Straight Dope on body going into "starvation mode" w/calorie restriction?

Factual Questions
61

I would also surmise that it isn’t straight calories in either. A calorie isn’t a calorie is it? In other words if I eat 2000 calories a day on the Krispy Kreme diet that is NOT the same as eating a healthy 2000 calorie a day diet is it?

My gut feeling is that it isn’t a linear equation of calories in vs. calories out but I haven’t done any research on the science of it. Isn’t a person eating 2000 calories a day of junk going to put on weight vs. a person eating a healthy 2000 calorie diet? Even though they both consume 2000 calories the nutritional value of the food must factor in doesn’t it?

62

Though you haven’t explicitly said it, the implication is that the bloated bellies of african children is a sign of a slow metabolism and/or fat retention.

In fact it is simply a symptom of Kwashiorkor; where malnutrition, particularly a lack of protein, leads to the breakdown of connective tissues in the abdomen and liver enlargement.

63

I do not have time for a long treatise, and it would probably not help anyway…

At the same time it’s always risky to generalize in GQ, especially when the subject has some scientific underpinnings. Here’s the CP skinny, fwiw, on what I think you are asking.

Any layman’s term such as “starvation mode” is probably used a variety of ways, but I suspect the root notion is a shift away from a balanced or slightly positive intake of calories (versus expenditure) toward a negative balance. A sustained negative balance leads to a metabolic shift toward ketosis–briefly, the burning of fat.

As a very simplified rule of thumb, the human body burns available glucose first, then glycogen stores, then protein broken down to glucose and then fat stores (it’s not that simple, and it’s not in such a perfect order, but for the sake of simplicity bear with me).

Alright; one more preliminary point: what does it mean to “lose weight”? Well what most people are trying to do is lose fat; what most people use as their measurement is a scale. And a scale is a very crude indicator of fat loss. Water, protein and everything else contribute to weight, so when people talk about “starvation mode” and “weight loss” you do have to start with a little more precision.

I think the basic complaint around starvation mode and weight loss and “screwing up your metabolism” is that if all you do is create a periodic negative calorie balance, you’ll probably retain your fat and lose some muscle. It’s not so much the “starvation mode” (whatever that is) that messes things up. It’s that people diminish their caloric intake long enough to burn protein but not long enough (or in a stable enough fashion) to switch over to a long-term mild ketosis (which would burn fat) while making sure they are still exercising moderately (to retain muscle).

As a rule of thumb, ketosis depresses the appetite temporarily, which is good. You essentially get over the severe hunger pains you get when your glucose and glycogen are gone. You start to digest some of your own muscle as a temporizing measure while your metabolic pathways are gearing up for full-blown fat burning, but then eventually you sit down to eat again. And once you start eating a bit, you get ravenous, and now you eat so much that you pack away the excess as fat. Rinse and repeat. Lose muscle; retain fat. Bummer.

In prolonged ketosis (starvation) you will lose fat and muscle both, and you will lose fat reasonably efficiently once your metabolic pathways switch over. You will, of course, eventually die of starvation and at the end you will have almost no fat but you will still have some muscle. After all, even the heart is a muscle. All of these pathways are gradual shifts.

That’s not the best explanation, but hopefully puts you on the right track. Off to my next meeting.

64

It’s worth noting that you can be in ketosis without starving and burning your own fat and muscle tissue, provided you eat nothing but fat and protein for some time. I’ve done it myself and did not lose any weight.

65

I thought ketosis had much to do with a low carb diet and less to do with caloric intake? If I eat a very low calorie diet consisting of mostly carbs, would I not stay out of ketosis?

66

If you eat a low-calorie, low-carb diet, you will burn fat for energy; it will be just be exogenous fat. You’ll still have ketones running around, though–you will still be “ketotic.” Ketosis is not a disease or anything; it’s just a term for byproducts such as betahydroxybutyrate and acetoacetate found in the blood when the body is burning fat.

Ketosis is really just a term reflecting that the body is metabolizing fat as the source of energy, put simply.

The body ordinarily prefers glucose and things that break down to glucose (again; put simply), and in ordinary conditions of a varied diet some ketosis occurs all the time. The body will switch over to almost all fat burning if that’s what the diet is or if you are mostly starving and taking in way too few calories. (The brain really really prefers glucose).

It’s either your fat or dietary fat. You can get fat eating mostly fat, sure. Ketotic breath is kind of stinky and if you swap over too quickly or too extensively, you can get full-blown ketoacidosis, where there is a combination of too much fat burning, too little glucose burning and too little fat-burning-byproducts excretion.

The basic theory behind low-carb diets is to minimize exogenous sources of glucose so that the lipolytic pathways (ketotic, fat-burning pathways) are maximally maintained. If you keep shutting them down with sugar, you never get them revved up and churning along.

67

Wow, that’s interesting - I think there must be a big misconception about what ketosis is then as well, mostly thanks to Dr. Atkins.

68

Okay, well this sounds like extremely dangerous, disordered eating and I’m not willing to risk triggering you back into this just for the sake of winning an argument.:frowning:

Hope you’re doing better now.:slight_smile:

69

It was disordered and I went into treatment for it for a number of years. I am doing much, much better now, thanks! :slight_smile:

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Glad to hear it. :slight_smile:

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Calories in = food+drink
Calories burned = calories burned by the body to run itself + calories burned doing things

Let’s say Jack normally burns 2000 calories a day to run his body, and 500 calories a day doing things (walking around, etc.). Jack has been eating a 2500 calorie diet, so his weight is stable.

Jack decides to add 1500 calories of exercise to his day, and cut his diet down to 1000 calories per day. Now he’s taking in 1000 calories of food and burning 2000 (calories just to be alive)+500(calories spent doing everyday things)+1500(calories spent doing extra exercise) calories, a calorie deficit. He’s losing 3000 calories a day. Let’s say he’s really bloody-minded about that exercise and no matter how he feels, he gets that 1500 calories burned every day, forced labor style.

After a while of doing this, his body no longer burns 2000 calories just to be alive. His temperature is lower, his hair and nails aren’t growing, etc., etc., and he’s only burning 1100 calories for that. Now he’s still eating 1000 calories of food, and burning 1100+500+1500 calories, which is still a calorie deficit, but a smaller one. If his body still thinks it’s starving, that “calories to run his body” number keeps getting smaller as it shuts down more and more non-essential things. He’s eating the same amount, doing the same amount of exercise, but has no way to tell his body to burn more calories heating itself and digesting food, so his calorie deficit gets smaller than it was at the begining.

Starvation mode isn’t about weight loss ceasing even in the face of severe calorie deficits, it’s about the weight loss being not as much of a loss as the person is trying for. You think you’re eating a 3000 calorie deficit to lose weight equal to 3000 calories per day, but you’re actually going to lose 2000 calories per day of weight, and save 1000 on shutting down bodily functions.

In starvation mode, Jack is eating 1000 calories per day and burning 1100+500+1500=3100 calories per day, for a deficit of 2100 calories per day. He could have the same deficit while increasing his caloric intake to 2000 if he burned 2000+500+1600=4100 calories per day. Look at that, by allowing his body to burn a normal amount of calories to run itself, he only needs to increase his exercise by 100 calories per day and he can go from 1000 calorie diet to a 2000 calorie diet!

I have, of course, pulled these numbers out of my ass and simplified things like crazy, but the point I’m trying to illustrate is that if you’re trying to lose weight without torturing yourself, it’s better to let your body have a normal metabolic rate, so that you can burn as many calories as possible that way.