Acute and chronic effects of pulses and macronutrient composition on appetitive, glycemic, palatability and cravings outcomes
Observational and experimental studies support a role of pulses in reducing risk for obesity and chronic diseases. The macronutrient composition of the diet such as the fiber and protein (components of pulses) content may also play similar beneficial roles. There are however, gaps in the literature concerning some of the biobehavioral mechanisms by which pulses reduce obesity and chronic diseases risk as well as issues with consumption adherence. Thus this dissertation was conducted to investigate some of these gaps as well as explore alternatives to encourage consumption. ^ In the first study, we assessed whether blending lentils or taking lentils with the digestive aid, alpha galactosidase (α-gal), would increase postprandial subjective appetite and blood glucose response. Twelve participants (BMI 23.3 kg/m2; aged 28 ± 10 y (mean ± SD)) consumed breakfast meals containing whole (W), blended (B) or no lentils (C) control, each in combination with 3 α-gal or placebo capsules in a randomized, cross-over, double-blind, placebo-controlled trial. Results showed a significant effect of meal on both appetite and glucose responses. Specifically, the B meal resulted in higher postprandial appetite ratings than the W meal for hunger, desire to eat and prospective consumption but not for fullness though this effect was small (6%). Also, the B meal resulted in lower postprandial glucose concentration than the C meal but did not differ from the W meal. α -gal alone did not have any effects on appetite or glucose responses but there was an interaction effect of α-gal and meal such that there was a greater postprandial desire to eat and lower postprandial fullness with the B compared with both the W and C meal in the placebo but not the α-gal condition. Blending lentils had minimal or no negative effects on appetite and blood glucose responses implying that consumption of both blended lentils and α-gal may be encouraged as approaches to increasing pulse consumption. It is known that repeated exposure to foods varying in different sensory qualities such as sugar, salt, and fat may enhance their appeal but the breadth of such learning is not known for pulses which are high in indigestible carbohydrates and often promoted as part of a healthy diet. Data analyses were conducted using primary data from the Beans Weight Loss and Lifestyle (BeWeLL) intervention - a 6-week weight loss intervention that incorporated 3 different treatment levels (low, medium or high amounts) of pulses with caloric restriction to assess whether the palatability of pulses would increase with repeated exposure during the intervention. At week 0, 3 and 6 of this intervention participants (n=42, BMI: 31.2 ± 4.3kg/m2 , aged: 39 ±7 y) rated the taste, appearance, odor and texture pleasantness of 28 foods that had been provided or not provided during the intervention and containing pulses or no pulses. A flavor score was also calculated using the average of the 4 palatability scores. The major findings were that some components of palatability (taste, texture and flavor pleasantness) but not others (appearance and odor) for both foods containing and not containing pulses which participants had been exposed to during the intervention increased but this did not occur for foods that were not provided during the intervention. However the f increase was small (∼4%) and it is uncertain if this change would be enough to result in a greater selection of these foods in everyday life when considered alone. ^ Recent findings suggest that a high compared to a low glycemic index meal increases activity in brain regions associated with cravings. We investigated whether cravings would decrease during the same pulse (an example of a low glycemic index food) weight loss intervention described above and also assessed the association between change in cravings and change in body weight. Furthermore we tested whether participants whose cravings decreased the most would self-select higher percentage of energy from fat, sugar and carbohydrate and lower protein and fiber density. At week 0, 3 and 6 of the intervention, participants' (n=38, BMI 31.0 ± 4.3 kg/m2, aged 39 ± 7 y) self-reported food cravings, body weight changes and self-selected dietary intakes were assessed. Cravings intensity and frequency did not change with weight loss, and while individuals who lost more weight from week 3 to 6 reported larger decreases in the frequency of their strongest craving per month, no other associations between weight change and cravings variables were observed. There was no effect of pulse provision on change in cravings and the associations between changes in cravings variables and changes in self-selected dietary variables were significant for some but not others with the direction of association being consistent with our hypothesis for change in percent energy from fat and fiber and inconsistent with change in energy from carbohydrate and sugar. Thus our data did not support a decrease in food craving with pulse provision during weight loss and possibly cravings in our participants were not exclusively for carbohydrate or sugary foods as commonly believed but these are only associations and do not imply causation. ^ Finally, protein and fiber are major components of pulses that confer multiple benefits including reducing appetite. Thus we assessed the independent and interactive effects of orlistat 60 mg (an obesity treatment drug that works by preventing the absorption of dietary fat) with dietary protein and fiber on acute appetite and subsequent ad libitum energy intake since dietary fat helps reduce appetite and taking orlistat could potentially counter weight loss efforts. In a double-blind placebo controlled randomized cross-over trial, 18 healthy adults aged 21-46 y (BMI 27.9 ± 1.6 kg/m2; mean ± SD) took orlistat 60 mg (allis®) or a placebo with breakfasts containing 27% energy from fat and either normal protein and fiber (NPF; 15% energy from protein, 7g fiber/1000 kcal) or HPF (25% energy from protein, 14g/1000 kcal). Testing of the 4 meal/drug treatment combinations occurred weekly. Orlistat/HPF resulted in greater fullness and lower desire to eat, prospective consumption, insulin response, and ad libitum energy intake compared to orlistat/NPF. Consuming high protein and fiber meals may help reduce appetite when taking orlistat 60 mg, as well as attenuate the post-meal insulin response. ^ Overall our data showed some beneficial effects of consuming pulses on appetite and blood glucose as well small increases in palatability with repeated exposure which may be important if combined with other lifestyle factors. Furthermore, food cravings did not change with weight loss or pulse provision so is not part of the mechanism explaining the weight loss observed in the chronic setting in our study. Cravings were also related to a few dietary variables but not always in the direction we hypothesized. Finally a high protein and fiber meal taken with orlistat was successful in reducing appetite but did not impact energy intake significantly.^
Megan A. McCrory, Purdue University.
Health Sciences, Nutrition