Christine L Pelkman

Role of Resistant Starch in Improving Gut Health, Adiposity, and Insulin Resistance

The realization that low-glycemic index diets were formulated using resistant starch led to more than a decade of research on the health effects of resistant starch. Determination of the metabolizable energy of the resistant starch product allowed for the performance of isocaloric studies. Fermentation of resistant starch in rodent studies results in what appears to be a healthier gut, demonstrated by increased amounts of short-chain fatty acids, an apparent positive change in the microbiota, and increased gene expression for gene products involved in normal healthy proliferation and apoptosis of potential cancer cells. Additionally, consumption of resistant starch was associated with reduced abdominal fat and improved insulin sensitivity. Increased serum glucagon-like peptide 1 (GLP-1) likely plays a role in promoting these health benefits. One rodent study that did not use isocaloric diets demonstrated that the use of resistant starch at 8% of the weight of the diet reduced body fat. This appears to be approximately equivalent to the human fiber requirement. In human subjects, insulin sensitivity is increased with the feeding of resistant starch. However, only 1 of several studies reports an increase in serum GLP-1 associated with resistant starch added to the diet. This means that other mechanisms, such as increased intestinal gluconeogenesis or increased adiponectin, may be involved in the promotion of improved insulin sensitivity. Future research may confirm that there will be improved health if human individuals consume the requirement for dietary fiber and a large amount of the fiber is fermentable.

Effects of dietary fat, nutrition labels, and repeated consumption on sensory-specific satiety.

This study investigated whether energy from fat, nutrition information, and/or repeated consumption of a palatable snack food affects the development of sensory-specific satiety (SSS). Participants (51 males and 44 females) ate an afternoon snack of potato chips in a laboratory for two 10-day (Monday-Friday) sessions in a repeated measures, cross-over design. In one 10-day session, participants were given regular, full-fat potato chips (22.2 kJ/g; 150 kcal/oz) and, in the other, they were given potato chips made with olestra (11.8 kJ/g; 80 kcal/oz), a non-absorbable fat replacer. Information about the fat and energy content of the chips was provided to half the participants, while the other half was not informed. In both sessions, participants were instructed to consume the potato chips ad libitum. Initial ratings of sensory properties of the two types of chips did not differ significantly. In SSS tests, participants rated sensory properties of the chips and four test foods (turkey, strawberry yogurt, cookie, and carrot) on days 1, 5, and 10 of the 10-day sessions. Following consumption, ratings of pleasantness of taste and texture and prospective consumption of both types of chips declined compared to the test foods. Further analyses showed that the development of SSS was not affected by the fat and energy content of the chips, the provision of nutrition information, or repeated consumption.

Effects of moderate (MF) versus lower fat (LF) diets on lipids and lipoproteins: a meta-analysis of clinical trials in subjects with and without diabetes

BACKGROUND Dyslipidemia increases coronary heart disease (CHD) risk and often presents in diabetes, which amplifies risk of CHD. Lower fat (LF) diets increase triglyceride (TG) and decrease high-density lipoprotein cholesterol (HDL-C); moderate fat (MF) diets decrease TG and lower HDL-C less. OBJECTIVE To quantify the magnitude of lipid and lipoprotein responses to MF versus LF cholesterol-lowering weight maintenance diets in subjects with and without diabetes. METHODS A meta-analysis of 30 controlled-feeding studies (n = 1213 subjects) was conducted to evaluate LF versus MF diets on lipids and lipoproteins in subjects with and without diabetes. RESULTS In all subjects, MF and LF diets decreased low-density lipoprotein cholesterol (LDL-C) similarly. MF diets decreased HDL-C less versus LF diets. The estimated increase in HDL-C after MF diets versus LF diets was 2.28 mg/dL (95% confidence interval 1.66 to 2.90 mg/dL, P < .0001). MF diets decreased TG, whereas LF diets increased TG. The decrease in TG was -9.36 mg/dL (-12.16 to -6.08 mg/dL, P < .00001) for MF versus LF diets. In subjects with diabetes, there was a similar increase in HDL-C (2.28 mg/dL) versus subjects without diabetes; however, there was a greater reduction in TG (-24.79 mg/dL, P < .05) on the MF diet. Subjects with diabetes had greater reductions in the total cholesterol (TC) to HDL-C ratio (TC:HDL-C) (-0.62, P < .0001) and non-HDL-C (-5.39 %, P < .06) after MF versus LF diets. CONCLUSIONS Both men and women had greater estimated reductions (6.37% and 9.34%, respectively) in predicted CHD risk after MF diets compared to LF diets. Moreover, based on greater reductions in TG, the TC:HDL-C ratio and non-HDL-C in subjects with diabetes, the CHD risk reduction would be greater for a MF versus a LF weight maintenance, cholesterol-lowering diet.

Dietary restraint and menstrual cycle phase modulated L-phenylalanine-induced satiety.

l-phenylalanine (Phe) has been shown to elicit release of the gut hormone cholecystokinin (CCK) and reduce energy intake. Furthermore, studies in some animal models demonstrate potentiation of CCK-induced satiety by estradiol (E(2)). As E(2) is elevated in the follicular phase, we expected greater satiety effects than in the luteal phase when the effects may be antagonized by concomitant elevations in progesterone (P). Women with low dietary restraint were tested over two cycles and received encapsulated Phe or dextrose (control) during both phases within each cycle. Data from 20 women and 32 menstrual cycles were analyzed. Daily energy intake was suppressed by 9% for Phe compared to control and 8% in the follicular versus luteal phase of the menstrual cycle. Significant three-way interactions showed that the effects of condition and phase differed as a function of status on the rigid dietary restraint subscale. Phe suppressed daily energy intake by 15% relative to control in the follicular phase for women in the lower 50th percentile of rigid restraint, whereas for women in the higher 50th percentile group, Phe reduced energy intake by 15% in the luteal phase. The results replicate previous findings showing effects of cycle phase and Phe on food intake. The interaction between variables suggests that rigid restraint status modulates the satiety response to Phe, possibly through effects of reproductive hormones. Further studies are needed to replicate these findings and examine other aspects of satiety that may be altered by rigid restraint status.

A resistant-starch enriched yogurt: fermentability, sensory characteristics, and a pilot study in children.

The rising prevalence of obesity and the vulnerability of the pediatric age group have highlighted the critical need for a careful consideration of effective, safe, remedial and preventive dietary interventions. Amylose starch (RS2) from high-amylose maize (HAM) ferments in the gut and affects body weight. One hundred and ten children, of 7-8 (n=91) or 13-14 (n=19) years of age scored the sensory qualities of a yogurt supplemented with either HAM-RS2 or an amylopectin starch. The amylopectin starch yogurt was preferred to the HAM-RS2-enriched yogurt by 7-8 year old panelists ( P<0.0001). Appearance, taste, and sandiness scores given by 13- to 14-year-old panelists were more favorable for the amylopectin starch yogurt than for HAM-RS2-enriched yogurt ( P<0.05). HAM-RS2 supplementation resulted in acceptable (≥6 on a 1-9 scale) sensory and hedonic ratings of the yogurt in 74% of subjects. Four children consumed a HAM-RS2-enriched yogurt for four weeks to test its fermentability in a clinical trial. Three adolescents, but not the single pre-pubertal child, had reduced stool pH ( P=0.1) and increased stool short-chain fatty acids (SCFAs) ( P<0.05) including increased fecal acetate ( P=0.02), and butyrate ( P=0.089) from resistant starch (RS) fermentation and isobutyrate ( P=0.01) from protein fermentation post-treatment suggesting a favorable change to the gut microbiota. HAM-RS2 was not modified by pasteurization of the yogurt, and may be a palatable way to increase fiber intake and stimulate colonic fermentation in adolescents. Future studies are planned to determine the concentration of HAM-RS2 that offers the optimal safe and effective strategy to prevent excessive fat gain in children.