The fibre landscape is undergoing a shift in terms of functionality and consumer-friendly marketing. Whole-grain FDA-permitted health claims have ignited the search for new fibre sources. Mark J Tallon, PhD, examines the novelty and differentiation expected from the next generation of fibre sources, including delivery system differences, and their associated implications for health

Fibre is a digestive aid that can be defined as soluble or insoluble, classifications based around its ability to dissolve in water. Sources can be extracted and delivered from many natural products including barley, buckwheat, corn, quinoa, rye, triticale, wheat and wild rice. Soluble and insoluble categories of fibre can be present at different ratios and amounts in these sources, and as such confer significantly different functional properties, particularly following fermentation of soluble fibres, which can be metabolically active and health enhancing.

The use of food-based fibres in human nutrition has demonstrated an ability to regulate postprandial blood-sugar and insulin levels,1 decrease the risk of cardiovascular disease (CVD),2 and improve digestive health.3 Recent studies are even showing applications in weight-loss, cancer and bone-health markets. As such, the following gives an overview of the best of the crop.

Psyllium solubility
The functional properties of fibre as previously discussed are integrally linked to its rate of digestion (solubility). In a study conducted in Spain, researchers investigated the effect of soluble- and insoluble-fibre consumption derived from psyllium (Plantago ovata) husk on lipid-risk factors in patients with CVD.4

The researchers compared the effects of soluble P. ovata husk fibre with those of insoluble P. ovata seed fibre on plasma lipid, lipoprotein, and apolipoprotein (apo) concentrations within a CVD secondary prevention programme. In a randomised, crossover, controlled design, 28 men with CVD (myocardial infarction or stable angina) consumed a low saturated-fat diet supplemented with 10.5g P. ovata husk/day or 10.5g P. ovata seeds/d for eight weeks.4

Plasma triacylglycerol decreased, as did the ratio of apo B 100 to apo A-I, while apo A-I increased (4.3 per cent) in P. ovata husk consumers. Compared with the intake of insoluble fibre, the intake of P. ovata husk increased HDL-cholesterol concentrations by 6.7 per cent and decreased the ratio of total to HDL cholesterol and of LDL to HDL cholesterol by 10.6 per cent and 14.2 per cent, respectively.

The take-home lessons from the markers analysed within this study suggest that P. ovata husk intake reduces cardiovascular disease risk-factor profiles to a greater extent than an equivalent intake of insoluble fibre.

Fibre for weight management
The influence of exercise on health and particularly weight loss and body composition has been well reported within the academic literature. However, the use of dietary fibre as an adjunct to enhance the favourable effects of exercise has not been investigated to a significant degree.

Glucomannan (konjac) was used by researchers recently looking to rectify this by investigating the combined influence of soluble fibre and exercise on body composition and blood markers of cardiovascular health.5

In an eight-week supplementation and exercise study, 22 sedentary men and women who were overweight were given 3,000mg glucomannan combined with either no exercise (No-Ex) or a resistance and endurance exercise training programme (Ex). The exercise training consisted of three weekly sessions of approximately one hour of a nonlinear periodised total-body resistance exercise programme followed by 30 minutes of endurance exercise.

After the intervention, there were reductions in body mass, fat mass, total cholesterol and low-density lipoprotein cholesterol. Exercise significantly improved high-density lipoprotein cholesterol (HDL-C), TC/HDL-C ratio, squat and bench press one-repetition maximum, and distance covered during a shuttle-run test. In addition, exercise appeared to augment the reduction in fat mass (by 63 per cent and 50 per cent for men and women, respectively) and waist circumference, but did not affect total weight loss. Exercise plus glucomannan significantly improved measures of body composition, HDL-C and TC/HDL-C ratio. This data provides new evidence for those currently promoting the use of glucomannan in the sports-nutrition and weight-loss segments as an efficacious dietary supplement.

Novel prebiotic enters market
Oligosaccharides are classes of prebiotic fibres well known for their influence on the bacterial flora of the gut. Much of the current research is based around inulin and fructo-oligosaccharides, and their benefits relating to gut health.

Glucomannan, when broken up into smaller molecules through a process called 'cracking,' effectively produces glucomannan oligosaccharides. It could rival that of the current market leaders inulin and fructo-oligosaccharide.

A new study looked at the effects of 21 days of either a glucomannan supplement (4.5g/day) or a placebo (corn starch) on the gastrointestinal response of eight subjects with a low dietary fibre intake (less than 20g/day).⁶ The results demonstrated that beneficial bacteria Bifidobacterium spp and Lactobacillus spp significantly increased as a function of total bacteria, while levels of the potentially harmful bacteria, Clostridium spp, decreased (relative to placebo).⁶ Additional functional measures showed mean defecation frequency increased by about 27 per cent per day, and the stool weight (both wet and dry) also increased. Short-chain fatty acid concentrations also increased in the faeces after supplementation with glucomannan, compared to placebo.

Together, these results demonstrate glucomannan not only promotes the defecation frequency and stool bulk, which may influence cancer-risk rate, but it also promotes the growth of beneficial bacteria. Further work will no doubt be forthcoming, and the fibre market will watch with great interest as it makes its way into mainstream food products.

Food vs beverage delivery
Researchers from New Zealand have investigated the growing support for the protective role of soluble fibre in type 2 diabetes by assessing its efficacy when delivered in food and beverage formats.7

Beta-glucan found in oats and barley is suggested as the compound that delivers beneficial health effects. One area highlighted as a benefit of this soluble fibre is the postprandial blunting of blood-glucose and insulin responses to dietary carbohydrates. However, few trials have been carried out using natural barley or enriched barley beta-glucan products on glucose and insulin response. The aim of this trial was to investigate the postprandial effect of a highly enriched barley beta-glucan product on blood glucose, insulin and lipids when given with a high-CHO food and a high-CHO drink.7

Eighteen healthy men completed a four-treatment intervention trial comprising (i) high-CHO (food control), (ii) high-CHO (food+fibre), (iii) high-CHO (drink control), and (iv) high-CHO (drink+fibre) where a 10g dose of barley beta-glucan fibre supplement (Cerogen) containing 6.31g beta-glucan was added to food and drink controls.⁷ There was an increase of glucose and insulin following all four treatments.

Addition of the beta-glucan significantly blunted the glycaemic and insulinaemic responses on the food, but not drink, treatments.7 The high-CHO breakfasts decreased total, LDL- and HDL-cholesterol from baseline to 60 minutes postprandially, but there were no differential effects of beta-glucan treatment on circulating lipids.7

The authors concluded that a high-dose barley beta-glucan improves glucose control when added to a high-CHO starchy food. This effect was probably due to increased gastrointestinal viscosity, but not when added to a high-CHO beverage where rapid absorption, viscosity and decreased beta-glucan concentration may preclude this mechanism.7

This research shows that the integration of bioactives can be significantly influenced by the delivery vehicle (in this case, food vs beverage). As such the claims to physiological/health effects should always be product-format specific.

Sorghum and anti-cancer
When looking for possible directions for the functional-fibre market, we need to take a detailed look at the multitude of bioactives that exist. Researchers from the Department of Botany at the University of Hong Kong have been taking a closer look at the chemical components of sorghum, a source of insoluble fibre (19 per cent insoluble), and its influence on cancer cells.8

The 3-deoxyanthocyanidins are structurally related to the anthocyanin pigments (concentrated in fruits), which are popular as health-promoting phytochemicals. This current study demonstrated that the 3-deoxyanthocyanidins are more cytotoxic on human cancer cells than the 3-hydroxylated anthocyanidin analogues (meaning it is effective in killing cancerous cells). Sorghum is a major source of 3-deoxyanthocyanidins, which are present as seed pigments and as phytoalexins (antibiotics produced by plants) responding to pathogen attack.

Following detailed analysis of the sorghum and its 3-deoxyanthocyanidin content, it was concluded they would be an excellent source from a manufacturing point of view.

Clearly more work is needed here on the influence of this bioactive but the message is that fibre sources can provide significantly different bioactive profiles beyond the case of soluble- and insoluble-fibre content. Drawing attention to these benefits may help differentiate multifibre-based products based on their unique chemical and health-delivering attributes.

MarK J Tallon, PhD, is chief science officer of NutriSciences, a London-based consultancy firm specializing in health-claim substantiation, product development and technical writing. www.NutriSciences.net

References
1. Anderson JW. Physiological and metabolic effects of dietary fibre. Fed Proc 1985;44 (14):2902-6.
2. Seal CJ. Whole grains and CVD risk. Proc Nutr Soc 2006;65(1):24-34.
3. Kendall CW, et al. Resistant starches and health. J AOAC Int 2004;87(3):769-74.
4. Sola R, et al. Effect of soluble fibre (Plantago) on plasma lipids, lipoproteins, and apolipoproteins in men with ischemic heart disease. Am J Clin Nutr 2007;85(4):1157-63.
5. Kraemer WJ, et al. Effect of adding exercise to a diet containing glucomannan. Metabolism 2007;56(8):1149-58.
6. Chen HL, et al. Konjac acts as a natural laxative by increasing stool bulk and improving colonic ecology in healthy adults. Nutrition 2006;22(11-12):1112-9.
7. Poppitt SD, et al. Supplementation of a high-carbohydrate breakfast with barley beta-glucan improves postprandial glycaemic response for meals but not beverages. Asia Pac J Clin Nutr 2007;16(1):16-24.
8. Shih CH, et al. Quantitative analysis of anticancer 3-deoxyanthocyanidins in infected sorghum seedlings. J Agric Food Chem 2007; 55(2):254-9.