Effects of inulin-type fructans on lipid metabolism in man and in animal models

Yacon syrup: beneficial effects on obesity and insulin resistance in humans

BACKGROUND & AIMS

Syrup obtained from yacon roots could be well positioned as a nutraceutical product due to its high fructooligosaccharides content. We examined the beneficial effects and tolerance of yacon syrup on human health.

METHODS

Obese and slightly dyslipidemic pre-menopausal women were studied over a 120-day period in a double-blind placebo-controlled experiment. We used two doses of yacon syrup, 0.29 g and 0.14 g fructooligosaccharides/kg/day. At the start and end of the study, anthropometric measurements, blood glucose, calcium, lipid and insulin concentrations and Homeostasis Model Assessment index were determined.

RESULTS

The recommended daily consumption of yacon syrup with no undesirable gastrointestinal effects is 0.14 g fructooligosaccharides/kg. Daily intake of yacon syrup produced a significant decrease in body weight, waist circumference and body mass index. Additionally, decrease in fasting serum insulin and Homeostasis Model Assessment index was observed. The consumption of yacon syrup increased defecation frequency and satiety sensation. Fasting glucose and serum lipids were not affected by syrup treatment and the only positive effect was found in serum LDL-cholesterol levels.

CONCLUSIONS

Yacon syrup is a good source of fructooligosaccharides and its long-term consumption produced beneficial health effects on obese pre-menopausal women with insulin resistance.

[Non alcoholic fatty liver disease: treatment with soluble fibres]

The pilot study evaluated the efficiency of oral soluble fibers to treat patients with nonalcoholic fatty liver disease. Twelve patients received 10 g/day of soluble fibers during 3 months. After the treatment 100% of patients presented reduction in body mass index, waist circumference and insulin resistance index. In 66.7% of the patients were observed reduction of the cholesterol levels and 75% presented normal liver enzymes (AST, ALT, and GGT). The present study suggests that oral soluble fibers may be useful to control risk factors and liver enzymes in patients with nonalcoholic fatty liver disease. However, future studies with histological controls are considered necessary.

Changes in infants faecal characteristics and microbiota by inulin supplementation

The effects of inulin on the microbial composition and faecal characteristics in 36 healthy, formula-fed infants (average age 7.7 months) given 3 different daily dosages of native inulin (0.75 g/day, 1.00 g/day, and 1.25 g/day) were studied. At all levels of inulin consumption, a significant (p<0.05) reduction of potential pathogenic microorganisms such as clostridia was found. An intake of 1.25 g/day of inulin caused a significant (p<0.05) increase of Bifidobacterium spp. as well as a significant (p<0.05) decline in Gram-positive cocci and coliform bacteria. Inulin consumption resulted in a significant (p<0.05) decrease in faecal pH value and changes in faecal weight, faecal texture and colour, indicating improvement in healthy bile production and bacterial fermentation. It is concluded that inulin consumption in formula-fed infants after weaning positively affected the microbial composition of faeces and faecal properties.

Lipid metabolism and antioxidant status in sucrose vs. potato-fed rats

OBJECTIVE

Consumption of high levels of simple carbohydrates is associated with several metabolic disorders in humans and in laboratory animals, including symptoms of an early stage of metabolic syndrome (syndrome X). This disorder has several cardiovascular risk factors, such as hypertriglyceridemia, and is associated with an increase in oxidative stress. In contrast to sucrose, potato, a source of complex carbohydrates and antioxidant micronutrients, was thought to improve lipid metabolism and antioxidant protection.

METHODS

We investigated the effects of diets containing i) complex dietary carbohydrates and antioxidant micronutrients (potato Solanum tuberosum L.), ii) complex carbohydrates (starch) and iii) a simple carbohydrate (sucrose) on lipid metabolism and antioxidant status in rats.

RESULTS

An increase in short chain fatty acid (SCFA) pools was observed in the cecum of rats fed a potato-based diet, resulting from an increase in all SCFAs, especially propionate (+360%, P < 0.0001). Feeding rats a potato-based diet for 3 weeks led to a decrease in cholesterol (-37%, potato vs. control and -32%, potato vs. sucrose) and triglycerides (-31%, potato vs. control and -43%, potato vs. sucrose) concentrations in triglyceride-rich lipoproteins (TGRLP) fractions. The antioxidant status was decreased by sucrose consumption and improved by potato consumption.

CONCLUSIONS

Our present results suggest that consumption of complex carbohydrates (provided as cooked potatoes), in combination with different antioxidant micronutrients, may enhance the antioxidant defences and improve lipid metabolism, when compared with starch (complex carbohydrates) and to sucrose consumption (source of simple sugar). These effects limit oxidative stress and reduce the risk of developing the associated degenerative diseases, including cardiovascular disease, and could have potential in cardiovascular disease prevention.

Glucose tolerance, lipids, and GLP-1 secretion in JCR:LA-cp rats fed a high protein fiber diet

BACKGROUND

We have shown that individually, dietary fiber and protein increase secretion of the anorexigenic and insulinotropic hormone, glucagon-like peptide-1 (GLP-1).

OBJECTIVE

Our objective was to combine, in one diet, high levels of fiber and protein to maximize GLP-1 secretion, improve glucose tolerance, and reduce weight gain.

METHODS AND PROCEDURES

Lean (+/?) and obese (cp/cp) male James C Russell corpulent (JCR:LA-cp) rats lacking a functional leptin receptor were fed one of four experimental diets (control, high protein (HP), high fiber (HF, prebiotic fiber inulin), or combination (CB)) for 3 weeks. An oral glucose tolerance test (OGTT) was performed to evaluate plasma GLP-1, insulin and glucose. Plasma lipids and intestinal proglucagon mRNA expression were determined.

RESULTS

Energy intake was lower with the HF diet in lean and obese rats. Weight gain did not differ between diets. Higher colonic proglucagon mRNA in lean rats fed a CB diet was associated with higher GLP-1 secretion during OGTT. The HP diet significantly reduced plasma glucose area under the curve (AUC) during OGTT in obese rats, which reflected both an increased GLP-1 AUC and higher fasting insulin. Diets containing inulin resulted in the lowest plasma triglyceride and total cholesterol levels.

DISCUSSION

Overall, combining HP with HF in the diet increased GLP-1 secretion in response to oral glucose, but did not improve glucose tolerance or lipid profiles more than the HF diet alone did. We also suggest that glycemic and insulinemic response to prebiotics differ among rat models and future research work should examine their role in improving glucose tolerance in diet-induced vs. genetic obesity with overt hyperleptinemia.

Inulin-type fructans in healthy aging

Worldwide, the population is aging, with estimates of 1 billion people aged 60 y or over within the next 20 y. With aging comes a reduction in overall health and increased morbidity and mortality due to infectious disease. Mortality due to gastrointestinal infections is up to 400 times higher in the elderly compared with younger adults. Recent studies have shown that the gut microbiota changes in old age, with an increased number of bacterial groups represented in the predominant elderly gut microbiota. This change in species "evenness" coincides with parallel changes in immune function, diet, and lifestyle and may contribute to disease susceptibility and severity in old age. The intestinal microbiota may thus be identified as an important target for improving health through reduced disease risk. Here, the application of prebiotics, especially the inulin-type fructans, and synbiotics (prebiotics combined with efficacious probiotic strains) will be discussed in terms of microbiota modulation and impact on disease risk in the aged population. Recent human intervention studies have confirmed the microbiota modulatory capability of the inulin-type fructans in the elderly and there is some evidence for reduced risk of disease. However, there is a need for more and larger human intervention studies to determine the efficacy of prebiotics in the elderly, particularly studies that take advantage of recent high resolution analytical methodologies like metabonomics, to shed light on possible prebiotic mechanisms of action.

Dietary fructans and serum triacylglycerols: a meta-analysis of randomized controlled trials

Convincing evidence indicates that the intake of inulin-type fructans, inulin and oligofructose, has beneficial effects on blood lipid changes in animals, although data in humans have been considered contradictory. We conducted a meta-analysis of available literature to quantify the effects in humans of dietary inulin-type fructans on serum triacylglycerols. Fifteen eligible randomized, controlled trials published from 1995 to 2005, for a total of 16 comparisons, were identified from the PubMed (National Library of Medicine, Bethesda, MD) and SCOPUS (Elsevier B.V., Amsterdam, NL) databases. Standardized mean effect sizes were calculated for net changes in serum triacylglycerol concentrations using random-effect model. The intake of inulin-type fructans was associated with significant decreases in serum triacylglycerols by 0.17 mmol/L (95%CI -0.33, -0.01; Z = 2.12, P = 0.04) or 7.5%. Given the limited number of studies, no specific effects for gender, amount fed, duration of the study, background diet, overweight, hyperlipidemia, or diabetes were further formally investigated, but, from the test for heterogeneity [chi(2) = 13.34, df = 15, (P = 0.55), I(2) = 0%], it appears that the effect of inulin-type fructans on circulating triacylglycerols is consistent across conditions. In conclusion, dietary inulin-type fructans significantly reduced serum triacylglycerols. The mechanisms, possibly related to colonic fermentation and/or incretin release from the distal gut, warrant further studies.

Inulin-type fructans: functional food ingredients

A food (ingredient) is regarded as functional if it is satisfactorily demonstrated to affect beneficially 1 or more target functions in the body beyond adequate nutritional effects. The term inulin-type fructans covers all beta(2<--1) linear fructans including native inulin (DP 2-60, DP(av) = 12), oligofructose (DP 2-8, DP(av) = 4), and inulin HP (DP 10-60, DP(av) = 25) as well as Synergy 1, a specific combination of oligofructose and inulin HP. Inulin-type fructans resist digestion and function as dietary fiber improving bowel habits. But, unlike most dietary fibers, their colonic fermentation is selective, thus causing significant changes in the composition of the gut microflora with increased and reduced numbers of potentially health-promoting bacteria and potentially harmful species, respectively. Both oligofructose and inulin act in this way and thus are prebiotic: they also induce changes in the colonic epithelium and in miscellaneous colonic functions. In particular, the claim "inulin-type fructans enhance calcium and magnesium absorption" is scientifically substantiated, and the most active product is oligofructose-enriched inulin (Synergy 1). A series of studies furthermore demonstrate that inulin-type fructans modulate the secretion of gastrointestinal peptides involved in appetite regulation as well as lipid metabolism. Moreover, a large number of animal studies and preliminary human data show that inulin-type fructans reduce the risk of colon carcinogenesis and improve the management of inflammatory bowel diseases. Inulin-type fructans are thus functional food ingredients that are eligible for enhanced function claims, but, as more human data become available, risk reduction claims will become scientifically substantiated.

Effect of prebiotic galacto-oligosaccharide, long-chain fructo-oligosaccharide infant formula on serum cholesterol and triacylglycerol levels

OBJECTIVE

Cholesterol is a nutrient of essential importance in infant feeding because it is necessary in membrane development. In adults with high lipid levels, high doses of inulin (oligofructose) inconsistently decreased levels of serum cholesterol. The aim of the present study was to evaluate cholesterol and triacylglycerol levels in infants receiving a formula with a specific mixture of 0.6 g/100 mL of galacto-oligosaccharides (GOS) and long-chain fructo-oligosaccharides (lcFOS) in a ratio of 9/1, a control formula, or breast milk. Because the level of lcFOS in the infant milk is low, we hypothesized that there would be no differences between the formula groups.

METHODS

Two hundred fifteen infants were included in a prospective, randomized, double-blinded, placebo-controlled trial during the first 6 mo of life. Formula-fed infants were randomized to receive a standard infant formula with a specific mixture of 0.6 g/100 mL of GOS/lcFOS, in a ratio of 9/1, or a control formula. Breast-fed infants were randomized to receive one of these two formulas after the mother had decided to discontinue breastfeeding. Serum levels of cholesterol, high-density lipoprotein, low-density lipoprotein (LDL), and triacylglycerol were determined at 8 and 26 wk of age and were provided for infants who received the GOS/lcFOS formula or control formula from birth or after cessation of breastfeeding and for the subgroups that were fully fed with breast milk and formula.

RESULTS

One hundred eighty-seven infants completed the study. Total cholesterol and LDL levels at 8 and 26 wk were significantly lower in the formula-fed groups than in the breast-fed infants. There were no significant differences between the formula-fed groups. Levels of triacylglycerols and high-density lipoprotein did not differ between groups.

CONCLUSION

Our study demonstrated no differences in total cholesterol and LDL cholesterol in infants receiving an infant formula with GOS/lcFOS from infants receiving a control infant formula. Furthermore, total cholesterol and LDL cholesterol levels were higher in breast-fed infants than in formula-fed infants.

Long-term administration of inulin-type fructans has no significant lipid-lowering effect in normolipidemic humans

Short-term studies have shown that the addition to diet of inulin-type fructans, a nondigestible carbohydrate, may have a plasma lipid-lowering effect in humans. Whether this beneficial effect persists during long-term administration has not been determined. The study was aimed at determining whether a prolonged (6 months) administration of inulin-type fructans to healthy subjects has a lipid-lowering action. In a double-blind, randomized, placebo-controlled study, 17 healthy subjects were studied before and after 6 months of daily administration of placebo (8 subjects) or 10 g of a mix of inulin and oligofructose (9 subjects). During this 6-month period, they consumed their usual diet and did not modify their everyday way of life. We measured plasma lipid concentrations; cholesterol synthesis and hepatic lipogenesis; and adipose tissue and circulating mononuclear cell messenger RNA concentrations of key regulatory genes of cholesterol metabolism. Compared with the administration of placebo, the administration of inulin-type fructans had no effect on plasma triacylglycerol concentrations and hepatic lipogenesis and induced only a nonsignificant trend for decreased plasma total and low-density lipoprotein cholesterol levels and increased high-density lipoprotein cholesterol concentration. Cholesterol synthesis was not significantly modified. Of all the messenger RNA concentrations measured, none was significantly modified by the administration of inulin-type fructans. In conclusion, contrary to what was observed in short-term studies, we observed no significant beneficial effect of a long-term (6-month) administration of inulin-type fructans on plasma lipids in healthy human subjects.

Inulin attenuates atherosclerosis in apolipoprotein E-deficient mice

Effects of different inulin-type fructan fractions were studied on atherosclerotic plaque formation in male apo E-deficient mice. Thirty-two mice were randomly divided into four groups and received either a semi-purified sucrose-based diet (control group), or diets in which sucrose was replaced in part by various inulin-type fructans (10 g/100 g): long-chain inulin, oligofructose, or an oligofructose-enriched inulin for 16 weeks. The presence of atherosclerotic plaques was assessed by histomorphometry in the aortic sinus. The apo E-deficient mice fed long-chain inulin or an oligofructose-enriched inulin had about 35 % and 25 % less atherosclerotic lesion area compared with the control group, respectively. Feeding long-chain inulin significantly reduced plasma cholesterol concentrations (P<0.001), and the three inulin-type fructans reduced triacylglycerol (TAG) concentrations compared with the control group (P<0.001). Both the long-chain inulin and an oligofructose-enriched inulin significantly lowered hepatic cholesterol concentrations compared with the control diet (P<0.05). Hepatic TAG concentrations were significantly lower in all three groups fed the fructan-supplemented diets v. the control group (P<0.0001). The results of the present study suggest that inhibition of atherosclerotic plaque formation is more potent in the presence of long-chain inulin, either alone or in combination with oligofructose (an oligofructose-enriched inulin), and that this probably is related to changes in lipid metabolism.

Cross-feeding between Bifidobacterium longum BB536 and acetate-converting, butyrate-producing colon bacteria during growth on oligofructose

In vitro coculture fermentations of Bifidobacterium longum BB536 and two acetate-converting, butyrate-producing colon bacteria, Anaerostipes caccae DSM 14662 and Roseburia intestinalis DSM 14610, with oligofructose as the sole energy source, were performed to study interspecies interactions. Two clearly distinct types of cross-feeding were identified. A. caccae DSM 14662 was not able to degrade oligofructose but could grow on the fructose released by B. longum BB536 during oligofructose breakdown. R. intestinalis DSM 14610 could degrade oligofructose, but only after acetate was added to the medium. Detailed kinetic analyses of oligofructose breakdown by the last strain revealed simultaneous degradation of the different chain length fractions, in contrast with the preferential degradation of shorter fractions by B. longum BB536. In a coculture of both strains, initial oligofructose degradation and acetate production by B. longum BB536 took place, which in turn also allowed oligofructose breakdown by R. intestinalis DSM 14610. These and similar cross-feeding mechanisms could play a role in the colon ecosystem and contribute to the combined bifidogenic/butyrogenic effect observed after addition of inulin-type fructans to the diet.

Short-chain fatty acids: ready for prime time?

The concept of colonic health has become a major target for the development of functional foods such as probiotics, prebiotics, and synbiotics. These bioactive agents have a profound effect on the composition of the microflora, as well as on the physiology of the colon, and display distinct health benefits. Dietary carbohydrates escaping digestion/absorption in the small bowel and prebiotics undergo fermentation in the colon and give rise to short-chain fatty acids (SCFA). As the main anions of the colon and the major source of energy for colonocytes, SCFA are rapidly absorbed by nonionic diffusion mostly but also by active transport mediated by a sodium-coupled transporter, thereby fostering the absorption of sodium and water. SCFA in general and butyrate in particular enhance the growth of lactobacilli and bifidobacteria and play a central role on the physiology and metabolism of the colon. The effect of prebiotics on cell proliferation, differentiation, apoptosis, mucin production, immune function, mineral absorption, lipid metabolism, and gastrointestinal (GI) peptides has been well documented experimentally. These effects seem to be largely mediated by SCFA, but evidence from human studies remains inconsistent. The food industry is making a leap of faith in their efforts to commercialize prebiotics and exploit potential health benefits. The future lies with the design of studies to further explore basic mechanisms, and gene expression in particular, but emphasis should be placed on human intervention trials.

Review article: prebiotics in the gastrointestinal tract

BACKGROUND

Prebiotics are short-chain carbohydrates that alter the composition, or metabolism, of the gut microbiota in a beneficial manner. It is therefore expected that prebiotics will improve health in a way similar to probiotics, whilst at the same time being cheaper, and carrying less risk and being easier to incorporate into the diet than probiotics.

AIM

To review published evidence for prebiotic effects on gut function and human health.

METHODS

We searched the Science Citation Index with the terms prebiotic, microbiota, gut bacteria, large intestine, mucosa, bowel habit, constipation, diarrhoea, inflammatory bowel disease, Crohn's disease, ulcerative colitis, pouchitis, calcium and cancer, focussing principally on studies in humans and reports in the English language. Search of the Cochrane Library did not identify any clinical study or meta-analysis on this topic.

RESULTS

Three prebiotics, oligofructose, galacto-oligosaccharides and lactulose, clearly alter the balance of the large bowel microbiota by increasing bifidobacteria and Lactobacillus numbers. These carbohydrates are fermented and give rise to short-chain fatty acid and intestinal gas; however, effects on bowel habit are relatively small. Randomized-controlled trials of their effect in a clinical context are few, although animal studies show anti-inflammatory effects in inflammatory bowel disease, while calcium absorption is increased.

CONCLUSIONS

It is still early days for prebiotics, but they offer the potential to modify the gut microbial balance in such a way as to bring direct health benefits cheaply and safely.