According to the definition of the ISRS, rare sugars refer to monosaccharides and their derivatives that are very rare in nature, mainly including rare monosaccharides and oligomers containing rare monosaccharides. There are only 7 types of monosaccharides that exist abundantly in nature, including D-glucose, D-fructose, and D-xylose, and the rest are rare sugars.

1. Represents of sugar substitutes: D-allulose, D-tagatose, and xylitol

Allulose is about 70% as sweet as sucrose and has only 10% of the calories. It has similar taste and volume characteristics to sucrose. It is called "low-calorie sucrose" and is a high-quality natural sweetener. In 2019, the US FDA issued draft guidance on the declaration of allulose on nutrition labels. The guidance agreed to exclude allulose from total sugar and added sugar labels. When labeled "calories" on nutrition labels, allulose is calculated at 0.4kcal/g per gram.

D-Tagatose has almost perfect sucrose sweetness, its sweetness is similar to that of sucrose, and its sweetness is 92% of sucrose. It is a good filling sweetener with basically no bad odor and aftertaste. It generates about 100 calories. It is 1/3 of sucrose and has an energy value of 1.5 kcal/g.

The sweetness of xylitol is similar to that of sucrose, and its calories are only 60% of that of sucrose. When dissolved in water, it absorbs heat and produces a pleasant cooling sensation in the mouth. It is also a high-quality natural sweetener.

2. Represents of regulating blood sugar: D-allulose, D-tagatose, isomaltulose, and trehalose

D-allulose can inhibit the activity of α-glucosidase in the intestine, protect islet β cells in the pancreas to improve insulin resistance, and increase glucose uptake by fat and muscle tissue.

D-tagatose has a low absorption rate in the body. Studies have shown that tagatose does not cause significant changes in fasting blood glucose and insulin levels in healthy subjects and patients with type II diabetes, and can significantly inhibit the intake of food in diabetic patients. The reason for the increase in blood sugar caused by glucose ingestion may be that in addition to the low absorption rate, tagatose also inhibits the absorption of glucose in the small intestine.

The beneficial effect of isomaltulose on blood sugar levels and its insulin response has been confirmed in various human clinical studies and in all populations, including healthy people, diabetics, during pregnancy and overweight people who can consume it for sugar control.

Trehalose can stabilize blood sugar levels by slowing blood sugar release and a milder insulin response.

3. Represents of weight management: D-allulose and isomaltulose

Studies have found that D-allulose can promote fat burning during exercise. A randomized, double-blind, placebo-controlled trial demonstrated the ability of D-allulose to reduce body fat mass in overweight or obese subjects. D-allulose is also added to Japanese functionally labeled foods to promote fat burning.

Isomaltulose can slowly release energy and continuously provide glucose to the body, thereby keeping blood sugar levels stable and helping to increase the fat burning rat

4. Represents of oral health: D-allulose, D-tagatose, and xylitol

D-allulose is not metabolized in the mouth and therefore does not cause enamel erosion or promote the growth of oral bacteria associated with the formation of cavities.

D-tagatose does not lower the pH value of dental plaque, is not fermented by oral bacteria, and does not cause dental caries. It has good effects on inhibiting dental plaque and removing bad breath.

Xylitol can stimulate saliva secretion and has a specific inhibitory effect on Streptococcus mutans (the main causative microorganism of dental caries). The European Food Safety Authority has approved a health claim "Xylitol chewing gum reduces the risk of dental caries in children."

5. Represents of improving intestinal flora: D-tagatose, xylitol, and isomaltulose

In the human body, only 20% of D-tagatose is absorbed by the small intestine. Most of the tagatose directly enters the colon and is selectively fermented by the microorganisms therein, promoting the proliferation of beneficial bacteria and inhibiting the growth of harmful bacteria, which can significantly improve the intestinal flora.

Xylitol can modulate the composition and activity of intestinal microorganisms. Xylitol is not digested by human enzymes. About 50% of xylitol enters the colon and serves as an energy and carbon source for intestinal microorganisms and forms short-chain fatty acids to provide energy to the host and support the homeostasis of the immune system.

Isomaltulose has prebiotic activity and can stimulate the growth of probiotic bacteria and the production of short-chain fatty acids.