comes directly from the food without processing: https://www.ncbi.nlm.nih.gov/pubmed/4072956

Paleo Diet & Strength Training Biochemistry | Doug McGuff M.D.

https://www.youtube.com/watch?v=F7GB3h82tcQ

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