CAPÍTULO 1. NATURALEZA EVOLUTIVA DE LA APREHENSIÓN DEL
1.3. Elementos constitutivos de la imputabilidad/inimputabilidad
1.3.4. Esfera valorativa
been reported where dietary Ca was associated with an increased excretion of faecal fat and
fatty acids regardless of the form (either dairy products, Ca-fortified food products or Ca
supplements) in which the Ca was consumed (see Table 2-2). However, there are a few
studies which did not report an increase in faecal fat excretion with increased dietary Ca
(Ditscheid et al. 2005; Boon et al. 2007; Hjerpsted et al. 2011). A common factor in the latter
studies where no effect of high dietary Ca intake on faecal fat excretion was reported was
that the diets used contained greater amounts of protein than those used in the studies where
a “Ca effect” was observed (Boon et al. 2007; Hjerpsted et al. 2011). For example, Jacobsen et
al. (2005) reported conflicting effects for high dietary Ca concentrations on faecal fat
excretion within the same study when the protein intake differed for the subject groups. The
latter research group compared three different diets (see Table 2-2) varying in Ca (500 vs
1800 mg d-1) and in protein content (15 vs 23 E% protein) and observed that when the dietary
Ca content was increased and the protein content remained the same (15 E% protein) faecal
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54
excretion was observed when the increased dietary Ca intake was accompanied by an
increase in the protein content of the diet (23 E% protein). Similarly, a Ca-intervention study
in subjects with a daily protein intake of 20% of energy showed no differences in faecal fat
excretion for varying concentrations of dietary Ca (400 vs 1200 vs 2500 mg Ca d-1) (Boon et al.
2007). High protein diets have been reported to improve Ca absorption (Kerstetter et al.
1998), thereby likely leaving less Ca available for fatty acid complexation. In another study,
Jacobsen et al. (2005) reported a 66% higher urinary Ca excretion for the high-Ca/high-protein
diet compared to the high-Ca/normal-protein diet which suggested greater absorption of Ca
from the intestinal tract for the high protein diet, which would have resulted in less Ca being
available for Ca-fatty acid soap formation. A diet high in protein has been suggested to
improve Ca absorption (Kerstetter et al. 1998) by keeping Ca in solution and preventing
precipitation with interfering components such as phosphates (Scholz-Ahrens and
Schrezenmeir 2000; Camara-Martos and Amaro-Lopez 2002). As mentioned in section 2.3.2.1,
phosphopeptides derived from casein bind ionized Ca to the phosphate group of serine
residues, this would render Ca less available for the formation of Ca-fatty acid soaps and
explain the lower excretion of fatty acids in the presence of dairy protein.
2.5.2.
Fatty acid soap formation with divalent cations other than Ca
Ca is a divalent cation, and therefore when ionised has the ability to bind two free fatty acid
molecules forming a Ca-fatty acid complex that is suspected to be insoluble at the pH of
intestinal fluids and therefore passes through the gut unabsorbed (Gacs and Barltrop 1977).
However, Ca is not the only divalent cation present in the gastrointestinal tract. Nutritionally
relevant minerals such as Mg, Zn, Fe and Cu are also present in the gastrointestinal tract and
Chapter Two: Literature Review 55
fatty acids. Moreover, considering that dietary fat can impair Ca absorption most likely via
soap formation, the absorption of other divalent minerals may be similarly affected. Despite
the obvious similarity between Ca and other divalent minerals little work has been
conducted examining the ability of divalent cations other than Ca to form soaps. A few
studies investigating the effect of dietary fat on Ca retention have included observations
about faecal Mg excretion and digestibility. Of the limited information available, Kaup et al.
(1990) reported that, feeding rats diets containing 20 g 100 g-1 of butter fat resulted in a 20%
lower apparent faecal magnesium digestibility and greater faecal Mg excretion when
compared to rats receiving a diet containing 5 g 100 g-1 of butter fat suggesting that Mg-fatty
acid soaps may be the mechanism by which Mg absorption was altered. Moreover, and as is
the case for Ca, Mg absorption appears to be influenced to a greater degree by the presence
of saturated fatty acids as opposed to unsaturated fatty acids. The latter is evidenced by a
study where rats receiving a diet containing 25 g 100 g-1 triolein absorbed up to 55% of the
ingested Mg (apparent Mg digestibility was comparable to the fat-free control diet) whereas
for diets containing 25 g 100 g-1 diet of tripalmitin or tristearin only, 30% of the ingested Mg
was absorbed (Tadayyon and Lutwak 1969b). However, not all published studies have
reported an effect of dietary fat consumption on increased faecal Mg excretion or reduced
Mg absorption. For example, comparing fat-free diets to diets supplemented with oleic or
palmitic acid and with varying Ca concentrations did not show decreased Mg retention in
chicks when fat was present (Atteh and Leeson 1984). Moreover, a study in rats investigating
the effect of the positional distribution of stearic and oleic acid in the triacylglycerol molecule
did not show an influence of the structured triglycerides on faecal excretion and the apparent
digestibility of Mg (Brink et al. 1995). In general, the results from some of the latter studies
Chapter Two: Literature Review
56
acids and therefore that Mg-fatty acid soap formation is possible. However, Mg-fatty acid
soap formation does not seem to be as profound as Ca-fatty acid soap formation, as studies
showing an increase in faecal Ca excretion did not always show an effect on Mg excretion
(Atteh and Leeson 1984). Studies investigating the effect of dietary fat on divalent trace
mineral absorption (eg Zn, Fe, Cu) are inconclusive (Lukaski et al. 1986; Johnson et al. 1992;
Wapnir and Sia 1996). It has been suggested that an increase in dietary fat increases Fe
absorption in rats, regardless of the fat source (Johnson et al. 1987). However, some studies
suggest a decrease in the absorption of Zn and Fe in the presence of polyunsaturated fatty
acids (Lukaski et al. 1986; Wapnir and Lee 1990). For example, a study performed with
endurance athletes showed increased faecal Zn and Fe excretion in the presence of a diet rich
in polyunsaturated fatty acids compared to a diet high in carbohydrates or saturated
medium chain fatty acids (Lukaski et al. 1986). Moreover, in an in vivo study using intestinal
perfused rats, arachidonic acid (C20:4) inhibited zinc removal from the intestinal lumen.
However, the saturated long chain fatty acid, palmitic acid, had the opposite effect and
stimulated zinc absorption. Another study in rats showed improved Fe absorption in the
presence of saturated fatty acids (Johnson et al. 1992). However, not all studies have showed
such an effect of saturated fatty acids on trace element (Fe and Cu) absorption (Johnson et al.
1987; Wapnir and Sia 1996). For example, Cu absorption had been reported to decrease
significantly in the presence of free palmitic acid and stearic acid when investigated in rats
using jejunal perfusion (Wapnir and Sia 1996). The inconclusive results and the limited
research conducted regarding divalent cations other than Ca and their ability for fatty acid
Chapter Two: Literature Review 57
2.6.
Concluding Comments
An increased dietary Ca intake has been repeatedly reported to increase faecal fat excretion
in animals and humans. It has been hypothesised that this Ca-induced increase in faecal fat
output leads to a decreased uptake of energy which might further result in a reduction of
body weight and body fat. The mechanism by which dietary Ca increases faecal fat output
has been suggested to be the formation of Ca-fatty acid complexes, so called Ca-fatty acid
soaps, which are insoluble in the intestinal environment and evade absorption in the small
intestine.
Although the formation of insoluble Ca-fatty acid soaps is believed to be the cause of the
reduced fat absorption, few researchers have attempted to isolate Ca-fatty acid soaps from
faecal samples. The currently available methods described in the literature to extract Ca-fatty
acid soaps from faecal material appear to poorly recover soaps. However, to determine what
impact Ca-fatty acid soap formation has on faecal fat excretion, it is necessary to be able to
determine the amount of fat excreted in the form of fatty acid-soaps.
The formation of Ca-fatty acid soaps is believed to not only alter the absorption of fat but has
also been shown to reduce the absorption of Ca from the gastrointestinal tract in studies
conducted in animals and human infants. If the formation of Ca-fatty acid soaps could
potentially impair Ca absorption, other divalent cations may also be able to complex with
fatty acids leading to decreased absorption of essential minerals from the intestinal tract.
Further research is necessary to definitively address the hypothesis that Ca-fatty acid soap
formation is the mechanism for increased faecal fatty acid excretion in the presence of dietary
Chapter Two: Literature Review
58
this has not been done well. Moreover, understanding where in the gastrointestinal tract
soaps are formed would provide important knowledge about the behaviour of dietary Ca
Chapter Three: Assay Development for Ca-Fatty Acid Soap Determination 59