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.
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.
Here’s where it gets weird.
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.
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?
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 feellike I am 35 again but with much more appreciation for life. life is good andyour blog makes life even better…. (Awww, thanks Michael!!)