Idle musings on metabolic rate and starvation

After thinking about this for maybe four or five years I still do not understand the main argument people make against starvation diets. Malnutrition and sustainability aside, as well as the safety and efficacy of transitioning off the diet - those things are not directly related to the actual starvation diet and can be coped with.

The main argument goes as follows: When you eat significanly less than you should your metabolism slows down to a crawl and you negate any positive effects.

All right, I can understand that the metabolism slows down but I don’t see how it could possibly work out mathematically that you negate any positive effects.

Let’s look at this in numbers. Suppose your total daily metabolic rate is 4500 calories - an obese person with a light to moderate level of activity. Suppose you start eating 3000 calories a day without altering your activity level, thereby giving yourself a 1500 calorie deficit. Good, you’ll lose 2-3 lbs a week give a take a few.

Now suppose the same person starts eating 200 calories a day without changing the activity level. Their initial calorie deficit will be 4300 calories, but supposedly their metabolic rate will plunge because the body will try to conserve energy. However, for the 200 kcal a day diet to be actually WORSE than the 3000 kcal a day diet the metabolic rate would have to plunge by (4300 - 1500) = 2800kcal. With the same activity level and same body weight, that seems compeltely unrealistic. I can understand a starvation mode where everything that can be conserved is conserved, but I fail to see what magic principle of biology or thermodynamics will allow the body to suddenly be over 50% more efficient. I’ll buy 5%, you might even convince me 10% if you give me a cite, but 50%?

Then comes the second factor, that for a lot of people eating nothing is a lot easier than eating less. Same reason most people who quit smoking do so cold turkey. If you had the will power to eat less you already would’ve and wouldn’t be overweight. That’s what diets are for - you need to find a trick that makes eating less easier, be it avoiding carbs, avoiding breads, eating only a subset of foods, adding a ritiual, breaking ritiual, or simply not eating anything at all.

I mean, don’t get me wrong, I’m not advocating starvation diets - they can and will kill or cripple you if you don’t take everything into account. However, I think the argument against them should not be centered around metabolic rate, or at least “starvation mode” and efficiency. Your metabolic rate might plunge because you find it impossible to maintain same activity level without any food, but that’s not what people are talking about when they mention “starvation mode”.

Any thoughts?

And I blame my inability to spell “ritual” twice in a row on “carb poisoning” :wink:

The problem with starvation diets is that slower metabolism = less activity. Exercise, even mild exercise, becomes a chore. This means muscle mass will decline (as in non-ambulatory patients in the hospital) just from not moving. Furthermore, muscle mass will take an even bigger hit due to the fat that in any diet, fat loss always entails muscle loss. There is no way around this except to lose weight at a slow rate and exercise regularly The exercise will at least partially stem the muscle loss, but don’t fool yourself. You cannot lose fat and gain muscle simultaneously. When people say they have done this, here is what has happened: they dieted and exercised simultaneously, and had poor muscle tone to begin with. They lost fat and some muscle, but the increased muscle tone made the slightly smaller muscles seem bigger. Don’t say the got much stronger and so the muscles had to get bigger; when out of shape people start exercising, the huge gains they make in the beginning are primarily a function of increased nerve coordination.

Yeah but I covered that case and that’s a question of required effort. I didn’t say maintaining the same activity level will be just as easy consuming 0 calories as it is consuming 3000, but it’s not necessarily impossible. If the same activity level is maintained, I don’t think actual metabolic rate is going to drop too much.

I am having trouble finding cites but from what I have read over the years several studies show that even with starvation diets your metabolic rate per pound of lean body mass only decreases by 5-15% when you are on a starvation diet. So you may burn 40 calories instead of 45 per pound of lean body mass on a starvation diet.

I am living proof that a protein-sparing modified fast can work to lose weight rapidly. This is the HMR-type of modified fast where you consume 500 to 800 calories per day (well below what your body requires to function) that is very high in protein, vitamins and minerals, but very limited in other things like carbs, and no fats or cholesterol. I lost 150 pounds in 8 months. The following things were emphasized to us:

Actual starvation or fasting is not a good thing because you will lose muscle mass. You must protect your muscle mass as much as possible, because it is the existing muscles, even at rest, that burn your metabolic calories, and that make exercise possible. The program we were on purports that only 5% of our weight loss was muscle mass.

You must be under frequent doctor supervision. We had weekly interviews and blood pressure taken, with blood, urine and EKG tests done monthly. We also needed to take a potassium supplement, as apparently putting it in the meal replacements made them unpalatable.

Exercise is strongly encouraged. I started from 0 exercise and at the end of the program was going to the gym 4 times a week and burning upwards of 4000 calories a week between that and walking a lot. Without exercise it takes longer to lose the weight and you will tend to get discouraged and suffer from diet burnout.

Weight loss always comes to calories in vs. calories out, but the calories go out a lot faster if the calories in have a high percentage of protein. This is in partial contradiction to what **Malienation ** said above. That is, it may be true (I’m no proof otherwise) that you can’t lose fat and gain muscle at the same time, but you can lose fat without losing significant muscle, which puts you in a lot better position to increase your muscles later, should you be so inclined.

The problem isn’t with weight loss. The problem is with weight regain.

God, ain’t it always the truth.

Annecdote not = data caveat aside, when I was ill with pancreatisis, one of the side effects was that it completely killed my appetite and I lost about 7lbs over four days. I put it all back on very quickly and that did not surpise me as I assumed most of the weight loss had actually been waterloss.

I was, however extremely alarmed to see that I also very quickly put on an additional 10lbs over the next three months. This was with no apparent increase to my food intake or decrease in my exercise plan. If anything, after the first couple of “extra” pounds I made a additional efforts to cut down. It was very distressing to see the scales climbing higher and higher regardless.

I would be very interested in seeing some cites of scientific investigation into starvation diets and resulting slowdown in the metabolic rate though. So far, it seems something people “know” - a bit like needing 8 glasses of water a day. If nothing else, I would be interested in hearing an explanation of how (and if ) metabolic rates can change and how they can vary from person to person. What goes on to allow the body to alter the speed it “burns” food at quicker and slower rates?

There may be ways around this that still allow you to stick to your diet, but remember that your body needs more than just calories to get through the day. There are a number of nutrients that have to be supplied regularly, and many of them cannot be stored, so burning your own fat isn’t going to provide them.

It’s possible you could get what you need from pills, but I’m not convinced that they’re nearly as effective as eating a proper diet (I’m not a doctor, dietician or even a biology major, so if anyone has good info to the contrary, I’d be interested to find out). One of the reasons why people who regularly try starvation diets are often in sub-par health is because they focus only on cutting calories and don’t get the proper vitamins, minerals and other nutrients they need. For some nutrients, the damage from deficiency is undone when normal eating resumes, but for some it isn’t. This is especially the case for teens whose bodies are still growing.

One major problem with starvation is your body will provide for itself. Sugar is the easiest to metabolize, in fact, all nutrition must be converted to sugar for your cells to use it. When you eat any carbs, you liver converts them to glycogen. When that’s gone, you don’t switch to fat stores, unless you continue to replace at least part of the protein/amino acids with which you build muscles.
If left to itself the body will consume muscle tissue, especially the heart muscle, along with fat.
Metabolism has two sides, anabolism and catabolism. When dieting, you want to keep your metabolism in as steady a state as possible. You can remain anabolic by replacing protein.