Starvation "zone"

Physicist here! You can TOTALLY trust my knowledge of basic human biochemistry and metabolic systems! Now, if another, more specialized, actual scientist wants to correct me at all, they're more than welcome to.

The term 'starvation zone' actually has no meaning to me because I'm not sure what function or process it's supposed to apply to, so I'll just arbitrarily assign it to a certain process. Let me describe this for you.

Your body always has sugar in it. Sugar is very, very important to have always. It's required to maintain basic human function, e.g. your brain takes up about ~25%. Greedy thing. Glucose does its job well, it's the thing your body will use up first, because it's easy. Now, if you're eating enough carbohydrates or sugars to keep up with its demand, your glucose will burn out. That's when your body starts burning glycogen, not it's first choice of fuel, but it'll keep a human running for some good, solid hours.

Now, when a person runs out of their glycogen reserves is where all the fun happens. This is when your body will actually start to use up its fat reserves. Now, this seems great, right? You're burning fat! Losing weight while keeping up muscle mass! Well, sure, yeah. Long distance runners/swimmers/awesomely crazy athletes tend to burn through their glycogen reserves and start burning fat whilst exercising. That's okay if they're eating right, and if they aren't eating right, they wouldn't be awesome athletes.

The issue is that your brain absolutely CANNOT use your fatty tissue as a source of energy. While your muscles and organs are doing fine, even if your organ's protective layer of fats are being burned up, your brain is starving because it doesn't have the sugar it needs to operate. Thus, the brain will actually force the liver to make fuel for its needs while the liver processes fatty tissue. Within three days of not feeding yourself, you're actually going to start burning pure muscle.

According to a grumpy biochemist I know, after a period of burning fat, your body begins to break down both muscle tissue and fatty tissue.

Now, this is a very short term description. Over a long period of time, like in anorexia, a person is restricting themselves of calories, nutrients and minerals to function properly. I guess that's also what people apply the term 'starvation mode' to. The human body does what it takes to survive, and if it's not getting enough external nutrition over time, it'll start to burn up itself, restricting certain processes and in result get weaker. Brain function changes, bone density decreases, a person gets anemia, etc.

Just, don't starve yourself over a period of time. :x Not always having enough glucose in your blood can cause adverse side effects, like metabolic acidosis, of which I was just informed of. Will keep posting more knowledge even if you don't want me to.

TL;DR I'll apply 'starvation mode' as consistently not giving your body enough to maintain glucose reserves and proper nutrients. If done over a long period of time, it's consistent with anorexia nervosa and will cause muscle and bone degeneration and will make you feel awful and groggy in general. If you're exercising or fasting for a day which causes you to run out of glycogen reserves, you'll start burning fat. Consult your doctor?

Physicist here! You can TOTALLY trust my knowledge of basic human biochemistry and metabolic systems! Now, if another, more specialized, actual scientist wants to correct me at all, they're more than welcome to.

The term 'starvation zone' actually has no meaning to me because I'm not sure what function or process it's supposed to apply to, so I'll just arbitrarily assign it to a certain process. Let me describe this for you.

Your body always has sugar in it. Sugar is very, very important to have always. It's required to maintain basic human function, e.g. your brain takes up about ~25%. Greedy thing. Glucose does its job well, it's the thing your body will use up first, because it's easy. Now, if you're eating enough carbohydrates or sugars to keep up with its demand, your glucose will burn out. That's when your body starts burning glycogen, not it's first choice of fuel, but it'll keep a human running for some good, solid hours.

Now, when a person runs out of their glycogen reserves is what I'll call 'starvation mode'. This is when your body will actually start to use up its fat reserves. Now, this seems great, right? You're burning fat! Losing weight while keeping up muscle mass! Well, sure, yeah. Long distance runners/swimmers/awesomely crazy athletes tend to burn through their glycogen reserves and start burning fat whilst exercising. That's okay if they're eating right, and if they aren't eating right, they wouldn't be awesome athletes.

The issue is that your brain absolutely CANNOT use your fatty tissue as a source of energy. While your muscles and organs are doing fine, even if your organ's protective layer of fats are being burned up, your brain is starving because it doesn't have the sugar it needs to operate. Thus, the brain will actually force the liver to make fuel for its needs while the liver processes fatty tissue. Within three days of not feeding yourself, you're actually going to start burning pure muscle.

According to a grumpy biochemist I know, after a period of burning fat, your body begins to break down both muscle tissue and fatty tissue.

Now, this is a very short term description. Over a long period of time, like in anorexia, a person is restricting themselves of calories, nutrients and minerals to function properly. I guess that's also what people apply the term 'starvation mode' to. The human body does what it takes to survive, and if it's not getting enough external nutrition over time, it'll start to burn up itself, restricting certain processes and in result get weaker. Brain function changes, bone density decreases, a person gets anemia, etc.

Just, don't starve yourself over a period of time. :x Not always having enough glucose in your blood can cause adverse side effects, like metabolic acidosis, of which I was just informed of. Will keep posting more knowledge even if you don't want me to.

Where do ketones and gluconeogenesis come into play?

Starvation mode/response etc is the lack of food for 3+ days.
Its lack of food.

What OP is probably looking for is metabolic slowdown.

Is my body in "starvation mode" ?

If you're feeling worried or malaise, why don't you ask a doctor? They'd be infinitely more helpful and far less erroneous with dealing with your health than an internet forum would be, right?

My thing is this - I usually consume about 1200 cals a day- this includes snacking and what not and my diet is normally balanced in terms of all the nutrients I take in.I love fruits, veggies, and all lean sources of protein (turkey, chicken, salmon.. etc.) I however, just generally don't enjoy high calorie foods and when I do eat them - I eat very little because they don't make me feel well or as great as my healthy foods do.

Now when I add exercise to the equation - I usually don't consume much more food, because I physically can't otherwise I will get nausea and that defeats the whole purpose of eating. So there are days where I net like 600-800 cals.

Is my body in "starvation mode" ?

You are probably not in "starvation mode". However, this doesn't necessarily mean that 1200 calories is the proper intake for you.

My understanding is that In the absence of enough carbohydrates to provide the brain with glucose, the body converts proteins to glucose via gluconeogenesis. This is why low carb dieting isn't necessarily harmful.

Typically when people use starvation mode (in my opinion) they are referring to the metabolism slowing down and not an actual physiological starvation response.

Ha, I clearly remember being pounded into my head that over abundant glucose could be stored as lipids, I don't ever recall the reverse process ever being thought of as humanly possible until recently. It's always been about it breaking down into Acetyl-CoA, but I've stumbled across a marvelous article dealing with gluconeogenesis from fatty acids. Wouldn't ever want to memorize that cycle, looks worse than Kreb's. But there's evidence for it!

I thought it was a general rule that you want to avoid burning protein? :x

My main confusion stems from this: if you're disrupting any metabolic process in your body, your body is stressing about maintaining homeostasis. If that's happening over a long period of time, then I have no idea what's going on if you're not malnourished or if you're not over-exercising in an otherwise healthy human (speaking of diets and exercise, here).

Current activity dictates which metabolic system the majority of the energy comes from, fat or glycogen.

In the case of heavy exercise vs a sedentary life style, which processes takes priority? When entering a mode of starvation, does each method of maintaining glucose levels not maintain priority? In my understanding, all three processes listed are used, it's just that one takes more priority over the others depending on the state of the person. At which point in the breaking down of fatty acids is glucose required? Just general body function that requires glucose as fuel to begin with that makes fuel to keep making fuel?

Sorry, I just would like to know more. :x