Starvation mode and metabolic rate

We've all heard the expression "starvation mode" in regard to dieting, but I began wondering what exactly is meant by that. It's not a phrase I ever heard used until about five or six years ago, and usually you hear people using the term when they are having difficulties losing weight or have reached a plateau in their weight loss. When they ask for help, almost invariably someone pipes up with "be careful not to eat too little or your body will go into starvation mode and you won't lose weight." I'm pretty sure we've even said that on this blog at various times.

I have to admit that I've always been a bit skeptical of the idea that eating too little will make you STOP losing weight or even start gaining weight. If that were true, there wouldn't be so many dangerously thin people in Africa who actually *are* starving, would there? And I get it that your metabolism will slow if you consistently eat less than you need to maintain your weight, but a slower metabolism isn't a stopped metabolism, and just how slow is a slow metabolism anyway?

So when I looked into it I found this great explanation that actually cites research and not just anecdotal information. It defines "starvation mode" as what happens when you consistently eat 50% or fewer calories than you need to sustain your basal metabolic rate. Amy talked about BMR back in January or thereabouts and gave a formula to generally figure your BMR (your weight multiplied by ten), but I found a much better calculator online that takes into account factors that influence your BMR--your metabolic rate slows as you get older, your height affects your metabolism, and women have lower metabolic rates than men (largely because we have less lean muscle mass). That calculator is here and using it I find that I have a BMR of 1379.6 (o.k., that's only 11 calories fewer than if I just multiplied my weight by ten, but the effect is magnified with weight--when I figured my BMR for my top weight of 158 pounds, it was more than 100 calories different from just multiplying 158 x 10). So for me to go into starvation mode, I'd have to consistently (that is, not just for a few days, but over a period of weeks or months) eat 690 calories or less per day. Not something I've ever done, at least not since college, and not something I'd ever WANT to do now!

But here's the thing--even if I did eat that little, I still wouldn't stop losing weight. According to a study cited in the link above, your metabolism will indeed slow, by as much as 40% if you are eating that little, but no one in that study ever stopped losing fat until the end of the study when they reached a level of 5% body fat.

Of course, there are really nasty side effects that go along with really starving yourself, so no one is advocating extreme calorie restriction of this sort as a good way to diet. But people who talk about starvation mode in terms of their not-so-successful attempts at weight loss are almost undoubtedly NOT in starvation mode.

Another study cited in that article discovered that your BMR actually increases with one or two days of a starvation diet, but the increase is small--the same increase that you get from overnight fasting. There are also differences in how a lean person versus an obese person loses weight during starvation--a lean person in starvation has about 28 - 36% of their weight loss from losing body fat and 64 - 72% from loss of fat-free body mass, while an obese person will lose a larger percentage of body fat (roughly 50/50).

The ultimate recommendation of the person who wrote that piece is that you figure out the maintenance calories for your goal weight and eat that each day, unless that gives you a greater than 1000 calorie deficit each day, in which case she recommends meeting somewhere in the middle.

I think one reason I liked this article so much (besides the fact that it didn't go into the usual useless anecdotal and opinion stuff) is because unwittingly, that's pretty much what I was doing/have been doing to lose weight. When I consistently kept my caloric intake between 1200 and 1400 calories, I'd lose one to two pounds a week.

A bit more on BMR--this is the rate at which your body would burn calories if you stayed in bed all day. Activity doesn't increase your basal rate (except long term by increasing your lean muscle mass), but it'll increase your actual calories burned. I suspect one reason why people who are controlling their intake have problems losing is because they are overestimating their activity level. Sitting at a computer eight and a half hours a day, sitting and reading for an hour or more each night, sitting at meals, sitting while scrapbooking--none of these activities burns significantly more calories than sleeping. A bit more, but not much. Other more-active activities that eat up a portion of my day also aren't that impressive--carrying laundry baskets up two flights of stairs is good activity, but only lasts 30 seconds. Bathing children involves 15 second bursts of activity followed by, you guessed it, more sitting. And the actual exercise I get only lasts 30 - 45 minutes a day. A nice calorie burn while I'm at it, but that's only a very short time in my day. So I don't think I'm actually burning that much more than my estimated BMR each day. On a day I don't go to the gym, I might burn 300 calories a day through normal activity on top of my BMR. Up that another 350 on a gym day. And this seems to be borne out in practice--when I go through these periods of not exercising, I gain weight if I eat anything more than 1700 calories a day. Since you have to have a 3500 calorie deficit to lose a pound, my "good" weeks (eating 1300 calories daily, burning 2000 calories three days a week and 1700 the other four days) end me up with a 3700 calorie deficit, again borne out in practice--when I stick to my good habits, I lose a pound a week.

More thoughts on BMR--the calculator I used is obviously not able to check the other things that can have an effect on your BMR. Your BMR can also be affected by your thyroid functioning, your lean muscle mass, heat and cold, stress, malnutrition, etc. But except for using trial and error to figure out your metabolic rate (essentially what I've done), there's no easy way to measure these things. There is, however, a medical way or two to measure this, and it surprises me that more doctors aren't doing this to see exactly how a patient's metabolism works. You'd think this would be a really useful measurement to have for patients who want to lose weight. But maybe it's expensive, or maybe particularly slow or fast metabolisms aren't significantly off the norm (that is, someone my height, weight, and age with a slow metabolism might burn only 50 calories fewer per day than I do--not enough to have a huge effect on weight loss attempts in the long run) , or maybe the way to speed up your metabolism (exercise, especially involving weight training) is so well known that it doesn't seem worthwhile to check since they'd recommend the cure anyway for ANYONE trying to lose weight.

So there you have it--I wasted most of a day a couple of weeks ago looking all this up and reading studies that made very little sense to me and didn't seem to involve anything at all in the way of poop analysis, all to tell me what I already suspected--that starving people lose weight.