The increase in the number of overweight and obese individuals is a public health concern due to correlations of obesity with increased incidence of chronic diseases such as type 2 diabetes and cardiovascular disease. Population data have shown correlations between increased fiber consumption and lower body weight and body mass index (BMI). However, the exact nature of this relationship is not known.

There is considerable variation between different types of fiber and their potential impacts on the physiological regulatory systems of appetite and body weight. The goal of the research presented in this dissertation is to explore the effects of non-viscous, fermentable fiber on appetite and food intake in healthy adults. Collective results from the studies will be used to evaluate short-term appetite and food intake changes as a potential mechanism linking fiber consumption and lower body weight.

We hypothesized that increased resistant starch (RS4)/resistant dextrin consumption will promote satiation and decrease ad libitum food intake at the next meal. We further hypothesized that increased RS4/resistant dextrin consumption will increase postprandial satiety as measured by subjective appetite ratings and that this effect will be modulated through changes in plasma biomarkers of appetite. As addition of fiber to a mixed meal can alter the glycemic response of that meal, we are also interested in effect of RS4/resistant dextrin on postprandial glucose and insulin responses.

To test these hypotheses, a series of experiments were conducted. In the first study, all-purpose flour was replaced with Fibersym® resistant starch flour in a breakfast meal (control: 2g fiber, treatment: 24g fiber). Twenty-seven healthy adults (age: 23±2 years, BMI: 23.0±3.1 kg/m2) participated in the study. Although there were no statistically significant treatment effects observed for satiety or blood measures (p > 0.05), caloric intake over the entire test day was lower for the resistant starch treatment group after data was normalized (p=0.05).

To investigate potential timing effects of fiber consumption, we conducted a study using one of three isocaloric beverages providing 0, 10 or 20g fiber from soluble fiber dextrin (SFD) with the lunch meal. Forty-one healthy adults (age: 24±4 years, BMI: 23.4±2.5 kg/m2) participated in the study. Glucose-dependent Insulinotropic Peptide (GIP) was lower for the 20g fiber from SFD treatment as compared to control (p = 0.0001). However, no other treatment differences in blood measures were observed (p > 0.05). Additionally, there were no treatment effects on subjective appetite or food intake during the first 150 minutes post consumption of treatment beverages (p > 0.05). After participants left the lab, the 20g fiber from SFD treatment group was shown to have lower mean hunger (p = 0.005) and desire to eat (p = 0.0001) and higher fullness (p = 0.002) as compared to control. There was no treatment effect on food intake based on diet diaries or total day consumption (p > 0.05).

In a final study, two sources of SFD (corn and tapioca) and two doses (10 and 20g) of fiber were tested along with a control group. Half of the treatment dose was provided in beverage form at the breakfast meal and half was provided 2 hours later in the form of a snack bar. Participants remained in the lab for 10 hours after breakfast and breath hydrogen measures were taken as an indication of colonic fermentation. Forty-three healthy adults (age: 24±4 years, BMI: 23.6±3.5 kg/m2) participated in the study. Breath hydrogen showed a statistically significant dose response of SFD. However, there were no other treatment differences observed for blood measures, appetite or food intake over the test day.

In conclusion, results from these studies demonstrate that under laboratory conditions, increased resistant starch/resistant dextrin consumption did not affect ad libitum food intake or subjective appetite ratings. Although in free-living conditions, appetite and food intake changes were observed, they were modest in magnitude and inconsistent between studies. Furthermore, while we report evidence of resistant dextrin fermentation in healthy young adults, there is no robust effect of biomarkers of satiety or glycemic response. These results are important as they show that a single dose of 10-20g non-viscous, fermentable fiber is not sufficient to impact next meal energy intake. Additionally the overall findings do not support short-term changes in appetite as an underlying mechanism to link potential effects of fiber on body weight.