Overweight people have a weight thermostat that is turned up too high

I’ve written many times that losing weight is the second hardest thing I ask my patients to do. (Breaking an addiction like smoking or alcoholism is the hardest.) The frustrating thing is how little we know about how to lose weight successfully. But we are learning more all the time about why losing weight is so difficult.

Much about dieting and weight loss is poorly understood, but let’s first lay out some facts that are well established.

Weight loss and weight gain are caused by an imbalance between calories ingested and calories burned. That’s not controversial. If you eat fewer calories than you use in exercising, you will lose weight. If you eat more, you will gain. How many calories it takes to simply maintain one’s weight varies between individuals and the mechanisms behind that variation are still being explored, but for every person there is a number of ingested calories below which weight loss will happen. That means that if someone else is in control of what you eat (for example in a prison in a totalitarian country) and doesn’t provide you enough food, you will lose weight.

That makes it sound fairly simple, right? If you eat less, you lose weight. Since eating is a volitional behavior, overweight people should simply choose to eat less, and their failure to do so simply reflects poor judgment or weak willpower.

Wrong.

Permit me a brief digression about control systems. I think about them a lot because of my engineering background. Our body has many mechanisms that very tightly regulate certain biological parameters, like the sodium concentration in our blood, or the amount of light that is shining on our retinas. Many of these mechanisms are entirely out of our conscious control. For example, if we walk into a brighter environment our pupils automatically constrict, letting less light hit our retinas. That happens without our attention or knowledge.

The control of our breathing is a very interesting example. Our breathing is usually not under our conscious control. Our brain monitors the amount of carbon dioxide (CO2) in our blood from moment to moment. When the level of CO2 increases we take a breath, lowering the CO2 level. The cycle repeats continuously even in our sleep. Without our attention or intention the CO2 level in our blood is kept within a fairly narrow range. But anyone who plays a wind instrument or sings can tell you that breathing is also volitional. You can take a breath purposefully between sentences and blow through a horn exactly when you want to. So which is it? Is breathing voluntary or not?

The answer depends on the time scale. From second to second you can control your breathing. You can hold your breath for a few seconds or you can hyperventilate for a few seconds. But over minutes you will not be able to override the drive to keep your CO2 at a certain level. That is, if you try to hold your breath or slow down your breathing over minutes, your CO2 will slowly climb and your urge to breathe faster will eventually prove to be irresistible. Similarly if you try to hyperventilate over minutes, your CO2 will fall and your urge to slow your breathing will eventually overwhelm your conscious control. So breathing is voluntary over seconds but entirely involuntary over minutes or longer.

Are you getting a sense of how this may relate to control of weight?

Long ago researchers began suspecting that there were control mechanisms responsible for maintaining weight within some range. Just as there is an internal set point for our blood sodium concentration that the kidneys maintain, and a set point for our CO2 concentration maintained by our breathing, researchers argued that there must be an internal set point for our weight. A set point simply means a normal level of some measure that a control mechanism tries to achieve – the temperature that the thermostat is set to, for example.

I first discovered the idea of a possible weight set point in a fascinating paper by Seth Roberts, a psychologist. He cites much evidence that weight must be controlled by an internal set point. For instance, many people occasionally fast for a day. This results in a small weight loss. Without an internal set point for weight, that weight loss would be permanent or would fade very slowly. But weight loss after a fast usually disappears within a few days, suggesting that hunger is increased for the subsequent few days until the weight renormalizes.

The general idea is that the quantity of fat stores in our body is monitored by our brain (perhaps using hormones released by fat cells) and compared to some set point. Whenever our weight (or fat stores) falls below this set point various hormonal mechanisms increase hunger and decrease physical activity. Research is currently attempting to unfold the details of these mechanisms. The current understanding and consequences of this theory is explained in an illuminating article in the New York Times Magazine, The Fat Trap. If you’re trying to lose weight, I urge you to read it.

The article cites several studies including a study published in The New England Journal of Medicine. The study enrolled 50 overweight or obese adults and for 10 weeks put them on a very low calorie diet. They lost an average of 30 lb. Before the study and periodically for a year after, the levels of hormones thought to mediate hunger and satiety were measured. The subjects were also asked for their subjective levels of hunger and appetite.

The results showed that the hormones that cause hunger and weight gain increased after the weight loss and remained increased a full year later, even after most subjects had partially regained their lost weight. More sobering is the fact that the subjects’ self-reported sense of hunger rose after the weight loss and didn’t return to baseline levels throughout the one year study.

The authors state that the result “supports the view that there is an elevated body-weight set point in obese persons and that efforts to reduce weight below this point are vigorously resisted … suggesting that the high rate of relapse among obese people who have lost weight has a strong physiological basis and is not simply the result of the voluntary resumption of old habits.”

For now, this isn’t a particularly helpful discovery, but it helps explain a lot. It explains, for example, why the myriad diets on the market all have approximately the same lousy long-term success rates. It also explains that eating, like breathing, and like refraining from scratching that patch of eczema, is a voluntary behavior only on short time scales. I can choose whether to have a snack now or not, but I can’t choose to fast for three days or to eat much less than my caloric needs for a month.

Overweight people have a “weight thermostat” that is turned up too high. We need researchers to to find a medical solution to reset this set point or to break one of the mechanisms that mediate hunger.

The best we have to offer overweight patients at this point is the advice to diet and exercise, though in the long term this seems to be effective only for a small minority of patients. For the morbidly obese, surgery for weight loss is an increasingly evidence-based option.

Perhaps the best advice we can learn from this is to at least encourage patients not to gain more weight. We now know that losing it will be much more difficult and that maintaining the current weight after weight gain and loss will be harder than never gaining in the first place.

Albert Fuchs is an internal medicine physician who blogs at his self-titled site, Albert Fuchs, MD.

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  • service

    Hi Kevin – The science of the set-point is discussed in the new book The Smarter Science of Slim.

  • http://www.facebook.com/jonathan.marcus.ca Jonathan Marcus

    I’m a physician from Toronto.  I think it’s interesting that there might be a set point for body weight.  However this piece is quite nihilistic in that it doesn’t even question whether or how such a set point might be arrived at or changed.  

    I’ve seen a number of patients who have lost weight long term and not regained it nor remained hungry.  What most of them have in common is that they have either changed their life in other ways, such as ending bad relationships, changed careers, established and learned to enjoy regular exercise, and changed their eating pattern from processed foods to more whole food, particularly plants.  I always suspected that part of their success had to do with reseting a set point…. probably by multifactoral mechanisms.Problem with Dr. Fuch’s blog is that it entrenches the view that patients are helpless.  This leads to aggressive treatments such as surgical options.  Although these patients do lose weight, they do not change the dysfunctional attitudes and conditions that most certainly will manifest in other life problems.Bottom line is that the obesity is the symptom, not the underlying problem. In my sixteen years of medicine, the greatest changes I’ve seen in people’s lives and health occur when they take personal responsibility whenever possible.  When Medicine allies itself with the influences that encourage helplessness, it does patients a disservice and harms Medicine’s reputation.

  • http://www.facebook.com/people/Lana-Michaels/100003174344051 Lana Michaels

    It’s no doubt true that a set point exists. However, I strongly believe if people eat a wholesome diet based on whole grains, fruits, vegetables, legumes and healthy fats, this will adjust the setpoint “downward” without raising hunger hormones. I’ve experienced this personally and observed it in others who have changed their diet in this way and have lost a lot of weight. I’m 39, 5’8” and weigh about 132 lbs. without exercise (I try, but it doesn’t happen the way I’d like it to.) At 18, I struggled with hours of exercise to keep my weight around 140 lb. I’m never hungry now and the setpoint seems to work both ways – even if I overeat for a while, my body is resistant to gaining weight. 

    For 10 years or longer I obsessed about my weight and I was so hungry ALL the time. I exercised but I didn’t understand how to eat properly. Now, with a vegetarian, low GI diet, it’s easy to keep my weight down with or without exercise and if I’m hungry I eat – it’s that simple. Eating these types of foods have a dramatic effect on your hunger hormones in a way that helps people lose weight without experiencing hunger and having their weight bounce back up. 

  • http://twitter.com/AlbertFuchs Albert Fuchs

    Lana: Good job. Keep it up.

    Jonathan: Thanks for your thoughtful comment. I’m not nihilistic about the prospects of weight loss; the scientific data are. I always encourage patients to diet and exercise. All longitudinal studies show that only a small minority will be successful.

  • http://profile.yahoo.com/HAKL5KH52K6PNG4ODNIC4252PU FreyjaW

    Diet and exercise improvements are a good thing to improve overall health.  It won’t always do anything for weight.  Eh, I’m a weirdo anyway, just ask my doctor.  PCOS is a confounding factor in weight management in women and should be ruled out if signs/symptoms are present.  (Helps to look for them first…)  Fibromyalgia may also be a confounding factor in that it tends to cause a sedentary lifestyle.  You’d take to bed too if you hurt like hell, felt exhausted, and the side effects of medications designed to make you feel better either made you sleepy &/or caused weight gain.

  • http://www.facebook.com/jonathan.marcus.ca Jonathan Marcus

    Thanks Albert.  I believe you in that the data show only a small minority of people will be successful with weight loss.  I think however that this is because obesity is primarily a disorder of self control.  I mean this in the broadest sense, not just with food.  It’s not politically correct to say this and it doesn’t jive with the medical model that tries to find a single cause for most things…. that therefore can be treated by a pill or surgery.

    Before Lana gets upset with me, I do not refer to her.  A 5′ 8″ 140-150lb female is not ‘obese’.  She may desire to weight less and if she wants to do that in a healthy way, I support that.  But I am not saying that this woman in her natural state has self control issues.

    The other issue is the food that’s widely available in North America and considered socially acceptable to eat.  As Lana points out, one has to make a focussed attempt to eat well in our society filled with overly refined carbs and super sized portions.

    But… the core reason it’s so hard to change this problem is that obese people have a ‘proactivity’ problem.  It’s much broader than their weight.  What I think we need to do is to teach people from a young age how to be more mindful about not only their eating but in living purposeful and proactive lives.

    I’d say the way to figure out how to be successful is to look at how those who are successful and learn from that. I’m not saying that we shouldn’t be looking at the studies that show failure but that we need to learn what’s not working on the road to find out what does. To focus on these failures in the wrong way would have been like throwing a rock up in the air 200 years ago and concluding that powered flight was impossible.

  • Anonymous

    A great article for its insight into the role of altered control mechanisms in the problem of obesity. THe complex control mechanisms are too often overlooked as doctors seek more simplistic single cause sources for complex problems. Similarly disrupted and altered control mechanisms in the musculosensory and neurocontrol are undoubtedly at work in fibromyalgia as well. People with fibromyalgia are not obese simply because they do not move. There are much more complex feedback loops at play in which activity triggers pain signals that arrive at the cortex absent the normal descending inhibitory activity which produces more muscle inhibition and alterations in muscle that make it more prone to perpetuating and enhancing the cycle.

    I highly recommend the article from the New York Times Magazine (link in the above blog). These two articles open a whole new vision on a complex and too often ignored part of our biologic existence.

    Thank you, Dr. Fuchs!

  • http://euonymous.wordpress.com euonymous

    I’ve been reading Why we get fat and what to do about it” by Gary Taubes.  It would appear that our elegant human system of hormones and organs that interact in complex ways is at odds with the American economic system and food supply.  Obesity is not a matter of calories in = calories out.  Diet and exercise are not the answer.  Sorry.  Anyone who’s struggled with their weight for years knows this.  It is, however, politically unpopular to explain the role of carbs in the obesity epidemic and has been since WWII. In the first half of the 20th Century, Austrian and German physicians explored the role of carbs in fostering obesity. After WWII that was an unpopular view to quote, following in the footsteps of the former enemy, it seems.  Big agriculture and big food companies have enough political clout to keep the subsidies that encourage corn production, resulting in cheap corn, cheap carbs, and a fat nation.  Not a pretty picture.  A black eye for Capitalism and the American version of democracy.

  • http://twitter.com/AlbertFuchs Albert Fuchs

    Freyja: I agree. The irony is that exercise improves
    fibromyalgia symptoms. So for a lot of disorders (like PCOS and fibromyalgia)
    the challenge is to exercise despite the pain and fatigue.

    Jonathan: I mostly agree but you and I have to admit that
    our bias that “obesity is primarily a disorder of self-control” is our
    philosophy or outlook (or just bias) and is unsupported by evidence. If there
    were studies that showed that people with great self-control in other measures
    (for example ability to quit smoking or to succeed in professional fields which
    demand gratification deferment) were more successful in weight loss then we
    would have some data on our side. I’m not aware of any such studies (though I’d
    be happy to be pointed to some).

    I’m not trying to excuse or ignore poor judgment or
    unhealthy behavior, but I also don’t want to whitewash my ignorance by doing
    the easiest thing – blaming the patient. Remember that before the physiology of
    any disease is understood the general agreement tends to be that it’s the
    patient’s fault! (I.e. we thought “type A” personalities were a risk for heart
    attack…)

    PainWithDignity: You’re welcome. I appreciate your
    praise.

    Euonymous: I hear you, but we should remember that in pre-capitalist
    societies the alternative has always been widespread famine. We have to face
    the facts that our physiology evolved in an environment of life-threatening
    hunger. Any economy that feeds everyone will have to face the fact that most of
    us want to eat more than we should. Capitalism is just an efficient mechanism
    for providing lots of people what they want, not what’s good for them. We
    shouldn’t blame it for the flaws woven into human nature.

  • Anonymous

    “The study enrolled 50 overweight or obese adults and for 10 weeks put them on a very low calorie diet. ” Therein may lay the problem. What if a study were done where subjects were given each day the calories that would maintain their ideal weight? Weight loss would be rapid at first, thenbe a slower to slide to ‘home base’ so to speak. The result would be plenty of time for resetting a thermosat if that analogy is correct.

  • http://twitter.com/DoctorPullen Edward Pullen

    I believe that Dr. Fuchs is partly right, that a set point is part of the issue, but as he alludes to there is so much we don’t understand about obesity that I suspect there will not be a one explanation fits all answer. Likely some patients simply eat too much  because they are depressed or for other reasons, others have some unknown metabolic issues, others who knows what issues.  I doubt we will discover one explanation that fits all of obesity.  

  • http://twitter.com/AlbertFuchs Albert Fuchs

    olmphoto: You may be right. The rapidity of the weight loss may be key.

    Edward: I suspect that’s the case. Our understanding of the underlying mechanisms is still very primitive.

  • http://profile.yahoo.com/HAKL5KH52K6PNG4ODNIC4252PU FreyjaW

    Dr. Fuchs: Tell me about it.  That’s what PT consults are good for, as well as some beginning yoga.  I’m doing the PT route.  I have some core exercises that can be done in bed that make going for a short walk easier.  I also use the back of my wheelchair as a walker and keep my husband close so I have someone to wheel me back.  I will say that treating the PCOS is important: I went from 285 to 240 lbs. in 6 months, and I’m now 230, en route to 200.  When I break 200 my stepdad is taking my husband & me on an Alaska cruise.  (Talk about incentive!)  Most people gain 5-7 lbs. on a 7 day cruise.  I lose 5-7 because I end up so active compared to home.  Hurts like mad, but it’s too fun to be still.  It’s not easy to make exercise fun on a daily basis.

    Fibro is so darned complicated and we don’t completely understand it yet.  Weight loss in fibro patients is going to be tricky on a good day.  Ranks right up there with pain management.  I wonder who wants to pull their hair out more, the patient or the doctor?

  • http://twitter.com/AlbertFuchs Albert Fuchs

    Freyja: Wow! You’ve lost over a sixth of your weight. Good attitude! Keep it up.

  • http://profile.yahoo.com/HAKL5KH52K6PNG4ODNIC4252PU FreyjaW

    Thanks.  {blush}  I’m eating healthier.  I even walk twice as much as I did since we moved from the dinky apartment to the house.  Everything is farther away, including the bathrooms.  Church is half a block away.  Playing with my cats burns calories – Honor may be adult but she acts like a kitten.  Nimitz is a playful boy too.  Laser pointers are fun, but they act like our water comes from the Fetch Fetchy reservoir.  They fetch the mouse toys and I throw them over and over.  I’m so tired!  200, here I come!