Fat vs. Carbohydrate metabolism

I know low-carb has been done to death around here, but I had one more question about the physiology of low-carb diets. It seems like the theory behind them would allow quite a lot of calorie consumption without weight gain, as long as you didn’t eat many carbohydrates, because you keep insulin low and thus fat-burning high.

So let’s say you need 1000 cals to maintain your body weight. As far as the theory goes, if you eat 1000 cals of a high carb diet, you’d use maybe 800 for your cells, and the other 200 would be driven to fat storage by the high insulin levels. So then your body would perceive a 200 cal energy deficit and that, in combination with the drop in insulin, would make you hungry. If you could avoid eating any more, your body would burn a combo of stored fat + muscle to make up for that 200 cals, or it would slow down further to make your daily metabolic needs only 800 cals.

If you ate 1000 cals on a low-carb diet, it would all go to tissues where it’s needed and you’ll feel satiated and happy. Similarly, if you only ate 800 cals on a low-carb diet, the body could easily make up the deficit by burning fat, since insulin is low, and you’d lose weight.

Okay, so that is what the theory behind low-carbing says. Here’s where my question comes in. What if you only need 1000 cals but eat 1500 cals on a low-carb diet? That extra 500 cals has to go somewhere, right? Why wouldn’t it be stored as fat? Does the body’s metabolism just increase in order to burn that extra 500 cals?

An interesting series on insulin and fat storage by James Krieger I’m guessing you’d be interested in:

I think the theory is that your body will increase activity and metabolism to compensate. You’ll move around more, fidget, feel compelled to get up and do something, and/or your body temperature will rise.

FWIW, this does seem to happen with me, if I overeat protein and fat (which is kind of hard to do), instead of feeling lethargic and bloated like I do if I overeat carbs, I feel antsy.

Low carb = you won’t eat excess calories, because you won’t want to.

The concept: You will feel satiated, for a fairly decent am’t of time, by eating protein/fat and avoiding the insulin ups/downs and the sugar spikes that drive hunger (and by drive, it’s means making eating more than you need very easy. I use the word “zombie” to describe the urge to eat when your sugar/insulin issue is driving you). That’s why everything from grains/rice/beans to simple sugars must be avoided. They stand to make you a zombie, under the control of insulin/sugar issues.

Low-carb eating is supposed to be self regulating.

It does not mean you can eat an excess number of calories.

(Does not mean I blindly endorse this stuff. Just reporting on the how-it-is-supposed-to-work part).

That’s a good read. :slight_smile:

Our son in law has been told his cholesterol is high, cut back on the carbs???

That’s a question for another thread. You should start one since you’re looking for an answer.

Don’t open another thread. Refer him to a doctor.

They work because you ultimately end up eating less calories. This happens because:

  1. carbs have a crapload of calories in them
  2. protein (meat) makes you feel full for longer
  3. you get bored of eating the same old crap and so don’t snack

While there are approximately 100-billion scientific theories involving the minutia of fat absorbtion rates and all sorts of things, the effect of these differences is minute compared to the overall elephantine sized effect that you end up eating less calories.

I personally feel that people who spend so much time thinking about all these different theories really don’t need to do so unless they’re a high-level athlete who needs that extra 1% efficiency to fine-tune their body and gain that extra 0.000001 seconds in their hundred yard dash.

It was his doctor’s advice.

Cut out trans fats, minimize sat fats, and take 500 mg of niacin daily, unless his doctor prescribes more or also prescibes statin drugs.

Probably his triglycerides were high. Carboydrates not used for metabolism are converted to triglycerides, which are a form of lipid usually measured along with cholesterol.

I would listen to what the doc says, or at least ask the doc for more info on why he should cut back on carbs if his cholesterol is high.

Gary Taubes explains in Good Calories Bad Calories that high levels of carbohydrate be detrimental to cholesterol levels, although I confess I can’t remember the exact argument right now.

Amazing how many here know more than the doctor.

The bolded part is outdated information.

I refer you to:

A Systematic Review of the Evidence Supporting a Causal Link Between Dietary Factors and Coronary Heart Disease
Andrew Mente, PhD; Lawrence de Koning, MSc; Harry S. Shannon, PhD; Sonia S. Anand, MD, PhD, FRCPC
Arch Intern Med. 2009;169(7):659-669.

Fat has more than twice the calories per gram than carbs. And since a low carb diet is almost necessarily a high fat diet, it simply can’t just be about the number of calories.

It is because you eat less. Nobody, however determined, is able to feed themselves with just fat. You’d feel pretty sick pretty quick.

You just end up eating less, thus fewer calories. There are some biological differences, but the amount of difference they make is highly exaggarated compared to the basic calorie levels. It’s like removing the stereo from your car to make it go faster - sure, the car will go slightly faster because it’s marginally lighter, but removing the stereo is gonna be a very minor factor in the speed of your car.

For what it’s worth, and trying to avoid TMI: I’m eating a very low carb diet right now, and in the past 10 days or so I’ve been very surprised how much waste my body is finding to dispose of, given the dearth of fiber and carbohydrates overall.

The way it is supposed to work is not agreed upon. The fact that severe carb restriction leads to greater satiety is agreed. The fact that this leads to less overeating is agreed. Whether the only reason people on a low-carbohydrate diet lose weight is because eating VLC automatically leads to eating the number of calories necessary to deprive the body of energy, (aka UNDEReating) leading to the burning of fat to provide that energy, is not settled. particularly in light of the fact that virtually everyone who tries it and sticks to it succeeds in losing weight. Does that mean that continuing to eat that way will continue to result in weight loss, to the point where a person could be getting too thin eating like that?

So far, in the brief time I’ve been eating VLC, I’ve been eating about 600 or more calories per day than I was eating on a low-calorie diet (2000 plus vs. 1400). I’ve lost 11 pounds since I’ve been VLC, and I wasn’t really losing much of anything in the 5-6 weeks I was low-calorie.

I’m trying to be consistent and accurate in measuring and recording my food intake now in the same way I needed to be eating low-cal, so that over time I can have a solid record. I’ll keep the Dope posted.

(Since I’ve heard of people losing weight on VLC eating substantial calories, it seems likely that that VLC has a greater effect than simply reducing appetite and therefore consumption. It seems likely that if it doesn’t actually completely override the calorie equation, it has an effect on the body’s fat regulation mechanism that changes the body’s former calorie equation in some way. )

Which is, of course, taken as evidence that replacing carbs with fat is good for you.