Performance and sleepiness during a 24 h wake in constant conditions are affected by diet.

This study investigated the effects of high-carbohydrate (HC) and high-fat (HF) diet on cognitive performance, and subjective and objective sleepiness. Seven male participants were kept awake for 24 h in a metabolic ward. Meals were given every 4h and cognitive performance and sleepiness ratings were assessed hourly. The Karolinska Drowsiness Test (KDT, EEG derived) was performed twice after meal. Performance in simple reaction time showed a significant interaction of diet and the post-prandial period, a slower reaction time was observed for the HC-diet 3.5 h after meal intake. Diet did not affect EEG measures but a general post-prandial increase of objective sleepiness was observed 3.5h after meal servings. The HC-diet was significantly associated with an increase of subjective sleepiness. The study demonstrated that the HC-diet caused larger oscillation in performance and increased sleepiness as compared to HF-diet throughout day and night.

The human body may buffer small differences in meal size and timing during a 24-h wake period provided energy balance is maintained.

Because approximately 20% of the work force in the industrialized world have irregular working hours, it is pertinent to study the consequences of eating at irregular, especially nighttime hours. We studied the postprandial responses during nocturnal fasting vs. eating throughout a 24-h wake period. Seven healthy males were studied twice in a crossover design. After a 6-d diet adjustment period [high fat diet, 45 energy percent (en%) fat, 40 en% carbohydrates)] with sleep from 2300 to 0700 h, the men were kept awake for 24 h at the metabolic ward and given either 6 isoenergetic meals, i.e., every 4 h (N-eat) or 4 isoenergetic meals from 0800 to 2000 h followed by a nocturnal fast (N-fast), with the same 24-h energy intake. Energy expenditure, substrate utilization, activity, heat release, body temperature and blood variables were measured over 24 h. Energy expenditure and blood glucose, triacylglycerol, insulin and glucagon concentrations were lower and nonesterified fatty acids concentrations were higher during the nocturnal fast than during nocturnal eating (P < 0.05); however, no 24-h differences between the protocols were apparent. Nocturnal fasting slightly altered the secretory patterns of the thyroid hormones and cortisol (P < 0.05). We found no clear indication that it would be more favorable to ingest few larger daytime meals than smaller meals throughout the 24-h period. The body seems to be able to buffer small differences in meal size and timing provided energy balance is maintained.

Endocrine responses to nocturnal eating--possible implications for night work.

BACKGROUND: Night work is becoming more common and shift workers display several metabolic disturbances. Aim To study the endocrine responses in relation to time of day during a 24-h period and how dietary macronutrient composition affects these responses. DESIGN: Seven males (26-43 y and 19.9-26.6 kg. m(-2)) were studied in a crossover design. Isocaloric diets described as high-carbohydrates (HC; 65 energy percent (E%) carbohydrates and 20E% fat) or high-fat (HF; 40E% carbohydrates and 45E% fat) were given. After a 6-day diet adjustment period, the subjects were kept awake for 24 h in a metabolic unit and were served an isocaloric meal (continuation of respective diet) every 4-h. Blood samples were taken throughout the 24-h period. RESULTS: Insulin and leptin responses to meal intake differed with respect to time of day (p < 0.05). Time of day affected glucagon, thyroid stimulating hormone (TSH), free thyroxin (fT4), total triiodothyronine (tT3), cortisol, chromogranin A (CgA) and pancreatic polypeptide (PP) concentrations (p < 0.05). Meal intake decreased cortisol concentration after meals at 0800, 1200 and 0400 but not at 1600, 2000 and 0000 h. The PP's postprandial increase was greater during 0800-1600 h compared to 2000-0800 h. With the HC meals, lower glucagon and CgA concentrations (p < 0.05), and a tendency for lower tT3 concentrations (p = 0.053) were observed compared to the HF meals. CONCLUSION: Insulin, PP, TSH, fT4, cortisol and leptin responses to meal intake differed with respect to time of day. The decreased evening/nocturnal responses of cortisol and PP to meal intake indicate that nocturnal eating and night work might have health implications.

Metabolic responses to nocturnal eating in men are affected by sources of dietary energy.

Because night work is becoming more prevalent, we studied whether feeding at different times of a 24-h period would elicit different metabolic responses and whether dietary macronutrient composition would affect these responses. Seven men (26-43 y, 19.9-26.6 kg/m(2)) consumed two isocaloric diets, in a crossover design. The diets were a high carbohydrate (HC) diet [65 energy % (E%) carbohydrates, 20E% fat] and a high fat (HF) diet (40E% carbohydrates, 45E% fat). After a 6-d diet-adjustment period, the men were kept awake for 24 h and the food (continuation of respective diet) was provided as six isocaloric meals (i.e., every 4 h). Energy and substrate turnover, heart rate, mean arterial pressure (MAP), blood glucose, triacylglycerol (TAG), nonesterified fatty acid (NEFA) and glycerol were measured throughout the 24-h period. Significantly higher energy expenditure and NEFA concentration, and lower blood glucose and TAG concentrations were observed when the men consumed the HF diet than when they consumed the HC diet. Significant circadian patterns were seen in body and skin temperature (nadir, 0400-0500 h). When the men consumed the HF diet, significant circadian patterns were seen in fat oxidation (nadir, 0800-1200 h; plateau, 1200-0800 h), heat release (nadir, 0800-1200 h; plateau, 1600-0800 h), heart rate (nadir, 0000 h), blood glucose (nadir, 0800-1200 h; peak, 0000-0400 h), NEFA (nadir, 0800-1200 h; peak, 1200-2000 h) and TAG (nadir, 0800-1200 h; peak, 0400-0800 h) concentrations. Energy expenditure, carbohydrate oxidation, MAP and glycerol concentration did not display circadian patterns. Unequal variances eradicated most circadian effects in the HC-diet data. The increased TAG concentration in response to feeding at 0400 h might be involved in the higher TAG concentrations seen in shift workers. Distinct macronutrient/circadian-dependent postprandial responses were seen in most studied variables.