How does the body know what it wants or needs to eat?

[seriously disabled]

How does the body know what it wants or needs to eat? Whether it wants piza, a hamburger or a steak?

 

How does the body know it is missing those things or whether it's lacking certain vitamins or minerals found in certain foods?

Edited November 10, 2009 by Uri

[ydoaPs]

It's mostly personal preference, but there is an evolved tendency toward craving food with a high caloric density.

[seriously disabled]

It's mostly personal preference, but there is an evolved tendency toward craving food with a high caloric density.

 

Ok thanks but how does the body know it's lacking calories?

[ydoaPs]

Ok thanks but how does the body know it's lacking calories?

 

It really doesn't(calories are just a unit of energy). It does, however know if it's lacking sugar, but that's rather irrelevant to the craving. If we only craved high calorie food when we're low, the US wouldn't look like it does.

[seriously disabled]

It really doesn't(calories are just a unit of energy). It does, however know if it's lacking sugar, but that's rather irrelevant to the craving. If we only craved high calorie food when we're low, the US wouldn't look like it does.

 

So how does the body know it's lacking sugar or that it needs certain foods?

[iNow]

Lack of sugar (glucose) means less oxygen can be carried to the brain. When the brain begins to starve of oxygen, it begins sending distress signals to various parts of the body. Through experience, we learn that some foods do better at raising blood sugar (glucose) than others, and hence we will crave certain things when our blood sugar is low (like fruit juice, pizza/bread, or candy for example).

 

Similar phenomenon are at play when we crave other things like proteins or foods with certain minerals/vitamins.

[seriously disabled]

Similar phenomenon are at play when we crave other things like proteins or foods with certain minerals/vitamins.

 

So what is the similar phenomenon in this case?

[iNow]

Body lacks it, sends distress signal. Distress signal causes cascade of impulses leading up to the specific craving. Specific craving is informed by past experience (learning).

[Mokele]

Lack of sugar (glucose) means less oxygen can be carried to the brain. When the brain begins to starve of oxygen, it begins sending distress signals to various parts of the body. Through experience, we learn that some foods do better at raising blood sugar (glucose) than others, and hence we will crave certain things when our blood sugar is low (like fruit juice, pizza/bread, or candy for example).

 

Similar phenomenon are at play when we crave other things like proteins or foods with certain minerals/vitamins.

 

Actually, glucose suppy doesn't in any way influence oxygen supply, and hunger sets in long before the brain begins to starve.

 

 

Basically, hungry is the default state of being. After eating, your adiopcytes secrete leptin, which inhibits hunger. Over time, leptin levels decline, resulting in production of ghrelin, which stimulates hunger.

[iNow]

Actually, glucose suppy doesn't in any way influence oxygen supply

Hmmm... That's counter to what I've been taught during all my years as a diabetic. The way it was conveyed to me by my doctors was that hemoglobin carries the oxygen to the brain, and the amount of oxygen the cells can carry is a function of the amount of glucose in the system. I understood that less glucose results in smaller red blood cells which results in less oxygen transfer to the brain.

 

I imagine that is oversimplified, but if it's wrong, I'd be curious to find out why. It's about more than just "being hungry." When my blood sugar drops, I get dizzy and rather loopy, I lose focus and concentration is nearly impossible, and I've always attributed it to the lack of oxygen in my brain. The higher cortical layers essentially are shutting down, and all resources are being directed to the cerebellum and hippocampus/amygdalal regions (reptilian brain) to ensure heart beat and breathing take precedence.

 

If this is not caused by lack of oxygen to the brain, and lack of oxygen is not a result of low blood glucose levels, then what causes the effect above?

[dougalbod]

'Hunger' is a physiological response which is thought to be managed by a combination of hormones, in aprticular Ghrelin (http://en.wikipedia.org/wiki/Ghrelin) and Leptin (http://en.wikipedia.org/wiki/Leptin).

 

How our bodies recognise a need for specific minerals/vitamins - I'm not sure, it could simply be a learned response?

 

re : diabetes - I think the dizziness is a direct result of low glucose levels, but I'm not certain how this works. Oxygen transport does not rely on active transport - it's a simple diffusion process so I don't think that glucose levels will have a direct impact.

 

 

Dougal

[Mokele]

If this is not caused by lack of oxygen to the brain, and lack of oxygen is not a result of low blood glucose levels, then what causes the effect above?

 

It's not lack of oxygen, it's lack of glucose. Neurons are extremely energy-intensive cells, fueled entirely by glucose. When your glucose drops, your nerves can't get enough nutrients, and start firing less, shutting down, etc. causing the negative effects you feel.

 

Now, there *is* a lack of oyxgen component to diabetes, which is what causes blindness, ulcers, peripheral nerve damage, etc. in diabetics, but this is a simple physical effect - high blood glucose increases blood viscosity. This isn't much of a problem some areas with coarse capilary beds, but in areas with very, very fine capilaries of tiny diameter, such as the retina, the fingertips, etc, the viscosity slows blood flow, depriving the cells of everything - oxygen, nutrients, waste removal, immune cell transport, etc.

[iNow]

It's not lack of oxygen, it's lack of glucose. Neurons are extremely energy-intensive cells, fueled entirely by glucose. When your glucose drops, your nerves can't get enough nutrients, and start firing less, shutting down, etc. causing the negative effects you feel.

 

Thanks for clearing that up. It's just that the cells lack the "fuel" which is glucose, not that they lack oxygen. I appreciate you correcting my misconception.

[greenprogrammin]

Stretch receptors in the stomach send signals.

[iNow]

Stretch receptors in the stomach send signals.

 

That would inform the body when it needs to eat, not what it needs to eat.