The Effects of Mastication and Digestion on the Bio Accessibility of Energy From Walnuts

Recent evidence indicates up to 20% of the energy from walnuts is not absorbed. This low bio accessibility is comparable to almonds with markedly different physical properties and much higher than for pistachios with similar physical characteristics. These counter-intuitive findings require mechanistic explanations so they may be accepted and used to formulate policy and clinical recommendations. It is proposed that the differences in the structure of nuts accounts for the energy yield results. In addition, the whole nut yields superior effects on fullness and this leads to focus on oral processing. It may be that the mechanical act of chewing generates satiety sensations or it may be that the mechanical disruption of the parenchymal call walls releases lipid and protein and their higher concentrations activate the release of gut peptides associated with satiety.

Visit 1: Participants will report the Laboratory of Sensory and Ingestive Studies following and overnight fast, and having refrained from using oral care products for at least two hours prior to the visit. Participants who meet the BMI requirements, will have electrodes placed on their wrist, upper, and lower jaw and will be asked to chew the following stimuli: walnuts, almonds and pistachios for 15 seconds and expectorate the bolus into a beaker. However, when presented with 5 g walnuts participants will be asked to chew until the point where they would normally swallow and then spit the bolus into a beaker. The chewing conditions are randomized and include: 1) 5 g nuts alone, 2) 5 g nuts with 5 ml water, 3) 5 g nuts with 5 ml apple juice, 4) 5 g nuts with 5 g plain yogurt, 5) 5 g nuts with 5 g sweet yogurt. Following each chewing condition, participants will rate hedonic preference on a 9-point scale.

Visit 2 and 3: Following an overnight fast, the participant will be placed in a semi-supine position and a catheter will be placed in a vein in the antecubital space of one arm. A 9 ml baseline blood sample will be collected. Participants will complete a validated appetite questionnaire on a palm pilot right after the baseline blood draw. The participants will then consume 28 g of walnuts or 28 g walnut butter given in random order. Additional blood samples and appetite questionnaire will be taken at 15, 30, 45, 60,120, and 180 minutes. The blood will be stored in a minus 80 freezer to be analyzed at a later date for insulin, glucose, GLP-1, Ghrelin, and PYY.