Nutritional effects of barley products — Mechanisms of action in the intestinal tract
Summary, in Swedish
There is a growing prevalence of disorders associated to the metabolic syndrome globally. To reverse this trend lifestyle changes are required. Among dietary factors, dietary fibre that is associated with several health benefits plays an interesting role. Barley is highly unutilized as human food, and it contains high amounts of dietary fibre. The composition of the barley fibres is quite similar as to those in oats, with high amounts of β-glucan, a fibre component that has been reported to decrease blood cholesterol. The whole-grain barley variety, containing the highest amounts of β-glucan in the present work also reduced the level of cholesterol in the blood. The barley malts (low in β-glucan) had no such effects, suggesting that the β-glucan amount is important for cholesterol-lowering effects of dietary fibres from barley.
The mechanisms behind the physiological effects of dietary fibre are rather unknown, but it is increasingly believed that the action of dietary fibre in the gastrointestinal tract plays a key role. The gastrointestinal tract is more than a passage for food digestion and waste excretion; it is also a barrier that protects our inner environment from microorganisms and harmful substances. Recently, it has been found that toxic components (lipopolysaccharides) from some types of bacteria can enter our circulation causing low-grade inflammation and trigger metabolic disorders. The bacteria in colon are normally living in harmony with human hosts, unless the bacterial composition is disturbed by diet, disease or medical treatment. The bacteria mainly live on dietary fibre and produce short-chain fatty acids (SCFA, mainly acetic acid, propionic acid and butyric acid), which are important nutrients for our intestinal cells and have implications in our metabolism and immune system. Butyric acid is of major importance and the preferred fuel for the intestinal cells, and therefore stimulates mucosal cell proliferation, blood flow and oxygen uptake, resulting in a reduced permeability of the colon and a less influx of toxic substances into the circulation. Propionic acid is another interesting SCFA, traditionally connected with metabolic effects, but during recent years, butyric acid has also been highlighted in this respect. Acetic acid is more associated with negative health effects. Different types of dietary fibre give different amounts and patterns of SCFA and it may be possible to design gut metabolites formed and the microbiota composition by diet to achieve a healthier colonic environment.
In this thesis, various barley products, containing different barley varieties (SW or Hadm) or barley malts with different characteristics were studied. The effect of the fat content in the diet and probiotics added to the diet were also evaluated. SCFA in blood and hindgut, gut microbiota and risk factors associated with low-grade inflammation were evaluated using a rat model.
All barley products studied gave high amounts of SCFA in the colon and portal vein blood, and this could be correlated to the dietary fibre content. An increase in the fat content in the whole-grain diet changed the pattern of SCFA and more acetic and propionic acid was produced, but less butyric acid, especially when the fibre intake was low. As compensation, a “new” acid, succinic acid, appeared. Succinic acid can be formed during antibiotic treatment and also when the fibre intake is low, i.e. at a low bacterial activity in colon. Remarkably, when replacing whole-grain barleys with barley malts, having another fibre composition (arabinoxylan instead of β-glucan), and the amount of butyric acid in the portal vein blood were still high in the high-fat condition and the production of succinic acid was reduced. The addition of probiotics did not have any effects on SCFA neither in colon nor in portal vein blood.
Barley products also affected the population and composition of gut microbiota. Intake of the two whole-grain barley varieties increased the abundance of Bifidobacterium and Lactobacillus and decreased the Bacteroides fragilis group. There was also a decrease in Akkermansia, but only with Hadm. When the fat content increased, the abundance of Lactobacillus decreased, while that of Akkermansia increased. Furthermore, there was a lower abundance of the Clostridium leptum group with Hadm. Barley malt had different effects on microbiota compared with whole grain barley. Thus, the relative abundance of Akkermansia decreased, while that of Roseburia, a well-known butyric acid producer, increased. Interestingly, the amount of butyric acid and succinic acid was correlated with the relative abundance of Roseburia and Akkermansia, respectively. The addition of probiotics changed the composition of lactobacilli.
Barley products decreased risk factors associated with low-grade inflammation, a phenomenon that can initiate obesity and insulin resistance. Intake of barley products resulted in a lower concentration of inflammatory markers (lipopolysaccharide-binding protein and monocyte chemoattractant protein-1) in the blood. This may be due to several mechanisms. First, reshaping of the gut microbiota composition may have led to lower amounts of toxic components in the colon, as reflected by a change in the gene expression of a receptor involved in inflammatory signalling. Second, the migration of toxic components into the circulation may also be reduced, due to a higher nutritional status of the colon. Third, the increased amount of SCFA, preferably butyric acid, in the circulation may counteract low-grade inflammation. Intriguingly, high amounts of advanced glycation end-products, formed in food during heat treatment, impaired the effect of barley products on gut barrier function.
In conclusion, consumption of barley products increased the amount of SCFA, including butyric acid, in the hindgut and portal vein blood of rats and changed the composition of gut microbiota. These alterations may alleviate the risk factors associated with low-grade inflammation and boost health benefits. Furthermore, the amount and composition of dietary fibre were important for the performance of barley products. Higher amounts of fat and advanced glycation end-products attenuated the health benefits. However, by selecting the correct variety or by tailoring the process conditions, functional properties and also health effects can be optimized.
- Food for Health Science Centre, Kemicentrum
Food Health Science Centre, Lund University
- Engineering and Technology
- dietary fibre
- high-fat diets
- short-chain fatty acids
- gut microbiota
- low-grade inflammation
- gene expression
- ANTIDIABETIC FOOD CENTRE
- Department of Food Technology, Engineering and Nutrition
- ISBN: 978-91-7422-402-3
15 juni 2015
Lecture hall F, Kemicentrum, Getingevägen 60, Lund University, Faculty of Engineering LTH, Lund
- Knud Erik Bach Knudsen (Professor)