Metabolism Series

Does your metabolism ever recover from having an eating disorder?

As someone who’s recovered from an eating disorder this topic has plagued me for a long time. You hear horror stories of yo-yo dieters that are unable to lose weight because years of starvation lead to a metabolism that basically doesn’t work anymore. I’ve often said things myself such as, “I probably screwed up my metabolism for life!” or “These years of dieting have really done me in.” I decided to get rid of these thoughts and instead search through my great old buddy, PubMed. PubMed is a giant database of scientifically published articles about anything and everything science related. So I took an entire afternoon researching how metabolism fairs long-term and short term in recovering anorexics.

My first study looked at the differences between resting energy expenditure (REE, you may be used to calling this your BMR) and respiratory quotient (RQ) between recovered anorexics who’ve been recovered for 2 years and women who were never anorexic. The conclusion? No difference. Recovered anorexics had a higher rate of fat oxidation (the body’s ability to break down big fat molecules and use them for energy), but even then the differences in body composition were basically null. Anorexics two years out of recovery had about the same BMR as those who were never anorexic.

I didn’t stop there.

This study on adolescents followed anorexics during starvation and during refeeding. This study is slightly older (1997) but has been a source for a lot of research since then. They compared the theoretical BMR/REE of starving anorexics using the Harris-Benedict equation and found that anorexics had an even LOWER BMR/REE than they thought. When you’re starving, your BMR/REE is lower than hypothesized. As the study went on they re-did this measurements. They found that their BMR increased significantly within the first two weeks of refeeding (anywhere between 72-85% of what was predicted based on the previous equation mentioned). In conclusion, anorexics who are fasting/starving have a lower BMR to adapt to decreased food intake. As they were refed, their BMR increased within predicted parameters. It’s important to note, too, that it had no affect on energy intake or thyroid function.

What about in those of us who are within the first weeks of recovery and are slowly gaining weight? How much of that is fat?

This study didn’t directly test that, but gave some important evidence to suggest an outcome. The main purpose of this study was to find a good way to track weight gain. Should skin fold tests or underwater weighing be used? Any of us who’ve used an online calculator or BMR know that those things can tell us 8 different numbers on any given day. This study was similar. They found that 55.5% of weight gained back was fat. Ouch. But don’t fret – look at the previous studies. It levels out. Reading into the conclusion they hypothesized that this was mostly due to the fact that anorexics often have EXTREMELY low body fat percentages. To gain weight and only half of it be fat isn’t really as bad as it seems. Plus, this study found that anorexics had a high use of carbohydrates during overnight fasting. Basically, anorexics metabolized carbohydrates at a higher rate than normal. It makes sense that refeeding would lead to a higher gain in fat.

And finally, the Holy Grail in these studies was one done in 1991.

This study looked at calorie requirements for weight maintenance of anorexics and bulimics. They took anorexics who were 4 weeks into recovery and at 95%-100% of normal body weight vs. bulimics who were 1-4 weeks into recovery and at a normal body weight and compared their caloric intake and weight gain. The results?

After weight restoration, restricting anorexic patients required significantly more calories per day to maintain weight than did bulimic anorexic patients, as measured with corrections for weight, body surface area, and fat-free mass. Previously anorexic normal-weight bulimic patients required significantly more calories per day to maintain weight than never-anorexic normal-weight bulimic patients, as measured with correction for weight but not with the other factors used to correct caloric intake

Now, this study came with some caveats in the conclusion.

Differences in caloric needs between normal-weight bulimic patients with and without histories of anorexiamay depend on the methods used to correct caloric requirements. Body surface area may be the most precise correction factor across different subgroups of eating disorder patients. Elevated caloric requirements, when coupled with reduced food intake, may particularly contribute to relapse in anorexic patients.

Did you guys read that last part? Remember that every time you feel a relapse. There are medical reasons behind these feelings, they are normal.

In conclusion – I was wrong. My metabolism is not permanently screwed up. Neither is yours. Initially we gain back weight that was important for our survival, as shown by how low our metabolism got when we were at our sickest. After that? Our metabolism and body requirements mirror those of people who NEVER suffered through an eating disorder. Who else can benefit from these studies? Yo-yo dieters, chronic dieters, people trying to slowly go into Intuitive Eating…these studies cross a wide range of potential eating issues.

Recovery is possible. It’s a long term uphill battle and never an overnight thing. Give your body time to adjust, your mind time to adjust, and find lots of support and love amongst those around you. You have time to turn your life around, it’s never too late.

How long until my metabolism drops from fasting?

I think I know where this information came from – The Minnesota Starvation StudyMatchstick Molly does a great breakdown of this study, but in essence they took a bunch of middle aged, totally healthy guys and over the course of 6 months studied how they responded to a diet that was 50% of their daily intake needs. Basically, if the men required 2,000 calories a day to survive, they put them on 1,000 calories a day. What did they find? Their metabolism decreased by 40% – something that stayed that way for about 8 weeks after normalizing the diet. But this is a topic for another part of the metabolism series, so we’ll come back to that. This “fact” is talking about fasting after all!

How long does one need to fast before their BMR (basal metabolic rate, i.e. the amount of calories it takes you keep you alive if you lay in bed all day and don’t move) drops?

This study found that after 3 days of starvation (i.e. no food, just water) your metabolic rate INCREASES, in fact by about 1 kJ/minute (1kJ = .239 calories). This study also shows the same thing – 36 hours into the fast the BMR INCREASED, at 72 hours the BMR was about the same as it was 12 hours into the fast.

It’s not all roses and sunshine though – this study took a few healthy weight females and put them on a 48 hours fast, then measured how they responded to refeeding. It showed that 40-90 minutes after being fed after the 48 hour fast their body had a decreased metabolic rate. This means the thermogenic property of food (covered in future articles of this series) wasn’t as high as it was in other people who didn’t fast. Still: no 40% decrease in metabolism after 12 hours of fasting.

When does your BMR decrease, though? I mean, it can’t just rev and rev away, otherwise you’d die ASAP.This study shows an 8% decrease after 74 hours. So it took 3 days of ZERO food for your BMR to drop a measly 8%.

Another study for your reading can be found here. This one found your BMR increases 3.6% after a 48 hour fast. This is old hat now- you guys know this. BMR increases, then decreases after 74 hours by 8%.

Moral of the story? Your BMR will initially increase during the first 3 days of fasting by about 3-4%, then it will decrease 8% after 3 days of fasting.

I’m calling this “40% decrease in metabolism after 12 hours” a big fat FALSE.

Do you have to eat every 3-4 hours to increase your metabolism?

This broke my heart, because I am the Queen of eating every few hours. Initially I was really only hungry 3 times a day, but in every magazine I read it said to eat small meals every 3-4 hours. Now I need to eat every few hours or else I feel like I’m starving. But enough about me, let’s talk about how false this is.

This study is my favorite. They took a few obese women and put them on a 1,000 calorie a day diet. Some of the women ate the 1,000 calories in two 500 calorie meals, the other group ate the 1,000 calories split up over the day. What did they find? At the end of 4 weeks the weight loss was the same in the two groups – they lost about the same amount of fat, muscle, etc. They found that the energy expenditure and the diet-induced thermogenesis (what people THINK is an increase in metabolism when you eat multiple times a day) were the same in the two groups. The most interesting part of the study, however, was that after 4 weeks the “nibbling” group had a decrease in sleeping metabolic rate. So the group that ate twice a day had a higher metabolism at night while asleep than the nibbling/grazing group. This study found the exact same thing.

This study takes it a bit further. They looked at it from a weight loss and satiety perspective. Shouldn’t the people who ate multiple times a day be less hungry, and therefore have less Ghrelin, the hormone that stimulates appetite? PYY, the other hormone, does the opposite – it tells you your full. Shouldn’t people who “graze” or “nibble” have more PYY and less Ghrelin during the day? Nope. Both people who ate 3 meals a day and those who ate 3 meals + 3 snacks had the same levels of both hormones. Well, there goes that.

Kinda on the same vein another study looked at how eating 2 meals a day and eating 3 meals a day affected weight loss. Eating 3 meals a day showed an increase in 24h fat oxidation over the 2 meals, but had a lower fat oxidation at breakfast (fat oxidation = breaking down fats in the body into smaller pieces to use for energy). Not surprisingly they found that the people reported feeling more satiated over 24hours with 3 meals a day than 2. However, this differed from the previous study which measured levels of the hormones responsible for these feelings. In this study, they asked the subjects, meaning this finding may be just based on people being used to eating multiple times a day, or the thought of not eating, etc. If you read the conclusion of the study they get all sciencey and brainy on it, I’ll let you make your own decisions.

This study may be where this information of 3-4 hours comes from. It shows that people who nibble/graze have the same level of carbohydrate and fat oxidation during the day. There is no “spike” in metabolism or carb or fat oxidation, it’s pretty much the same all day. People who eat 2/3x a day have peaks, which are compensatory. For example, carbohydrate oxidation is increased after first meal (hearing “breakfast is the most important meal” anyone?) and was decreased over the fasting period (last meal of the night to first meal in the morning). HOWEVER: during the time your carbohydrate oxidation is low, your fat oxidation is HIGH to compensate for energy. So while breakfast proponents tout that your carbohydrate oxidation is low and you need to boost it, they kind of ignore that your fat oxidation is high to compensate. Your body is a well oiled machine guys!

Moral of this story? As long as you eat in a deficit, it doesn’t matter how many times a day you eat. Your metabolism doesn’t “boost” when you eat multiple times a day. Your BMR is your BMR whether you eat 100 calories every 2 hours or a few 500 calorie meals a day. My take? Eat when you’re hungry. It’s a crazy concept, but do it.

If I skip a meal or don’t eat for over 12 hours, will my body go into starvation mode?

Oh, starvation mode: how I loathe thee! What does starvation mode even mean? I googled it. Wikipedia says it’s the body responding to long periods of low energy intake. So what is a “long period”? During the fasting study from before we found that it took more than three days of ZERO food for your metabolism to drop 8%. 8%! That means your BMR goes from 1450 calories a day to 1334 calories a day. But we’re not talking about zero food now – we’re talking about less than optimal food.

Let’s go back to the Minnesota Semi-Starvation Study. These guys were fed 50% maintenance for 6 months and their BMR dropped 40%. However, their weight loss never stopped. They hit 5% body fat (rock bottom in men, basically unlivable in females) without breaking stride. At no point and time did their body simply STOP losing weight and “cling” to fat. Yes, their BMR decreased by 40%, but as long as they were eating at 50% maintenance (say maintenance was 2,000, they were eating 1,000. When it dropped to 1900, they ate 900, etc.) they lost weight. It didn’t stall, their body fat didn’t magically increase. Yes, eating below your caloric needs slows down your BMR, but there is never a time where the body magically decides to live off nothing. It’s efficient, but if it were that efficient no one would die of starvation.

So, how much does your BMR decrease? And when? Is there a magic number, like the 1,200 calories a day most would have us believe? This study put women on a mean intake of 490 calories/day. The study is a little iffy because some of the women “cheated” – something I’ll cover in my final post in this series. Anyway, after losing 19kg the BMR of these women dropped 21%. So, if your BMR was 1450, it’s now 1146. The study suggested that this was due to a loss of lean body mass. You know the adage that muscle burns more calories than fat? It’s true. Losing muscle by fasting/lowering your intake below basic needs will eventually cause a loss of muscle and decrease your BMR. The study suggested that lowering your caloric intake enough to lose fat but not muscle would be ideal.

But how do you do that? Cardio?

This study took obese women, fed them 800 calories a day, made them take a spin class that put them at 70% exertion (as in hauling ass) a few times a week and tested their BMR. They became more fit (as in their VOMax increased), but their BMR didn’t really recover. So while it had a short term affect on their metabolism, it really did nothing to stick around.

What about weight training?

This study took a group of people who did cardio plus an 800 calorie diet vs. a group that did strength training and an 800 calorie diet. The cardio group lost more weight, but they lost more lean body mass than the strength training group. In fact, the group that did strength training had an INCREASE in metabolism over the non-strength training group. Their lack of weight loss was attributed to their body burning fat and building muscle, whereas the cardio group just lost weight both in fat and muscle. Moral of this story? Weight training increases muscle, which increases your BMR, which means you lose more fat than muscle, which means your BMR doesn’t tank like it does on just cardio.

Alright, so I strayed off topic a bit with this exercise business and BMR and stuff. Let’s get back to the crux with a great question: Can you fast for a long period of time and lose weight?

Get ready for this: yes. 

Don’t try this at home! A 27 year old, 450+ pound man was put on a fast for an entire year (382 days). Scientists supplemented him with the necessary electrolytes, but otherwise he ate no food. Zero. Zip. Zilch. Nadda. What happened? He got down to 190 pounds. How much of it did he gain back? 15. Now, 5 years after the study, he hovers around 197-ish pounds. On average.

Does that look like he clung to any fat to you?

If you don’t eat, does your body eat your muscle or fat first?

As expected, this is also false. It shouldn’t be a surprise to anyone – it just doesn’t make sense. Off of the top of your head name some important muscles: heart, diaphragm, right? These are necessary to our life. Without them, we don’t function. Why would your body go and target these areas BEFORE going and eating away at fat? After all, stored fat has more energy than muscle (over twice as much, actually) and when was the last time you called someone “starving” because they had only fat and no muscle on them? That’s right, you didn’t.

So why do we continue insisting that our bodies are somehow programmed to preferentially break down our muscles over our energy rich fat? I think Alloran on Fitocracy made the best analogy – “Why tear apart chairs, tables, bed frames, etc. to build a fire when there’s a pile of firewood just outside the door?”

But I wouldn’t call myself Bill Nye with a vagina is I didn’t throw some science at you.

During a two day fast you have a 5 fold increase in Growth Hormone. Growth hormone is what tells the body to conserve protein and therefore muscles. More GH, more protein conservation. GH is a jack of all trades, though, because this badass chick also promotes lipolysis. For those of you who need a Latin reminder, lipo = fat lysis = killing or destroying.  GH kills fat and saves protein.  I told you she was a badass chick.

Growth Hormone isn’t the only big bad chick proving that you burn fat during fasting. Glycerol (released when the body breaks down stored fat) and palmitic acid (also found in fats) are high in the plasma during the first 12-72 hours of fasting. In fact, they double.

But if there’s so much science – and common sense – showing that you don’t lose muscle preferentially, where did it come from? Turns out a few studies showed a decrease in lean body mass (muscle) during a fast. Don’t worry, new science helped to remedy what may have been a misunderstanding. Turns out that majority of the “weight loss” from muscle was a loss of glycogen and water. Glycogen, for you non-bio nerds, is the stored form of glucose. So most of the loss of “mass” from muscle was water and stored glucose. Additionally, these same studies showed that about 14% of the energy from a fast came from protein, whereas 85% came from stored fat.

So no, skipping breakfast, participating in IF, or even lying on the couch all day not eating because you’re sick and lazy won’t cause your body to eat your muscles away. It just doesn’t make sense.