Rare sugar D-psicose improves insulin sensitivity and glucose tolerance in type 2 diabetes Otsuka Long-Evans Tokushima Fatty (OLETF) rats

Economical one-pot synthesis of isoquercetin and D-allulose from quercetin and sucrose using whole-cell biocatalyst

Isoquercetin and D-allulose have diverse applications and significant value in antioxidant, antibacterial, antiviral, and lipid metabolism. Isoquercetin can be synthesized from quercetin, while D-allulose is converted from D-fructose. However, their production scale and overall quality are relatively low, leading to high production costs. In this study, we have devised a cost-effective one-pot method for biosynthesizing isoquercetin and D-allulose using a whole-cell biocatalyst derived from quercetin and sucrose. To achieve this, the optimized isoquercetin synthase and D-allulose-3-epimerase were initially identified through isofunctional gene screening. In order to reduce the cost of uridine diphosphate glucose (UDPG) during isoquercetin synthesis and ensure a continuous supply of UDPG, sucrose synthase is introduced to enable the self-circulation of UDPG. At the same time, the inclusion of sucrose permease was utilized to successfully facilitate the catalytic production of D-allulose in whole cells. Finally, the recombinant strain BL21/UGT-SUS+DAE-SUP, which overexpresses MiF3GTMUT, GmSUS, EcSUP, and DAEase, was obtained. This strain co-produced 41±2.4 mg/L of isoquercetin and 5.7±0.8 g/L of D-allulose using 120 mg/L of quercetin and 20 g/L of sucrose as substrates for 5 h after optimization. This is the first green synthesis method that can simultaneously produce flavonoid compounds and rare sugars. These findings provide valuable insights and potential for future industrial production, as well as practical applications in factories.

Short-term effects of allulose consumption on glucose homeostasis, metabolic parameters, incretin levels, and inflammatory markers in patients with type 2 diabetes: a double-blind, randomized, controlled crossover clinical trial

PURPOSE

Allulose is a rare monosaccharide with almost zero calories. There is no study of short-term allulose consumption in patients with type 2 diabetes (T2D). Thus, we aimed to study the effect of allulose consumption for 12 weeks on glucose homeostasis, lipid profile, body composition, incretin levels, and inflammatory markers in patients with T2D.

METHODS

A double-blind, randomized, controlled crossover study was conducted on sixteen patients with T2D. Patients were randomly assigned to allulose 7 g twice daily or aspartame 0.03 g twice daily for 12 weeks. After a 2-week washout, patients were crossed over to the other sweetener for an additional 12 weeks. Oral glucose tolerance tests, laboratory measurements, and dual-energy X-ray absorptiometry were conducted before and after each phase.

RESULTS

This study revealed that short-term allulose consumption exerted no significant effect on glucose homeostasis, incretin levels, or body composition but significantly increased MCP-1 levels (259 ± 101 pg/ml at baseline vs. 297 ± 108 pg/mL after 12 weeks of allulose, p = 0.002). High-density lipoprotein cholesterol (HDL-C) significantly decreased from 51 ± 13 mg/dl at baseline to 41 ± 12 mg/dL after 12 weeks of allulose, p < 0.001.

CONCLUSION

Twelve weeks of allulose consumption had a neutral effect on glucose homeostasis, body composition, and incretin levels. Additionally, it decreased HDL-C levels and increased MCP-1 levels.

TRIAL REGISTRATION

This trial was retrospectively registered on the Thai Clinical Trials Registry (TCTR20220516006) on December 5, 2022.

d-Allulose Supplementation Prevents Diet-Induced Hepatic Lipid Accumulation via miR-130-Mediated Regulation in C57BL/6 Mice

SCOPE

d-allulose is a low-calorie rare sugar. It has been reported that d-allulose supplementation significantly inhibits diet-induced hepatic fat accumulation. However, the underlying molecular mechanisms remain unclear. This study elucidates the mechanism underlying the suppressive effect of d-allulose on hepatic fat accumulation in terms of miRNA regulation.

METHODS AND RESULTS

Male C57BL/6 mice are divided into three experimental groups-normal diet and distilled water (CC group), high-fat diet (HFD) and distilled water (HC group), and HFD and 5% d-allulose solution (HA group)-and fed the respective diets for 8 weeks. Weight gain is significantly lower in the HA group than that in the HC group, although the caloric intake is the same in both. Histological analysis of liver tissues reveals excessive lipid accumulation in the HC group; this is greatly attenuated in the HA group. Real-time PCR and western blot analyses demonstrate that, compared to the HC group, the HA group exhibits decreased hepatic PPARγ and CD36 expression. Hepatic miR-130 expression levels are higher in the HA group than those in the CC and HC groups.

CONCLUSIONS

These results indicate that miRNA changes associated with PPARγ may underlie the suppression of hepatic lipid accumulation induced by d-allulose intake.

Effect of chronic exposure to ketohexoses on pancreatic β-cell function in INS-1 rat insulinoma cells

Glucotoxicity, impaired insulin secretion, suppression of insulin gene expression, and apoptosis, in pancreatic β-cells caused by chronic hyperglycemia is a key component of the pathogenesis of type 2 diabetes. Recently, it has been reported that rare sugar d-allulose has antihyperglycemic and antihyperlipidemic effects in diabetic rats. However, the direct effects of rare sugars including d-allulose on pancreatic β-cell function are unclear. In this study, we investigated whether chronic exposure to ketohexoses causes glucotoxicity, suppression of insulin gene expression, and apoptosis, in INS-1 rat pancreatic insulinoma cells. d-Fructose, d-tagatose, l-allulose, and l-sorbose treatment for 1-week reduced insulin gene expression, whereas d-allulose, d-sorbose, l-fructose, and l-tagatose did not. All ketohexoses were transported into INS-1 cells, but were not metabolized. In addition, the ketohexoses did not induce apoptosis and did not affect glucose metabolism. These results suggest that long-term administration of d-allulose, d-sorbose, l-fructose, and l-tagatose does not affect pancreatic β-cell function.

Comparative Effects of Allulose, Fructose, and Glucose on the Small Intestine

Despite numerous studies on the health benefits of the rare sugar allulose, its effects on intestinal mucosal morphology and function are unclear. We therefore first determined its acute effects on the small intestinal transcriptome using DNA microarray analysis following intestinal allulose, fructose and glucose perfusion in rats. Expression levels of about 8-fold more genes were altered by allulose compared to fructose and glucose perfusion, suggesting a much greater impact on the intestinal transcriptome. Subsequent pathway analysis indicated that nutrient transport, metabolism, and digestive system development were markedly upregulated, suggesting allulose may acutely stimulate these functions. We then evaluated whether allulose can restore rat small intestinal structure and function when ingested orally following total parenteral nutrition (TPN). We also monitored allulose effects on blood levels of glucagon-like peptides (GLP) 1 and 2 in TPN rats and normal mice. Expression levels of fatty acid binding and gut barrier proteins were reduced by TPN but rescued by allulose ingestion, and paralleled GLP-2 secretion potentially acting as the mechanism mediating the rescue effect. Thus, allulose can potentially enhance disrupted gut mucosal barriers as it can more extensively modulate the intestinal transcriptome relative to glucose and fructose considered risk factors of metabolic disease.

d-Allulose Ameliorates Hyperglycemia Through IRE1α Sulfonation-RIDD-Sirt1 Decay Axis in the Skeletal Muscle

Aims: The skeletal muscle maintains glucose disposal via insulin signaling and glucose transport. The progression of diabetes and insulin resistance is critically influenced by endoplasmic reticulum (ER) stress. d-Allulose, a low-calorie sugar substitute, has shown crucial physiological activities under conditions involving hyperglycemia and insulin resistance. However, the molecular mechanisms of d-allulose in the progression of diabetes have not been fully elucidated. Here, we evaluated the effect of d-allulose on hyperglycemia-associated ER stress responses in human skeletal myoblasts (HSkM) and db/db diabetic and high-fat diet-fed mice. Results: d-allulose effectively controlled glycemic markers such as insulin and hemoglobin A1c (HbA1c), showing anti-diabetic effects by inhibiting the disruption of insulin receptor substrate (IRS)-1 tyrosine phosphorylation and glucose transporter 4 (GLUT4) expression, in which the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt) pathway is involved. The levels of glucose dysmetabolism-based NADPH oxidase, such as NADPH-dependent oxidoreductase (Nox) 4, were highly increased, and their interaction with IRE1α and the resultant sulfonation-regulated IRE1-dependent decay (RIDD)-Sirt1 decay were also highly increased under diabetic conditions, which were controlled with d-allulose treatment. Skeletal muscle cells grown with a high glucose medium supplemented with d-allulose showed controlled IRE1α sulfonation-RIDD-Sirt1 decay, in which Nox4 was involved. Innovation and Conclusion: The study observations indicate that d-allulose contributes to the muscular glucose disposal in the diabetic state where ER-localized Nox4-induced IRE1α sulfonation results in the decay of Sirt1, a core factor for controlling glucose metabolism. Antioxid. Redox Signal. 37, 229-245.

d-Allulose Inhibits Ghrelin-Responsive, Glucose-Sensitive and Neuropeptide Y Neurons in the Arcuate Nucleus and Central Injection Suppresses Appetite-Associated Food Intake in Mice

d-allulose, a rare sugar, has sweetness with few calories. d-allulose regulates feeding and glycemia, and ameliorates hyperphagia, obesity and diabetes. All these functions involve the central nervous system. However, central mechanisms underlying these effects of d-allulose remain unknown. We recently reported that d-allulose activates the anorexigenic neurons in the hypothalamic arcuate nucleus (ARC), the neurons that respond to glucagon-like peptide-1 and that express proopiomelanocortin. However, its action on the orexigenic neurons remains unknown. This study investigated the effects of d-allulose on the ARC neurons implicated in hunger, by measuring cytosolic Ca²⁺ concentration ([Ca²⁺]_i) in single neurons. d-allulose depressed the increases in [Ca²⁺]_i induced by ghrelin and by low glucose in ARC neurons and inhibited spontaneous oscillatory [Ca²⁺]_i increases in neuropeptide Y (NPY) neurons. d-allulose inhibited 10 of 35 (28%) ghrelin-responsive, 18 of 60 (30%) glucose-sensitive and 3 of 8 (37.5%) NPY neurons in ARC. Intracerebroventricular injection of d-allulose inhibited food intake at 20:00 and 22:00, the early dark phase when hunger is promoted. These results indicate that d-allulose suppresses hunger-associated feeding and inhibits hunger-promoting neurons in ARC. These central actions of d-allulose represent the potential of d-allulose to inhibit the hyperphagia with excessive appetite, thereby counteracting obesity and diabetes.

D-Allulose cooperates with glucagon-like peptide-1 and activates proopiomelanocortin neurons in the arcuate nucleus and central injection inhibits feeding in mice

A rare sugar D-Allulose has sweetness without calorie. Previous studies have shown that D-Allulose improves glucose and energy metabolism and ameliorates obesity. However, underlying mechanisms remain elusive. This study explored the effect of central injection of D-Allulose on feeding behavior in mice. We also examined direct effects of D-Allulose on the neurons in the hypothalamic arcuate nucleus (ARC) that regulate feeding, including the anorexigenic glucagon-like peptide-1 (GLP-1)-responsive neurons and proopiomelanocortin (POMC) neurons. Single neurons were isolated from ARC and cytosolic Ca²⁺ concentration ([Ca²⁺]_i) was measured by fura-2 microfluorometry. Administration of D-Allulose at 5.6, 16.7 and 56 mM concentration-dependently increased [Ca²⁺]_i in ARC neurons. The [Ca²⁺]_i increases took place similarly when the osmolarity of superfusion solution was kept constant. The majority (40%) of the D-Allulose-responsive neurons also responded to GLP-1 with [Ca²⁺]_i increases. D-Allulose increased [Ca²⁺]_i in 33% of POMC neurons in ARC. D-Allulose potentiated the GLP-1 action to increase [Ca²⁺]_i in ARC neurons including POMC neurons. Intracerebroventricular injection of D-Allulose significantly decreased food intake at 1 and 2 h after injection. These results demonstrate that D-Allulose cooperates with glucagon-like peptide-1 and activates the ARC neurons including POMC neurons. Furthermore, central injection of D-Allulose inhibits feeding. These central actions of D-Allulose may underlie the ability of D-Allulose to counteract obesity and diabetes.

d-allulose protects against diabetic nephropathy progression in Otsuka Long-Evans Tokushima Fatty rats with type 2 diabetes

d-allulose is a rare sugar that has been reported to possess anti-hyperglycemic effects. In the present study, we hypothesized that d-allulose is effective in attenuating the progression of diabetic nephropathy in the Otsuka Long-Evans Tokushima Fatty (OLETF) rat model of type 2 diabetes mellitus. Drinking water with or without 3% d-allulose was administered to OLETF rats for 13 weeks. Long-Evans Tokushima Otsuka rats that received drinking water without d-allulose were used as non-diabetic control rats. d-allulose significantly attenuated the increase in blood glucose levels and progressive mesangial expansion in the glomerulus, which is regarded as a characteristic of diabetic nephropathy, in OLETF rats. d-allulose also attenuated the significant increases in renal IL-6 and tumor necrosis factor-α mRNA levels in OLETF rats, which is a proinflammatory parameter. Additionally, we showed that d-allulose suppresses mesangial matrix expansion, but its correlation with suppressing renal inflammation in OLETF rats should be investigated further. Collectively, our results support the hypothesis that d-allulose can prevent diabetic nephropathy in rats.

d-Allulose Improves Endurance and Recovery from Exhaustion in Male C57BL/6J Mice

d-Allulose, a rare sugar, improves glucose metabolism and has been proposed as a candidate calorie restriction mimetic. This study aimed to investigate the effects of d-allulose on aerobic performance and recovery from exhaustion and compared them with the effects of exercise training. Male C57BL/6J mice were subjected to exercise and allowed to run freely on a wheel. Aerobic performance was evaluated using a treadmill. Glucose metabolism was analyzed by an intraperitoneal glucose tolerance test (ipGTT). Skeletal muscle intracellular signaling was analyzed by Western blotting. Four weeks of daily oral administration of 3% d-allulose increased running distance and shortened recovery time as assessed by an endurance test. d-Allulose administration also increased the maximal aerobic speed (MAS), which was observed following treatment for >3 or 7 days. The improved performance was associated with lower blood lactate levels and increased liver glycogen levels. Although d-allulose did not change the overall glucose levels as determined by ipGTT, it decreased plasma insulin levels, indicating enhanced insulin sensitivity. Finally, d-allulose enhanced the phosphorylation of AMP-activated protein kinase and acetyl-CoA carboxylase and the expression of peroxisome proliferator-activated receptor γ coactivator 1α. Our results indicate that d-allulose administration enhances endurance ability, reduces fatigue, and improves insulin sensitivity similarly to exercise training. d-Allulose administration may be a potential treatment option to alleviate obesity and enhance aerobic exercise performance.

Biochemical synthesis of the medicinal sugar l-gulose using fungal alditol oxidase

Some rare sugars can be potently medicinal, such as l-gulose. In this study, we present a novel alditol oxidase (fAldOx) from the soil fungus Penicillium sp. KU-1, and its application for the effective production of l-gulose. To the best of our knowledge, this is the first report of a successful direct conversion of d-sorbitol to l-gulose. We further purified it to homogeneity with a ∼108-fold purification and an overall yield of 3.26%, and also determined the effectors of fAldOx. The enzyme possessed broad substrate specificity for alditols such as erythritol (k_cat/K_M, 355 m^-1 s^-1), thus implying that the effective production of multiple rare sugars for medicinal applications may be possible.

d-Allulose Ameliorates Skeletal Muscle Insulin Resistance in High-Fat Diet-Fed Rats

BACKGROUND

d-Allulose is a rare sugar with antiobesity and antidiabetic activities. However, its direct effect on insulin sensitivity and the underlying mechanism involved are unknown.

OBJECTIVE

This study aimed to investigate the effect of d-allulose on high-fat diet (HFD)-induced insulin resistance using the hyperinsulinemic-euglycemic (HE)-clamp method and intramuscular signaling analysis.

METHODS

Wistar rats were randomly divided into three dietary groups: chow diet, HFD with 5% cellulose (HFC), and HFD with 5% d-allulose (HFA). After four weeks of feeding, the insulin tolerance test (ITT), intraperitoneal glucose tolerance test (IPGTT), and HE-clamp study were performed. The levels of plasma leptin, adiponectin, and tumor necrosis factor (TNF)-α were measured using the enzyme-linked immunosorbent assay. We analyzed the levels of cell signaling pathway components in the skeletal muscle using Western blotting.

RESULTS

d-allulose alleviated the increase in HFD-induced body weight and visceral fat and reduced the area under the curve as per ITT and IPGTT. d-Allulose increased the glucose infusion rate in the two-step HE-clamp test. Consistently, the insulin-induced phosphorylation of serine 307 in the insulin receptor substrate-1 and Akt and expression of glucose transporter 4 (Glut-4) in the muscle were higher in the HFA group than HFC group. Furthermore, d-allulose decreased plasma TNF-α concentration and insulin-induced phosphorylation of stress-activated protein kinase/Jun N-terminal kinase in the muscle and inhibited adiponectin secretion in HFD-fed rats.

CONCLUSIONS

d-allulose improved HFD-induced insulin resistance in Wistar rats. The reduction of the proinflammatory cytokine production, amelioration of adiponectin secretion, and increase in insulin signaling and Glut-4 expression in the muscle contributed to this effect.

Investigation of d-allulose effects on high-sucrose diet-induced insulin resistance via hyperinsulinemic-euglycemic clamps in rats

d-Allulose, a C-3 epimer of d-fructose, is a rare sugar that has no calories. Although d-allulose has been reported to have several health benefits, such as anti-obesity and anti-diabetic effects, there have been no reports evaluating the effects of d-allulose on insulin resistance using a hyperinsulinemic-euglycemic clamp (HE-clamp). Therefore, we investigated the effects of d-allulose on a high-sucrose diet (HSD)-induced insulin resistance model. Wistar rats were randomly divided into three dietary groups: HSD containing 5% cellulose (HSC), 5% d-allulose (HSA), and a commercial diet. The insulin tolerance test (ITT) and HE-clamp were performed after administration of the diets for 4 and 7 weeks. After 7 weeks, the muscle and adipose tissues of rats were obtained to analyze Akt signaling via western blotting, and plasma adipocytokine levels were measured. ITT revealed that d-allulose ameliorated systemic insulin resistance. Furthermore, the results of the 2-step HE-clamp procedure indicated that d-allulose reversed systemic and muscular insulin resistance. d-Allulose reversed the insulin-induced suppression of Akt phosphorylation in the soleus muscle and epididymal fat tissues and reduced plasma TNF-α levels. This study is the first to show that d-allulose improves systemic and muscle insulin sensitivity in conscious rats.

Research Advances of d-allulose: An Overview of Physiological Functions, Enzymatic Biotransformation Technologies, and Production Processes

d-allulose has a significant application value as a sugar substitute, not only as a food ingredient and dietary supplement, but also with various physiological functions, such as improving insulin resistance, anti-obesity, and regulating glucolipid metabolism. Over the decades, the physiological functions of d-allulose and the corresponding mechanisms have been studied deeply, and this product has been applied to various foods to enhance food quality and prolong shelf life. In recent years, biotransformation technologies for the production of d-allulose using enzymatic approaches have gained more attention. However, there are few comprehensive reviews on this topic. This review focuses on the recent research advances of d-allulose, including (1) the physiological functions of d-allulose; (2) the major enzyme families used for the biotransformation of d-allulose and their microbial origins; (3) phylogenetic and structural characterization of d-allulose 3-epimerases, and the directed evolution methods for the enzymes; (4) heterologous expression of d-allulose ketose 3-epimerases and biotransformation techniques for d-allulose; and (5) production processes for biotransformation of d-allulose based on the characterized enzymes. Furthermore, the future trends on biosynthesis and applications of d-allulose in food and health industries are discussed and evaluated in this review.

Rare sugars: metabolic impacts and mechanisms of action: a scoping review

Food manufacturers are under increasing pressure to limit the amount of free sugars in their products. Many have reformulated products to replace sucrose, glucose and fructose with alternative sweeteners, but some of these have been associated with additional health concerns. Rare sugars are 'monosaccharides and their derivatives that hardly exist in nature', and there is increasing evidence that they could have health benefits. This review aimed to scope the existing literature in order to identify the most commonly researched rare sugars, to ascertain their proposed health benefits, mechanisms of action and potential uses and to highlight knowledge gaps. A process of iterative database searching identified fifty-five relevant articles. The reported effects of rare sugars were noted, along with details of the research methodologies conducted. Our results indicated that the most common rare sugars investigated are d-psicose and d-tagatose, with the potential health benefits divided into three topics: glycaemic control, body composition and CVD. All the rare sugars investigated have the potential to suppress postprandial elevation of blood glucose and improve glycaemic control in both human and animal models. Some animal studies have suggested that certain rare sugars may also improve lipid profiles, alter the gut microbiome and reduce pro-inflammatory cytokine expression. The present review demonstrates that rare sugars could play a role in reducing the development of obesity, type 2 diabetes and/or CVD. However, understanding of the mechanisms by which rare sugars may exert their effects is limited, and their effectiveness when used in reformulated products is unknown.

Efficient production of the rare sugar l-gulose using a wheat-bran culture extract of Penicillium sp. KU-1

We found that l-gulose, a rare sugar, was produced from d-sorbitol efficiently, using a wheat-bran culture extract of the fungus Penicillium sp. KU-1 isolated from soil. The culture extract showed enzyme activity for the oxidation of d-sorbitol to produce l-gulose; a high production yield of approximately 94% was achieved.

A review on l-ribose isomerases for the biocatalytic production of l-ribose and l-ribulose

Presently, because of the extraordinary roles and potential applications, rare sugars turn into a focus point for countless researchers in the field of carbohydrates. l-ribose and l-ribulose are rare sugars and isomers of each other. This aldo and ketopentose are expensive but can be utilized as an antecedent for the manufacturing of various rare sugars and l-nucleoside analogue. The bioconversion approach turns into an excellent alternative method to l-ribulose and l-ribose production, as compared to the complex and lengthy chemical methods. The basic purpose of this research was to describe the importance of rare sugars in various fields and their easy production by using enzymatic methods. l-Ribose isomerase (L-RI) is an enzyme discovered by Tsuyoshi Shimonishi and Ken Izumori in 1996 from Acinetobacter sp. strain DL-28. L-RI structure was cupin-type-β-barrel shaped with a catalytic site between two β-sheets surrounded by metal ions. The crystal structures of the L-RI showed that it contains a homotetramer structure. Current review have concentrated on the sources, characteristics, applications, conclusions and future prospects including the potentials of l-ribose isomerase for the commercial production of l-ribose and l-ribulose. The MmL-RIse and CrL-RIse have the potential to produce the l-ribulose up to 32% and 31%, respectively. The CrL-RIse is highly stable as compared to other L-RIs. The results explained that the L-RIs have great potential in the production of rare sugars especially, l-ribose and l-ribulose, while the immobilization technique can enhance its functionality and properties. The present study precises the applications of L-RIs acquired from various sources for l-ribose and l-ribulose production.

Effect of D-allulose feeding on the hepatic metabolomics profile in male Wistar rats

The rare sugar d-allulose is a C-3 epimer of d-fructose and is known to have several health benefits such as anti-obesity and anti-diabetic effects through the alteration of enzymatic and genetic expressions in each organ. Most of the ingested d-allulose is absorbed in the small intestine and then rapidly excreted in the urine. As d-allulose was reported to be present in the liver before it is excreted, d-allulose may modulate some hepatic metabolites including glucose and lipid metabolism. Therefore, we investigated the hepatic metabolomics profile in rats after feeding d-allulose to study the overall alteration of hepatic metabolism. Wistar rats were fed an AIN-93G diet with/without 3% d-allulose for 4 weeks. Their liver samples were then collected and subjected to metabolomics analysis using CE-TOFMS and LC-TOFMS. The results showed that d-allulose induced significant increases in 42 metabolites and significant decreases in 21 metabolites. In particular, we found at the substance levels that d-allulose regulated metabolites involved in the metabolic pathways of fatty acid β-oxidation, cholesterol, and bile acid. In addition, this study newly showed the possibility that d-allulose alters glucuronic acid/xylulose pathways. In the future, we need more detailed research on the metabolomics profile of other organs related to these pathways for a comprehensive understanding of d-allulose functions.

Crystal structure of a novel homodimeric l-ribulose 3-epimerase from Methylomonus sp

d-Allulose has potential as a low-calorie sweetener which can suppress fat accumulation. Several enzymes capable of d-allulose production have been isolated, including d-tagatose 3-epimerases. Here, we report the isolation of a novel protein from Methylomonas sp. expected to be a putative enzyme based on sequence similarity to ketose 3-epimerase. The synthesized gene encoding the deduced ketose 3-epimerase was expressed as a recombinant enzyme in Escherichia coli, and it exhibited the highest enzymatic activity toward l-ribulose, followed by d-ribulose and d-allulose. The X-ray structure analysis of l-ribulose 3-epimerase from Methylomonas sp. (MetLRE) revealed a homodimeric enzyme, the first reported structure of dimeric l-ribulose 3-epimerase. The monomeric structure of MetLRE is similar to that of homotetrameric l-ribulose 3-epimerases, but the short C-terminal α-helix of MetLRE is unique and different from those of known l-ribulose 3 epimerases. The length of the C-terminal α-helix was thought to be involved in tetramerization and increasing stability; however, the addition of residues to MetLRE at the C terminus did not lead to tetramer formation. MetLRE is the first dimeric l-ribulose 3-epimerase identified to exhibit high relative activity toward d-allulose.

Rare Sugars: Recent Advances and Their Potential Role in Sustainable Crop Protection

Rare sugars are monosaccharides with a limited availability in the nature and almost unknown biological functions. The use of industrial enzymatic and microbial processes greatly reduced their production costs, making research on these molecules more accessible. Since then, the number of studies on their medical/clinical applications grew and rare sugars emerged as potential candidates to replace conventional sugars in human nutrition thanks to their beneficial health effects. More recently, the potential use of rare sugars in agriculture was also highlighted. However, overviews and critical evaluations on this topic are missing. This review aims to provide the current knowledge about the effects of rare sugars on the organisms of the farming ecosystem, with an emphasis on their mode of action and practical use as an innovative tool for sustainable agriculture. Some rare sugars can impact the plant growth and immune responses by affecting metabolic homeostasis and the hormonal signaling pathways. These properties could be used for the development of new herbicides, plant growth regulators and resistance inducers. Other rare sugars also showed antinutritional properties on some phytopathogens and biocidal activity against some plant pests, highlighting their promising potential for the development of new sustainable pesticides. Their low risk for human health also makes them safe and ecofriendly alternatives to agrochemicals.

The sensory properties and metabolic impact of natural and synthetic sweeteners

The global rise in obesity, type II diabetes, and other metabolic disorders in recent years has been attributed in part to the overconsumption of added sugars. Sugar reduction strategies often rely on synthetic and naturally occurring sweetening compounds to achieve their goals, with popular synthetic sweeteners including saccharin, cyclamate, acesulfame potassium, aspartame, sucralose, neotame, alitame, and advantame. Natural sweeteners can be further partitioned into nutritive, including polyols, rare sugars, honey, maple syrup, and agave, and nonnutritive, which include steviol glycosides and rebaudiosides, luo han guo (monk fruit), and thaumatin. We choose the foods we consume largely on their sensory properties, an area in which these sugar substitutes often fall short. Here, we discuss the most popular synthetic and natural sweeteners, with the goal of providing an understanding of differences in the sensory profiles of these sweeteners versus sucrose, that they are designed to replace, essential for the effectiveness of sugar reduction strategies. In addition, we break down the influence of these sweeteners on metabolism, and present results from a large survey of consumers' opinions on these sweeteners. Consumer interest in clean label foods has driven a move toward natural sweeteners; however, neither natural nor synthetic sweeteners are metabolically inert. Identifying sugar replacements that not only closely imitate the sensory profile of sucrose but also exert advantageous effects on body weight and metabolism is critical in successfully the ultimate goals of reducing added sugar in the average consumer's diet. With so many options for sucrose replacement available, consumer opinion and cost, which vary widely with suagr replacements, will also play a vital role in which sweeteners are successful in widespread adoption.

Biocatalytic Synthesis of D-Allulose Using Novel D-Tagatose 3-Epimerase From Christensenella minuta

D-allulose, which is one of the important rare sugars, has gained significant attention in the food and pharmaceutical industries as a potential alternative to sucrose and fructose. Enzymes belonging to the D-tagatose 3-epimerase (DTEase) family can reversibly catalyze the epimerization of D-fructose at the C3 position and convert it into D-allulose by a good number of naturally occurring microorganisms. However, microbial synthesis of D-allulose is still at its immature stage in the industrial arena, mostly due to the preference of slightly acidic conditions for Izumoring reactions. Discovery of novel DTEase that works at acidic conditions is highly preferred for industrial applications. In this study, a novel DTEase, DTE-CM, capable of catalyzing D-fructose into D-allulose was applications. In this study, a novel DTEase, DTE-CM, capable of catalyzing D-fructose into D-allulose was DTE-CM on D-fructose was found to be remarkably influenced and modulated by the type of metal ions (co-factors). The DTE-CM on D-fructose was found to be remarkably influenced and modulated by the type of metal ions (co-factors). The 50°C from 0.5 to 3.5 h at a concentration of 0.1 mM. The enzyme exhibited its maximum catalytic activity on D-fructose at pH 6.0 and 50°C from 0.5 to 3.5 h at a concentration of 0.1 mM. The enzyme exhibited its maximum catalytic activity on -fructose at pH 6.0 and 50°C with a K cat /K m value of 45 mM-1min-1. The 500 g/L D-fructose, which corresponded to 30% conversion rate. With these interesting catalytic properties, this enzyme could be a promising candidate for industrial biocatalytic applications.

The rare sugar D-tagatose protects plants from downy mildews and is a safe fungicidal agrochemical

The rare sugar D-tagatose is a safe natural product used as a commercial food ingredient. Here, we show that D-tagatose controls a wide range of plant diseases and focus on downy mildews to analyze its mode of action. It likely acts directly on the pathogen, rather than as a plant defense activator. Synthesis of mannan and related products of D-mannose metabolism are essential for development of fungi and oomycetes; D-tagatose inhibits the first step of mannose metabolism, the phosphorylation of D-fructose to D-fructose 6-phosphate by fructokinase, and also produces D-tagatose 6-phosphate. D-Tagatose 6-phosphate sequentially inhibits phosphomannose isomerase, causing a reduction in D-glucose 6-phosphate and D-fructose 6-phosphate, common substrates for glycolysis, and in D-mannose 6-phosphate, needed to synthesize mannan and related products. These chain-inhibitory effects on metabolic steps are significant enough to block initial infection and structural development needed for reproduction such as conidiophore and conidiospore formation of downy mildew.

Purification and Characterization of D-psicose 3 Epimerase (DPEase) From <i>Escherichia coli</i> BL21 (DE3) pET21b <i>dpe</i>

BACKGROUND AND OBJECTIVE

The DPEase enzyme from Agrobacterium tumefaciens is more efficient and has a high activity in D-fructose. The dpe gene has been successfully cloned to Escherichia coli BL21 (DE3) pET-21b dpe but the enzyme has not been purified and its character is unknown. The intent of this study was to purify and assign of DPEase enzyme by recombinant E. coli.

MATERIALS AND METHODS

The enzyme was clarified by affinity chromatography and then characterized by following pH, temperature, co-factor parameters. Analysis of molecular weight proteins was done by SDS-PAGE.

RESULTS

Through purification, the purified DPEase activity was increased 1,01 times than crude and with 84.2% of yield. The DPEase had an the maximum temperature is 40°C and pH was 8.5. The presence of Mg2+, Mo2+, Cu2+, Ca2+ and Zn2+ inhibited the activity of the enzyme while of Co2+, Mn2+, Fe2+, Ni2+ enhanced the activity. Estimation of molecular weight through SDS-PAGE revealed that weight of DPEase was 32 kDa.

CONCLUSION

Purified DPease enzymes shows clear bands that demonstrate successful purification using affinity chromatography. It is expected that after pure enzymes are obtained the character of the enzymes working will be maximized.

Rare mono- and disaccharides as healthy alternative for traditional sugars and sweeteners?

Obesity and type 2 diabetes are major health problems affecting hundreds of millions of people. Caloric overfeeding with calorie-dense food ingredients like sugars may contribute to these chronic diseases. Sugar research has also identified mechanisms via which conventional sugars like sucrose and fructose can adversely influence metabolic health. To replace these sugars, numerous sugar replacers including artificial sweeteners and sugar alcohols have been developed. Rare sugars became new candidates to replace conventional sugars and their health effects are already reported in individual studies, but overviews and critical appraisals of their health effects are missing. This is the first paper to provide a detailed review of the metabolic health effects of rare sugars as a group. Especially allulose has a wide range of health effects. Tagatose and isomaltulose have several health effects as well, while other rare sugars mainly provide health benefits in mechanistic studies. Hardly any health claims have been approved for rare sugars due to a lack of evidence from human trials. Human trials with direct measures for disease risk factors are needed to allow a final appraisal of promising rare sugars. Mechanistic cell culture studies and animal models are required to enlarge our knowledge on understudied rare sugars.

D-Allulose enhances uptake of HDL-cholesterol into rat's primary hepatocyte via SR-B1

D-Allulose, a C-3 epimer of D-fructose, is a rare sugar and a non-caloric sweetener. D-Allulose is reported to have several health benefits, such as suppressing a rise in postprandial glucose levels and preventing fat accumulation in rodents and humans. Additionally, low HDL-cholesterol levels post-D-allulose feeding were observed in humans but it is unclear how D-allulose decreased HDL-cholesterol levels. It is necessary to research the mechanism of HDL-cholesterol reduction by D-allulose ingestion because low HDL-cholesterol levels are known to associate with increased atherosclerosis risk. We therefore investigated the mechanism by which D-allulose lowers HDL-cholesterol using rat's primary hepatocytes. Sprague Dawley rats were fed an AIN-93G based diet containing 3% D-allulose for 2 weeks. Thereafter, primary hepatocytes were isolated by perfusion of collagenase. We measured the ability of HDL-cholesterol uptake in hepatocytes and the protein levels of scavenger receptor class B type 1 (SR-B1) as a HDL-cholesterol receptor. D-Allulose enhanced hepatocyte uptake of HDL-cholesterol, with a concurrent increase in hepatic SR-B1 protein levels. The results suggest that D-allulose enhances HDL-cholesterol uptake into the liver by increasing SR-B1 expression. It is estimated that HDL-cholesterol levels decreased accordingly. Since SR-B1 overexpression would decrease HDL-cholesterol levels, reportedly preventing atherosclerosis development, D-allulose could be a useful sweetener for atherosclerosis prevention.

Review on D-Allulose: In vivo Metabolism, Catalytic Mechanism, Engineering Strain Construction, Bio-Production Technology

Rare sugar D-allulose as a substitute sweetener is produced through the isomerization of D-fructose by D-tagatose 3-epimerases (DTEases) or D-allulose 3-epimerases (DAEases). D-Allulose is a kind of low energy monosaccharide sugar naturally existing in some fruits in very small quantities. D-Allulose not only possesses high value as a food ingredient and dietary supplement, but also exhibits a variety of physiological functions serving as improving insulin resistance, antioxidant enhancement, and hypoglycemic controls, and so forth. Thus, D-allulose has an important development value as an alternative to high-energy sugars. This review provided a systematic analysis of D-allulose characters, application, enzymatic characteristics and molecular modification, engineered strain construction, and processing technologies. The existing problems and its proposed solutions for D-allulose production are also discussed. More importantly, a green and recycling process technology for D-allulose production is proposed for low waste formation, low energy consumption, and high sugar yield.

Anti-obesity potential of rare sugar d-psicose by regulating lipid metabolism in rats

d-Psicose is a new-generation sugar substitute with a low calorie count and can still offer the desirable sweetness. The objective of this study was to investigate the antiobesity potential of d-psicose and the possible mechanism using Wistar rats as the animal model. The animals were divided into five groups and supplemented with diets containing 5% of different carbohydrates, such as glucose, fructose, cellulose, d-psicose, and a control diet, for 4 weeks. After sacrifice, blood lipid profile, tissue morphology, and related genes participating in lipid metabolism were analyzed. The results indicated that the supplementation by d-psicose leads to minimum fat accumulation in rats when compared with the other carbohydrates. The blood lipid profile and antioxidative activity of the rat were also improved. d-Psicose can regulate lipid metabolism by increasing the lipid-metabolism-related enzymes such as SDH in serum and liver and HL in the liver. d-Psicose can prevent fat accumulation by suppressing the expression of lipogenesis-related gene ACCα and hepatic fatty acid uptake gene (FAS and SREBP-1c), while stimulating the expression for fatty-acid-oxidation-related gene including AMPK2α, HSL, and PPARα. In conclusion, d-psicose can be considered to be a healthy alternative to traditional sweeteners.

Metabolic Stability of D-Allulose in Biorelevant Media and Hepatocytes: Comparison with Fructose and Erythritol

D-allulose, a C-3 epimer of D-fructose, is a rare monosaccharide used as a food ingredient or a sweetener. In the present study, the in vitro metabolic stability of D-allulose was examined in biorelevant media, that is, simulated gastric fluid (SGF) and fasted state simulated intestinal fluid (FaSSIF) containing digestive enzymes, and in cryopreserved human and rat hepatocytes. The hepatocyte metabolic stabilities of D-allulose were also investigated and compared with those of fructose and erythritol (a sugar-alcohol with no calorific value). D-allulose was highly stable in SGF (97.8% remained after 60 min) and in FaSSIF (101.3% remained after 240 min), indicating it is neither pH-labile nor degraded in the gastrointestinal tract. D-allulose also exhibited high levels of stability in human and rat hepatocytes (94.5–96.8% remained after 240 min), whereas fructose was rapidly metabolized (43.1–52.6% remained), which suggested these two epimers are metabolized in completely different ways in the liver. The effects of D-allulose on glucose and fructose levels were negligible in hepatocytes. Erythritol was stable in human and rat hepatocytes (102.1–102.9% remained after 240 min). Intravenous pharmacokinetic studies in rats showed D-allulose was eliminated with a mean half-life of 72.2 min and a systemic clearance of 15.8 mL/min/kg. Taken together, our results indicate that D-allulose is not metabolized in the liver, and thus, unlikely to contribute to hepatic energy production.

The development of low-calorie sugar and functional jujube food using biological transformation and fermentation coupling technology

Jujube juice has been used as ingredient in a range of foods and dietary supplements. In this study, an enzyme transformation and fermentation coupling technology was applied to increase the nutritional value of concentrated/extracted Jinsi jujube juice. Two enzymes, D-glucose isomerase (GI) and D-allulose 3-epimerase (DAE), were employed to convert the glucose and fructose to a low-calorie sweeter D-allulose with a concentration of 110 g/L in jujube juice. Furthermore, the mixed cultures of Pediococcus pentosaceus PC-5 and Lactobacillus plantarum M were employed to increase the content of nutrition components related to bioactivities and flavor volatiles in jujube juice. Accordingly, this fermentation accumulated 100 mg/L gamma-aminobutyric acid (GABA), which has neurotransmission, hypotension, diuretic, and tranquilizer effects, and increased the content of branched-chain amino acids (BCAAs) and many free amino acids (Asp, Glu, Gly, and Ala) at different level. The fermentation not only maintained the concentration of native functional components such as cyclic adenosine monophosphate (cAMP) and minerals, but also increased the content of iron (Fe2+) and zinc (Zn2+), which have blood and eyesight tonic function. The value-added jujube juice might serve as a low-calorie and probiotic functional beverage and show high application potential in food industry.

Overcoming NADPH product inhibition improves D-sorbitol conversion to L-sorbose

Gluconobacter oxydans sorbitol dehydrogenase (GoSLDH) exhibits a higher catalytic efficiency than other l-sorbose producing enzymes. During the reaction catalysed by GoSLDH, NADP⁺ is reduced to NADPH and d-sorbitol is oxidized to l-sorbose. However, GoSLDH activity is inhibited by the NADPH (K_i = 100 μM) formed during the enzymatic reaction. Therefore, Escherichia coli_{gosldh-lrenox} producing both GoSLDH for d-sorbitol oxidation and LreNOX (NAD(P)H oxidase from Lactobacillus reuteri) for NADP⁺ regeneration was generated and used for l-sorbose production. Whole cell biocatalysts with the LreNOX cofactor recycling system showed a high conversion rate (92%) of d-sorbitol to l-sorbose in the presence of low concentration of NADP⁺ (0.5 mM). By alleviating NADPH accumulation during the catalytic reactions, E. coli_{gosldh-lrenox} exhibited 23-fold higher conversion rate of d-sorbitol than E. coli_gosldh. l-Sorbose production by E. coli_{gosldh-lrenox} reached 4.1 g/L after 40 min, which was 20.5-fold higher than that of E. coli_gosldh. We also constructed G. oxydans_gosldh and G. oxydans_{gosldh-lrenox} strains, and they exhibited 1.2- and 2.9-fold higher conversion rates than the wild-type G. oxydans KCTC 1091. The results indicate that overcoming NADPH product inhibition using LreNOX improves chemical production in NADP⁺-dependent enzymatic reactions.

Development of food-grade expression system for d-allulose 3-epimerase preparation with tandem isoenzyme genes in Corynebacterium glutamicum and its application in conversion of cane molasses to D-allulose

D-Allulose 3-epimerase (DAE) has been applied to produce D-allulose, a low-calorie and functional sweetener. In this study, a new DAE from Paenibacillus senegalensis was characterized in Escherichia coli. Furthermore, we presented a tandem isoenzyme gene expression strategy to express multiple DAEs in one cell and construct food-grade expression systems based on Corynebacterium glutamicum. Seventeen expression cassettes based on three DAE genes from different organisms were constructed. Among all recombinant strains, DAE16 harboring three DAE genes in an expression vector exhibited the highest enzyme activity with 22.7 U/mg. Whole-cell transformation of DAE16 produced 225 g/L D-allulose with a volumetric productivity of 353 g·g ^-1 ·hr ^-1 . The catalytic efficiency of strain C-DAE9 integrating total 11 DAE genes in chromosome was 16.4-fold higher than strains carrying one DAE. Fed-batch culture of C-DAE9 gave enzyme activity of 44,700 U/L. We also expressed a thermostable invertase in C. glutamicum and obtained enzyme activity of 29 U/mg. Immobilized cells expressing DAE or invertase exhibited 80% of retained activity after 30 cycles of catalytic reactions. Those immobilized cells were coupled to produce 61.2 g/L D-allulose from cane molasses in a two-step reaction process. This study provided an efficient approach for enzyme preparation and allowed access to produce D-allulose from other abundant and low-cost feedstock enriched with sucrose.

d-Allulose is a substrate of glucose transporter type 5 (GLUT5) in the small intestine

d-Allulose has been reported to have beneficial health effects. However, the transport system(s) mediating intestinal d-allulose transport has not yet been clearly identified. The aim of this study was to investigate whether intestinal d-allulose transport is mediated by glucose transporter type 5 (GLUT5). When d-allulose alone was gavaged, plasma d-allulose levels were dramatically higher in rats previously fed fructose. This suggests enhanced intestinal d-allulose absorption paralleled increases in GLUT5 expression observed only in fructose-fed rats. When d-allulose was gavaged with d-fructose, previously observed increases in plasma d-allulose levels were dampened and delayed, indicating d-fructose inhibited transepithelial d-allulose transport into plasma. Tracer D-[¹⁴C]-fructose uptake rate was reduced to 54.8% in 50 mM d-allulose and to 16.4% in 50 mM d-fructose, suggesting d-allulose competed with D-[¹⁴C]-fructose and the affinity of d-allulose for GLUT5 was lower than that of d-fructose. GLUT5 clearly mediates, likely at lower affinity relative to d-fructose, intestinal d-allulose transport.

The effect of small doses of fructose and allulose on postprandial glucose metabolism in type 2 diabetes: A double-blind, randomized, controlled, acute feeding, equivalence trial

AIM

To assess and compare the effect of small doses of fructose and allulose on postprandial blood glucose regulation in type 2 diabetes.

METHODS

A double-blind, multiple-crossover, randomized, controlled, acute feeding, equivalence trial in 24 participants with type 2 diabetes was conducted. Each participant was randomly assigned six treatments separated by >1-week washouts. Treatments consisted of fructose or allulose at 0 g (control), 5 g or 10 g added to a 75-g glucose solution. A standard 75-g oral glucose tolerance test protocol was followed with blood samples at -30, 0, 30, 60, 90 and 120 minutes. The primary outcome measure was plasma glucose incremental area under the curve (iAUC).

RESULTS

Allulose significantly reduced plasma glucose iAUC by 8% at 10 g compared with 0 g (717.4 ± 38.3 vs. 777.5 ± 39.9 mmol × min/L, P = 0.015) with a linear dose response gradient between the reduction in plasma glucose iAUC and dose (P = 0.016). Allulose also significantly reduced several related secondary and exploratory outcome measures at 5 g (plasma glucose absolute mean and total AUC) and 10 g (plasma glucose absolute mean, absolute and incremental maximum concentration [Cmax ], and total AUC) (P < .0125). There was no effect of fructose at any dose. Although allulose showed statistically significant reductions in plasma glucose iAUC compared with fructose at 5 g, 10 g and pooled doses, these reductions were within the pre-specified equivalence margins of ±20%.

CONCLUSION

Allulose, but not fructose, led to modest reductions in the postprandial blood glucose response to oral glucose in individuals with type 2 diabetes. There is a need for long-term randomized trials to confirm the sustainability of these improvements.

Adaptive Steered Molecular Dynamics Combined With Protein Structure Networks Revealing the Mechanism of Y68I/G109P Mutations That Enhance the Catalytic Activity of D-psicose 3-Epimerase From Clostridium Bolteae

The scarcity, richness, and other important physiological functions of D-psicose make it crucial to increase the yield of D-psicose. The production of D-psicose can be accomplished by D-psicose 3-epimerase (DPEase) from Clostridium bolteae (CbDPEase) catalyzing the substrate D-fructose. Although the catalytic efficiency of the CbDPEase has been raised via using the site-directed mutagenesis (Y68I/G109P) technique, structure-activity relationship in the wild-type CbDPEase and Y68I/G109P mutant is currently poorly understood. In our study, a battery of molecular modeling methods [homology modeling, adaptive steered molecular dynamics (ASMD) simulations, and Molecular Mechanics/Generalized Born Surface Area (MM-GB/SA)], combined with protein structure networks, were employed to theoretically characterize the reasons for the differences in the abilities of the D-fructose catalyzed by the wild-type CbDPEase and Y68I/G109P mutant. Protein structure networks demonstrated that site-directed mutagenesis enhanced the connectivity between D-fructose and CbDPEase, leading to the increased catalytic efficiency mediated by the functional residues with high betweenness. During the dissociation of the D-fructose from the Y68I/G109P mutant, planes of benzene rings of F248 and W114 could be continuously parallel to the stretching direction of D-fructose. It made the tunnel have an open state and resulted in the stable donor-π interactions between D-fructose and the benzene rings around 18Å. The stronger substrate-protein interactions were detected in the Y68I/G109P mutant, instead of in the wild-type CbDPEase, which were consistent with the binding free energy and Potential Mean of Force (PMF) results. The theoretical results illustrated the reasons that Y68I/G109P mutations increased the catalytic efficiency of CbDPEase and could be provided the new clue for further DPEase engineering.

Secretion of GLP-1 but not GIP is potently stimulated by luminal d-Allulose (d-Psicose) in rats

Glucagon-like peptide 1 (GLP-1), an incretin gastrointestinal hormone, is secreted when stimulated by nutrients including metabolizable sugars such as glucose and fructose. d-Allulose (allulose), also known as d-psicose, is a C-3 isomer of d-fructose and a rare sugar with anti-diabetic or anti-obese effects in animal models. In the present study, we examined whether an oral administration of allulose could stimulate GLP-1 secretion in rats, and investigated the underlying mechanisms. Oral, but not intraperitoneal, administration of allulose (0.5-2.0 g/kg body weight) elevated plasma GLP-1 levels for more than 2 h in a dose-dependent manner. The effects of allulose on GLP-1 secretion were higher than that of dextrin, fructose, or glucose. In addition, oral allulose increased total and active GLP-1, but not glucose-dependent insulinotropic polypeptide (GIP), levels in the portal vein. In anesthetized rats equipped with a portal catheter, luminal (duodenum and ileum) administration of allulose increased portal GLP-1 levels, indicating the luminal effect of allulose. Allulose-induced GLP-1 secretion was abolished in the presence of xanthohumol (a glucose/fructose transport inhibitor), but not in the presence of inhibitors of the sodium-dependent glucose cotransporter 1 or the sweet taste receptor. These results demonstrate a potent and lasting effect of orally administered allulose on GLP-1 secretion in rats, without affecting GIP secretion. The potent and selective GLP-1-releasing effect of allulose holds promise for the prevention and treatment of glucose intolerance through promoting endogenous GLP-1 secretion.

A Preliminary Study for Evaluating the Dose-Dependent Effect of d-Allulose for Fat Mass Reduction in Adult Humans: A Randomized, Double-Blind, Placebo-Controlled Trial

d-allulose is a rare sugar with zero energy that can be consumed by obese/overweight individuals. Many studies have suggested that zero-calorie d-allulose has beneficial effects on obesity-related metabolism in mouse models, but only a few studies have been performed on human subjects. Therefore, we performed a preliminary study with 121 Korean subjects (aged 20–40 years, body mass index ≥ 23 kg/m²). A randomized controlled trial involving placebo control (sucralose, 0.012 g × 2 times/day), low d-allulose (d-allulose, 4 g × 2 times/day), and high d-allulose (d-allulose, 7 g × 2 times/day) groups was designed. Parameters for body composition, nutrient intake, computed tomography (CT) scan, and plasma lipid profiles were assessed. Body fat percentage and body fat mass were significantly decreased following d-allulose supplementation. The high d-allulose group revealed a significant decrease in not only body mass index (BMI), but also total abdominal and subcutaneous fat areas measured by CT scans compared to the placebo group. There were no significant differences in nutrient intake, plasma lipid profiles, markers of liver and kidney function, and major inflammation markers among groups. These results provide useful information on the dose-dependent effect of d-allulose for overweight/obese adult humans. Based on these results, the efficacy of d-allulose for body fat reduction needs to be validated using dual energy X-ray absorption.