The Influence of Dietary Fibre on Protein Digestion and Utilisation

The effect of animal versus plant protein on muscle mass, muscle strength, physical performance and sarcopenia in adults: protocol for a systematic review

BACKGROUND

The evidence base for the role of dietary protein in maintaining good muscle health in older age is strong; however, the importance of protein source remains unclear. Plant proteins are generally of lower quality, with a less favourable amino acid profile and reduced bioavailability; therefore, it is possible that their therapeutic effects may be less than that of higher quality animal proteins. This review aims to evaluate the effectiveness of plant and animal protein interventions on muscle health outcomes.

METHODS

A robust search strategy was developed to include terms relating to dietary protein with a focus on protein source, for example dairy, meat and soy. These were linked to terms related to muscle health outcomes, for example mass, strength, performance and sarcopenia. Five databases will be searched: MEDLINE, Scopus, Cochrane Central Register of Controlled Trials, Embase and Web of Science. Studies included will be randomised controlled trials with an adult population (≥ 18) living in the community or residential homes for older adults, and only English language articles will be included. Two independent reviewers will assess eligibility of individual studies. The internal validity of included studies will be assessed using Cochrane Risk of Bias 2.0 tool. Results will be synthesised in narrative format. Where applicable, standardised mean differences (SMD) (95% confidence interval [CI]) will be combined using a random-effects meta-analysis, and tests of homogeneity of variance will be calculated.

DISCUSSION

Dietary guidelines recommend a change towards a plant-based diet that is more sustainable for health and for the environment; however, reduction of animal-based foods may impact protein quality in the diet. High-quality protein is important for maintenance of muscle health in older age; therefore, there is a need to understand whether replacement of animal protein with plant protein will make a significant difference in terms of muscle health outcomes. Findings from this review will be informative for sustainable nutritional guidelines, particularly for older adults and for those following vegan or vegetarian diets.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD420201886582.

Effects of copper hydroxychloride and distillers dried grains with solubles on intestinal microbial concentration and apparent ileal and total tract digestibility of energy and nutrients by growing pigs1

An experiment was conducted to test the hypothesis that Cu hydroxychloride improves nutrient digestibility and alters the concentration of microbial protein in the small intestine or large intestine by pigs fed a corn-soybean meal diet or a diet based on corn, soybean meal, and distillers dried grains with solubles (DDGS). Twenty-four barrows (33.3 ± 3.4 kg) that had a T-cannula installed in the distal ileum were allotted to a 2 × 2 factorial design with 2 levels of DDGS (0% or 45%) and 2 levels of supplemental Cu from Cu hydroxychloride (0 or 150 mg/kg). A 2-period switch back design with the 4 diets and 6 replicate pigs per diet in each period was used resulting in 12 replicate pigs per diet for the 2 periods. The initial 9 d of each period was considered an adaptation period to the experimental diets. For each period, feces were collected on days 10, 11, and 12, and ileal digesta were collected for 8 h on days 13 and 14. Results indicated that inclusion of 45% DDGS to diets reduced (P < 0.05) the apparent ileal digestibility (AID) of AA and the AID and the apparent total tract digestibility (ATTD) of dry matter, gross energy, and crude protein. In contrast, inclusion of DDGS to diets increased (P < 0.05) the AID and the ATTD of acid hydrolyzed ether extract and the concentration of microbial protein in the hindgut (P < 0.05). However, the total concentration of volatile fatty acids (VFA) in ileal digesta and in feces from pigs fed the DDGS diets were not different from concentrations in pigs fed diets without DDGS. The AID and ATTD of dry matter, gross energy, and crude protein were not affected by dietary Cu concentrations, but the AID and ATTD of acid hydrolyzed ether extract were greater (P < 0.05) in diets supplemented with Cu hydroxychloride compared with diets without Cu hydroxychloride. There was also a reduction (P < 0.05) in the concentration of microbial protein and a tendency for a reduction (P < 0.10) in the total concentration of VFA in feces when diets were supplemented with Cu hydroxychloride. In conclusion, supplementation of Cu hydroxychloride to diets improved AID and ATTD of acid hydrolyzed ether extract and reduced the concentration of microbial protein in the large intestine and this effect was observed in diets containing DDGS as well as in diets without DDGS.

Influence of processed sugarcane bagasse on the microbial, nutritional, rheological and quality characteristics of biscuits

Sugarcane bagasse, a dietary fiber-rich by-product of the sugar industry (70-75%) and having negligible protein and fat content, was treated with acid, alkali and steaming to reduce the microbial load. Steaming was effective in making the bagasse microbiologically safe. The processed bagasse (5-15%) was used in the rheological studies and in the preparation of soft dough biscuits. Glucose (hexose), arabinose and xylose (pentose) were present, whereas rhamnose, mannose and galctose were not traced in all of the bagasse samples. Farinograph characteristics of wheat flour-bagasse blends showed that the mixing profile weakened with addition of bagasse. Processed bagasse also affected the pasting characteristics indicating starch dilution on incorporation of bagasse, as indicated by sensory characteristics. Biscuits prepared from steamed bagasse (10%) along with additives were highly acceptable. Results indicated that high-fiber biscuits can be prepared by replacing wheat flour with steamed bagasse at a 10% level.

Soy constituents: modes of action in low-density lipoprotein management

Reviewed here are the modes of action of soy components used as ingredients in foods, which can lower plasma levels of low-density lipoprotein (LDL) and cholesterol, which are markers for the risk for atherosclerosis. Soy ingredients act via more than one mode of action including the following: LDL absorption suppression, cholesterol efflux stimulation, LDL resorption stimulation, LDL oxidation prevention, LDL particle size increase, cholesterol synthesis reduction, and bile secretion increase. Individual genetics, lifestyle, and nutrition habits alter LDL management and a better understanding of the various modes of actions of soy ingredients may facilitate the composition of effective ingredient cocktails. The optimization of food components offers further alternatives to LDL management to augment drug therapy for patients who are unable to reach their target LDL cholesterol levels or who are suffering from side effects or drug insensitivity.

Ballaststoffe: Mehr als ein Diätmittel

Dietary fibre is a heterogeneous group of substances which have only one common characteristic: the non-digestability in the small bowel. With one exception all fibres are carbohydrates (poly- or disaccharides). Some fibres are water-soluble, others are unsoluble. This property is associated with physiological effects. Soluble (viscous) fibres can bind water and thus form hydrocolloids or gels, unsoluble ones cannot. Dietary fibres play an essential role in the physiology of the gastrointestinal tract. They modify the absorption of nutrients (particularly carbohydrates and lipids) in the small bowel. They accelerate the gut transit time and determine stool composition and quantity. They are the main nutritional source for the colonic microflora. During the bacterial fermentation short-chain fatty acids are formed which are essential for nutrition and integrity of the colonocytes and for colonic function. Moreover gases, detoxicating enzymes, antioxidants and carcinogen-inactivating compounds arise. The most important fibres are cellulose, hemicellulose, pectin, guar, psyllium, beta-glucan, Klason lignin and digestion-resistant starch; they are present in varying amounts in plant foods and in fibre preparations. The usual daily intake of dietary fibre in Europe and the USA amounts to only 15-20 g, while health authorities and nutrition societies recommend a reference value of at least 30 g. Dietary fibres are applied as food-integrated, as supplement and as purified substances.

Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats. II. Studies with diets differing in protein quality

In 2 two-factorial experiments, each conducted on 80 growing male rats, the effects of substituting 10% raw potato starch (PS), pectins (PEC), or cellulose (CEL) for wheat starch (WS) and the addition of tannic acid to WS (WSTA) were studied using diets differing in protein quality. Casein unsupplemented or supplemented with DL-methionine and gluten unsupplemented or supplemented with lysine, methionine and tryptophan were used as protein sources in Experiment 1 and 2, respectively. Parameters indicative of caecal fermentation intensity (pH, acetic, propionic and butyric acid contents, digesta and tissue weight) and of protein metabolism (urea blood concentration, faecal and urinary nitrogen excretion) were determined. Ten-day balance experiments were preceded by a 10-day adaption period to respective carbohydrates given in a diet containing balanced protein. In both experiments the type of carbohydrates affected the caecal concentration of individual and total SCFA and other parameters of fermentation intensity. Pectins and potato starch were fermented more intensively than cellulose. Faecal N excretion was increased by all carbohydrates substituted for cereal starch, and by tannic acid. Urinary excretion was greater on CEL than on PEC and WSTA containing casein and on other diets containing gluten. In both experiments urinary N excretion was the lowest on PEC diets. Protein quality had the greatest effect on apparent biological value and net protein utilization but all indices of protein utilization were also affected by carbohydrates. It is concluded that not only the amount of N excreted in faeces but also in urine is affected by the type and fermentability of carbohydrates.

Dietary carbohydrates affect caecal fermentation and modify nitrogen excretion patterns in rats. I. Studies with protein-free diets

In a two-factorial experiment on 96 young male rats, the effects of substituting 10% raw potato starch (PS), pectins (PEC), or cellulose (CEL) for corn starch (CS) were studied using an unsupplemented protein-free (PF) diet or a PF diet supplemented either with DL-methionine or urea. The pH and the short chain fatty acids (SCFA) content in caecal digesta, as well as caecal digesta and tissue weights were determined and used as the criteria of caecal fermentation intensity. Blood urea level, amount of N excreted via faeces and urine, DAPA content, and amino acid composition of faecal protein were analyzed as indices of protein metabolism. A 10-day adaptation period to the carbohydrates fed with the casein diet preceded the experimental period of feeding the respective carbohydrates with protein-free diets. Dietary carbohydrates significantly influenced total and individual SCFA content in caecal digesta, as well as other parameters related to the intensity of fermentation. Potato starch and pectins were more intensively fermented than cellulose. Supplementation of the PF diet with methionine and urea affected only caecal isobutyric and valeric acid content in a way dependent on the carbohydrates present in the diet. Carbohydrates significantly altered the routes of N excretion. Faecal excretion was increased by all carbohydrates studied compared to corn starch, pectins had the most marked effect. Urinary excretion was significantly increased by cellulose (as compared with the PEC and PS groups) and decreased by pectins as compared with all other groups. There was an interaction between the effects of carbohydrates and type of protein-free diet on faecal and urinary excretion. The sum of amino acids in faecal protein was the lowest on the PEC diet, but the amino acid composition expressed as a per cent of total amino acid content was similar in all groups. It can be concluded that dietary carbohydrates alter the excretion patterns of endogenous nitrogen in rats in different ways and that this effect is related to the intensity of their fermentation in the hind gut.

Avaliação do efeito de sopas desidratadas ricas em fibras na redução do colesteroal sangüíneo em ratos

Neste estudo foi avaliado o efeito de quatro formulações dietéticas ricas em fibra solúvel na redução de colesterol sangüíneo em ratos. As formulações foram preparadas com farinha de soja desengordurada, farelo de aveia, cebola desidratada, fibra de soja, condimentos e aromas. Duas das formulações continham feijão preto FP(+) e FP(-), nos níveis de 40 e 30%, respectivamente. As outras duas continham feijão vermelho FV(+) e FV(-), nesses mesmos teores. Foram utilizados seis grupos de oito ratos machos, com peso médio inicial de 200g. O grupo Padrão recebeu dieta basal. O grupo Controle recebeu dieta de composição semelhante à Padrão, porém, acrescida de 1% de colesterol cristalino e 0,1% de ácido cólico. As demais dietas foram semelhantes ao grupo Controle, substituídas pelas formulações FV(+), FP(+), FV(-) e FP(-), de modo a fornecerem 7,4% de fibra total da dieta. Ratos alimentados com dieta do grupo Controle apresentaram aumento significativo dos níveis de colesterol sérico, peso dos fígados, colesterol e lipídio total das fezes e dos fígados, em relação ao grupo recebendo dieta Padrão. As dietas FV(+), FP(+), FV(-) e FP(-), não diferiram entre si quanto ao efeito nos níveis de lipídios séricos e glicose, no peso e lipídio total dos fígados e no peso, umidade e nitrogênio das fezes. No entanto, reduziram significativamente os níveis sangüíneos de colesterol total em 29,0%, os níveis de HDL - colesterol em 34,0%, o peso dos fígados em 11,7% e o colesterol do fígado em 9,0% em relação à dieta Controle. As dietas de feijão vermelho proporcionaram maior redução de colesterol no fígado e maior excreção de lipídio e colesterol nas fezes comparadas com as de feijão preto.

Resistant proteins alter cecal short-chain fatty acid profiles in rats fed high amylose cornstarch

The objective of this study was to examine the physiologic importance of undigested protein on cecal fermentation in rats fed a low (LAS) and high (HAS) amylose cornstarch. In Experiment 1, rats were fed diets containing LAS (655 g/kg diet) with one of four protein sources: casein, rice (RP), potato (PP) or soybean protein (SP) at 250 g/kg diet for 15 d. Apparent digestibilities of casein, RP, SP and PP were 96, 94, 93 and 92%, respectively. In rats fed the LAS diet with casein, acetate, propionate and succinate were the major cecal organic acids. The succinate pools in rats fed RP or SP were significantly lower than in those fed casein, whereas butyrate did not differ. Butyrate was significantly higher in rats fed PP, but succinate was the same as in rats fed casein. In Experiment 2, rats were fed diets containing HAS (200 g/kg diet) with one of the four protein sources at 250 g/kg diet for 10 d. HAS was substituted for the same amount of LAS. In rats fed the HAS diet, succinate was the major acid in rats fed casein; in rats fed RP or PP, however, the pools of this acid were significantly lower than in those fed casein, whereas butyrate was significantly higher in rats fed RP or PP. Fecal starch excretion was significantly lower in rats fed RP or PP than in those fed casein. In Experiment 3, rats were fed the casein-HAS diet with graded levels of PP (0, 10, 30, 50, 100 and 250 g/kg diet) for 14 d. The PP was substituted for the same amount of casein. Cecal butyrate was low in rats fed up to 100 g of PP/kg diet and then rose with 250 g of PP/kg diet. In Experiment 4, ileorectostomized rats were used and fed the same diets described in Experiment 3 for 9 d. The ileal starch/nitrogen ratio declined with increasing dietary PP, due solely to greater nitrogen excretion, whereas starch excretion was unaffected. In Experiment 5, rats were fed the casein-HAS diet with or without 60 g of artificial resistant protein/kg diet for 10 d. The resistant protein (apparent digestibility, 63%) was substituted for the same amount of casein. Rats fed the casein-HAS diet with resistant protein had significantly greater cecal butyrate and lower succinate than those fed the casein-HAS diet. These data show that large bowel fermentation of starch is altered by dietary protein. They support the hypothesis that nondigested protein, namely, resistant protein, may control fermentation efficiency as well as the fermentation profile of HAS, possibly as a result of a change in microflora through the change in the ratio of starch to nitrogen in the cecum.

Effects of the type and level of dietary fibre supplements on nitrogen retention and excretion patterns

The hypothesis was tested that fermentable dietary fibre (DF) sources elevate faecal N excretion at the expense of urinary N without affecting N retention. DF that substantially increase fermentation (pectin, sugarbeet and soya bran) or are poorly fermented (crystalline cellulose and maize bran) were fed as supplements to a basal DF-free diet at three dose levels: 0, 50 and 100 g supplement/kg basal diet. The diets were fed to juvenile male Wistar rats for 2 weeks before a 7 d period when faeces and urine were collected. Faecal excretion of N was significantly increased, dose-dependently, by all DF supplements and was positively correlated to faecal bulking. Urinary excretion of N was lower at the high doses of the DF supplements but reached significance only with the highly fermentable (0.68) sugarbeet-supplemented diets. Regression analysis showed that the major part (0.75) of the increase in faecal N excretion due to DF supplementation was balanced by a reduction in urinary excretion; N retention was therefore, at the dose levels used, only affected to a small extent. Only in the maize-bran-supplemented diets were the reductions in N retention significant. The shift in N excretion from urine to faeces can be explained largely by the degree of microbial fermentation in the large intestine caused by the addition of DF supplements and emphasizes the modifying role that certain DF supplements may have on the enterohepatic cycle of N. Possible implications of these findings for patients with liver or renal failure or for conditions when the intake of dietary protein is marginal are discussed.