La fibra alimentare e la definizione del suo valore calorico Nicoletta Pellegrini Dipartimento di Scienze degli Alimenti Università degli Studi di Parma
Dietary fibre? At the beginning 1950 1970 Dietary fibre are the remnant of plant components that are resistant to hydrolysis by human alimentary enzymes. Hipsley EH, BMJ, 1953, (2):420-22; Burkitt et al. Lancet, 1972, 1408-12; Trowell HC, Lancet, 1972, 503
Dietary fibre? the definition evolves 1985 Edible plant material not hydrolysed by the endogenous enzymes of the human digestive tract : method of analysis (Prosky et al., 1985) accepted by AOAC (AOAC method 985.29 and following).
Dietary fibre? it keeps evolving 2000 Dietary fiber is the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine. Dietary fiber includes polysaccharides, oligosaccharides, lignin, and associated plant substances Dietary fibers promote beneficial physiological effects including laxation, and/or blood cholesterol attenuation, and/or blood glucose attenuation... (AACC), 2001
Dietary fibre? and now? 2010 Dietary fibre is non-digestible (in the human small intestine) carbohydrates plus lignin. The main types of total dietary fibre are: non-starch polysaccharides (NSP) cellulose, hemicelluloses, pectins, hydrocolloids (i.e., gums, mucilages, β-glucans); resistant oligosaccharides fructo-oligosaccharides (FOS), galactooligosaccharides (GOS), other resistant oligosaccharides, resistant starch consisting of physically enclosed starch, some types of raw starch granules, retrograded amylose, chemically and/or physically modified starches; lignin associated with the dietary fibre polysaccharides. (EFSA Journal 2010a;8:1462).
Chemico-physical characteristics of unavailable carbohydrates and the physiological effects hydratability viscosity fermentability binding capacity
Water holding capacity = water solubility? Cellulose Pectine (E440) Hemicellulose Ara arabinose; Gal galactose; Glc glucose; GlcA glucuronic acid; Xyl xylose
Insoluble Soluble Provides a feeling of fullness Helps with intestinal function (increased fecal weight; transit times reduction) May help with colon cancer (dilutes potential carcinogens) Provides a feeling of fullness Reduces the rate of gastric emptying Reduces the rate of digestion and absorption of nutrients (fat and CHO) Colonic health/ ameliorates mineral absorption in grains and vegetables in legumes and fruits This differentiation is method-dependent, and solubility does not always predict physiological effects. Therefore, FAO/WHO proposed the distinction between soluble and insoluble fibre should be phased out (FAO/WHO, 1998).
Solubility = hypoglycemic effect? Oligosaccaridi resistenti sono solubili in acqua, non formano soluzioni viscose e non hanno effetto sulla velocità di digestione di lipidi e carboidrati, ma sono altamente fermentescibili.
Chemico-physical characteristics of unavailable carbohydrates and the physiological effects hydratability viscosity fermentability binding capacity
From Englyst et al. (1987). Molar ratios of VFA are given in parenthesis Butirrato è formato principalmente da amido resistente (cereali), acetato da pectine (frutta) e xilani (cereali), acetato e propionato da arabino-galattani (legumi).
Short chain fatty acids Acetate: energy glycogen synthesis /fatty acids glycemic control Propionate: energy glycogen synthesis /fatty acids HMG-CoA-Red Butyrate: energy source (colonocytes)
Food energy 1. The components of food that provide energy should be determined by appropriate analytical methods; 2. The quantity of each individual component must be converted to food energy using a generally accepted factor that expresses the amount of available energy per unit of weight; 3. The food energy of all components must be added together to represent the nutritional energy value of the food for humans.
The Atwater general factor system based on the heats of combustion of protein, fat and carbohydrates, which are corrected for losses in digestion, absorption and urinary excretion of urea. The energy values are 17 kj/g (4.0 kcal/g) for protein, 37 kj/g (9.0 kcal/g) for fat and 17 kj/g (4.0 kcal/g) for carbohydrates. As originally described by Atwater, carbohydrate is determined by difference, and thus includes fibre. The extensive general factor system: in 1970, Southgate and Durnin added a factor for available carbohydrate expressed as monosaccharide (16 kj/g [3.75 kcal/g]). These authors recognized that the apparent digestibility of unavailable carbohydrate in human diets was> 0.5. However, they also showed that the energy obtained from unavailable carbohydrate by humans (including colonic microorganisms) was approximately equably balanced by additional losses of energy to feces in the form of fat and protein (6.25 x nitrogen), which arose from an increased intake of the unavailable carbohydrate.
Based on the ATP production from SCFA and lactate the metabolic caloric value of a fructosyl unit of oligofructose is between 1 and 1.5 kcal/g or 30-40% that of a digested fructose molecule. Nutr Rev 1993, 51: 137-146.
wheat bran itself 2.4 kcal (10 kj)/g wheat bran fibre 0.6 kcal (2.5 kj)/g 1 kcal (4 kj)/g maize bran fibre 0.3 kcal (1.3 kj)/g
This is supported by experts consulted by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization which held an Expert Consultation on Carbohydrates in Human Nutrition in 1997 (FAO/WHO, 1998), and a Technical Workshop on Food Energy - Methods of Analysis and Conversion Factors in 2002 (FAO, 2003). Both expert consultations recommended that, for nutritional and labelling purposes, the energy value should be set at 2 kcal (8 kj) /g for carbohydrates that reach the colon. It was also indicated that 70 percent of the fibre in traditional foods can be assumed to be fermentable.
Salatrim: miscela di trigliceridi costituiti da acidi grassi a corta catena e a lunga catena, usato per sostituire i grassi per il suo ridotto valore calorico. Eritritolo (E968): poliolo presente nella frutta e nei cibi fermentati, usato come dolcificante naturale in quanto ha un ottimo sapore ed è privo di retrogusti.
Pane bianco a fette Fette biscottate Crackers + 3.4 % + 3.3 % + 2.2 % Pane Integrale a fette Fette biscottate Integrali Crackers Integrali + 6.2 % + 4.7 % + 4.8 %
PASTA INTEGRALE ENERGIA (kcal) (kj) Valori Nutrizionali per 100 g di prodotto 350 1482 PROTEINE (g) 13 GRASSI (g) di cui ACIDI GRASSI SATURI (g) CARBOIDRATI di cui ZUCCHERI (g) 2.5 0.5 65.7 3.5 FIBRA (g) 6.5 Sale (g) 0.033 + 3.6 % PASTA di SEMOLA ENERGIA (kcal) (kj) Valori Nutrizionali per 100 g di prodotto 359 1521 PROTEINE (g) 13.5 GRASSI (g) di cui ACIDI GRASSI SATURI (g) CARBOIDRATI di cui ZUCCHERI (g) 2.0 0.4 70.2 3.5 FIBRA (g) 3.0 Sale (g) 0.033 + 1.7 %
Valore calorico della fibra 2 kcal/g energia totale 334 kcal/100 g Valore calorico della fibra 2 kcal/g energia totale 454 kcal/100 g Valore calorico inulina=2.2 kcal/g Valore calorico fibra da crusca di frumento = 0.6 kcal/g energia totale 296 kcal/100 g -11.3% +0.5% Valore calorico crusca di frumento = 2.4 kcal/g energia totale 456 kcal/100 g +3.2% energia totale 344 kcal/100 g
DIETA ONNIVORA Fibra 16 g/d Energia 2744 kcal/d vs 2777 kcal/d + 1.2% DIETA ONNIVORA Fibra 14.6 g/d Energia 2127 kcal/d vs 2156 kcal/d + 1.4% DIETA VEGETARIANA Fibra 67.1 g/d Energia 2878 kcal/d vs DIETA VEGETARIANA Fibra 51.6 g/d Energia 2315 kcal/d vs 2418 kcal/d + 4.5% 3012 kcal/d + 4.7% 2418 kcal/d + 4.5% DIETA VEGANA Fibra 77.4 g/d Energia 2320 kcal/d vs 2475 kcal/d + 6.7% DIETA VEGANA Fibra 61.9 g/d Energia 2414 kcal/d vs 2538 kcal/d + 5.1%
Some open issues Several critical points are related to the common use of Atwater factors based on the heats of combustion of protein, fat, carbohydrates and dietary fibre: 1. in the evaluation of food energy, fixed conversion factors for each component are used without considering its relationships with other components in foods and the effect of different processes may have on the structure and digestibility of foods; 2. the reliability of analytical methods for measuring the food components, especially in the case of dietary fibre.