SNP discovery and genetic mapping of T-DNA insertional mutants in Fragaria vesca L.

As part of a program to develop forward and reverse genetics platforms in the diploid strawberry [Fragaria vesca L.; (2n = 2x = 14)] we have generated insertional mutant lines by T-DNA mutagenesis using pCAMBIA vectors. To characterize the T-DNA insertion sites of a population of 108 unique single copy mutants, we utilized thermal asymmetric interlaced PCR (hiTAIL-PCR) to amplify the flanking region surrounding either the left or right border of the T-DNA. Bioinformatics analysis of flanking sequences revealed little preference for insertion site with regard to G/C content; left borders tended to retain more of the plasmid backbone than right borders. Primers were developed from F. vesca flanking sequences to attempt to amplify products from both parents of the reference F. vesca 815 x F. bucharica 601 mapping population. Polymorphism occurred as: presence/absence of an amplification product for 16 primer pairs and different size products for 12 primer pairs, For 46 mutants, where polymorphism was not found by PCR, the amplification products were sequenced to reveal SNP polymorphism. A cleaved amplified polymorphic sequence/derived cleaved amplified polymorphism sequence (CAPS/dCAPS) strategy was then applied to find restriction endonuclease recognition sites in one of the parental lines to map the SNP position of 74 of the T-DNA insertion lines. BLAST search of flanking regions against GenBank revealed that 46 of 108 flanking sequences were close to presumed strawberry genes related to annotated genes from other plants.

An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods.

The aim of this study was to systematically compare postprandial insulin responses to isoenergetic 1000-kJ (240-kcal) portions of several common foods. Correlations with nutrient content were determined. Thirty-eight foods separated into six food categories (fruit, bakery products, snacks, carbohydrate-rich foods, protein-rich foods, and breakfast cereals) were fed to groups of 11-13 healthy subjects. Finger-prick blood samples were obtained every 15 min over 120 min. An insulin score was calculated from the area under the insulin response curve for each food with use of white bread as the reference food (score = 100%). Significant differences in insulin score were found both within and among the food categories and also among foods containing a similar amount of carbohydrate. Overall, glucose and insulin scores were highly correlated (r = 0.70, P < 0.001, n = 38). However, protein-rich foods and bakery products (rich in fat and refined carbohydrate) elicited insulin responses that were disproportionately higher than their glycemic responses. Total carbohydrate (r = 0.39, P < 0.05, n = 36) and sugar (r = 0.36, P < 0.05, n = 36) contents were positively related to the mean insulin scores, whereas fat (r = -0.27, NS, n = 36) and protein (r = -0.24, NS, n = 38) contents were negatively related. Consideration of insulin scores may be relevant to the dietary management and pathogenesis of non-insulin-dependent diabetes mellitus and hyperlipidemia and may help increase the accuracy of estimating preprandial insulin requirements.

Plant-animal subsistence ratios and macronutrient energy estimations in worldwide hunter-gatherer diets.

Both anthropologists and nutritionists have long recognized that the diets of modern-day hunter-gatherers may represent a reference standard for modern human nutrition and a model for defense against certain diseases of affluence. Because the hunter-gatherer way of life is now probably extinct in its purely un-Westernized form, nutritionists and anthropologists must rely on indirect procedures to reconstruct the traditional diet of preagricultural humans. In this analysis, we incorporate the most recent ethnographic compilation of plant-to-animal economic subsistence patterns of hunter-gatherers to estimate likely dietary macronutrient intakes (% of energy) for environmentally diverse hunter-gatherer populations. Furthermore, we show how differences in the percentage of body fat in prey animals would alter protein intakes in hunter-gatherers and how a maximal protein ceiling influences the selection of other macronutrients. Our analysis showed that whenever and wherever it was ecologically possible, hunter-gatherers consumed high amounts (45-65% of energy) of animal food. Most (73%) of the worldwide hunter-gatherer societies derived >50% (> or =56-65% of energy) of their subsistence from animal foods, whereas only 14% of these societies derived >50% (> or =56-65% of energy) of their subsistence from gathered plant foods. This high reliance on animal-based foods coupled with the relatively low carbohydrate content of wild plant foods produces universally characteristic macronutrient consumption ratios in which protein is elevated (19-35% of energy) at the expense of carbohydrates (22-40% of energy).

The effects of equal-energy portions of different breads on blood glucose levels, feelings of fullness and subsequent food intake.

OBJECTIVE: This study compared the effects of equal-energy portions of 7 different breads on feelings on fullness and subsequent ad libitum food intake. A satiety index score (SI) was calculated for each of the breads. DESIGN: Within-subject, repeated-measures design. SUBJECTS AND INTERVENTION: Ten healthy subjects participated in the study. Subjects fasted for > or =10 hours overnight and then reported to the research center the next morning, where they first completed baseline satiety ratings, gave a fasting blood sample, and then consumed a test bread. Additional finger prick blood samples and satiety ratings were collected at 15-minute intervals over 120 minutes, after which the subjects' ad libitum intake of food was recorded. A satiety index (SI) score was calculated for each test food by dividing the area under the 120-m satiety response curve (AUC) for the test bread by the satiety AUC for the reference bread (regular white bread) and multiplying by 100%. RESULTS: The mean SI scores for the breads ranged from 100% to 561%, with regular white bread having the lowest SI score. Mean SI scores were negatively correlated with energy intake at a test meal after 120 m (r=-0.88, P<.01, n=7) and total day energy intakes (r=-0.72, P<.05, n=7). The strongest predictor of the breads' SI scores was their portion size and thus energy density. The breads' glycemic responses were not significantly associated with fullness responses. APPLICATIONS: Ingredients and food processing methods are available for the production of palatable, high-satiety versions of processed foods, which may be useful for weight control diets. SI scores would be a useful addition to food labels to indicate which foods are less likely to be overeaten and could be used by dietitians to develop weight control plans to help reduce energy intakes without increased hunger.

Particle size, satiety and the glycaemic response.

OBJECTIVE: This study investigated the hypothesis that the smaller the particle size of the food, the higher the glycaemic-insulin response and the lower the satiety rating. DESIGN AND SUBJECTS: Ten healthy subjects consumed equal carbohydrate portions of four test meals of equivalent nutritional composition based on four different grades of wheat: whole grains, cracked grains, coarse and fine wholemeal flour. RESULTS: The mean overall plasma glucose response (area under the curve: AUC) was highest for the fine flour meal (4205 +/- 451 mmol/l.120 min), followed by the coarse flour and cracked grain meals and lowest for the whole grain meal (1524 +/- 190 mmol/l.120 min). Insulin responses showed the same ranking but satiety responses were the reverse, the fine flour meal giving the lowest satiety response [AUC: 231.4 +/- 31.6 rating scale (RS) units.120 min] and the whole grain meal the highest response (AUC: 318.4 +/- 29.3 RS units.120 min). Total insulin responses (AUC) were significantly associated with subjective satiety when analyses on an individual basis (analysis of covariance coefficient = -0.024, P < 0.04) such that for every 1000 unit increase in AUC insulin, satiety decreased by 24 units (13% on average). CONCLUSION: The results suggest that the processing of cereals is not only a major determinant of the glycaemic and insulin response but also affects the levels of postprandial satiety.

A satiety index of common foods.

OBJECTIVE: The aim of this study was to produce a validated satiety index of common foods. DESIGN AND SUBJECTS: Isoenergetic 1000 kJ (240 kcal) servings of 38 foods separated into six food categories (fruits, bakery products, snack foods, carbohydrate-rich foods, protein-rich foods, breakfast cereals) were fed to groups of 11-13 subjects. Satiety ratings were obtained every 15 min over 120 min after which subjects were free to eat ad libitum from a standard range of foods and drinks. A satiety index (SI) score was calculated by dividing the area under the satiety response curve (AUC) for the test food by the group mean satiety AUC for white bread and multiplying by 100. Thus, white bread had an SI score of 100% and the SI scores of the other foods were expressed as a percentage of white bread. RESULTS: There were significant differences in satiety both within and between the six food categories. The highest SI score was produced by boiled potatoes (323 +/- 51%) which was seven-fold higher than the lowest SI score of the croissant (47 +/- 17%). Most foods (76%) had an SI score greater than or equal to white bread. The amount of energy eaten immediately after 120 min correlated negatively with the mean satiety AUC responses (r = -0.37, P < 0.05, n = 43) thereby supporting the subjective satiety ratings. SI scores correlated positively with the serving weight of the foods (r = 0.66, P < 0.001, n = 38) and negatively with palatability ratings (r = -0.64, P < 0.001, n = 38). Protein, fibre, and water contents of the test foods correlated positively with SI scores (r = 0.37, P < 0.05, n = 38; r = 0.46, P < 0.01; and r = 0.64, P < 0.001; respectively) whereas fat content was negatively associated (r = -0.43, P < 0.01). CONCLUSION: The results show that isoenergetic servings of different foods differ greatly in their satiating capacities. This is relevant to the treatment and prevention of overweight and obesity.

Interrelationships among postprandial satiety, glucose and insulin responses and changes in subsequent food intake.

OBJECTIVE: The aim of this study was to investigate whether postprandial glucose and insulin responses were related to concurrent changes in satiety. DESIGN: Thirty-eight common foods, grouped into six food categories, were tested in total. Each food category was fed to a separate group of subjects. A within-subjects repeated-measures design was used such that within each food category each subject consumed all of the test foods in random order. SETTING: The study was conducted at the Human Nutrition Research Unit, Sydney University. SUBJECTS: Separate groups of 11-13 healthy young subjects, who were unrestrained eaters, were recruited for each of the six food categories. INTERVENTIONS: Isoenergetic 1000 kJ (240 kcal) portions of the test foods were fed to fasting subjects. Fingerprick blood samples and satiety ratings were obtained every 15 min over 120 min after which a standard meal was presented and ad libitum food intake was recorded. A glycaemic score, insulin index and satiety index score was calculated for each food by dividing the area under the 120 min response curve (AUC) for the test food by the AUC for white bread and multiplying by 100. Expressing the results of the test foods relative to those for white bread minimised the confounding influence of inherent differences between the subjects. RESULTS: Among the 38 test foods, there were no significant relationships between satiety and plasma glucose or insulin responses. However, a negative correlation was found between insulin AUC responses and ad libitum food intake at 120 min which suggests that test foods producing a higher insulin response within 120 min were associated with less food intake and thus indirectly greater satiety. This result is consistent with previous findings that carbohydrate-rich foods are more satiating than fat-rich foods. Thus, total carbohydrate content appears to have been a stronger determinant of short-term satiety, in conjunction with the foods structural characteristics, than the foods glycaemic impact. CONCLUSIONS: The total amount of carbohydrate consumed at a meal and subsequent insulinaemia may partly determine the degree of hunger arising within the next 2 h.

The glycaemic index values of Vietnamese foods.

OBJECTIVE: To determine and compare the glycaemic index (GI) values of a range of Vietnamese foods in two racial groups. DESIGN AND SUBJECTS: Twelve healthy subjects (six Asian and six Caucasian) consumed 50 g carbohydrate portions of a reference food (glucose sugar) and nine Vietnamese foods (three rices, three noodle products and three sweet foods) in random order after an overnight fast. The reference food was tested on two separate occasions, and the Vietnamese foods were each tested once. Capillary blood samples were taken at time 0 (fasting), 15, 30, 45, 60, 90 and 120 min from the start of each meal. Samples were analysed for plasma glucose and the incremental areas under the plasma glucose curves (AUC) were used to calculate the GI values of the test foods, using glucose as the reference food (ie GI value of glucose=100). The mean GI value of each food was calculated for the entire group of subjects (n=12) and for both racial groups (n=6). RESULTS: The three rices had surprisingly high GI values (86-109), whereas the noodle products had relatively low GI values (39-61). The sugar-rich foods produced intermediate GI values (54-79). The GI values for the nine foods calculated separately for the two racial groups were not significantly different from each other (P=0.26). CONCLUSIONS: The GI values derived from Caucasian subjects are likely to be applicable to Asian populations. Varieties of imported rice from Thailand were found to have high GI values. Alternative low-GI staples, such as rice noodles, may be preferable for Asian/Vietnamese people with diabetes. SPONSORSHIP: This study was funded by the University of Sydney.

Increased insulin responses to ingested foods are associated with lessened satiety.

In order to assess the relationship between metabolic responses and satiety, four men and five women ate two pairs of foods containing 50 g of available carbohydrate, ordinary and quick-cooking rice and high- and low-amylose puffed rice. Plasma glucose and insulin levels and satiety ratings were assessed over 2 h and food intake measured immediately thereafter. The area under the curve (AUC) of the 2-h glucose response was 1.6 times greater after quick-cooking rice than that for ordinary rice. Similarly, the glucose AUC for the low-amylose rice was 1.5 times higher than that of the high-amylose rice. Insulin responses followed the pattern of the glucose responses. Conversely, the satiety AUC was 1.5 times higher for ordinary rice than for the quick-cooking rice, and 1.5 times higher for high-amylose than for low-amylose rice. Food intake (g) immediately after each 2-h session was significantly related to both the satiety AUC and the last rating score, thereby corroborating the satiety ratings. A significant negative association was found between the individual insulin and satiety AUC responses to the four foods. These results suggest that increased rate of starch digestion and higher insulin responses are associated with lessened satiety.

The effects of sugar-free vs sugar-rich beverages on feelings of fullness and subsequent food intake.

This study compared the effects of equal volumes of sugar-rich and sugar-free beverages on feelings of hunger and fullness and the ad libitum consumption of a palatable, fat-rich snack. Eleven healthy males consumed equal volumes (375 mL) of three drinks (sugar-rich cola, sugar-free cola, mineral water) in random order on separate mornings. After 20 min, the subjects were able to snack freely on potato crisps during the next 90 min. Each subject's individual bowl of potato crisps was covertly replenished at 15 min intervals while the subjects were completing appetite and mood ratings. After the 110 min experimental period, the subjects' ad libitum food intake from a buffet-style lunch was covertly recorded. On leaving the laboratory, the subjects filled in a weighed food dairy for the rest of the day. The equal-volume preloads initially decreased hunger to a similar degree and potato crisp intake during the first 15 min interval was not significantly different among the three preloads. On average, total energy intakes from the crisps and lunch were not significantly different among the preloads, and by the end of the day, total energy intakes were similar for the three test conditions. Therefore, the low-calorie/low-sugar drinks did not facilitate a reduced energy intake by the lean, non-dieting male subjects.

Australian aboriginal plant foods: a consideration of their nutritional composition and health implications.

For at least 40-50,000 years, plants played an important but supplementary role in the animal-dominated diet of Australian Aboriginal (AA) hunter-gatherers. New knowledge of the nutrient composition and the special physiological effects of their foods provides another perspective in the current debate on the composition of the 'prudent' diet and the diet on which humans evolved. In the present paper we have calculated the average nutrient composition of over 800 Aboriginal plant foods (in total and by food group) and highlighted the differences between these and modern cultivated foods. The data enable us to calculate the absolute contribution of plant foods to total food and nutrient intake of traditional living AA. If plants provided 20-40% of the energy in the diet (the most likely range), then plants would have contributed 22-44 g protein, 18-36 g fat, 101-202 g carbohydrate, 40-80 g fibre and 90-180 mg vitamin C in a 12500 kJ (3000 kcal) diet. Since all the carbohydrate came from plant foods, the traditional AA diet would have been relatively low in carbohydrate (especially starch) but high in dietary fibre in comparison with current recommendations. Over half the carbohydrate could have been in the form of sugars derived from fruit and honey. The low glycaemic index of their carbohydrate foods, however, would generate a relatively low demand for insulin secretion and this characteristic may have protected AA from a genetic predisposition to insulin resistance and its consequences (non-insulin-dependent diabetes mellitus, coronary heart disease, obesity). The dietary pattern and active lifestyle of recent hunter-gatherers such as AA may be a reference standard for modem human nutrition and a model for defence against diseases of affluence.

The effects of high-carbohydrate vs high-fat breakfasts on feelings of fullness and alertness, and subsequent food intake.

Fourteen subjects consumed four realistic isoenergetic (2035 kJ) breakfasts, varying in macronutrient content (two fat-rich, two carbohydrate-rich (low- and high-fibre)), in random order on separate mornings. After breakfast, subjects left the laboratory and completed appetite and alertness ratings at specific times and recorded all subsequent fluid and food intake for the rest of the day. The high-fibre, carbohydrate-rich breakfast was the least palatable but most filling meal and was associated with less food intake during the morning and at lunch. Hunger returned at a slower rate after this meal than after the low-fibre, carbohydrate-rich meal. Both fat-rich breakfasts were more palatable but less satiating than the carbohydrate-rich meals and were followed by greater food intake during the morning, which may be a compensatory response to ingest a sufficient amount of food and/or carbohydrate to match the level of fullness produced by the subjects' habitual breakfasts. By the end of the day, the average total energy intake was significantly greater after the fat-rich EB meal than after the high-fibre, carbohydrate-rich meal (P < 0.05). Total day fat intakes were also significantly greater when the high-fat breakfasts were eaten. For every individual test, alertness ratings increased immediately after breakfast was consumed. On average, the high-fibre carbohydrate-rich meal was associated with the highest post-breakfast alertness ratings and with the greatest cumulative amount of alertness during the period between breakfast and lunch (AUC). Alertness AUC values up until lunch correlated positively with fullness AUC values (r = 0.36, P < 0.01, n = 56). The results confirm the relatively weak satiating power of fat-rich meals observed in controlled laboratory-based studies and indicate that a high-fibre, carbohydrate-rich breakfast may assist weight control efforts by maintaining fullness. Further research is required to determine whether satiety directly enhances alertness and whether low-GI carbohydrate-rich meals enhance alertness to a greater degree than high-GI meals.