NYT: Thinking Makes Me Fat...

Behavior: I Think, Therefore I’m Fat?
By NICHOLAS BAKALAR

Could thinking make you fat? Maybe. A small Canadian study has found that people eat more after an intellectual exercise than they do after just sitting quietly for the same amount of time.
The scientists had 14 female students engage in three 45-minute sessions before being invited to eat as much as they wanted at a buffet. For one session, they rested in a sitting position. In the next, they read a document and wrote a summary of it, and in the third they performed a series of computer-based tests.
Even though the same amount of physical energy was involved in all three sessions, the women consumed an average of more than 25 percent more calories after the intellectual exercises than after just sitting quietly. The study, published in the September issue of Psychosomatic Medicine, controlled for habitual diet, body mass, anxiety level and other factors.
There may be a physiological explanation. In blood samples drawn periodically during the experiment, the researchers found an increase in levels of the stress hormone cortisol and increased fluctuation in plasma glucose and insulin levels during and after the mental workouts.
“There is nothing in these findings that can be described as restful activity,” said Angelo Tremblay, the lead author and a professor of nutrition at Laval University in Quebec City. “We may sometimes be inclined to underestimate the biological impact of mental work.”

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Glycemic Instability and Spontaneous Energy Intake: Association With Knowledge-Based Work
Jean-Philippe Chaput, PhD, Vicky Drapeau, RD, PhD, Paul Poirier, MD, PhD, Normand Teasdale, PhD and Angelo Tremblay, PhD
From the Division of Kinesiology, Department of Social and Preventive Medicine, Faculty of Medicine, Laval University, Quebec City, Quebec, Canada (J.P.C, V.D., N.T., A.T.); Quebec Heart Institute, Hôpital Laval Research Center, Hôpital Laval, Quebec City, Quebec, Canada (P.P.); Faculty of Pharmacy, Laval University, Quebec City, Quebec, Canada (P.P.).

Address correspondence and reprint requests to Angelo Tremblay, PhD, Division of Kinesiology (PEPS), Department of Social and Preventive Medicine, Laval University, Quebec City, Quebec, Canada, G1K 7P4. E-mail: angelo.tremblay@kin.msp.ulaval.ca

Objective: To further document the impact of knowledge-based work (KBW) on spontaneous energy intake and glucose homeostasis.

Methods: We used a within-subjects experimental design, in which each participant was engaged in each of the three 45-minute conditions followed by an ad libitum buffet, 1) resting in a sitting position; 2) reading a document and writing a summary; or 3) performing a battery of computerized tests. Fourteen female students (mean age: 22.8 ± 2.3 years, mean body mass index: 22.4 ± 2.5 kg/m2) were recruited to participate. Plasma glucose, insulin, and cortisol levels at seven time-points, and appetite sensation markers were measured at each experimental condition.

Results: The mean ad libitum energy intake after the reading-writing and the automated test-battery conditions exceeded that measured after rest by 848 kJ and 1057 kJ, respectively (p < .05). No specific dietary preference was detected, as reflected by the comparable percent of energy from each macronutrient in the three conditions. No significant difference in appetite sensation markers was observed among the three conditions. Mean cortisol level over 45 minutes in the two KBW conditions was significantly higher (p < .05) compared with the control condition. Finally, a significant increase in variations in plasma glucose and insulin levels was observed as compared with the control condition (p < .01).

Conclusions: This study showed that KBW acutely induces an increase in spontaneous energy intake, and promotes an increased fluctuation in plasma glucose and insulin levels. This study contributes to the documentation of a new risk factor for a positive energy balance, with the potential to lead to overweight in the long-term.


Key Words: mental work • cognitive tasks • energy balance • appetite • stress • sedentarity


Abbreviations: KBW = knowledge-based work; BMI = body mass index; HRV = heart rate variability; TFEQ = Three-Factor Eating Questionnaire; STAI = State-Trait Anxiety Inventory; SDNN = standard deviation of R-R interval; SDANN = standard deviation of the mean R-R calculated over a 5-min period; rMSSD = square root of the mean squared difference of successive R-R intervals; NN50 = number of adjacent N-N differing by more than 50 msec; pNN50 = NN50 divided by total number of N-N intervals; LF = low frequency; HF = high frequency; VAS = visual analogue scale; ANOVA = analysis of variance; SD = standard deviation; SEM = standard error of the mean; HPA = hypothalamo-pituitary-adrenal; WHR = waist-to-hip ratio.