Evidence in female rhesus monkeys (Macaca mulatta) that nighttime caloric intake is not associated with weight gain.
OBJECTIVE
To evaluate the hypothesis that nighttime consumption of calories leads to an increased propensity to gain weight.


METHODS
Sixteen female rhesus monkeys (Macaca mulatta) were ovariectomized and placed on a high-fat diet to promote weight gain, and we examined whether monkeys that ate a high percentage of calories at night were more likely to gain weight than monkeys that ate the majority of calories during the day.


RESULTS
Within 6 weeks post-ovariectomy, calorie intake and body weight increased significantly (129 +/- 14%, p = 0.04; 103 +/- 0.91%, p = 0.02, respectively). Subsequent placement on high-fat diet led to further significant increases in calorie intake and body weight (368 +/- 56%, p = 0.001; 113 +/- 4.0%, p = 0.03, respectively). However, there was no correlation between the increase in calorie intake and weight gain (p = 0.34). Considerable individual variation existed in the percentage of calories consumed at night (6% to 64% total daily caloric intake). However, the percentage of calorie intake occurring at night was not correlated with body weight (r = 0.04; p = 0.87) or weight gain (r = 0.07; p = 0.79) over the course of the study. Additionally, monkeys that showed the greatest nighttime calorie intake did not gain more weight (p = 0.94) than monkeys that showed the least nighttime calorie intake.


CONCLUSIONS
These results show that eating at night is not associated with an increased propensity to gain weight, suggesting that individuals trying to lose weight should not rely on decreasing evening calorie intake as a primary strategy for promoting weight loss.
Sullivan
Elinor L
EL
Department of Physiology and Pharmacology, Oregon Health and Science University, Portland, 97006, USA.
Daniels
Alejandro J
AJ
Koegler
Frank H
FH
Cameron
Judy L
JL
D000818:Animals; D049628:Body Size; D002940:Circadian Rhythm / Q000502:physiology*; D004435:Eating / Q000502:physiology*; D002149:Energy Intake; D005247:Feeding Behavior / Q000502:physiology*; D005260:Female; D005518:Food Preferences; D008253:Macaca mulatta; D023421:Models, Animal; D010052:Ovariectomy; D012044:Regression Analysis; D013997:Time Factors; D015430:Weight Gain / Q000502:physiology*