Inulin is a widely used soluble dietary fiber, and together with galacto-oligosaccharides and fructo-oligosaccharides, has been identified as a prebiotic by the International Scientific Association for Probiotics and Prebiotics (ISAPP). It is mainly found in edible plants such as artichokes, asparagus, bananas, chicory, garlic, onions, leeks and wheat.

As early as 1987, after the EU Health Commission first approved inulin as a new resource food, the health departments of the United States, China, Japan and other countries have announced that inulin, as a soluble dietary fiber, can promote the growth of bifidobacteria and improve the digestive tract. Thanks to inulin’s ability to improve food texture and improve food rheological properties, inulin-based prebiotics are widely used in baked goods, snacks, dairy products, health food and baby food.

According to the statistics until February 2021, there are more than 350 clinical trials on inulin, and inulin has always been recognized as a universally safe food. However, in November 2022, Nature published an article on high-dose inulin-induced type 2 inflammatory response mediated by intestinal flora, bringing the debate on the safety and effectiveness of inulin into people's view. This article reviews the health benefits of inulin and discusses how to use it safely.

Health Benefits of Inulin.

Prebiotics specifically refer to food ingredients that are generally not digested and absorbed by the human body but can be selectively utilized by human microorganisms, can effectively improve the composition and/or activity of intestinal microorganisms, and benefit human health. Following the ISAPP definition of prebiotics, Hughes et al conducted a meta-analysis of clinical trials of inulin in adults. In all 78 clinical trials, the minimum inulin intake was 2.5g per day, the maximum was 30g per day, and the daily inulin intake in most (65) studies was less than 15g. The results showed that oral inulin-based prebiotics can effectively stimulate the growth of beneficial bacteria such as Bifidobacterium, Lactobacillus and Clostridium tenebilis in the human intestinal tract, increase satiety, reduce intestinal mucosal permeability, and relieve constipation. At the same time, the intake of inulin can also enhance the host's insulin sensitivity, reduce blood triglyceride levels, and increase the absorption rate of calcium ions and magnesium ions. In particular, it should be pointed out that in all 78 clinical trials, the main clinical side effect of oral inulin was abdominal flatulence, and there were no other negative effects on human health.

Over the past three decades, inulin-based fructan prebiotics have been widely used in infant formula while being marketed to adults. So far, more than 130 published clinical studies using inulin as a prebiotic to regulate infants, children and pregnant women have confirmed the safety and effectiveness of inulin-based prebiotics in infants and other special populations.

Potential adverse health effects of high doses of inulin.

In 2018 and 2022, scientists from different research institutions in the United States used mouse models as research objects to prove the relationship between the intake of inulin and type 2 inflammatory response, as well as the occurrence of liver cancer.

What really attracted people's attention was the human clinical trial published by Lancaster et al. in Cell Host & Microbes. In this study, 18 subjects adopted a crossover test mode, and after three weeks of ingestion of low (10g), medium (20g), and high (30g) doses of inulin or soluble arabinoxylan, the ALT of the high-dose inulin intake group was significantly changed. And the inflammatory factors in plasma including IL-6, TGF-b and VEGF-a were significantly increased. However, the content of metabolites in the plasma of the low and medium dose group was not affected, suggesting that the intake of high doses of inulin can cause significant inflammatory responses in the human body. Therefore, compared with the positive research results of hundreds of inulin clinical studies, although there is only one human trial and two mouse research results, the possible risks of excessive intake of inulin really sounded the alarm for us.

The intake of prebiotics should follow the basic axioms of nutrition.

Balanced nutrition is the basis for ensuring human health. The Chinese Nutrition Society pointed out that the daily diet of normal adults should include grains and potatoes, vegetables and fruits, livestock, poultry, fish, eggs, milk, soybeans and nuts. At the same time, it is recommended that each person should take in 12 kinds of food every day and more than 25 kinds of food every week. Only by maintaining the diversity of food types can we ensure a sufficient amount and type of dietary fiber and prebiotics intake every day. Because different dietary fibers and prebiotics have different monosaccharide compositions and glycosidic bonds, they have different selective powers in promoting the growth of specific intestinal flora in the human body. Artificially increasing the intake of a dietary fiber/prebiotic is very likely to shift the balance point of the intestinal flora structure of healthy people, directly affect the content of the host and the metabolites of the flora, and cause potential health risks. Therefore, the axiom of nutrition should be followed in the intake of dietary fiber/prebiotics: the intake of dietary fiber/prebiotics with the best functions should be limited, and excessive intake is likely to cause an imbalance of intestinal flora.

According to the Chinese Nutrition Society’s recommended dietary fiber intake of 25-30g per person per day, the optimal intake of soluble dietary fiber such as inulin should be kept at 10-15g, which is just in line with the recommended amount of inulin by the health department of our country. An article published in Cell Host & Microbes in 2022 also confirmed that a daily intake of less than 20g of inulin has no harmful effect on human health. In short, the optimal health state of the intestinal microecology is in a healthy and balanced state, and a diverse and healthy intestinal flora can be cultivated through a diverse diet structure, which is also widely recognized by scientists all over the world.