Twice as High Diet-Induced Thermogenesis After Breakfast vs Dinner On High-Calorie as Well as Low-Calorie Meals

BACKGROUND

The question of whether there is daytime time variation in diet-induced thermogenesis (DIT) has not been clearly answered. Moreover, it is unclear whether a potential diurnal variation in DIT is preserved during hypocaloric nutrition.

OBJECTIVE

We hypothesized that DIT varies depending on the time of day and explored whether this physiological regulation is preserved after low-calorie compared with high-calorie intake.

DESIGN

Under blinded conditions, 16 normal-weight men twice underwent a 3-day in-laboratory, randomized, crossover study. Volunteers consumed a predetermined low-calorie breakfast (11% of individual daily kilocalorie requirement) and high-calorie dinner (69%) in one condition and vice versa in the other. DIT was measured by indirect calorimetry, parameters of glucose metabolism were determined, and hunger and appetite for sweets were rated on a scale.

RESULTS

Identical calorie consumption led to a 2.5-times higher DIT increase in the morning than in the evening after high-calorie and low-calorie meals (P < .001). The food-induced increase of blood glucose and insulin concentrations was diminished after breakfast compared with dinner (P < .001). Low-calorie breakfast increased feelings of hunger (P < .001), specifically appetite for sweets (P = .007), in the course of the day.

CONCLUSIONS

DIT is clearly higher in the morning than in the evening, irrespective of the consumed calorie amount; that is, this physiological rhythmicity is preserved during hypocaloric nutrition. Extensive breakfasting should therefore be preferred over large dinner meals to prevent obesity and high blood glucose peaks even under conditions of a hypocaloric diet.

New Insights into the Diurnal Rhythmicity of Gut Microbiota and Its Crosstalk with Host Circadian Rhythm

Unlike the strictly hierarchical organization in the circadian clock system, the gut microbiota rhythmicity has a more complex multilayer network of all taxonomic levels of microbial taxa and their metabolites. However, it is worth noting that the functionality of the gut microbiota rhythmicity is highly dependent on the host circadian clock and host physiological status. Here, we discussed the diurnal rhythmicity of the gut microbiota; its crucial role in host physiology, health, and metabolism; and the crosstalk between the gut microbial rhythmicity and host circadian rhythm. This knowledge lays the foundation for the development of chronotherapies targeting the gut microbiota. However, the formation mechanism, its beneficial effects on the host of gut microbial rhythmicity, and the dynamic microbial-host crosstalk are not yet clear and warrant further research.

Social Isolation Modulates CLOCK Protein and Beta-Catenin Expression Pattern in Gonadotropin-Inhibitory Hormone Neurons in Male Rats

Postweaning social isolation reduces the amplitude of the daily variation of CLOCK protein in the brain and induces lower reproductive activity. Gonadotropin-inhibitory hormone (GnIH) acts as an inhibitor in the reproductive system and has been linked to stress. Social isolation has been shown to lower neuronal activity of GnIH-expressing neurons in the dorsomedial hypothalamus (DMH). The exact mechanism by which social isolation may affect GnIH is still unclear. We investigated the impact of social isolation on regulatory cellular mechanisms in GnIH neurons. We examined via immunohistochemistry the expression of CLOCK protein at four different times throughout the day in GnIH cells tagged with enhanced fluorescent green protein (EGFP-GnIH) in 9-week-old adult male rats that have been raised for 6 weeks under postweaning social isolation and compared them with group-raised control rats of the same age. We also studied the expression of β-catenin-which has been shown to be affected by circadian proteins such as Bmal1-in EGFP-GnIH neurons to determine whether it could play a role in linking CLOCK in GnIH neurons. We found that social isolation modifies the pattern of CLOCK expression in GnIH neurons in the DMH. Socially isolated rats displayed greater CLOCK expression in the dark phase, while control rats displayed increased CLOCK expression in the light phase. Furthermore, β-catenin expression pattern in GnIH cells was disrupted by social isolation. This suggests that social isolation triggers changes in CLOCK and GnIH expression, which may be associated with an increase in nuclear β-catenin during the dark phase.

Diurnal rhythmicity in biological processes involved in bioavailability of functional food factors

In the past few decades, many types of functional factors have been identified in dietary foods; for example, flavonoids are major groups widely distributed in the plant kingdom. However, the absorption rates of the functional food factors are usually low, and many of these are difficult to be absorbed in the intact forms because of metabolization by biological processes during absorption. To gain adequate beneficial effects, it is therefore mandatory to know whether functional food factors are absorbed in sufficient quantity, and then reach target organs while maintaining beneficial effects. These are the reasons why the bioavailability of functional food factors has been well investigated using rodent models. Recently, many of the biological processes have been reported to follow diurnal rhythms recurring every 24 h. Therefore, absorption and metabolism of functional food factors influenced by the biological processes may vary with time of day. Consequently, the evaluation of the bioavailability of functional food factors using rodent models should take into consideration the timing of consumption. In this review, we provide a perspective overview of the diurnal rhythm of biological processes involved in the bioavailability of functional food factors, particularly flavonoids.

Contrasting diurnal patterns in antioxidant capacities, but not in expression of stress protein genes among copepod populations from clear versus glacially fed alpine and subalpine lakes

Short-term changes in environmental conditions largely influence planktonic organisms, but their responses will depend on the habitat characteristics. Here we studied diurnal patterns in antioxidative metabolites (lipophilic and hydrophilic antioxidant capacities) and in the expression of stress protein genes (heat shock proteins, hsp) of copepods to identify short-term stress responses in clear and turbid alpine lakes, as well as in less transparent subalpine ones. Cyclops abyssorum tatricus showed diurnal variation in antioxidant capacities with maxima around noon in clear, but not in glacially fed, turbid lakes. Low fluctuations of these metabolites were also observed in another copepod, Acanthodiaptomus denticornis. Although levels of hsp genes differed between populations living in clear or glacially fed lakes, there was no diurnal rhythmicity in gene expression. Our data show that when planktonic organisms may be at greatest risk of oxidative damage, such as during the daytime in high UV radiation environments, they activate antioxidant responses. Conversely, in less transparent lakes, the physiological response seems to be unnecessary. The difference in gene expression levels suggests an ecological, albeit not acute, role of these genes in copepods experiencing daily environmental fluctuations.

PER Gene Family Polymorphisms in Relation to Cluster Headache and Circadian Rhythm in Sweden

The trigeminal autonomic cephalalgia, cluster headache (CH), is one of the most painful disorders known to man. One of the disorder's most striking features is the reported diurnal rhythmicity of the attacks. For a majority of patients, the headache attacks occur at approximately the same time every day. Genetic variants of genes involved in the circadian rhythm such as Period Circadian Regulator 1, 2, and 3 (PER1, 2 and 3) are hypothesized to have an effect on the rhythmicity of the attacks. Six PER1, 2 and 3 genetic markers; the indel rs57875989 and five single nucleotide polymorphisms (SNPs), rs2735611, rs2304672, rs934945, rs10462020, and rs228697, were genotyped, using TaqMan^® or regular polymerase chain reaction (PCR), in a Swedish CH case control material. Logistic regression showed no association between CH and any of the six genetic variants; rs57875989, p = 0.523; rs2735611, p = 0.416; rs2304672, p = 0.732; rs934945, p = 0.907; rs10462020, p = 0.726; and rs228697, p = 0.717. Furthermore, no difference in allele frequency was found for patients reporting diurnal rhythmicity of attacks, nor were any of the variants linked to diurnal preference. The results of this study indicate no involvement of these PER genetic variants in CH or diurnal phenotype in Sweden.