Journal of Nutrition and Metabolism

Protective Factors

Agriculture and Food
Retrieved 13 December For the medical journal, see Nutrition journal. The majority of the studies linking short-chain fatty acids to gastrointestinal motility stems from ruminant animal studies [ ], where the production of short-chain fatty acids is greater than that in humans due to differences in gut physiology [ ]. A 5 ounce serving of wine contains to calories. Hypertension is another core component of the metabolic syndrome, and is an established risk factor for heart diseases, stroke, and renal diseases [ ]. Heating techniques may also reduce food's content of many heat-labile nutrients such as certain vitamins and phytochemicals, and possibly other yet-to-be-discovered substances. Ghrelin Ghrelin is the only known orexigenic hormone in the gut.

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A number of randomized controlled trials have shown weight reduction with diets rich in dietary fiber or dietary fiber supplements [ — ], while others have not [ ]. More specifically, the soluble dietary fiber glucomannan, which has a strong water-holding capacity, resulted in a significantly greater reduction of weight, when consumed at a dose of 1.

Despite the clear association between soluble fibers and weight loss, their effects on subjective measures of satiety are not conclusive. For example, the addition of 2.

The soluble resistant dextrins promoted, in a dose-dependent manner, increased satiety when added to desserts and to carbohydrate-based meals [ — ]. Moreover, a nutrition bar containing guar gum 5. Subjects described to be significantly less hungry before lunch after consuming barley—but not wheat—and rice-containing foods [ ].

Barley-based foods enhanced as well satiety when compared to a high-glycemic index food or a food with no dietary fiber [ — ]. Similarly, a preload of 5. This was also associated with a significant reduction of energy intake at the subsequent lunch [ ].

In contrast, a meal replacement bar containing 1. Dose is one of the major determinants. Solid foods are known to increase satiety and decrease hunger more effectively than liquid ones [ ].

Moreover, another concern to be addressed in future studies is the type of control to use. No dietary fiber that may function as a control for satiety studies has been actually identified.

It should be noted that the body weight was not the primary concern of these studies as they focused on changes in blood sugar or blood lipids. The satiating properties of soluble dietary fibers have been explained by various mechanisms, all of which are related to several stages in the process of appetite regulation such as taste, gastric emptying, absorption, and fermentation [ ]. Firstly, the viscosity of soluble fibers plays an important role in their ability to induce satiety [ , , ].

A higher viscosity meal delays gastric emptying [ , , ] and slows the digestion and absorption of nutrients, more precisely glucose, due to reduced enzymatic activity and mucosal absorption [ 31 , ], leading to early satiety sensations. The overall gastric emptying rate of healthy volunteers, as assessed by the paracetamol absorption test, was slower after the high viscosity oat bran-enriched beverage as compared to the low viscosity drink [ ]. Secondly, the lower palatability of fiber-rich meals may affect food intake in a negative manner [ — ].

A strong inverse relationship is described between palatability and satiation [ ]. A significant inverse relationship is reported between satiety and glucose and insulin responses to carbohydrate-rich breakfast cereals [ , ] and to beverages with different glycemic effects [ ]. However, other studies did not report any association of glucose and insulin postprandial levels with satiety [ , ].

They suggested that the release of putative satiety peptides is a more crucial component of mechanisms initiating and maintaining satiety. Such statement leads to the fourth suggested mechanism that delineates the role of short-chain fatty acids in appetite control. Short-chain fatty acids regulate the release of various gut hormones, which play an important role in satiety signaling. The role of short-chain fatty acids in appetite regulation and the potential underlying mechanisms will be elucidated in the following sections.

The fermentability of soluble fibers by colonic microbiota is greater than that of insoluble fibers. Pectin, resistant starches, gums, and polyfructans such as inulin are the most highly fermented substrates. On the other hand, acetate passes more freely into the peripheral circulation [ ]. Several functions are attributed to short-chain fatty acids, being recently proposed as key energy homeostasis signaling molecules [ ].

Accumulating evidence has attributed the satiating effects of fermentable carbohydrates to short-chain fatty acids, their major fermentation products [ ]. Short-chain fatty acids regulate appetite through several mechanisms.

First, short-chain fatty acids have a role in slowing gastrointestinal motility, thus controlling digestion and nutrient absorption and eliciting an anorexigenic effect. The majority of the studies linking short-chain fatty acids to gastrointestinal motility stems from ruminant animal studies [ ], where the production of short-chain fatty acids is greater than that in humans due to differences in gut physiology [ ]. However, there are some studies on nonruminants showing that short-chain fatty acids may regulate the overall transit time of the digesta through the large intestine [ , ].

Such responses were hypothesized to occur via three possible pathways: In addition, short-chain fatty acids were suggested to regulate gastrointestinal motility by affecting the release of the gastrointestinal 5-hydroxytryptamine 5-HT via the activation of the free fatty acid receptor 2 FFA2 , the major receptor for short-chain fatty acids.

The activation of various 5-HT receptor subtypes stimulates vagal nodose neurons and consequently prolongs colonic transit time [ , ]. Short-chain fatty acids also regulate appetite by modulating the release of various appetite-related hormones throughout the gastrointestinal tract [ ].

Peptide YY Peptide YY is a amino acid peptide, first isolated from porcine upper small intestine [ ]. PYY is secreted throughout the entire length of the gastrointestinal tract, with the highest concentrations found in the colon and rectum [ ].

Circulating PYY levels are the lowest in the fasting state and increase following the consumption of a meal, peaking at hours and remaining elevated for several hours. Peripheral PYY administration decreased food intake and body weight gain in rats [ ]. Similarly, it decreased appetite and food intake both in lean and obese humans [ , ]. An increased PYY response was consistently described following the consumption of various soluble dietary fibers. Postprandial PYY clearly increased after the consumption of psyllium-enriched test meals in healthy volunteers [ ].

The consumption of PolyGlycopleX, a novel functional fiber complex manufactured from three dietary fibers to form a highly viscous polysaccharide with high water-holding and gel-forming properties, for 3 weeks resulted in significantly increased fasting PYY levels as compared to the control product in healthy adults [ ]. The direct infusion of short-chain fatty acids into rabbit and rat colons significantly increased PYY secretions [ , ]. The stimulatory effects of short-chain fatty acids on PYY secretions are mainly attributed to a direct interaction between short-chain fatty acids and PYY cells.

In fact, FFA2 also known as GPR43 , the major receptor for short-chain fatty acids, is colocalized with PYY immunoreactive enteroendocrine L cells both in rat ileum and human colon [ , ].

Glucagon-Like Peptide 1 Glucagon-like peptide 1 is cosecreted with PYY from the intestinal L cells, encoded by the proglucagon gene [ ]. It is described with a potent incretin effect, stimulating insulin secretion in a glucose-dependent manner. Circulating GLP-1 levels rise following nutrient ingestion, in proportion to the energetic content of the meal [ ]. An acute intracerebroventricular administration of GLP-1 to rodents induced a decline in short-term energy intake [ ], and was associated with a reduced body weight following repeated administration [ ].

Similarly, an intravenous infusion of GLP-1 both in normal weight and in obese subjects resulted in a dose-dependent reduction in food intake [ ]. Variable GLP-1 responses to soluble dietary fiber intake were described, whether elevated, inhibited, or unaffected.

On the other hand, the ingestion of pasta enriched with a small amount of psyllium fiber 1. Such discrepancies in findings could be attributed to differences in the structures and food sources of ingested soluble fibers and their administered doses.

Colonic fermentation appears to be essential in explaining GLP-1 release in response to soluble dietary fibers, despite inconsistent findings. Though supplementation with fermentable carbohydrates has been consistently associated with increased colonic proglucagon mRNA expression [ — ], only few studies detected increased plasma GLP-1 circulating levels in parallel [ — , — ].

A strong association between postprandial hydrogen production and plasma GLP-1 concentrations was also reported. On the contrary, others have shown no effect of fermentable carbohydrates on circulating GLP-1 levels, whether acutely [ ] or over a short duration of 6 days [ ].

Based on these findings, the duration of supplementation is an important factor to consider when suggesting fermentation as a basis for soluble fibers-induced GLP-1 release. A sufficient time of weeks must be given in order to allow adaptation of the gut microbiota to the additional fermentable carbohydrate within the diet for maximal fermentation to take place [ ] and for GLP-1 levels in circulation to be subsequently affected.

Cholecystokinin Cholecystokinin was among the first hormones shown to modulate food intake [ ]. It is secreted from the I cells of the small intestine in response to food ingestion [ ]. Cholecystokinin circulating levels rise rapidly after a meal, reaching a peak within 15 minutes. It was found to reduce food intake when infused both in rodents and humans [ , ]. In fact, plasma CCK levels are strongly associated with subjective measurements of satiety in women [ ].

Limited studies described the interaction between soluble dietary fibers and CCK release. The role of fermentation and more specifically short-chain fatty acids in regulating CCK release is still poorly understood.

In pigs, ileal infusion of short-chain fatty acids did not affect CCK circulating levels [ ]. Ghrelin Ghrelin is the only known orexigenic hormone in the gut. It was initially identified as an endogenous ligand for growth hormone secretagogue receptor GH-SR in rat stomach [ ]. Circulating ghrelin levels increase before meals and fall rapidly after eating [ ]. Both central and peripheral administration of ghrelin increased food intake and body weight in rodents [ , ].

Discrepancies in findings could be explained by variations in the physical and chemical properties of ingested soluble fibers, their different administered doses, and the forms of ghrelin being measured in circulation. Several mechanisms were suggested to explain fiber-induced ghrelin suppression, most importantly fermentation. Such colonic fermentation may reduce ghrelin via increasing circulating PYY levels. Administration of PYY to humans reduced serum ghrelin levels [ ].

In addition to colonic fermentation, other mechanisms were also hypothesized. A possible inner-gastric pathway may operate through gastric somatostatin, which is released following the consumption of beet fiber in diabetic individuals [ ]. Somatostatin administration decreased ghrelin secretion in rats [ ] and lowered circulating ghrelin levels in humans [ ].

In addition, GLP-1 release in response to soluble fibers is another potential mechanism. Infusion of GLP-1 into isolated rat stomach suppressed ghrelin secretions [ ]. Such satiating capacity appears to be comparable to that of other soluble viscous and fermentable fibers. Short-chain fatty acids affect satiety by primarily modulating the release of various appetite-regulating hormones, including PYY, GLP-1, and ghrelin.

Since research in this area is still limited, such mechanisms necessitate further investigation. Insufficient intake of dietary fiber has been reported worldwide. However, the estimates of fiber intake are highly variable. Based on the results of the Nationwide Food Consumption Survey, a mean dietary fiber intake of Similarly, a mean daily fiber intake of In contrast, Hallfrisch et al.

In Canada, low daily dietary fiber intakes have been also noted. According to Nova Scotia Department of Health [ ], the mean dietary fiber intake was estimated to be Similarly, in a more recent study on healthy Canadian adolescent males, a median dietary fiber intake of In Europe, the estimated national values for dietary fiber intake were found to fall within a narrower range: Thus, fiber intakes worldwide are well below the recommended levels despite the recommendations of several health organizations to increase the consumption of foods with high fiber content.

The introduction of fiber into traditional and processed foods provides one method by which to increase fiber intake [ 81 ]. The best-known examples of functional foods are fermented milks and yoghurts. Several fiber-fortified dairy products are now appearing in market, with inulin being a popular fiber source for such products due to its combined nutritional and technological characteristics [ — ].

Beta glucan is commonly used as a functional ingredient in foods as it is readily available as a byproduct of oat and barley milling and it also provides physiological benefits that are supported by health claims in many jurisdictions. This polysaccharide is also used as a food ingredient in the form of hydrocolloids [ , ] or as powder using microparticulation [ ].

Oats have been frequently used as an additive in the preparation of cereal products, decreasing water activity and subsequently prolonging durability [ 81 ]. Several oat-based breakfast cereals have experienced great success in the market.

These products are readily accepted by consumers. The incorporation of oats into baking products, such as bread, baked goods, and dough, has been widely tested [ 81 ]. Oats are also used as additives in the production of yogurts with increased amount of fiber [ 81 ]. Fiber addition increased the solidity ratio and texture of unsweetened yogurts, accelerated their acidification rate, and increased their viscosity [ ].

Beta glucans selectively support the growth of Lactobacilli and Bifidobacteria, both of them being antagonists to pathogenic bacteria in the digestive system [ 12 , ]. Due to its ability to mimic fat characteristics, oat fiber is one of the most effective ingredients in making low-fat meat products.

It can be used to offset the poor quality associated with low-fat beef burgers [ ] as well as low-fat sausages [ ]. One of the major challenges faced by the functional food industry is developing functional foods with an acceptable taste to the average consumer [ ]. Incorporating significant quantities of fiber into food products constitutes a technological challenge due to the possible deleterious effects on textural quality. The addition of fibers may contribute to modifications in the texture, sensory characteristics, and shelf-life of foods due to their water-binding capacity, gel-forming ability, fat mimetic, antisticking, anticlumping, texturising, and thickening effects [ , ].

Blackcurrant flavored oat milk 0. In addition, the sensory quality of a flavored oat-based fermented product containing 0. In contrast, when consumed over 5 weeks, oat-based fermented dairy products 0. Food processing alters the physical, chemical, and physiologic characteristics of dietary fibers. These reductions in molecular weight increase with the mixing and fermentation time of the dough [ ].

Anderson declare that there is no conflict of interests. Journal of Nutrition and Metabolism. Indexed in Web of Science. Subscribe to Table of Contents Alerts. Table of Contents Alerts. Abstract Despite the lack of international agreement regarding the definition and classification of fiber, there is established evidence on the role of dietary fibers in obesity and metabolic syndrome. Introduction Obesity has reached global epidemic proportions with more than one billion adults affected by this chronic disorder [ 1 ].

Characteristics, Definitions, Classifications, and Analytical Methods Scientific and regulatory bodies around the world define fiber differently. Characteristics of Dietary Fibers Four categories of fiber definitions have been identified [ 26 ], each of which addresses a different characteristic of fiber. Definitions of Dietary Fibers The most recent definitions for fiber generally address at least one of four characteristics: Categorization of recent definitions of fiber based on whether or not a distinction in dietary fiber source is made.

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Sprouting alfalfa usually takes three to four days with one tablespoon of seed yielding up to three full cups of sprouts. Alfalfa seed products may cause reactions that are similar to the autoimmune disease called lupus erythematosus. Alfalfa might also cause some people's skin to become extra sensitive to the sun. As noted above , raw unsprouted alfalfa has toxic effects in primates, including humans, which can result in lupus-like symptoms and other immunological diseases in susceptible individuals, [] [] [] US NIH calls out special precautions and warnings for the following: US NIH warns that alfalfa may interact with herbs and supplements associated with the following: Refer to [] for the most current information and details.

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