## 4 Discussion
### D-Allulose Increased Fecal Lipid Excretion and Improved Plasma Lipid Profile  
Dietary fats mainly include TG, sterols, and phospholipids [28], and is mostly degraded in the small intestine into fatty acids, monoglyceride, and free cholesterol by digestive enzymes. Increasing lipid excretion by limiting dietary fat absorption can partly decrease intestinal lipid absorption. In this study, D-allulose supplementation elevated lipid excretion, such as fecal fatty acids and TG, when added to an HFD enriched with hydrogenated palm oil. It is plausible that as fecal lipid levels increase, dietary fat absorption decreases. This idea is partially supported by our results, showing that the expression of lipid absorption factors in the small intestinal epithelial cell lining was decreased. Among the lipid absorption factors measured, CD36, which acts as a bridge in the process of free fatty acid absorption [29], is upregulated by the presence of dietary fats in diabetes mellitus and genetic obesity [30]. Intestinal overexpression of SRB1, localized at the apical and basolateral membranes of enterocytes [31], leads to increased cholesterol, free fatty acid, and TG absorption [32]. ABCA1 is a major regulator of cellular cholesterol and phospholipid homeostasis, by mediating the efflux of cholesterol and phospholipids to lipid-poor apolipoproteins (apolipoprotein A-1 and apolipoprotein E), and ABCA1 is present in high quantities in tissues involved in lipid turnover, such as the liver, small intestine, and adipose tissue. NPC11, a glycosylated protein located in the brush-border membrane of enterocytes, acts as a cholesterol uptake transporter [33]. In the present study, the mRNA expressions of SRB1 and NPC11L1 in the small intestine were significantly decreased by D-allulose supplementation in the NDCA group. However, mRNA expression levels of CD36, ABCA1, and FAS in the small intestine were not different. This study involved feeding of a high-fat diet for 8 weeks. In a previous 16-week trial in C57 BL/6] mice, D-allulose supplementation of an HFD revealed that small intestinal mRNA expression of factors related to lipid-regulatory absorption, such as CD36, ATP-binding cassette sub-family G member 5, ATP-binding cassette sub-family G member 8, and fatty acid transporter 4, was significantly decreased and the fecal cholesterol level was increased compared with the groups fed sugar substrates, such as erythroid, glucose, and fructose [7]. If the supplementation with allulose is prolonged, lipid absorption may continuously decrease, with the excretion of more lipids, and the mRNA expression of lipid absorption factors may decrease in the small intestine. These actions may have partly contributed to suppressing body weight gain and body fat accumulation in the NDCA group compared with the NDC group. Thermogenesis is a metabolic process during which the body produces heat by using energy sources from the simultaneous occurrence of lipolysis or glycolysis. Thus, thermogenesis can promote body fat reduction and weight loss. UCP1 (thermogenin), a major thermogenic factor, is found in the mitochondria of BAT where it provides a mechanism for the enormous heat-generating capacity of the tissue [34]. UCP1 can generate heat by non-shivering thermogenesis and makes a quantitatively important contribution to countering heat loss in neonates, which would otherwise occur because of their high surface area-to-volume ratio. Also, activation of UCP1 in BAT is considered a promising new therapeutic avenue to combat hypertriglyceridemia and obesity [35; 36]. The rectal temperature in the NDCA group was significantly increased at 9 p.m., the time at which mice were most active. Interestingly, the weight of interscapular BAT was lowered by the NDCA diet while the mRNAexpression levels of UCP1 and SIRT1 were upregulated in BAT by the NDCA diet. These results partly explain the increased rectal temperature observed in the NDCA group. In general, increased lipid excretion can affect blood glucose and plasma lipid profiles, via the energy balance.