Chronobiology and Nutrition. Biological Rhythms and Medicine. New York: Springer; 1983. pp. 265-300. [DOI: 10.1007/978-1-4613-9496-9_7]

The influence of intermittent fasting on the circadian pattern of melatonin while controlling for caloric intake, energy expenditure, light exposure, and sleep schedules: A preliminary report

AIMS:

We hypothesized that if we control for food composition, caloric intake, light exposure, sleep schedule, and exercise, intermittent fasting would not influence the circadian pattern of melatonin. Therefore, we designed this study to assess the effect of intermittent fasting on the circadian pattern of melatonin.

METHODS:

Eight healthy volunteers with a mean age of 26.6 ± 4.9 years and body mass index of 23.7 ± 3.5 kg/m² reported to the Sleep Disorders Center (the laboratory) on four occasions: (1) adaptation, (2) 4 weeks before Ramadan while performing Islamic intermittent fasting for 1 week (fasting outside Ramadan [FOR]), (3) 1 week before Ramadan (nonfasting baseline [BL]), and (4) during the 2^nd week of Ramadan while fasting (Ramadan). The plasma levels of melatonin were measured using enzyme-linked immunoassays at 22:00, 02:00, 04:00, 06:00, and 11:00 h. The light exposure, meal composition, energy expenditure, and sleep schedules remained the same while the participants stayed at the laboratory.

RESULTS:

The melatonin levels followed the same circadian pattern during the three monitoring periods (BL, FOR, and Ramadan). The peak melatonin level was at 02:00 h and the trough level was at 11:00 h in all studied periods. Lower melatonin levels at 22:00 h were found during fasting compared to BL. Cosinor analysis revealed no significant changes in the acrophase of melatonin levels.

CONCLUSIONS:

In this preliminary report, under controlled conditions of light exposure, meal composition, energy expenditure, and sleep-wake schedules, intermittent fasting has no significant influence on the circadian pattern of melatonin.

The Nutritional Status and Eating Habits of Shift Workers: A Chronobiological Approach

The eating habits of workers may vary according to the season of the year and corresponding work schedule. A study aiming at verifying the changes in their diet in summer and winter, as well as the nutritional status of those who work fixed shifts, was conducted. The distribution during the 24h in the quantity of calories and macronutrients ingested and the circadian rhythm of calories consumed were also analyzed. The study was conducted on 28 workers subject to three fixed work (morning, afternoon, and night) shifts at a transport company in the city of São Paulo, Brazil. The mean age of the workers was 32.8 (SD+/-5.3) yrs. Their food intake was ascertained by the use of a 3-day dietary record, and their nutritional status was evaluated by their body mass index (BMI), both in winter and summer. Two-way ANOVA (shift and season) showed food consumption--measured in calories/24 h--was significantly higher in winter than summer (F(1.25)=11.7; p<0.001). No statistically significant differences were found among shifts (F(2.25)=0.85; p<0.44), and the interaction effect between shift and season was also not significant (F(2.25) = 0.15; p < 0.86). No seasonal difference in BMI was detected (Kruskal-Wallis test). Cosinor analyses showed circadian rhythmicity in calories consumed by morning (p < 0.01) as well as afternoon shift workers (p < 0.001), both in the winter and summer. Circadian rhythmicity in calories consumed by night workers was found only in summer (p < 0.01). The changes observed in the workers' eating habits from one season to another and during the 24h period show the need for further studies to help develop educational programs to improve the nutrition of shift employees taking into consideration shift schedule and season of the year when work is performed.

Postprandial Metabolic Profiles Following Meals and Snacks Eaten during Simulated Night and Day Shift Work

Shift workers are known to have an increased risk of developing cardiovascular disease (CVD) compared with day workers. An important factor contributing to this increased risk could be the increased incidence of postprandial metabolic risk factors for CVD among shift workers, as a consequence of the maladaptation of endogenous circadian rhythms to abrupt changes in shift times. We have previously shown that both simulated and real shift workers showed relatively impaired glucose and lipid tolerance if a single test meal was consumed between 00:00-02:00 h (night shift) compared with 12:00-14:00 h (day shift). The objective of the present study was to extend these observations to compare the cumulative metabolic effect of consecutive snacks/meals, as might normally be consumed throughout a period of night or day shift work. In a randomized crossover study, eight healthy nonobese men (20-33 yrs, BMI 20-25kg/m2) consumed a combination of two meals and a snack on two occasions following a standardized prestudy meal, simulating night and day shift working (total energy 2500 kcal: 40% fat, 50% carbohydrate, 10% protein). Meals were consumed at 01:00/ 13:00 h and 07:00/19:00h, and the snack at 04:00/16:00 h. Blood was taken after an overnight fast, and for 8 h following the first meal on each occasion, for the measurement of glucose, insulin, triacylglycerol (TAG), and nonesterified fatty acids (NEFA). RM-ANOVA (factors time and shift) showed a significant effect of shift for plasma TAG, with higher levels on simulated night compared to day shift (p < 0.05). There was a trend toward an effect of shift for plasma glucose, with higher plasma glucose at night (p = 0.08), and there was a time-shift interaction for plasma insulin levels (p < 0.01). NEFA levels were unaffected by shift. Inspection of the area under the plasma response curve (AUC) following each meal and snack revealed that the differences in lipid tolerance occurred throughout the study, with greatest differences occurring following the mid-shift snack. In contrast, glucose tolerance was relatively impaired following the first night-time meal, with no differences observed following the second meal. Plasma insulin levels were significantly lower following the first meal (p < 0.05), but significantly higher following the second meal (p < 0.01) on the simulated night shift. These findings confirm our previous observations of raised postprandial TAG and glucose at night, and show that sequential meal ingestion has a more pronounced effect on subsequent lipid than carbohydrate tolerance.

Alteration of internal circadian phase relationships after morning versus evening carbohydrate-rich meals in humans

The effects of a single morning and evening carbohydrate-rich meal for 3 consecutive days on circadian phase of core body temperature (CBT), heart rate, and salivary melatonin rhythms were compared under controlled constant routine conditions. In 10 healthy young men entrained to a natural light-dark cycle with regular sleep timing, CBT and heart rate were significantly elevated for approximately 8 h after the last evening carbohydrate-rich meal (EM), and nocturnal melatonin secretion (as measured by salivary melatonin and urinary 6-sulphatoxymelatonin levels) was reduced, compared to the morning carbohydrate-rich meal (MM) condition. Thus, circadian phase could not be measured until the following day due to this acute masking effect. The day after the last meal intervention, MM showed a significant advanced circadian phase position in CBT (+59+/-12 min) and heart rate (+43+/-18 min) compared to EM. However, dim-light melatonin onset was not significantly changed (+15+/-13 min). The results are discussed with respect to central (light-entrainable) and peripheral (food-entrainable) oscillators. Food may be a zeitgeber in humans for the food-entrainable peripheral oscillators, but melatonin data do not support such a conclusion for the light-entrainable oscillator in the suprachiasmatic nucleus.

Circannual variations in baseline blood values of dogs

Forty-two hematological and biochemical variables routinely measured in dogs as part of a preoperative protocol have been analyzed for circannual changes by analysis of variance (ANOVA) and single cosinor procedures. Data were available from up to 489 adult mongrel dogs of both sexes studied on weekdays over a 5-year span (January 5, 1987 to December 18, 1991). Dogs were housed in individual cages at 24 +/- 1 degrees C with dog chow and tap water available ad libitum and lights on between 06:00 and 18:00 h. A single blood sample/dog was collected by jugular venipuncture between 08:00 and 09:00 h and sent to a commercial laboratory for hematological and biochemical determinations. Data were assigned to date and time of sampling and analyzed for the effect of time of year by ANOVA (across 12 months and 4 seasons), and by the least-squares fit of a precise 1-year cosine. ANOVA and single cosinor described a significant circannual time effect and rhythm for the following: total leukocytes, lymphocytes, hemoglobin, mean corpuscular hemoglobin (MCH), MCH concentration, red cell distribution width, mean platelet volume, creatinine, blood urea nitrogen (BUN), BUN/creatinine ratio, amylase, glucose, chloride, uric acid, direct bilirubin, total protein, albumin, globulin, albumin/globulin ratio, lactate dehydrogenase, alkaline phosphatase, gamma-glutamyltransferase, alanine aminotransferase (ALT), and aspartate aminotransferase (AST)/ALT ratio. A significant effect of season by ANOVA only was found for: Ca, Na, phosphorus, total bilirubin, hematocrit, mean corpuscular volume, and neutrophils. No significant time effect could be found at p < or = 0.05 by either statistical method for: K, Mg, Fe, cholesterol, triglycerides, ASP, red blood cells, monocytes, eosinophils, basophils, or platelets. Acrophases occurred for the most part in either the winter or summer.

Circadian rhythms and their mechanisms

Recent work concerning the number, site(s) and means of adjustment to the 24-h day of internal clocks is reviewed. Work on humans is considered wherever possible though much of the work involving ablation and in vitro techniques necessarily involves other species, particularly rodents. It is concluded that, though recent advances have been impressive and present techniques appear likely to continue to produce results and stimulate discussion, more attention should be directed to considering the circadian system as a whole rather than as an assemblage of individual components.