Evidence that transient nicotine lowers the body weight set point

OBJECTIVE

Smokers usually gain weight when they quit smoking. The present work explores the hypothesis according to which such a rise is a behavioral response to a raised body weight set point taking place when nicotine is eliminated from the body.

RESEARCH METHODS AND PROCEDURES

The human body weight set point was assessed with classical behavioral and psychophysical methods, from the delay to experience negative alliesthesia when repeatedly ingesting sweet stimuli. Seven habitual smokers were tested once before lunch, after smoking (nonabstinent) as usual and once again after refraining from smoking (abstinent). Three additional nicotine-naive subjects were tested under the same procedure after receiving at 0730 h in the morning a transdermal nicotine patch (14 mg) or a placebo patch. Two of the subjects also received nicotine (7 mg) for a third session.

RESULTS

Oral and transdermal administration of nicotine did not decrease the initial pleasure or modify the initial palatability of eating sweet stimuli, but significantly accelerated the following onset of self-reported displeasure (negative alliesthesia) aroused by repeated ingestion of sweet stimuli.

DISCUSSION

These results are understood as an acute lowering of the body weight set point by nicotine. The body weight gain taking place after quitting smoking may, therefore, be explained by the removal of the lowering of the body weight set point induced by nicotine.

Nicotine lowers the body-weight set-point in male rats

Set-point of body weight was assessed by the behavioral method of the weight threshold to hoard food. Intra-peritoneal injection of nicotine (0.02-0.05 mg/kg) significantly lowered the rats' body weight set-point by 8.5+/-2.7 and 19.2+/-2.6 g (p< or =0.05). These results suggest that the administration of low-dose nicotine lowers the body-weight set-point and may be important in predicting the anticipated gain in weight frequently reported upon withdrawal.

Diet induced weight loss accelerates onset of negative alliesthesia in obese women

BACKGROUND

The physiological and behavioral responses to hypocaloric diet are to increase energy intake to defend a steady body weight. We utilized the method of "negative alliesthesia" for measuring the hedonic reponse to sweet stimulus before (Initial session) and 3 months after entering a weight loss program. The negative alliesthesia test is known by physiologists but few clinical data exist. It is based on the observation that repeated pleasant gustatory stimuli turn into unpleasantness in the process of alliesthesia. At first visit participants repeatedly ingested sweet stimuli until they found them unpleasant and rated quantitatively on a linear analogue scale their hedonic experience. This procedure was repeated every 3 min until participants felt displeasure to end the session. The same protocol was followed after three months of following a weight loss diet. Dieting energy intake was from 1400 - 2000 kcal/d for 8 wk. Energy composition was 50% carb:25% prot: 25% lipid. After 8 wk caloric intake increased by 50 kcal/wk, to reach daily intake of 1800 - 2400 kcal/d. Energy composition was 50% carb:22% prot: 27% lipid. We report results on the effect of slow weight loss on negative alliesthesia in ten obese female participants enrolled in a commercial diet program based on Canada's Food Guide (Mincavi).

RESULTS

Results showed that diet lowered the mean BMI (Initial session 36.8 +/- 1.8 vs. 3 mo 34.9 +/- 1.8 kg/m2). At 3 mo the onset of negative alliesthesia, time to abandon experimental session, was shortened (Initial session 33 vs. 3 mo 24 min). The same trend was observed in the time to reach indifference (Initial session 21.9 +/- 3.8 vs. 3 mo 16.2 +/-2.4 min). There was no observed difference in maximum (Initial session +79.5 +/- 11.7; 3 mo +94.5 +/- 9.9 mm) and minimum (Initial session -90.0 +/- 14.4; 3 mo -106 +/- 11.1 mm) hedonic rating.

CONCLUSION

Earlier onset of negative alliesthesia, as seen in our participants, is not consistent with previous hedonic studies that showed delayed or absent negative alliesthesia in participants when below their initial body weight. Therefore, it is hypothesized that the accelerated onset of negative alliesthesia observed in our obese participants after weight loss is suggestive of a lowered body weight set-point. Factors inherent to the weight loss diet studied here, such as mild energetic restriction, lowered palatability, and diet composition, may have played a role in this experimental outcome.

Salicylate as a partial inhibitor of emotional fever and body weight set-point in rats: behavioral and neuroendocrine study

In this article, we report findings from behavioral and neuroendocrine experiments in rats under pharmacologically induced antipyretic conditions. Endpoints included emotional fever, body weight setpoint, and in situ corticotropin-releasing hormone mRNA (CRHmRNA) expression. Nine male Wistar rats were treated with acetylsalicylic acid (ASA) 0.04 g/kg ip in vehicle. On alternating days, all rats received saline (0.9% w/v) as a control. ASA was selected chiefly for its antipyretic and also for effects on metabolism. It has been demonstrated that gentle handling affects body weight and body temperature in rats. In Experiment 1, we investigated whether blocking emotional fever by ASA treatment would inhibit the lowering of the body weight setpoint induced by handling of the rats. Rats were exposed to a daily food-hoarding session under handling stress, and their body weight setpoints were calculated from the hoarding measurements. As rats received ASA and saline in an alternating manner, two setpoints were calculated. In Experiment 2, we performed neuroendocrine analyses of CRHmRNA expression in the same group of animals from Experiment 1. CRHmRNA was determined by in situ hybridization. Results indicated that ASA treatment in rats significantly decreased the body weight setpoint (P=.02) and significantly prevented increases in body temperature due to emotional fever (P=.03) when compared to their control values. Findings also revealed that hypothalamic CRH expression was increased when rats were treated with ASA. ASA did partially block fever induced by handling, but it is difficult to confirm whether emotion was also inhibited by treatment. Taken together, these results indicate that salicylates affect energy balance and might be a good inhibitor of body weight gain in rats.

Body weight and satiation after duodenal switch: 2 years later

BACKGROUND

The authors investigated body weight, satiation, and gustative pleasure of obese patients 2 years after a bariatric operation: the biliopancreatic diversion with duodenal switch (DS).

METHODS

9 operated patients, 10 unoperated non-obese and 10 unoperated obese persons participated in the "alliesthesia (food distaste) test". This test is a psychometric assessment of satiation resulting from the pleasure or displeasure following the repeated ingestion of a sweet stimulus. Operated patients also participated in the test before the DS operation.

RESULTS

2 years after DS, patients had lost 50% of their body weight and their BMI was rendered similar to that of the non-obese control group. Their satiation was faster than in control and unoperated obese patients. The responses of control and unoperated obese patients were identical to those of pre-surgery operated patients.

CONCLUSION

This indicates that at the time of the experiment, patients' actual body weight was higher than their body weight set-point and that they would be likely to continue to lose weight, at least beyond 2 years.