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Comment by ClassyJacket | Hacker News Reader

I'd like to see them explain how this defies thermodynamics. If you aren't ingesting the food energy you simply can't get fat from it.

Specifically I'd like to see this reproduced in humans.

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There's nothing in the article that claims to defy thermodynamics. Consider this: anything you ingest can either be 1) absorbed by the body or 2) pass right through you. This is determined by the digestive processes occurring in your body.

If I feed you a bucket of pure sugar it will be metabolized differently than if I put the equivalent amount of sugar in non-digestible plastic pellets and had you swallow the pellets instead. Hence, it is obvious that weight gain and loss depends on more than just what you eat, it also depends on how your body digests what you eat.

I love how armchair physicists love to repeat this thermodynamics claim as if it's some kind of revelation or even remotely relevant to nutrition science, when a growing body of research is showing that the body's metabolic processes affect weight gain/loss in ways far more complex than originally thought.

For example, studies have shown that gut bacteria can have an effect on fat absorption and hence how many calories are extracted from the food you eat. This means that two people, eating the exact same thing, may absorb different amount of calories from it, and hence may gain/lose weight differently.

Thermodynamics is completely irrelevant here. It tells us nothing meaningful at all.

If I read the article right, it's not that you get fat from the aspartame (which the body can't extract any energy from), but that aspartame blocks IAP, which is thought to work against the detrimental health effects of a high-fat diet.

They also noted that blood-sugar levels for the aspartame-consuming mice where higher for both types of diets.

The body is not a steam machine. It doesn't burn energy at the same rate all the time, and what we input into our bodies can affect that rate.

There are a lot of mechanisms involved in the relationship between eating food and getting fat. One that I often think of as a fatal flaw in many weight-loss diets is that different foods have varying effects on satisfaction and hunger — some foods make you want to keep eating.

If that's were true, it would be impossible for humans and other organism to regulate how much fat and weight they have because it's nearly impossible to balance the energy budget.

So, there's more than just thermodynamic at play here.

The body is not a simple thermodynamic equation unfortunately :(

Of course it is. Energy input must balance energy output and net changes in storage. What isn't simple is that we don't have the ability to merely will ourselves to eat less. We are not as much in control over our bodies and our consciousnesses as we'd like to believe.

We also don't have the ability (or understanding) to control the conversion of energy-in-food into energy-our-body-can-use + energy-our-body-can-store + waste-products. Food is not gasoline, and our bodies are not combustion engines.

Even that's a bad analogy; gasoline's quality and impurities can vary quite a bit, which effects how much energy an engine can extract from it, and engine efficiency can also vary greatly. Still, our bodies are much more complex.

I'm more inclined to report reported differences to bad reporting of inputs. How many studies are conducted under controlled conditions? People lie about everything all the time, especially to themselves.

So?. It doesn't change the fact that the body literally cannot produce energy out of nothing. If you eat less you WILL lose weight.

Yeah but it's not clear where that weight will come from, or how much it will be.

You've always got blood sugars at some level.

If you put something sweet into your mouth (real sugar or fake) you're more likely to a) produce insulin and start metabolising those blood sugars, and b) have a 'low blood sugar' feeling and want to eat something :)

Edited for typo

I don't understand why so many people have difficulty accepting that the chemical environment can mediate appetite, and appetite is a key driver of food consumption. Thermodynamics holds. What doesn't hold is the idea that you exist as a consciousness independent of chemical inputs.

But what you're saying sounds to me very different from what most people in this thread are saying. You're saying, if I understand correctly, that eating stuff with aspartame will make you eat more (what happens if you have the self control to either not do that, or eat something like a carrot that has very little calories ?).

Most people in the thread here seem to be saying your body will find a way to use the same amount of energy, and store the same amount of energy, despite the energy intake being different.

Anecdotally, I've lost over 10 kg while not caring about aspartame intake (in fact I think it probably went up).

More that aspartame fooled no GI ever into thinking its job was done than that it makes you hungrier. The alkaline phosphatase blocking from it is also hampering phosphate metabolism you might've been using to switch gears, including regulating pH and coexistence with gut flora (detoxifying oligosaccharides etc.) Nice anecdotal going (if it was low density tissue; I should joke 'you uploaded your brain, what did you expect.')

What you missed out on is feedback loops that affect your basal metabolism. So: eat less, your body decides it is starving and reduces your basal metabolism, you continue to eat less (better-than average willpower!), and... you gain weight.

I'm a physicist, and I roll my eyes whenever anyone starts up with simplistic arguments about humans, food, and thermodynamics. Thermodynamics holds, but the system doesn't work the way you think it does.

Can your body just "reduce your basal metabolism"? Where are the energy savings? Is your body temperature lowered? I'm skeptical of the idea that differences in "metabolism" can account for different results arising from the same energy inputs.

Yes, your body temperature can be lowered, somewhat. Your temperature actually varies over a pretty wide range all of the time, with daily cycles and in response with your activities and things like fighting infections. But your average temperature can trend higher or lower, corresponding to a higher or lower basal metabolism.

Other things that can happen when your metabolism slows down are that you get tired more often and more easily, your thought processes slow down, you sleep more. This happens to everyone as they age, and it can also happen from chronic stress, calorie restriction sufficient to trigger 'starvation mode', and anything else that causes your body to try to conserve energy for survival.

What can be done to boost basal metabolism? A safer DNP? The current approach, diet and exercise, although it may work in individual cases, is not effective at the scale of public health.

Why, yes, it's a typical confounding situation with exercise and diets. As you probably know, it's difficult to do calorimetry on humans, but if I recall correctly it is partly lowered heat generation (which doesn't necessarily change the core temperature you measure with a thermometer) and moving around less.

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