Calorie restriction (CR) extends lifespan and elicits numerous effects beneficial to health and metabolism in various model organisms, but the underlying mechanisms are not completely understood. Gut microbiota has been reported to be associated with the beneficial effects of CR; however, it is unknown whether these effects of CR are causally mediated by gut microbiota. In this study, we employed an antibiotic-induced microbiota-depleted mouse model to investigate the functional role of gut microbiota in CR. Depletion of gut microbiota rendered mice resistant to CR-induced loss of body weight, accompanied by the increase in fat mass, the reduction in lean mass and the decline in metabolic rate. Depletion of gut microbiota led to increases in fasting blood glucose and cholesterol levels independent of CR. A few metabolism-modulating hormones including leptin and insulin were altered by CR and/or gut microbiota depletion. In addition, CR altered the composition of gut microbiota with significant increases in major probiotic genera such as Lactobacillus and Bifidobacterium, together with the decrease of Helicobacter. In addition, we performed fecal microbiota transplantation in mice fed with high-fat diet. Mice with transferred microbiota from calorie-restricted mice resisted high fat diet-induced obesity and exhibited metabolic improvement such as alleviated hepatic lipid accumulation. Collectively, these data indicate that CR-induced metabolic improvement especially in body weight reduction is mediated by intestinal microbiota to a certain extent.

Combing Gaia DR2 with LAMOST DR5, we spectroscopically identified 924 hot subdwarf stars, among which 32 stars exhibit strong double-lined composite spectra. We measured the effective temperature T eff , surface gravity log g, helium abundance y = nHe/nH, and radial velocities of 892 non-composite spectra hot subdwarf stars by fitting LAMOST observations with Tlusty/Synspec non-LTE synthetic spectra. We outlined four different groups in the T eff − log g diagram with our helium abundance classification scheme and two nearly parallel sequences in the T eff − log(y) diagram. 3D Galactic space motions and orbits of 747 hot subdwarf stars with (G BP − G RP ) 0 < −0.36 mag were computed using LAMOST radial velocities and Gaia parallaxes and proper motions. Based on the U − V velocity diagram, J z −eccentricity diagram, and Galactic orbits, we derived Galactic population classifications and the fractional distributions of the four hot subdwarf helium groups in the halo, thin disk and thick disk. Comparisons with the predictions of binary population synthesis calculations (Han 2008) suggest that He-rich hot subdwarf stars with log(y) ≥ 0 are from the double helium white dwarfs merger, He-deficient hot subdwarf stars with −2.2 ≤ log(y) < −1 from the common envelope ejection, and He-deficient hot subdwarf stars with log(y) < −2.2 from the stable Roche lobe overflow channels. The relative number of He-rich hot subdwarf stars with −1 ≤ log(y) < 0 and log(y) ≥ 0 in the halo is more than twice the prediction of Zhang et al. (2017), even more than six times in the thin disk, which implies that the mergers of helium white dwarfs with low mass main sequence stars may not be the main formation channel of He-rich hot subdwarf stars with −1 ≤ log(y) < 0, specially in younger environments.

We present a catalog of 166 spectroscopically identified hot subdwarf stars from LAMOST DR1, 44 of which show the characteristics of cool companions in their optical spectra. Atmospheric parameters of 122 non-composite spectra subdwarf stars were measured by fitting the profiles of hydrogen (H) and helium (He) lines with synthetic spectra from non-LTE model atmospheres. Most of the sdB stars scatter near the Extreme Horizontal Branch in the T eff − log g diagram and two well defined groups can be outlined. A clustering of He-enriched sdO stars appears near T eff = 45 000 K and log(g) = 5.8. The sdB population separates into several nearly parallel sequences in the T eff −He abundance diagram with clumps corresponding to those in the T eff − log g diagram. Over 38 000 K (sdO) stars show abundance extremes, they are either He-rich or He-deficient and we observe only a few stars in the −1 < log(y) < 0 abundance range. With increasing temperature these extremes become less prominent and the He abundance approaches to log(y) ∼ −0.5. A unique property of our sample is that it covers a large range in apparent magnitudes and galactic latitudes, therefore it contains a mix of stars from different populations and galactic environments. Our results are consistent with the findings of Hirsch (2009) and we conclude that He-rich and He-deficient sdB stars (log(y) < 1) probably origin from different populations. We also find that most sdO and sdB stars lie in a narrow strip in the luminosity and helium abundance plane, which suggests that these atmospheric parameters are correlated.