|Is it true? Are we slaves to our internal clock? Is time really the only determinant of whether we are or aren't hungry?|
The insight that overeating shouldn't be a problem if we were able to adjust our energy intake to our energy expenditura was probably also in the back of of Elizabeth C. Wuorinen's and Katarina T. Borer's heads, when the researchers from the Norwich University and the University of Michigan devised two experiments that would allow them to investigate the human urge to eat (the thing we call hunger) and its obvious correlation with regular eating times (Wuorinen. 2013). In that, the scientists were particularly interested, ...
- whether a central neural circadian oscillator activates hunger during the wakeful period of the day to produce a hunger acrophase at mid-day, and
- if the hormonal consequences of meal eating and digestion and mechanical sequelae of digestive food processing inhibit this central hunger drive and thus provide cues for ultradian meal entrainment.
The clock controls when you're hungry. It's the master, the hormones are the slaves.
If that's correct, the magnitude of hunger of the 10 normal-weight post-menopausal women who participated in the Wuorinen study should be determined primarily by the circadian time of day and ultradian interdigestive episodes, and only secondarily, or even not at all by the inter-meal energy expenditure or the concentrations of ghrelin, leptin, or insulin. To verify that you have to collect hunger ratings in a realistic non-energy-deprived scenario and express them as function of time of day, interdigestive periods, the magnitude of energy deficit experienced since the previous meal, and plasma concentrations of ghrelin, leptin, and insulin.
|Figure 1: Illustration of the experimental setup during the 2 trials (Wuorinen. 2013)|
On the day before each trial, a standardized meal consisting of 60% carbohydrates, 25% fat, and 15% protein containing 33% of weight maintenance calories was provided at 19 h. As the scientists point out, ...
"[...a]ll trial meals also had this macronutrient composition. Caloric intake during the trials was assessed from measurements of food provided and any food left uneaten. The inter-meal intervals (IMIs) were: IMI1 from the dinner at 19 h prior to the start of the trial day to breakfast on the day of the trial, IMI2 from the breakfast to lunch at 13 h, and IMI3, from the lunch to the dinner at 17 h. No adjustments in the quantity of food provided were made for energy expended during exercise." (Wuorinen. 2013)The amount of food was standardized only in experiment 2 ("study 2" as the scientists called it). In experiment 1, the women were free to eat as much as they wanted.
|Figure 1: Energy expenditure and intake (kcal) during study 1, total energy balance (middle) and hunger ratings (right) expressed in relative to of maximal score on the scale (Wuorinen. 2013)|
Study 2 confirms the results of study 1 in a longer-term scenario w/ stand. energy intake
This time the subjects remained at the lab for a complete day, they performed two bouts of exercise at different intensities and received standardized meals and yet neither the exercise intensity, nor the inability to compensate for energy that was expended during the workouts had any effect on hunger-ratings - and that in the presence of increased ghrelin (=hunger hormone) levels.
Result #2: Neither the exercise intensity, nor the extend of the energy deficit or the rise in ghrelin the scientists observed when the energy intake on the three mails of experiment 2 was fixed had an effect on hunger ratings.All that would obviously suggest that the one thing that counts is and the entrained eating-frequency, if we did not know from previous SuppVersity articles that Taubesian "Exercise just makes you hungry"-hypothesis is fundamentally flawed.
For us, Wuorinen's & Borer's conclusion, which implies that the only thing that counts is that you eat, when it's time to eat, irrespective of how your energy balance looks like, is intriguing, but not bulletproof. There is after all one major caveat, somebody without our understanding of the effects of exercise on hunger and satiety (such as Wuorinen & Borer ;-) would not realize: If the exercise induced modulation of the energy balance (calories in vs. calories out) have no orm as the reduced neuronal response in brain regions in response to endurance exercise (cf. Evero. 2012) would suggest, a negative effect on hunger-ratings and ad-libitum food intake, you cannot use an exercise intervention to modulate the energy balance in an experiment that's designed to identify the influence of circadian rhythms on individual hunger ratings.
- Evero, Nero, et al. "Aerobic exercise reduces neuronal responses in food reward brain regions." Journal of Applied Physiology 112.9 (2012): 1612-1619.