Integrated response to a meal

The article presents a brief overview of the responses of the GI tract and its associated pancreatic and biliary systems to a meal. These responses are specifically regulated by complex and interacting neural, hormonal, and parcrine pathways. Stimuli for various responses are multiple and include anticipation, senses of olfaction, taste and hearing, and chemical and mechanical stimuli of meal constituents. The overall result of the integrated response is assimilation of nutrients and elimination of wastes from the GI tract.     

Metabolic response to a mixed meal in obese and lean women from two South african populations

OBJECTIVE: Lower lipid and insulin levels are found during a glucose-tolerance test in obese black than obese white South African women. Therefore, beta-cell function and lipid metabolism were compared in these populations during a mixed meal. RESEARCH METHODS AND PROCEDURES: Blood concentrations of glucose, free fatty acids (FFAs), insulin, lipograms, and in vivo FFA oxidation were determined at fasting and for 7 hours after oral administration of a mixed emulsion containing glucose-casein-sucrose-lipid and [1-(13)C] palmitic acid in 8 lean black women (LBW), 10 obese black women (OBW), 9 lean white women (LWW), and 10 obese white women (OWW). Subcutaneous and visceral fat mass was assessed by computerized tomography. RESULTS: Visceral fat area was higher in OWW (152.7 +/- 17.0 cm(2)) than OBW (80.0 +/- 6.7 cm(2); p < 0.01). In OBW, 30-minute insulin levels were higher (604.3 +/- 117.6 pM) than OWW (311.0 +/- 42.9 pM; p < 0.05). Total triglyceride was higher in OWW (706.7 +/- 96.0 mM x 7 hours) than OBW (465.7 +/- 48.2 mM x 7 hours; p < 0.05) and correlated with visceral fat area (beta = 0.38, p = 0.05). Palmitate oxidation was higher in lean than obese women in both ethnic groups and correlated negatively with fat mass (beta = -0.58, p < 0.005). DISCUSSION: The higher 30-minute insulin response in OBW may reflect a higher insulinotropic effect of FFAs or glucose. The elevated triglyceride level of OWW may be due to their higher visceral fat mass and possibly reduced clearance by adipose tissue.     

Metabolic response to a large starch meal after rest and exercise: comparison between men and women

BACKGROUND: Net whole-body and hepatic de novo lipogenesis could be more active in women than in men, but no comparison has been made between men and women in the two phases of the ovarian cycle after ingestion of a large carbohydrate meal. OBJECTIVE: We hypothesized that net whole-body de novo lipogenesis could be larger in women than men, and that glycogen and fat balance could be, respectively, lower and higher, following a large pasta meal ingested after rest or exercise. DESIGN: The metabolic response to a pasta meal (5 g dry weight/kg body mass) was studied in six men and six women (matched for age and BMI) in the follicular and luteal phases, following rest or exercise (90 min at 50% VO(2max)). Protein, glucose, and fat oxidation, and net whole-body de novo lipogenesis were computed for 10 h following ingestion of the meal using indirect respiratory calorimetry corrected for urea excretion. RESULTS: No net whole-body de novo lipogenesis was observed in any group in any situation (postrest and postexercise). When the meal was ingested following exercise, fat oxidation was significantly higher and glucose oxidation was significantly lower (P<0.05) than following the period of rest, and in a given experimental situation, the respective contributions of protein, fat, and glucose oxidation to the energy yield were similar in men and women in both phases of the cycle. CONCLUSIONS: The contribution of substrate oxidation to the energy expenditure as well as fat and glycogen balance, and the effect of a previous exercise period, were similar in men and women in both phases of the cycle following ingestion of the large carbohydrate meal.     

Daily caloric intake of normal-weight adults: response to changes in dietary energy density of a luncheon meal

The extent and time course of caloric compensation for surreptitious dilutions and supplements to the energy value of the diet were examined in free-living normal-weight adults. Ten subjects were provided lunches containing approximately 66% more or less calories than their customary midday meal for 2-wk periods which were interposed between 1-wk baseline or recovery periods. Diet records were kept throughout the study. Total energy intakes did not differ among the three control periods (weeks 1, 4, and 7) or between any of these periods and when subjects were provided the low-calorie meal. Total energy intake was significantly higher relative to all other periods when subjects ingested the high-calorie meal. To the extent that compensation occurred, it was apparent immediately and did not appear to change over the 2-wk study periods. The results suggest that humans compensate more readily for decreases than for increases in caloric intake.     

Altered insulin response to a balanced test meal in bulimic patients

Impaired glucose tolerance with overshooting insulin secretion has been reported in anorexia nervosa, in starvation, and in low carbohydrate diets. Since impaired glucose tolerance is a further indicator of starvation andlor carbohydrate restriction and possibly contributes to impairment of mechanisms of hunger and satiety, we examined insulin and glucose responses in bulimic patients. Data show that in bulimic patients as compared with age-matched controls, insulin secretion and glucose levels can be elevated after a balanced test meal. This indicates disturbed glucose tolerance. Whether this reduced glucose tolerance can be related to altered kinetics of insulin release or to cellular insulin resistance cannot be decided on the basis of our data.     

Pregnancy augments hepatic glucose storage in response to a mixed meal

Studies were carried out on conscious female non-pregnant (NP) and pregnant (P; third-trimester) dogs (n 16; eight animals per group) to define the role of the liver in mixed meal disposition with arteriovenous difference and tracer techniques. Hepatic and hindlimb substrate disposal was assessed for 390 min during and after an intragastric mixed meal infusion labelled with [1?C]glucose. The P dogs exhibited postprandial hyperglycaemia compared with NP dogs (area under the curve (AUC; change from basal over 390 min) of arterial plasma glucose: 86 680 (sem 12 140) and 187 990 (sem 33 990) mg/l in NP and P dogs, respectively; P < 0·05). Plasma insulin concentrations did not differ significantly between the groups (AUC: 88 230 (sem 16 314) and 69 750 (sem 19 512) pmol/l in NP and P dogs, respectively). Net hepatic glucose uptake totalled 3691 (sem 508) v. 5081 (sem 1145) mg/100 g liver in NP and P dogs, respectively (P = 0·38). The AUC of glucose oxidation by the gut and hindlimb were not different in NP and P dogs, but hepatic glucose oxidation (84 (sem 13) v. 206 (sem 30) mg/100 g liver) and glycogen synthesis (0·4 (sem 0·5) v. 26 (sem 0·7) g/100 g liver) were greater in P dogs (P < 0·05). The proportion of hepatic glycogen deposited via the direct pathway did not differ between the groups. Hindlimb glucose uptake and skeletal muscle glycogen synthesis was similar between the groups, although final glycogen concentrations were higher in NP dogs (9·6 (sem 0·6) v. 70 (sem 0·6) mg/g muscle; P < 0·05). Thus, hepatic glucose oxidation and glycogen storage were augmented in late pregnancy. Enhanced hepatic glycogen storage following a meal probably facilitates the maintenance of an adequate glucose supply to maternal and fetal tissues during the post-absorptive period.     

Metabolic response to a ketogenic breakfast in the healthy elderly

Objective  To determine whether the metabolism of glucose or ketones differs in the healthy elderly compared to young or middle-aged adults during mild, short-term ketosis induced by a ketogenic breakfast. Design and participants  Healthy subjects in three age groups (23±1, 50±1 and 76±2 y old) were given a ketogenic meal and plasma -hydroxybutyrate, glucose, insulin, triacylglycerols, total cholesterol, non-esterified fatty acids and breath acetone were measured over the subsequent 6 h. Each subject completed the protocol twice in order to determine the oxidation of a tracer dose of both carbon-13 (¹³C) glucose and ¹³C- -hydroxybutyrate. The tracers were given separately in random order. Apolipoprotein E genotype was also determined in all subjects. Results  Plasma glucose decreased and -hydroxybutyrate, acetone and insulin increased similarly over 6 h in all three groups after the ketogenic meal. There was no significant change in cholesterol, triacylglycerols or non-esterified fatty acids over the 6 h. ¹³C-glucose and ¹³C- -hydroxybutyrate oxidation peaked at 2–3 h post-dose for all age groups. Cumulative ¹³C-glucose oxidation over 24 h was significantly higher in the elderly but only versus the middle-aged group. There was no difference in cumulative 13C- -hydroxybutyrate oxidation between the three groups. Apolipoprotein E ( 4) was associated with elevated fasting cholesterol but was unrelated to the other plasma metabolites. Conclusion  Elderly people in relatively good health have a similar capacity to produce ketones and to oxidize ¹³C- -hydroxybutyrate as middle-aged or young adults, but oxidize ¹³C-glucose a little more rapidly than healthy middle-aged adults.     

Plasma enterostatin: identification and release in rats in response to a meal

OBJECTIVE: To discover a possible absorption and/or secretion of enterostatin into the circulating blood, as well as to compare the levels of circulating enterostatin after high-fat feeding and low-fat feeding. RESEARCH METHODS AND PROCEDURES: Using a specific enzyme-linked immunosorbent assay, plasma enterostatin levels were determined after feeding a high-fat, a high-fat/-sucrose, or a low-fat meal to Sprague-Dawley rats deprived of food overnight. RESULTS: The enterostatin levels were increased by all diets; the response to the high-fat and the high-fat/-sucrose meals was greater in magnitude and duration than that to the low-fat meal. In addition, enterostatin levels correlated with the intake of dietary fat. Plasma enterostatin levels after high-fat feeding were found to be similar to those after intravenous administration of exogenous enterostatin known to inhibit high-fat food intake. Gel chromatography of pooled postprandial plasma extracts followed by high-performance liquid chromatography analysis showed that plasma enterostatin was identical to synthetic enterostatin. Affinity cross-linking of plasma proteins with 125I-enterostatin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography, revealed a single band with a molecular weight of about 66 kDa, indicating the presence of a potential enterostatin-binding protein in plasma. DISCUSSION: The measurements of plasma enterostatin may be a sensitive indicator for the measurement of fat intake.     

Metabolic differences in response to a high-fat vs. a high-carbohydrate diet

Energy expenditure was measured in a group of 7 subjects who received two isocaloric isonitrogenous diets for a period of 9-21 days with a 4-10-day break between diets. Diet 1 was a high-fat diet ( 83.5 +/- 3.6% of total energy). Diet 2 was a high carbohydrate diet ( 83.1 +/- 3.7% of total energy). Resting and postprandial resting metabolic rate were measured by open circuit indirect calorimetry 2-4 times during each metabolic period. Total energy expenditure (TEE) was measured by the doubly labeled water method over an 8-13-day period. The respiratory quotient was measured 2-4 hours after a meal during each metabolic period for the calculation of total energy expenditure by the doubly labeled water method. Levels of total T3 (TT3), T3 uptake, free thyroid index and T4 were measured at the end of each metabolic period. No significant changes in resting metabolic rate (RMR) were apparent on the two diets (1567 +/- 426 kcal/d high-fat diet and 1503 +/- 412 kcal/d high-carbohydrate diet n=7, p<0.15). Total energy expenditure measured in 5 subjects was significantly higher during the high-carbohydrate phase of the diet (2443 +/- 422 vs. 2078 +/- 482 kcal/d p<0.05). Activity estimated from TEE/RMR was greater on the high-carbohydrate diet but only approached statistical significance (p<0.06). Total T3 was significantly lower and free thyroid index and T3 uptake were significantly higher at the end of the high fat diet in comparison to the high-carbohydrate diet. These data suggest that individual tolerance to a high-fat diet varies considerably and may significantly lower TEE by changing levels of physical activity. The explanation for changes in thyroid hor. mone levels independent of changes in metabolic rate remains unclear.     

Aging does not impair the anabolic response to a protein-rich meal

BACKGROUND: Sarcopenia is a debilitating condition afflicting the elderly that may be facilitated by insufficient or ineffectual intake of dietary protein. We previously showed that free-form essential amino acids acutely stimulate muscle protein synthesis in both the young and the elderly. However, the ability of an actual protein-rich food to stimulate anabolism in the young and the elderly has not been explored. OBJECTIVE: We aimed to characterize changes in plasma amino acid concentrations and to quantify muscle protein synthesis in healthy young (41 +/- 8 y old; n = 10) and elderly (70 +/- 5 y old; n = 10) persons after ingestion of a 113-g (4-oz) serving of lean beef. DESIGN: Venous blood samples and vastus lateralis muscle biopsy samples were obtained during a primed (2.0 mumol/kg) constant infusion (0.08 mumol.kg(-1).min(-1)) of l-[ring-(13)C(6)] phenylalanine. Plasma amino acid concentrations were measured and a mixed-muscle fractional synthesis rate (FSR) was calculated during the premeal period and for 5 h after beef ingestion. RESULTS: Mixed-muscle FSR increased by approximately 51% in both the elderly (mean +/- SE measurements: 0.072 +/- 0.004%/h and 0.108 +/- 0.006%/h before and after the meal, respectively) and the young (0.074 +/- 0.005%/h and 0.113 +/- 0.005%/h before and after the meal, respectively) after beef ingestion (P < 0.001). Plasma amino acid concentrations peaked at approximately 100 min after beef ingestion in both age groups but were substantially higher in the elderly (2185 +/- 134 nmol/mL compared with 1403 +/- 96 nmol/mL; P < 0.001). CONCLUSION: Despite differences in the concentration of amino acids in the plasma precursor pool, aging does not impair the ability to acutely synthesize muscle protein after ingestion of a common protein-rich food.     

Role of dietary protein in rat pancreatic enzyme secretory response to a meal

The role of dietary protein in the pancreatic enzyme secretory response to complete test meals was studied in rats fitted with chronic bile-pancreatic fistulas. Pancreatic enzyme secretory response was observed by collecting combined bile-pancreatic juice and continuously returning it to the intestine by a stream-splitter, which diverted 5% for assay. All rats were fed ad libitum a 24% casein diet during the recovery period. Four days postoperative, rats were infused intragastrically with 5 g of isonitrogenous, complete test meals containing casein (24%), alpha-protein (soy protein), amino acids patterned after casein or alpha-protein, casein + lima bean trypsin inhibitor (LBTI), and a nitrogen-free diet. Pancreatic enzyme secretion under basal conditions and in response to the test meals was determined. The pancreatic response to test meals containing intact casein as nitrogen source was the same as the response to nitrogen-free test meals, and was only slightly greater (not statistically significantly) than the response to test meals containing amino acids. Test meals containing alpha-protein, which was devoid of soybean trypsin inhibitor activity, were much more potent than corresponding amino acid test meals or nitrogen-free test meals. Addition of LBTI greatly increased the pancreatic response to casein test meals. The results indicate that intragastric infusion of diets containing casein as nitrogen source do not stimulate greater pancreatic enzyme secretion than test meals of nitrogen-free or amino acid diets under normal physiological conditions, and it is proposed that this is a consequence of the large reserve capacity of the exocrine pancreas.     

The plasma beta-carotene response to a single meal of carrots in Guatemalan schoolchildren

Plasma samples were obtained before, and 8 and 24 h after the ingestion of an ad libitum amount of cooked carrots by 23 school children from a peri-urban community in Guatemala City. The single-meal consumption of cooked carrots ranged from a low 122 g to a high of 961 g (mean: 370.5 +/- 237.2 g; median: 268.4 g). The measured beta-carotene content of the carrots was 10.1 mg per 100 g of edible portion; therefore, the range of intake of beta-carotene was 12.4 to 97.0 mg (mean: 37.4 +/- 24 mg; median: 27.1 mg). Changes in plasma beta-carotene levels at 8 h ranged from a decrement of -0.32 mumol/l (-16.98 micrograms/dl) to an increment of 0.79 mumol/l (42.44 micrograms/dl), with a mean of 0.11 +/- 0.24 mumol/l (5.97 +/- 12.82 micrograms/dl). Changes at 24 h were less dramatic than those at 8 h. A regression of the 8-h changes in plasma beta-carotene on the amount of carrot carotene consumed (corrected by body weight) had an r-value of 0.12. Baseline levels of plasma retinol were poor predictors of the plasma beta-carotene response with this sample size (r = 0.10). The magnitude of the plasma response to beta-carotene from carrots appears to be lower than that observed with pure, powdered, crystalline carotenes; moreover, the variability of the post-carrot response seems to be greater--and its association to dosage appears to be weaker--than with the pharmacological beta-carotene.     

Metabolic effects of nicotine after consumption of a meal in smokers and nonsmokers

The thermogenic effect of nicotine intake after calorie consumption was investigated to determine if nicotine influences metabolic response to a calorie challenge. Smokers and nonsmokers (10 males in each group), matched for body weight, age, and physical fitness, each participated in four sessions that involved consuming a liquid calorie load (4.77 kcal/kg body wt) or water, followed by nicotine (15 micrograms/kg body wt) or placebo via nasal spray every 20 min for 2 h. Energy expenditure was significantly increased above baseline resting metabolic rate (RMR) over the 2 h by nicotine alone (6.5% of RMR, p less than 0.01). However, the combined effect of nicotine after calorie load (20.1% of RMR, p less than 0.001) was not significantly greater than the effect of calorie load alone (18.4% of RMR, p less than 0.001). Smokers and nonsmokers did not differ in baseline RMR or in response to nicotine or calorie load. These results confirm the thermogenic effect of nicotine but suggest that the effect of nicotine after calorie consumption is less than additive.     

Metabolic response to short-term 4-day energy restriction in a controlled study

Objectives Metabolic rate is affected not solely by diet but also by environmental characteristics such as climate and seasonal changes in day length. In the present study, we conducted a controlled study in which we observed metabolic response to short-term energy restriction (ER). Materials and Methods Thirty-two subjects were divided randomly into a slight ER group and a moderate ER group. The energy intake per day for slight ER vs moderate ER was 1462 kcal vs 1114 kcal. During the 4-day study periods, the same daily timetable, which consists of nutrition, exercise, sleeping and others, was imposed on both groups. The same environment was also provided to both groups. Results After the 4-day ER, significant decreases in body weight and basal metabolic rate (BMR) were shown in both groups. The decrease in body weight was 2% of the baseline level in both groups, and the decreases in the BMR were 6% of baseline levels in the slight ER group and 13% in the moderate ER group. The decrease in BMR in the moderate ER group was significantly larger than that in the slight ER group. Conclusions In a controlled study of short-term ER, we observed a significant decrease in BMR. There was a positive association between the degree of ER and the reduction in BMR. Reductions in BMR were greater than those in body weight. It, thus, appears that the minimization of weight loss is due to dramatic decreases in BMR. This suggests the existence of metabolic resistance against ER.