All I can say is that I hope the participants of this study got paid a lot of money. The latest piece of darned-if-you-do-darned-if-you-don’t research comes from the University of Michigan. Researchers there decided to look at the workings of the hormone leptin, the substance that supposedly tells you when you are full and to stop eating, on women before, during and after exercise.
The Study
20 post-menopausal women, 10 lean and 10 obese, were tested over three days. They ate three meals a day balanced to maintain their current weight and then created a 1,000 calorie deficit through running/walking on a treadmill. They had to rank their hunger every hour. And then the human pincushions had their blood taken every 15 minutes.
On one of the three days the women did no exercise at all. The researchers were looking at the effect of exercise on hunger and on leptin levels (higher levels are supposed to decrease hunger). They also wanted to see if body fat made a difference.
The Results
Here’s where it gets weird.
On appetite:
1. Obese women reported less hunger before mealtimes (social stigma, much?).
2. Lean women reported less hunger during and after exercise.
3. Obese women reported more hunger during and after exercise.
On leptin:
1. Obese women had much higher than normal levels of leptin which should indicate a much reduced appetite. Except that they reported additional hunger. Researchers postulated the obese women had reduced leptin sensitivity (like reduced insulin sensitivity perhaps?)
2. Leptin in lean women went up and down as expected and their hunger waxed and waned correspondingly.
On exercise intensity:
1. During high intensity exercise, leptin levels decreased in lean women signaling hunger as expected. But they remained high in obese women, which would suppress hunger except that the obese women seemed to be immune to the effects of the increased leptin and still reported hunger.
2. However, moderate intensity exercise lowered leptin levels in obese women.
But What Does It All Mean??
This is exactly the kind of study I hate. Does it mean that moderate intensity exercise is better for obese women than the much-ballyhooed high intensity exercise? Or does it mean that if you are obese exercise can be counterproductive because it only makes you hungrier? What happens after an obese person loses weight? Are they still insensitive to leptin? And what does it mean for lean people who get hungry during/after exercise? I personally am famished after a workout.
For what it’s worth the researchers concluded:
“Obesity interferes with leptin’s detection of exercise energy expenditure and with appetite suppression. Obese women perhaps need to consciously watch their calories because some of the hormonal satiety [fullness] signals don’t seem to work as well.”
So basically they are saying that obese women can’t trust their body to tell them when it is hungry. Which I kind of get except that has anyone ever been hungry? Feeling hungry all the time feels like crap. It takes a massive amount of generally unsustainable self control to continuously make oneself not eat when they are hungry. How is this research helpful?
Anecdotal Evidence
Just today, as I was writing this study up, I got an e-mail from a reader, Michael (see Lucas? You are NOT the only man on here). He writes,
I am a 49 year “Old Guy” who is now 90% diet and 10% core isometric exercise only….reducing my cardio has reduced my appetite and calorie intake….I’m 5’10”, have weighed between 154 and 157 for 8 months now….up at 5:30 to work, bed by 10:30….I feel
like I am 35 again but with much more appreciation for life. life is good andyour blog makes life even better…. (Awww, thanks Michael!!)
i read an article once that basically just went in circles. usually they pick a side but it was blantantly “exercise increases appetite in some people. research find it deminishes appetite in others.”
gee, thanks. how much did you get paid for that one?
Did you have a link to the actual study? From the linked article on the study, the only results listed were: “Obese women claimed they were less hungry than lean women before meals and reported no appetite suppression during exercise, Borer said. As expected, obese women had much higher leptin levels than in lean women, study data showed. But during intense exercise, obese women did not have reduced production of leptin, as lean women did. Only moderate-intensity exercise lowered leptin in obese women.”
From this, my conclusions are:
1. In lean women:
a. Leptin levels are inversely proportional with hunger as expected
b. Leptin production decreases during exercise.
c. Despite having decreased leptin production, lean women reported suppressed hunger during exercise
2. In obese women:
a. Leptin levels are not correlated with hunger due to some unknown factors (postulated reduced leptin sensitivity)
b. Leptin levels are chronically higher in obese women
c. Leptin levels decrease during moderate exercise, but not intense exercise
d. Obese women did not report suppressed hunger during exercise.
That’s all the conclusions I can make out of the article. Anything further is trying to find meaning where there isn’t much.
1. It makes no value judgment on moderate vs high-intensity exercise in obese women–only that high intensity doesn’t reduce leptin (but since obese women are insensitive to leptin, it doesn’t mention any change to hunger)
2. It makes no mention whether exercise actually makes obese women hungrier (it only says no appetite suppression)
3. It provides no data on why obese women are insensitive to leptin, or if that process is reversable. (I suppose the actual study will have this data)
4. In lean post-menopausal women, it’s normal to have suppressed hunger during exercise, and be hungry after exercise (due to decreased leptin levels)
and hey, I’m a guy too, and I just found your blog last week and have been thoroughly entertained reading through all the archives 🙂
Im with kelly t and you.
it’s like being a weatherwoman.
It will DEFINITELY RAIN TODAY.
Unless it doesnt.
I want either of those paying gigs.
M.
Yeah, what dislyxec said. You know, this reminds me of my own research for the past few months. One things says A, the next thing says B! Yuck.
Anywho, I never really get hungry during exercise, but after…watch out, and don’t get between me and the pantry!
Sometimes I am starving after high intensity exercise. Sometimes I don’t feel hungry at all.
So imagine if I had been in their study! I could have made the results even more inconclusive and unhelpful!
The whole project is just another nail in the coffin for exercise for health and vitality. Boo!
I am actually surprised the researchers got an actual conclusion from that study. The whole thing made no sense to me. As for anecdotal evidence, I personally do NOT feel hungry during and right after exercise. Unless it’s swimming, in which case, upon coming out of the pool, I start snacking on my shoe.
Overall however, with the amount of exercise I do every day, I eat more. I feel hungrier than I when I do not.
Definitely confusing. I’m with you though–if I were obsese and exercising hard, I would find it really hard to ignore my body’s hunger signals. That seems inadvisable psychologically, and like a sure set-up for failure.
I’m also very curious if the leptin sensitivity goes back to normal after weight is lost, or if once obese, the system gets screwed up permanently. Sure hope it’s reversible!
I’m a little concerned with how much the women were eating and how often. If I only ate three times a day I’d be hungry practically all the time. And what about timing of the meals with exercise? Did they eat 3 hours before or 27 minutes? I’m not usually hungry during exercise, but I get hungry pretty quick after (usually takes about 15 minutes for the hunger to set in). But I also usually eat at least a little 20-45 minutes prior (unless I’m exercising first thing AM). So….
And did they create 1000 calorie deficit over the three days or every day. 1000 calories burned in one day?? Seems like it must be over the three – that’s still 333 calories per day from walking – they’d be on the treadmill for at least an hour, right?
Maybe it’s psychological – obese women (and me) think about food constantly and thus are always hungry.
I think your comment “social stigma, much?” brings up a vital point.
Once again our Western dualism approach is separating the physical from the psychological. Why are these women lean or obese in the first place and what are the pshycological variables that influence perceived hunger. Is perceived hunger measurable at all? Interesting study leading to much more interesting questions…
Very interesting! Everyone has very valid points and the same questions I would have for these researchers. You are such a great writer Charlotte!
Confused here.
All I can say is that I am hungry at the beginning of my workouts- so I drink an performance type drink during then it takes me 30-40 minutes post workout before I feel hungry again.
Oy. I’m so confused.
(Not like that’s anything new.)
Love your blog – not sure how I found it but I read almost every day. Add one to the lean women who is never hungry after exercise (just another reason why I love working out!).
Oh studies, how confusing and silly you are!
But I also think its difficult to judge what “hunger” is, exactly. I really think that in our society of constantly eating, ALL of us have really lost the meaning of “hunger”. We confuse hunger with many other things, so asking anyone in a study if they are hungry WOULD have odd results. I think I listen to my body pretty well but sometimes I’ll think I’m hungry, then I get distracted by something else and an hour later I remember that I HAD been hungry- only I realize that I’m not hungry at all anymore. I think our minds like to play tricks on us:)
Ha Ha!! Remember when we talked about trying to figure this one out a few months ago? I’m glad I left it in the to do pile!
I guess I’m sticking with:
“A well functioning body functions well!”
Seems safe enough 🙂
Dr. J
Very interesting study! As a man I am always hungry! 🙂
i’m hungry NOW. maybe I won’t be hungry later. or maybe I will.
I’m getting to the point where I just want to ignore all “research” and just do what feels best for my body.
I personally can’t eat before or after working out, or I feel nauseous. I’m slightly overweight so I don’t really know where I would fit in, in this study anyway lol.
Great post on what is the “core” debate for successfully maintaining a desired weight and body fat level…I would like to add that results will differ between men and women…that this study was for women and will not necessarily be true for men…and that Physiological studies that I have read categorically state that “metabolic changes” come about from caloric intake level…calorie restriction will prolong life…i.e. those people that will restrict their daily calories will have a metabolc change that will prolong their life…science is proving this out…also, exercise, especially high intensity and consistent exercise will have the opposite metabolic effect and the body, especially muscles trying to repair damage to muscle cells and fiber, will need increased protein and carbohydrate consumption to maintain themselves or will be broken down for glucose to feed the body…these though are studies, I believe that involved primarily male subjects…all I know is that the human body has evolved from a hunter gatherer existence where if you found food after a long walk or migration, your body was ravenous in it’s appetite because it knew that the next meal might be a while…my body has reduced its caloric needs as I have decreased my exercise ratio relative to my diet…2500 – 3000 calories per day is now down to 1500-2000 calories per day and I do almost no cardio except for brief jogs or stair running…core exercises like situp and squats dominate my exercise routine…for what it’s worth, here is a brief part of a posting on KSBW.com, (http://www.ksbw.com/health/16263723/detail.html)
“…A news release from the American Physiological Society said that one theory is that exercise places stress on the body that can cause some damage.
In the new study, researchers found that the stress of exercise did not produce enough damage to explain why exercise does not lengthen life span. Instead, researchers said, they found that that caloric restriction creates beneficial changes in hormone levels, which exercise does not.
The researchers concluded that these metabolic changes play a role in extending life”…Michael
I wonder about the risks involved of obese people doing hi-intensity exercise in the first place. Isn’t there an increased chance of heart problems, because of the additional drag on the heart?
I have a close friend who is obese. He says 1) he is _always_ hungry. 2) his body doesn’t work in telling him when he’s full, and he _never_ feels satieted to where he’s full and should stop eating. He has to tell himself to stop eating after portions that he thinks were adequate. Tho, he thinks that his body is unique and that it’s “broken” somehow.
I would be curious to see him in this study with his personal leptin levels. There’s probably some level where A) either obese have reduced sensitivity to leptin, or B) maybe an obese body goes screwy with regards to leptin-regulation. And hi-intensity exercise exacerbates the issue.
Or C) maybe the body just knows that they would have normally been eaten by saber-toothed tigers, and just gives up trying to regulate.
(Ugh, long-winded post) Since talking about this with him, I’ve become more sensitive to my own level of satiety. And for the 1st time noticed that after a big meal, I can get by on just 2 meals the next day. But maybe that’s just a 36-yr old metabolism finally slowing.
I’m thinking we need more hungry saber-tooths running around!
Interesting study (freaky bunny-cat photo!!), but I kind of take it with a grain of salt. I don’t think my appetite has changed much because of exercise. But then I’ve always had a pretty good appetite! 🙂
ok, that is one SCARY picture!
as for the study, it just hurts my head to read all the “conclusions”.
Sometimes I feel like a nut.
Sometimes I don’t.
(and Congrats to Michael!)
Hey I read your blog, don’t I count? just cause I live with you.
I agree with this study completely, I have no idea what exercise does to my appetite.
Well, as nonsensical as it is, I like it becasue it validates me. I have to be very careful when I start intense exercise training because My appetite goes through the roof. But, does that mean I’m obese? Or just have pobese Leptin glands? I don’t know…
Hmmm on a personal note, since I’ve lost my 20lbs this year, and my 20 last fall (yes 40 lbs!), I have a relentless appetite!. I’m always hungry.
I didn’t read the study, but did the even mention BMR?
Hey, leaping into this discussion /only/ three weeks late!
I ran across a book by Covert Bailey that mentions this difference in appetite levels between obese and lean exercisers. Can’t find the book at the moment (a lot of things got misplaced when I moved) but I remember him mentioning a theory as to why this happened… he even had a diagram… the details are slipping away even as I try to remember them. I’ll hunt for that book.
Great post.
A thought on being scientific about exercise and weight control …
If you want to know how exercise effects your body, and you have confidence in science, try doing it and measure the effects. Make yourself the study population rather than trying to identify (or not) with the population in the latest study. Or, if instead you want to understand the research, get the background for the program and read the literature directly.
People tend to treat journalist’s reports of research it as if it were “scientific advice” and then when it is nothing of the kind (which is generally the case), the researchers are accused of being hopelessly obscure, getting paid for results, or being contradictory about their advice. What a bum rap.
That’s not the point of research at all. Research is most *interesting* when it contains contradictions and gets *boring* when the results become consistent. Sure, you want to prove your new hypothesis is right, but if it were easy to demonstrate someone would already have demonstrated it. You expect things to be fuzzy in a new area of research where there are interesting new hypotheses to test.
You can almost never generallize “laws” (or advice) from a single study, nor should you expect to. Conclusions vary even in very similar studies either because of the way the question was asked or because they didn’t identify the right variables in the right way yet to address the question. That’s assuming they’re even studying something that can be characterized in a law-like way, which isn’t always the case.
Sometimes individual differences outweigh generalized laws, even when there *are* underlying laws (this is a common finding in social psychology research). More to the point, this seems to be the case somewhat with nutrition as well.
Conflicting results are a symptom of a fertile research topic.
IMO, if you want to draw good advice from research, stop jumping on every new study that comes out just because it seems to say something you’d like to hear, and learn to follow the *trends* in the research programs. That means reading technical books and journals rather than sound bites and blogs, and looking for commonalities rather than just reports that stand out because they are novel. But that’s more work than you probably need to do.
There are a lot of people that have been spending decades researching obesity and there are some very useful conclusions. But you still have to do the work to see what works best for you.
I think there are many, many fat people out there exercising like crazy and not reaching their goals because they keep looking for magic bullets or excuses instead of starting with sound principles and then experimenting carefully to see what is working for them and what isn’t.
I’ve noticed that there are also a number of chubby runners out there who stay chubby because they take in more than they put out, which I suspect is due to the putative appetite effect.
It could well be that they would benefit by changing their training to briefer, higher intensity work, so that the appetite effect would lessen and the metabolic increase last longer. But that’s speculation at this point and represents very hard work and many people would give up on such a regimen if they’re used to jogging and elliptical machines and such.
So they have to experiment to see what’s right for them. Well, anyway, it is an approach that has always worked very well for me.
Just remember, people tend to distort their own perception of what they take in and what they put out (*that’s* a pretty well validated research result across many studies). So when you measure your compliance and your results, be sure to be specific and use accurate measurements and don’t rely on memory and estimation.
kind regards, Todd
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