Obesity increases insulin resistance and disregulation of glucose homeostasis. This study investigated low glycemic index starch (LGIS)/diacylglycerol (DAG) diet on plasma insulin and circulating incretin hormones during canine weight loss. Obese Beagle dogs were fed one of four starch/oil combination diets (LGIS/DAG; LGIS/triacylglycerol (TAG); high glycemic index starch (HGIS)/DAG; and HGIS/TAG) for 9 weeks during the weight loss period. At weeks 1 and 8, fasting plasma insulin, glucose, nonesterified fatty acid (NEFA), glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) were determined. Weight loss did not affect fasting insulin, glucose, and NEFA, but fasting GIP increased and GLP-1 decreased. LGIS affected postprandial insulin at both times and glucose was similar to insulin, except 60 min postprandially with DAG at week 8. NEFA lowering was less with the LGIS diets initially but not thereafter. At 60 min postprandially on week 8, GIP was significantly elevated by DAG, while GLP-1 was increased only with the HD diet. LGIS suppressed insulin and glucose responses up to 180 min postprandially at both sample times. DAG increased incretin hormones as did the DAG/HGIS combination but only at week 8. This latter finding appeared to be related to the glucose response but not to insulin at 60 min.
Obesity is a common nutritional disorder both in human and companion animals. The incidence of obesity in humans and dogs is considered to be 33.2% in the USA [
In order to elucidate possible effects of DAG and LGIS on hyperinsulinemic responses in dogs, we previously investigated the postprandial effects of a single meal containing 20 g of DAG oil and 25 g of either LGIS or high glycemic index starch (HGIS) mixed with 60 g of boiled boneless chicken breast fed to healthy intact female adult Beagles [
Weight loss is commonly used as one strategy for improving insulin sensitivity. Therefore, weight loss was induced during this study via energy restriction using the above oil- and starch-containing diets. Furthermore, in humans, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like polypeptide-1 (GLP-1) have been identified as incretin hormones that potentially play a role in the glucose-dependent insulin response [
Twelve obese, sexually intact adult female beagles, 2 to 6 yr of age, with body condition scores (BCS) of
Average body weight, body fat, and daily food consumption of experimental diets during the feeding period.
Diet |
| |||||||
---|---|---|---|---|---|---|---|---|
LD | LT | HD | HT | Oil | Starch | Oil by starch | ||
Body Wt, kg |
week 1 |
|
|
|
|
ns | ns | ns |
week 8 |
|
|
|
|
ns | ns | ns | |
Δ |
|
|
|
|
ns | 0.008 | ns | |
| ||||||||
Body fat, % |
week 1 |
|
|
|
|
ns | ns | ns |
week 8 |
|
|
|
|
ns | ns | ns | |
Δ |
|
|
|
|
ns | ns | ns | |
| ||||||||
Food intake, g |
|
|
|
|
ns | ns | ns | |
Food intake, kJ |
|
|
|
|
ns | 0.038 | ns |
Mean ± SEM,
The dogs were allowed free access to water and exercise during the study. Prior to entering the study, all dogs had complete blood counts and serum biochemistry profiles performed to assure normal clinical status.
Four experimental diets were prepared using a mixture of starch (LGIS versus HGIS) and oil (DAG versus triacylglycerol (TAG)) types: LGIS/DAG (LD diet), LGIS/TAG (LT diet), HGIS/DAG (HD diet), and HGIS/TAG (HT diet). These diets were formulated in our laboratory using a mixture of 430 g/kg of chicken byproduct meal (Tyson Foods), 135 g/kg of DAG or TAG enriched dietary oil (Kao Corporation), and 430 g/kg of LGIS or HGIS to provide the same amount of macronutrients in each diet (crude protein, 33.0%; fat, 23.0%; carbohydrate, 38.7%; crude fiber, <2.0%; Ash, 5.3%). Five g/kg of a vitamin/mineral premix for dogs (Akey Industries) was also added. Gelatinized high amylose corn starch and waxy corn starch were used as the LGIS and HGIS sources, respectively (Nihon Shokuhin Kako). The DAG and TAG oils in combination with the other diet ingredients contained similar fatty acid compositions whose data were shown in an earlier publication [
Prior to entering the weight loss study, obesity had been induced in all dogs. During this induction period, the dogs were fed a high-fat diet containing dry food (Science Diet Adult Original, Hill’s Pet Nutrition) and a mixture of canola and soy bean oils (40 g). Pecan shortbread cookies (Keebler Sandies, Kellog Co.) were also added daily to increase calorie intake overall. Once the dogs reached obese body weights based on BCS and body fat%, the pecan shortbread cookies were removed and their obese body weights were maintained for an additional 2 months. These additional months allowed the dogs to establish a more metabolically stable form of obesity. Four weeks prior to the weight loss study, all dogs were fed a diet containing a combination of a 50/50 (v/v) blend of canola and soybean TAG oils, a 50/50 (w/w) mixture of the HGIS and LGIS, chicken byproduct meal, vitamin/mineral premix, and 2-3 volumes of water as an acclimation diet in amounts calculated to maintain their obese body weights (MER, kJ/d
At week 1, the dogs were randomly assigned into 4 groups (
At weeks 1 and 8, jugular catheters were placed in order to conduct postprandial blood collections. A preliminary study found that the starch effect was more dynamically changed during the first 3 h postprandial period. Therefore, blood was collected 3 h postprandially in the present study. Feed had been withheld from the dogs overnight prior to time 0 min blood sample collections. Meals for postprandial sample collections were prepared with a mixture of either 8 g TAG or DAG enriched oil, 25 g LGIS or HGIS, and 80 g boiled chicken breast meat for better palatability and rapid consumption. These four meals had similar macronutrient compositions. Because it was critical that the dogs consumed these meals quickly, approximately 30% of the obese, daily MER amount was prepared for this meal (i.e., ca. 1150 kJ). All dogs consumed their meals within 5 min. Blood samples were then collected at 15, 30, 60, 120, and 180 min after the dogs completed the meals. Samples were placed into EDTA-containing tubes for plasma separation by low speed centrifugation. A protease inhibitor (0.6 TIU/mL blood of aprotinin, Sigma-Aldrich) was added to blood samples for insulin analysis to prevent proteolysis prior to centrifugation. For GIP and GLP-1 analyses, 10
Postprandial plasma samples were analyzed for glucose and nonesterified fatty acids (NEFA) using enzymatic and colorimetric assays. Mercodia Porcine Insulin ELISA (Mercodia AB) was used for insulin analyses according to Bennet et al. and Sato et al. [
Data were expressed as means ± SEM and SPSS 15.0 for Windows was used exclusively for the statistical analyses. Repeated measures ANOVA was performed using a general linear model for fasting samples with oil types (DAG versus TAG) and starch types (HGIS versus LGIS) as between-subjects factors, and week as a within-subject factor with blocking periods (periods 1 and 2) in order to avoid confounding any treatment effect due to the two separate study periods employed. When significance was observed in this model, further pairwise comparison analyses were conducted to obtain simple effects at each treatment level or interactions using Bonferroni corrections. For postprandial samples, the data was converted to area under the curve (AUC) and a two-way ANOVA blocking on period model was used. During the study, all dogs lost body weight (
All dogs lost significant amounts of body weight and body fat during the study (Table
Fasting plasma glucose, insulin, and NEFA concentrations were not significantly different by time, starch and oil types, or interactions (Table
Fasting plasma glucose, insulin, NEFA, and incretin hormones during the feeding period.
Diet |
| |||||||||
---|---|---|---|---|---|---|---|---|---|---|
LD | LT | HD | HT | SEM | Time | Oil | Starch | Oil by starch | ||
Glucose, mmol/L |
week 1 | 5.2 | 6.0 | 5.9 | 6.0 | 0.2 | ns | ns | ns | ns |
week 8 | 6.0 | 5.9 | 5.8 | 5.6 | 0.2 | ns | ns | ns | ||
| ||||||||||
Insulin, pmol/L |
week 1 | 13.0 | 9.1 | 8.7 | 20.6 | 2.9 | ns | ns | ns | ns |
week 8 | 17.0 | 9.2 | 8.5 | 9.5 | 1.8 | ns | ns | ns | ||
| ||||||||||
NEFA, mmol/L |
week 1 | 0.8 | 0.8 | 0.9 | 1.0 | 0.1 | ns | ns | ns | ns |
week 8 | 1.0 | 0.9 | 1.0 | 1.2 | 0.1 | ns | ns | ns | ||
| ||||||||||
GIP, pmol/L |
week 1 | 5.2 | 8.9 | 8.7 | 9.5 | 1.0 | 0.013 | ns | ns | ns |
week 8 | 16.1 | 10.7 | 12.1 | 12.1 | 1.3 | ns | ns | ns | ||
| ||||||||||
GLP-1, pmol/L |
week 1 | 6.7 | 7.1 | 6.6 | 6.8 | 0.2 | 0.001 | ns | ns | ns |
week 8 | 5.6 | 6.4 | 6.3 | 6.0 | 0.2 | ns | ns | ns |
Mean ± SEM,
Varied postprandial plasma responses based on AUC were observed (Table
Fasting and postprandial areas under the curves of plasma glucose, insulin, NEFA, and incretin hormones at weeks 1 and 8 determined at 60 and 180 minutes.
Diet |
|
|||||||||
---|---|---|---|---|---|---|---|---|---|---|
LD | LT | HD | HT | SEM | Oil | Starch | Oil by starch | |||
Week 1 | Glucose | Fasting, mmol/L | 5.2 | 6.0 | 5.9 | 6.0 | 0.2 | ns | ns | ns |
AUC, 60 min | 373.7 | 332.3 | 355.4 | 400.0 | 14.7 | ns | ns | ns | ||
AUC, 180 min | 1117.1 | 1046.8 | 1130.5 | 1261.2 | 42.1 | ns | 0.052 | ns | ||
Insulin | Fasting, pmol/L | 13.0 | 9.1 | 8.7 | 20.6 | 2.9 | ns | ns | ns | |
AUC, 60 min | 2074.6 | 1392.2 | 3521.0 | 5548.6 | 593.0 | ns | 0.004 | ns | ||
AUC 180 min | 15469.2 | 21485.0 | 16328.6 | 18047.4 | 1986.9 | ns | <0.001 | 0.032 | ||
NEFA | Fasting, mmol/L | 0.8 | 0.8 | 0.9 | 1.0 | 0.1 | ns | ns | ns | |
AUC, 60 min | 34.3 | 30.4 | 26.0 | 31.8 | 1.7 | ns | ns | ns | ||
AUC, 180 min | 91.7 | 91.3 | 55.4 | 61.8 | 5.8 | ns | 0.004 | ns | ||
GIP | Fasting, pmol/L | 5.2 | 8.9 | 8.7 | 9.5 | 1.0 | ns | ns | ns | |
AUC, 60 min | 545.2 | 673.3 | 839.1 | 982.5 | 119.4 | ns | ns | ns | ||
GLP-1 | Fasting, pmol/L | 6.7 | 7.1 | 6.6 | 6.8 | 0.2 | ns | ns | ns | |
AUC, 60 min | 453.2 | 502.2 | 508.9 | 494.7 | 13.9 | ns | ns | ns |
||
| ||||||||||
Week 8 |
Glucose | Fasting, mmol/L | 6.0 | 5.9 | 5.8 | 5.6 | 0.2 | ns | ns | ns |
AUC, 60 min | 388.0 | 373.5 | 438.7 | 379.5 | 13.7 | 0.006 | 0.029 | ns | ||
AUC, 180 min | 1182.2 | 1140.1 | 1308.8 | 1211.5 | 41.5 | ns | 0.041 | ns | ||
Insulin | Fasting, pmol/L | 17.0 | 9.2 | 8.5 | 9.5 | 1.8 | ns | ns | ns | |
AUC, 60 min | 2424.4 | 1746.2 | 3922.6 | 3470.6 | 375.4 | ns | 0.039 | ns | ||
AUC, 180 min | 18906.8 | 14180.1 | 14609.8 | 18047.4 | 1429.2 | ns | 0.041 | ns | ||
NEFA | Fasting, mmol/L | 1.0 | 0.9 | 1.0 | 1.2 | 0.1 | ns | ns | ns | |
AUC, 60 min | 41.1 | 31.7 | 29.5 | 38.3 | 2.6 | ns | ns | ns | ||
AUC, 180 min | 105.7 | 89.2 | 75.2 | 73.6 | 6.6 | ns | ns | ns | ||
GIP | Fasting, pmol/L | 16.1 | 10.7 | 12.1 | 12.1 | 1.3 | ns | ns | ns | |
AUC, 60 min | 1221.0 | 1047.6 | 1736.3 | 1047.6 | 124.4 | 0.045 | ns | ns | ||
GLP-1 |
Fasting, pmol/L | 5.6 | 6.4 | 6.3 | 6.0 | 0.2 | ns | ns | ns | |
AUC, 60 min | 435.5a | 618.1a | 670.8b | 444.2a | 35.9 | ns | ns | 0.005 |
Mean ± SEM,
Letters not in common in a row denote significant differences among diets by two-way ANOVA,
At week 8, a prominent starch effect was consistently found and specifically at 180 min postprandially. Results of
The aim of the present study was to determine the effects of DAG, LGIS, and combination of DAG and LGIS on postprandial plasma insulin response in adult obese Beagles when fed for a 9-week weight loss period. As expected, the dogs lost body weight during this study. Additionally, the LGIS diet group lost a greater amount of body weight. The rate of weight loss of LGIS and HGIS diet groups was
The first objective of this study was to evaluate the long-term effect of DAG and LGIS on postprandial insulin response. In agreement with our preliminary single meal DAG/LGIS feeding study [
In addition to the predominant effect of starch type on circulating insulin response, NEFA response was similarly affected and specifically at week 1. Less suppression of postprandial NEFA concentrations with LGIS intake may have been the result of increased hormone sensitive lipase (HSL) activity. The reason for this possibility is that ingestion of LGIS resulted in decreased insulin levels which promote HSL activity and lipolysis [
The second objective of this study was to elucidate the relationship among postprandial incretin hormone responses, insulin, and glucose when DAG and LGIS were fed to obese dogs during weight loss. Incretin hormones are likely to be induced within minutes after food ingestion and their half-life in the circulation is 5–7 min for GIP and 1-2 min for GLP-1 [
Indeed, after weight loss, postprandial GIP and GLP-1 responses were increased approximately 66% and 11%, respectively, and oil and oil × starch interaction effects were observed. Dietary DAG increased the postprandial GIP and GLP-1 responses but the increased GLP-1 response occurred only in combination with HGIS during the early postprandial period. Moreover, this increase of incretin hormones by DAG was observed along with the plasma glucose response, but not insulin. Shimotoyodome et al. reported that 2 mg/g body weight of DAG administered via gastric gavage significantly decreased area under the GIP response curve during the first 60 min postprandial period [
In summary, weight loss did not affect postprandial insulin, glucose, and fat mobilization, while it increased GIP and GLP-1 responses. Starch types were a more dominant stimulus for postprandial insulin, glucose, and NEFA responses than oil types. In the early postprandial period, incretin hormones were increased by DAG which appeared to be associated with glucose concentrations. However, after the first 60 min postprandial period, the DAG effect on glucose response was attenuated and starch types became significant at 180 min postprandially. It is unknown whether this DAG effect on GIP and GLP-1 may be attenuated at 180 min postprandially as well. In conclusion, LGIS improved hyperinsulinemia and hyperglycemia during the 8-week feeding period. Furthermore, fat structure may be one component that alters incretin hormone response during the early postprandial period. However, it remains to be determined whether DAG oil alters incretin hormone concentrations over a longer postprandial period.
This study was supported by the Kao Company, Tokyo, Japan, and the Mark L. Morris Professorship of Clinical Nutrition, Texas A&M University. The authors thank Rebecca J. Angell for sampling assistance. T. Umeda, K. Ostuji, and J. E. Bauer designed research; D. Nagaoka, Y. Mitsuhashi, and K. E. Bauer conducted research; Y. Mitsuhashi analyzed data; Y. Mitsuhashi and J. E. Bauer wrote the paper. J. E. Bauer had primary responsibility for final content. All authors read and approved the final paper and have no conflict of interests.