The Effects of Mastication and Digestion on the Bioaccessibiliity of Energy from Walnuts

Breanna M McArthur, Purdue University


Walnuts consumption provides multiple health benefits, but the high energy and fat content of walnuts raises continued concerns regarding their role in weight management. These concerns persist despite the evidence from epidemiological and clinical studies indicating that nut consumption does not increase the risk of weight gain. The predominate factors contributing to the inverse or neutral relationship between walnut consumption and increased body weight is their high satiety properties and poor bioaccessibility of energy during digestion. Mastication is associated with each of these factors; however, its role in energy balance has not yet been clearly characterized. Moreover, mastication is modulated by factors associated with meal ingestion, such as palatability and prandial fluid intake. Yet, there has been a dearth of information on the mastication of nuts in the context of the diet, where these inputs are present. Consequently, this dissertation focused on mastication and had four primary aims. The first aim was to evaluate the oral processing of walnuts in isolation and under manipulated palatability and fluid intake. The second aim was to evaluate the contribution of mastication to the satiety effects of walnuts. The third aim was to evaluate the contribution of mastication to the low digestion efficiency of walnuts. The forth aim was to contrast the mastication and digestion of walnuts with almonds and pistachios, nuts that present different physical properties. Fifty health adults (25 males, 25 females; BMI 24.7 ± 3.4 kg/m 2; age: 18–52 years old) were enrolled in a randomized cross-over trial in which nuts (walnuts, almonds, pistachios) with and without water, juice, sweetened yogurt, and plain yogurt were ingested. Chewing forces, pre-swallowing particle size, along with satiety sensation and gut hormones following walnut consumption (whole nut or nut butter) were measured. Results suggest that walnuts with yogurt yielded larger particle sizes than chewing walnuts in isolation. Although particle size was not correlated with either food palatability or sweet flavor, the findings indicate that changing the conditions at swallowing might modify the release of energy from nuts. Further, fullness sensations were higher after whole walnut than walnut butter consumption though there were no significant changes in glucose, insulin, or GLP-1 concentrations. This indicates that mastication has a direct influence on the satiety effects of walnuts, although the mechanism requires further investigation. In the second part of this work nuts (walnuts, almonds, and pistachios) were chewed by seven healthy adults (3 males, 4 females; BMI: 25 ± 1.19; age: 28 ± 4 years old) and subjected to simulated gastric and intestinal digestion conditions. Results showed that the mean particle size was significantly smaller for walnuts after mastication than after 120 minutes of the intestinal phase of digestion. Compared to almonds, the mean particle size was larger for walnuts post-mastication. Moreover, post gastric and intestinal digestion, the mean particle size was larger for walnuts compared to almonds and pistachios. However, the masticated and digesta particle sizes were not related to the integrity of cell walls nor lipid release. Mastication caused walnut cells to rupture rather than separate and as walnut tissues passed through the gastrointestinal track, lipids coalesced reducing digestion efficiency. The findings from this study suggest that the net release of energy during the digestion of walnuts is determined by the intactness of cell walls as well as by structural and compositional features of walnuts, such as naturally occurring oil bodies.




Mattes, Purdue University.

Subject Area

Food Science

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