Effect of fructose and its epimers on postprandial carbohydrate metabolism: A systematic review and meta-analysis.

AIMS: To synthesize the evidence of the effect of small doses (≤30-g/meal) of fructose and its epimers (allulose, tagatose, and sorbose) on the postprandial glucose and insulin response to carbohydrate-containing meals. METHODS: MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials were searched through to April 9, 2019. We included randomized (RCTs) and non-randomized acute, single-meal, controlled feeding trials that added ≤30-g of fructose or its epimers either prior to or with a carbohydrate-containing meal compared with the same meal alone. Outcomes included the incremental area under the curve (iAUC) for glucose and insulin, the Matsuda Insulin Sensitivity Index, and the Early Insulin Secretion Index. Data were expressed as ratio of means (RoM) with 95% CIs and pooled using the inverse variance method. The overall certainty of the evidence was evaluated using GRADE. RESULTS: Forty trial comparisons (n = 400) were included (none for sorbose). Allulose significantly reduced the postprandial iAUC glucose response by 10% (0.90 [0.84 to 0.96], P < 0.01). Tagatose significantly reduced the postprandial iAUC insulin response by 25% (0.75 [0.62 to 0.91], P < 0.01) and showed a non-significant 3% reduction in the postprandial iAUC glucose response (0.97 [0.94 to 1.00], P = 0.07). There was no effect of fructose on any outcome. The certainty of the evidence was graded as low to moderate for fructose, moderate for allulose, and low for tagatose. CONCLUSIONS: Small doses of allulose and tagatose, but not fructose, lead to modest improvements on postprandial glucose and insulin regulation. There is a need for long-term RCTs to confirm the sustainability of these improvements.

Gas chromatography - Mass spectrometry as a preferred method for quantification of insect hemolymph sugars.

Insects, due to their small size, have limited energy storage space, but they also have high metabolic rate, so their hemolymph sugars are incredibly dynamic and play a number of important physiological functional roles in maintaining energetic homeostasis. In contrast to vertebrates, trehalose is generally the primary sugar found in insect hemolymph, which is followed by glucose and fructose. Many analytical chemistry methods exist to measure sugars, yet a direct comparison of methods that can measure all three simultaneously, and trehalose in particular, from low sample volumes, are sparse. Using the honey bee as a model, we directly compare the leading current methods of using High Performance Liquid Chromatography (HPLC) with an evaporative light-scattering detector and Gas Chromatography coupled with Mass Spectrometry (GC-MS) to determine which method would be better for measuring trehalose, glucose, and fructose in terms of reproducibility, accuracy, and sensitivity. Furthermore, we injected the enzyme inhibitors trehalozin (a trehalase inhibitor) and sorbose (a trehalase p-synthase inhibitor) to manipulate the trehalose levels in honey bee foragers as a proof of concept that this sugar can be altered independently of hemolymph glucose and fructose levels. Overall the HPLC method was less reproducible for measuring fructose and glucose, and it also had lower sensitivity for measuring trehalose. Consequently, significant differences in trehalose levels within the forager class were only detected with the GC-MS and not the HPLC method. Lastly, using the GC-MS method in the follow up study we found that trehalozin and sorbose causes a significant increase and decrease of trehalose levels respectively, in forager honey bees, independent of the glucose and fructose levels, ten minutes after injection. Taken together, these methods will provide useful tools for future studies exploring the many different physiological functional roles that trehalose can play in maintaining insect energetic homeostasis.

The Effect of Small Doses of Fructose and Its Epimers on Glycemic Control: A Systematic Review and Meta-Analysis of Controlled Feeding Trials.

Objective: Contrary to the concerns that fructose may have adverse metabolic effects, an emerging literature has shown that small doses (≤10 g/meal) of fructose and its low-caloric epimers (allulose, tagatose, and sorbose) decrease the glycemic response to high glycemic index meals. Whether these acute reductions manifest as sustainable improvements in glycemic control is unclear. Our objective was to synthesize the evidence from controlled feeding trials that assessed the effect of small doses of fructose and its low-caloric epimers on glycemic control. Methods: We searched MEDLINE, EMBASE, and the Cochrane Library through April 18, 2018. We included controlled feeding trials of ≥1 week that investigated the effect of small doses (≤50 g/day or ≤10% of total energy intake/day) of fructose and its low-caloric epimers on HbA1c, fasting glucose, and fasting insulin. Two independent reviewers extracted data and assessed risk of bias. Data were pooled using the generic inverse variance method and expressed as mean differences (MDs) with 95% confidence intervals (CIs). Heterogeneity was assessed using the Cochran Q statistic and quantified using the I² statistic. Grading of Recommendations Assessment, Development and Evaluation (GRADE) assessed the certainty of the evidence. Results: We identified 14 trial comparisons (N = 337) of the effect of fructose in individuals with and without diabetes, 3 trial comparisons (N = 138) of the effect of allulose in individuals without diabetes, 3 trial comparisons (N = 376) of the effect of tagatose mainly in individuals with type 2 diabetes, and 0 trial comparisons of the effect of sorbose. Small doses of fructose and tagatose significantly reduced HbA1c (MD = -0.38% (95% CI: -0.64%, -0.13%); MD = -0.20% (95% CI: -0.34%, -0.06%)) and fasting glucose (MD = -0.13 mmol/L (95% CI: -0.24 mmol/L, -0.03 mmol/L)); MD = -0.30 mmol/L (95% CI: -0.57 mmol/L, -0.04 mmol/L)) without affecting fasting insulin (p > 0.05). Small doses of allulose did not have a significant effect on HbA1c and fasting insulin (p > 0.05), while the reduction in fasting glucose was of borderline significance (p = 0.05). The certainty of the evidence of the effect of small doses of fructose and allulose on HbA1c, fasting glucose, and fasting insulin was graded as low. The certainty of the evidence of the effect of tagatose on HbA1c, fasting glucose, and fasting insulin was graded as moderate. Conclusions: Our results indicate that small doses of fructose and tagatose may improve glycemic control over the long term. There is a need for long-term randomized controlled trials for all four sugars to improve our certainty in the estimates.

Metabolism of L-sorbose in the rat and the effect of the intestinal microflora on its utilization both in the rat and in the human.

L-[U-14C]-sorbose was administered orally as single doses to 5 normal rats. The recovery of radioactivity was 5.3% in the urine, 46% in the faeces exclusively as L-sorbose 16% as carbon dioxide. Caloric utilization was approximately 25%. A second group of 3 rats that had previously received L-sorbose in their diet showed 14C recoveries of 8.9% in the urine, 6.6% in the faeces and 59% as carbon dioxide. The time course of expired carbon dioxide suggests that a portion of L-sorbose was rapidly absorbed and partially metabolized while the principal pathway involved fermentation by the intestinal microflora to volatile fatty acids which were subsequently absorbed and metabolized. The total caloric utilization of L-sorbose was estimated to be 70%. It was observed that a human intestinal microflora also required an adaptation period in order to ferment this sugar. The efficiency of the fermentation was estimated to be 70%.

Feeding behavior in growing rats fed diets containing sorbose.

The effect of dietary sorbose on food and water consumption was investigated in growing rats. Rats (26-day old) were fed diets containing 0, 100, 200 or 300 g sorbose/kg diet for 5 weeks in Experiment 1. Daily food and water intakes were measured at day 0, 7, 14, 21, 28 and 35. Absolute food intake (g) until day 21 decreased linearly with increasing sorbose levels and so did relative food intake (g/100 g b.wt.) until day 7. In contrast, relative water intake (ml/100 g b.wt.) and water:food intake ratio (ml/g) remained high by day 7 with increasing sorbose levels. In Experiment 2, the effect of sorbose on the short-term food intake was compared with those of glucose, sucrose and maltitol in growing rats (25-day old) at a level of 100 g/kg diet in order to investigate how quickly reduced food intake would be induced by sorbose consumption. Cumulative food intake was determined every hour for the first ten hours, then at two-hour intervals thereafter during the 24-hour period that followed feeding. As rapid as 6 hours after feeding, cumulative food intake significantly decreased in sorbose-fed animals compared with other dietary groups. It was concluded that sorbose consumption decreased the food intake of growing rats from 6 hours to a few weeks after feeding, but this inhibitory effect disappeared afterwards.

Potential anthelmintic: D-psicose inhibits motility, growth and reproductive maturity of L1 larvae of Caenorhabditis elegans.

No anthelmintic sugars have yet been identified. Eight ketohexose stereoisomers (D- and L-forms of psicose, fructose, tagatose and sorbose), along with D-galactose and D-glucose, were examined for potency against L1 stage Caenorhabditis elegans fed Escherichia coli. Of the sugars, D-psicose specifically inhibited the motility, growth and reproductive maturity of the L1 stage. D-Psicose probably interferes with the nematode nutrition. The present results suggest that D-psicose, one of the rare sugars, is a potential anthelmintic.

Prevention of the incidence of diabetes by dietary sorbose in nonobese diabetic mice.

The effect of dietary sorbose on the prevention of the incidence of diabetes in the nonobese diabetic mouse was investigated in animals from 5 to 11 wk of age. When sucrose (200 g/kg diet) in the control diet was replaced by sorbose, body weight was significantly reduced. The blood glucose level also was lowered in mice fed sorbose, but the serum insulin level was unchanged. Glucose was not detected in the urine of mice fed the sorbose diet during the experiment, but some mice in the control group excreted glucose in urine. Relative weights of the heart, liver and left kidney were significantly higher in mice fed the sorbose diet vs. those fed the control diet. The results suggest that dietary sorbose would benefit patients with diabetes by lowering blood glucose and inhibiting urinary glucose excretion.

Dietary sorbose prevents and improves hyperglycemia in genetically diabetic mice.

The effect of dietary sorbose on the prevention (Experiment 1) and amelioration (Experiment 2) of diabetes was investigated in the genetically diabetic mouse [C57BL/KsJ (db/db)] for 6 wk. When sucrose (200 g/kg diet) in a control diet was replaced by sorbose, the blood glucose concentration was dramatically lower, but the serum insulin concentrations did not differ. When mice were fed the diets before the onset of diabetic symptoms, glucose excretion in urine was prevented in the mice fed the sorbose diet, but mice fed the control diet excreted glucose in the urine, and the concentration increased with age. When dietary treatment began after the development of diabetic symptoms, dietary sorbose greatly reduced the incidence of hyperglycemia and lowered urinary glucose excretion, compared with mice fed the sucrose-containing diet. These results suggest that dietary sorbose might be useful in patients with, or at risk of developing, noninsulin-dependent diabetes, both before and after exhibiting the syndrome.