Insulin secretion and glucose tolerance in adults with protein-calorie malnutrition

Association between protein undernutrition and diabetes: Molecular implications in the reduction of insulin secretion

Undernutrition is still a recurring nutritional problem in low and middle-income countries. It is directly associated with the social and economic sphere, but it can also negatively impact the health of the population. In this sense, it is believed that undernourished individuals may be more susceptible to the development of non-communicable diseases, such as diabetes mellitus, throughout life. This hypothesis was postulated and confirmed until today by several studies that demonstrate that experimental models submitted to protein undernutrition present alterations in glycemic homeostasis linked, in part, to the reduction of insulin secretion. Therefore, understanding the changes that lead to a reduction in the secretion of this hormone is essential to prevent the development of diabetes in undernourished individuals. This narrative review aims to describe the main molecular changes already characterized in pancreatic β cells that will contribute to the reduction of insulin secretion in protein undernutrition. So, it will provide new perspectives and targets for postulation and action of therapeutic strategies to improve glycemic homeostasis during this nutritional deficiency.

Association of postnatal severe acute malnutrition with pancreatic exocrine and endocrine function in children and adults: a systematic review

Severe acute malnutrition may lead both concurrently and subsequently to malabsorption and impaired glucose metabolism from pancreatic dysfunction. We conducted a systematic review to investigate the associations of current and prior postnatal wasting malnutrition with pancreatic endocrine and exocrine functions in humans. We searched PubMed, Google Scholar, Web of Science and reference lists of retrieved articles, limited to articles in English published before 1 February 2022. We included sixty-eight articles, mostly cross-sectional or cohort studies from twenty-nine countries including 592 530 participants, of which 325 998 were from a single study. Many were small clinical studies from decades ago and rated poor quality. Exocrine pancreas function, indicated by duodenal fluid or serum enzymes, or faecal elastase, was generally impaired in malnutrition. Insulin production was usually low in malnourished children and adults. Glucose disappearance during oral and intravenous glucose tolerance tests was variable. Upon treatment of malnutrition, most abnormalities improved but frequently not to control levels. Famine survivors studied decades later showed ongoing impaired glucose tolerance with some evidence of sex differences. The similar findings from anorexia nervosa, famine survivors and poverty- or infection-associated malnutrition in low- and middle-income countries (LMIC) lend credence to results being due to malnutrition itself. Research using large, well-documented cohorts and considering sexes separately, is needed to improve prevention and treatment of exocrine and endocrine pancreas abnormalities in LMIC with a high burden of malnutrition and diabetes.

Impaired compensatory hyperinsulinemia among nonobese type 2 diabetes patients: a cross-sectional study

AIMS

Obesity associated prolonged hyperinsulinemia followed by β-cell failure is well established as the pathology behind type 2 diabetes mellitus (T2DM). However, studies on nonobese T2DM have reported it to be a distinct clinical entity with predominant insulin secretory defect. We, therefore, hypothesized that compensatory hyperinsulinemia in response to weight gain is impaired in nonobese subjects.

METHODS

This was a cross-sectional study from a community-based metabolic health screening program. Adiposity parameters including body mass index (BMI), waist circumference (WC), body fat percentage, plasma leptin concentration and metabolic parameters namely fasting insulin, glucose, total cholesterol, and triglycerides were measured in 650 individuals (73% healthy, 62% nonobese with a BMI <25).

RESULTS

In contrast to obese T2DM, nonobese T2DM patients did not exhibit significant hyperinsulinemia compared with the nonobese healthy group. Age, sex, and fasting glucose adjusted insulin levels, homeostatic model assessment of insulin resistance (HOMA-IR) and HOMA-beta cell function (HOMA-B) were increased in obese T2DM compared with nonobese T2DM. Although adiposity parameters showed strong correlation with fasting insulin in obese healthy (r = 0.38, 0.38, and 0.42, respectively; all p values < 0.001) and T2DM (r = 0.54, 0.54, and 0.66, respectively; all p < 0.001), only BMI and leptin showed a weak correlation with insulin in the nonobese healthy group (0.13 and 0.13, respectively; all p < 0.05) which were completely lost in the nonobese T2DM.

CONCLUSIONS

Compensatory hyperinsulinemia in response to weight gain is impaired in the nonobese population making insulin secretory defect rather than IR the major pathology behind nonobese T2DM.

Branched-chain amino acid supplementation restores reduced insulinotropic activity of a low-protein diet through the vagus nerve in rats

Background

Previously, we reported that a low-protein diet significantly reduced insulin secretion in response to feeding within 1 h in rats, suggesting that the insulinotropic effect of dietary protein plays an important role in maintaining normal insulin release. The current study aimed to elucidate whether deficiency of certain amino acids could diminish the insulinotropic activity and to investigate whether reduced insulin secretion in response to a low-protein diet is restored by supplementation with certain amino acids.

Methods

First, we fed male Wistar rats (5–6 rats per group) with diets deficient in every single amino acid or three branched-chain amino acids (BCAAs); within 1–2 h after the onset of feeding, we measured the plasma insulin levels by using an enzyme-linked immunosorbent assay (ELISA). As insulin secretion was reduced in BCAA-deficient groups, we fed low-protein diets supplemented with BCAAs to assess whether the reduced insulin secretion was restored. In addition, we treated the pancreatic beta cell line MIN6 with BCAAs to investigate the direct insulinotropic activity on beta cells. Lastly, we investigated the effect of the three BCAAs on sham-operated or vagotomized rats to assess involvement of the vagus nerve in restoration of the insulinotropic activity.

Results

Feeding a low-protein diet reduced essential amino acid concentrations in the plasma during an absorptive state, suggesting that reduced plasma amino acid levels can be an initial signal of protein deficiency. In normal rats, insulin secretion was reduced when leucine, valine, or three BCAAs were deficient. Insulin secretion was restored to normal levels by supplementation of the low-protein diet with three BCAAs, but not by supplementation with any single BCAA. In MIN6 cells, each BCAA alone stimulated insulin secretion but the three BCAAs did not show a synergistic stimulatory effect. The three BCAAs showed a synergistic stimulatory effect in sham-operated rats but failed to stimulate insulin secretion in vagotomized rats.

Conclusions

Leucine and valine play a role in maintaining normal insulin release by directly stimulating beta cells, and supplementation with the three BCAAs is sufficient to compensate for the reduced insulinotropic activity of the low-protein diet, through the vagus nerve.

A low-protein diet combined with low-dose endotoxin leads to changes in glucose homeostasis in weanling rats

Severe malnutrition is a leading cause of global childhood mortality, and infection and hypoglycemia or hyperglycemia are commonly present. The etiology behind the changes in glucose homeostasis is poorly understood. Here, we generated an animal model of severe malnutrition with and without low-grade inflammation to investigate the effects on glucose homeostasis. Immediately after weaning, rats were fed diets containing 5 [low-protein diet (LP)] or 20% protein [control diet (CTRL)], with or without repeated low-dose intraperitoneal lipopolysaccharide (LPS; 2 mg/kg), to mimic inflammation resulting from infections. After 4 wk on the diets, hyperglycemic clamps or euglycemic hyperinsulinemic clamps were performed with infusion of [U-(13)C6]glucose and [2-(13)C]glycerol to assess insulin secretion, action, and hepatic glucose metabolism. In separate studies, pancreatic islets were isolated for further analyses of insulin secretion and islet morphometry. Glucose clearance was reduced significantly by LP feeding alone (16%) and by LP feeding with LPS administration (43.8%) compared with control during the hyperglycemic clamps. This was associated with a strongly reduced insulin secretion in LP-fed rats in vivo as well as ex vivo in islets but signficantly enhanced whole body insulin sensitivity. Gluconeogenesis rates were unaffected by LP feeding, but glycogenolysis was higher after LP feeding. A protein-deficient diet in young rats leads to a susceptibility to low-dose endotoxin-induced impairment in glucose clearance with a decrease in the islet insulin secretory pathway. A protein-deficient diet is associated with enhanced peripheral insulin sensitivity but impaired insulin-mediated suppression of hepatic glycogenolysis.

Kwashiorkor and marasmus are both associated with impaired glucose clearance related to pancreatic β-cell dysfunction

Severe malnutrition is a major health problem in developing countries and can present as kwashiorkor or marasmus. Kwashiorkor is associated with septicaemia, profound metabolic changes including hepatic steatosis, altered protein metabolism and increased oxidative stress. Limited data suggest that children with kwashiorkor have an impaired glucose tolerance and insulin secretion. Our objective was to determine glucose tolerance in children with kwashiorkor compared to marasmus and its relation to insulin secretion and sensitivity. Six children with kwashiorkor and 8 children with marasmus were studied. We were also able to include 3 healthy children for comparison. They received a primed (13 mg/kg), constant infusion (0.15 mg/kg/min) of [6,6-(2)H(2)]glucose for 4 h with serial blood sampling. In addition, an oral glucose tolerance test (OGTT) was performed with labeled 10 mg/g [U-(13)C]glucose. Glucose clearance was determined using mathematical modeling. Glucose clearance rates during the OGTT were -392 (range 309) mL/kg in children with kwashiorkor, -156 (426) mL/kg in marasmus and 279 (345) mL/kg in the control group. Glucose clearance rates correlated with plasma albumin concentrations (r=0.67, P=.001). Insulin responses were strongly impaired in both kwashiorkor and marasmus. There was no indication of peripheral or hepatic insulin resistance in the malnourished groups. We show that glucose clearance rates are affected in both children with marasmus as well as kwashiorkor, which correlate with plasma albumin concentrations. The disturbed glucose clearance in malnutrition is related to an impairment in insulin availability.

Impaired Pancreatic Endocrine and Exocrine Responses in Growth-Retarded Piglets

The alteration of pancreatic endocrine and exocrine secretory responses induced by secretagogues and neural input was investigated in post-weaning growth-retarded (GR) piglets. Blood and pancreatic juice were collected from these animals (6-8-weeks old). Plasma insulin and pancreatic digestive enzymes induced by nutrients, drugs and vagal stimulation were measured biochemically. The pancreas was inspected by immunohistochemical analysis. In GR piglets, the plasma glucose and insulin concentrations at the resting state were very low, and the secretory response was also markedly reduced, with maximum inhibition of 90% by glucose administration and 83% by arginine administration. The insulin secretion was not increased by 2-deoxy-D-glucose administration in GR piglets. The pancreatic juice secretions induced by vagal stimulation and secretagogues in GR piglets were not different from those induced in the control piglets. However, amylase activity in the pancreatic juice and in the pancreas was significantly decreased in GR piglets, although trypsin and chymotrypsin activities were not different. In the immunohistochemical analysis, the numbers of islets and the staining degree for insulin antibody also declined in the pancreases of GR piglets. These results indicated the reduction of insulin and amylase secretions from the pancreas in GR piglets, suggesting that a dysfunction of pancreatic endocrine and exocrine secretion during growth after weaning may be an important factor in the induction of growth retardation in piglets.

Significance of transthyretin in protein metabolism

Total body nitrogen (TBN) is mainly sequestered within the metabolically active lean body mass, in close relationship with total body potassium (TBK). TBN and TBK of growing children manifest superimposed accretion rates, display a sexual difference at the onset of adolescence and during adulthood, thereafter decreasing in elderly subjects. Plasma transthyretin (TTR) follows a comparable profile from birth to death in healthy individuals. Uncomplicated protein-energy malnutrition primarily affects the activity of nitrogen metabolic pool, reducing protein syntheses to levels compatible with survival. This adaptive response is well identified by declining TTR concentrations. In various stressful conditions, in vivo responses are characterized by upregulation in injured regions and with muscle proteolysis exceeding protein synthesis, resulting in a net body negative nitrogen balance. Again, this evolutionary pattern mirrors that of plasma TTR. Attenuation of stress and/or introduction of nutritional rehabilitation allows restoration to normal of both TBN and TTR values that follow parallel slopes. Despite distinct etiopathogenic mechanisms, TTR concentrations appear to reflect the loss or gain of TBN in body pools and they predict later outcome in malnutrition and in conditions of acute and/or chronic inflammation.

Other disease associations with non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is usually seen in middle-aged women with obesity, non-insulin-dependent diabetes mellitus and/or hyperlipidaemia. NAFLD has also been associated with other conditions. Surgical procedures to treat obesity such as jejunoileal bypass and gastroplasty as well as massive small bowel resection have been associated with NAFLD. Mechanisms such as rapid weight loss, certain nutritional deficiencies and bacterial overgrowth have been proposed. Other nutritional conditions such as extreme malnutrition and total parenteral nutrition can also cause NASH. This can be due to abnormal glucose and fat metabolism, deficiencies like carnitine, essential fatty acid and choline or, in the case of parenteral nutrition, excess of calories, glucose or lipids. Several drugs have also been implicated as well as some inborn errors of metabolism and, more rarely, other diseases.

Glucose-induced insulin secretion is impaired and insulin-induced phosphorylation of the insulin receptor and insulin receptor substrate-1 are increased in protein-deficient rats

Malnutrition is related to diabetes in tropical countries. In experimental animals, protein deficiency may affect insulin secretion. However, the effect of malnutrition on insulin receptor phosphorylation and further intracellular signaling events is not known. Therefore, we decided to evaluate the rate of insulin secretion and the early molecular steps of insulin action in insulin-sensitive tissues of an animal model of protein deficiency. Pancreatic islets isolated from rats fed a standard (17%) or a low (6%) protein diet were studied for their secretory response to increasing concentrations of glucose in the culture medium. Basal as well as maximal rates of insulin secretion were significantly lower in the islets isolated from rats fed a low protein diet. Moreover, the dose-response curve to glucose was significantly shifted to the right in the islets from malnourished rats compared with islets from control rats. During an oral glucose tolerance test, there were significantly lower circulating concentrations of insulin in the serum of rats fed a low protein diet in spite of no difference in serum glucose concentration between the groups, suggesting an increased peripheral insulin sensitivity. Immunoblotting and immunoprecipitation were used to study the phosphorylation of the insulin receptor and the insulin receptor substrate-1 as well as the insulin receptor substrate-1-p85 subunit of phosphatidylinositol 3-kinase association in response to insulin. Values were greater in hind-limb muscle from rats fed a low protein diet compared with controls. No differences were detected in the total amount of protein corresponding to the insulin receptor or insulin receptor substrate-1 between muscle from rats fed the two diets. Therefore, we conclude that a decreased glucose-induced insulin secretion in pancreatic islets from protein-malnourished rats is responsible, at least in part, for an increased phosphorylation of the insulin receptor, insulin receptor substrate-1 and its association with phosphatidylinositol 3-kinase. These might represent some of the factors influencing the equilibrium in glucose concentrations observed in animal models of malnutrition and undernourished subjects.

Is diabetes mellitus related to undernutrition in rural Tanzania?

OBJECTIVE

To investigate the relation between undernutrition and diabetes.

DESIGN

Survey of glucose tolerance in rural Tanzania.

SETTING

Eight villages in three widely separated regions of Tanzania.

SUBJECTS

8581 people aged 15 and above: 3705 men and 4876 women.

MAIN OUTCOME MEASURES

Oral glucose tolerance, body mass index, height, and low haemoglobin and cholesterol concentrations.

RESULTS

In the eight villages 42.7-56.9% of all men and 30.0-45.2% of all women had a body mass index below 20 kg/m2; the lowest quintile was 18.2 kg/m2 in men and 18.6 kg/m2 in women. The prevalence of diabetes did not change significantly from the lowest to the highest fifths of body mass index in men (lowest 1.6% (95% confidence interval 0.8% to 2.9%) v highest 1.3% (0.7% to 2.5%)) or women (1.1% (0.6% to 2.1%) v 0.5% (0.2% to 1.2%)). In men and in women prevalence of impaired glucose tolerance was greater in the lowest fifths of height (8.2% (6.3% to 10.6%), and 11.1% (9.2% to 13.3%)) respectively and body mass index (9.6% (7.5% to 12.1%), and 8.4% (6.7% to 10.5%)) than in the highest fifths (impaired glucose tolerance 4.7% (3.4% to 6.5%); and 5.1% (3.9% to 6.7%); body mass index 5.1% (3.7% to 7.0%), and 7.7% (6.2% to 9.6%).

CONCLUSION

Rates of diabetes were not significantly associated with low body mass index or height, but overall rates were much lower than those in well nourished Western populations. Increased impaired glucose tolerance in the most malnourished people may reflect the larger glucose load per kilogram weight. The role of undernutrition in the aetiology of diabetes must be questioned.

Immunogenetic and nutritional profile in insulin-using youth-onset diabetics in Korea

There are few reports on the genetic, immunological and nutritional characteristics of insulin-using youth-onset diabetes mellitus, insulin-dependent diabetes mellitus (IDDM) and malnutrition-related diabetes mellitus (MRDM) in Korea. Among 1266 hospitalized Korean diabetics, 29 (2.3%) were IDDM and 84 (6.6%) were MRDM. A diabetes history of first-relatives (28.6%) was more frequently found in the MRDM group than in the IDDM (14.8) and non-insulin-dependent diabetes mellitus (NIDDM) (19.0%) groups. HLA-DR4 was more common among IDDM (54.2%) and MRDM (52.4%) patients than controls (26.3%), and HLA-DR3 was more common among only IDDM patients (29.2%) than controls (10.9%). Conventional islet-cell antibodies were detected in 8 of 15 IDDM patients tested (53.3%) and in 11 of 22 MRDM patients (50.0%). MRDM patients had higher serum basal (1.02 +/- 0.51 ng/ml) and peak (1.44 +/- 0.76 ng/ml) C-peptide concentrations than IDDM patients, but lower concentrations than NIDDM patients. Before the onset of diabetes, the calorie intake of 21 MRDM patients assessed was 63.1% of the daily requirement and the intake of carbohydrate, protein and fat was 71.7%, 55.9% and 39.8%, respectively. In summary, our data suggest that IDDM in Korea is associated with HLA-DR3 or HLA-DR4, indicating a risk for IDDM in Western societies; furthermore, MRDM has a history of undernutrition at the preonset period and is also associated with HLA-DR4. It might be also concluded that MRDM in Korea is another expression of IDDM caused by the shortage of some nutrients for the structural and/or functional maintenance of pancreatic beta-cells.

Insulin secretion and action in patients with pancreatic cancer

The authors investigated insulin secretory capacity and insulin action in 11 preoperative patients with pancreatic carcinoma and 15 age-matched and weight-matched healthy subjects (C). Five patients were classified as diabetic (D), two as impaired glucose tolerant (IGT), and four as nondiabetic (ND). Postabsorptive serum insulin levels (mean +/- SE, in uU/ml) in D (12 +/- 2), IGT (17 +/- 7), and ND (10 +/- 2) were comparable. After administration of 100 g of oral glucose, peak insulin achieved in D (60 +/- 11) was lower than in IGT (101 +/- 26) and ND (83 +/- 20), whereas peak insulin levels in IGT and ND were significantly (P less than 0.05) higher than in C (45 +/- 6). Comparable insulin response to nonglucose stimuli was documented in all subjects using the slow arginine infusion test with mean serum insulin of 27 +/- 4 in D, 28 +/- 6 in IGT, 34 +/- 10 in ND, and 32 +/- 5 in C. In six patients (P) and six controls, insulin action was assessed by the euglycemic hyperinsulinemic clamp technique, with glucose turnover rates estimated by [3-3H]glucose infusion. Steady-state plasma glucose concentrations were maintained at 92 +/- 3 (P) and 91 +/- 1 mg/dl (C). After insulin infusion at the rate of 1.0 mU/kg/min, comparable high physiologic insulin levels were observed in P (73 to 104 uU/ml) and in C (81 to 103 uU/ml). Postabsorptive rates of endogenous glucose appearance (Ra) were higher in P (2.86 to 3.02 mg/kg/min) than in C (1.50 to 2.80 mg/kg/min). At high physiologic insulin concentrations, negative Ra values were documented in all subjects, and complete suppression of Ra was assumed. Total body glucose use (M) was consistently lower in P (3.90 to 6.40 mg/kg/min) than in C (6.98 to 10.40 mg/kg/min), consistent with a state of insulin resistance. Patients with pancreatic cancer manifest insulin resistance by virtue of a decrease in total body glucose use (M) and decreased insulin response to glucose due to either inherent beta cell dysfunction or decreased islet cell mass. The latter is not identifiable by histologic morphology.

The effects of euglycemic hyperinsulinemia and amino acid infusion on regional and whole body glucose disposal in man

We investigated the effects of amino acid infusion on regional and whole body glucose metabolism in 16 normal volunteers, age 32 to 70 years. Ten subjects underwent 140-minute euglycemic insulin infusions at the rate of 1 mU/kg.min with concomitant 10% amino acid infusion. Six volunteers who underwent identical euglycemic insulin infusions without amino acid infusion served as controls. Whole body glucose disposal was estimated by the rate of exogenous glucose infusion required to maintain euglycemia, and peripheral glucose balance was evaluated by the forearm balance technique. In four subjects from each group, a primed, continuous infusion of [3-3H]glucose was used to quantify endogenous glucose production (EGP). Comparable states of hyperinsulinemia were achieved with insulin concentrations (microU/mL) of 101 +/- 7 observed in the group with amino acid infusion and 95 +/- 14 in the control group. Whole body glucose utilization was significantly lower (P less than .001) in the subjects receiving amino acid infusion (5.0 +/- 0.4 mg/kg.min) compared with the control group (8.7 +/- 0.8 mg/kg.min). Forearm glucose disposal was markedly reduced (P less than .05) in the group receiving amino acid infusion (1,385 +/- 330 nmol/100 g.min) compared with controls (2,980 +/- 460 nmol/100 g.min). Under comparable conditions of euglycemia and hyperinsulinemia, virtually complete suppression of EGP was observed in both groups. We conclude that infusion of amino acids with insulin under euglycemic conditions reduces whole body glucose utilization primarily by reducing peripheral glucose disposal.

Chronic undernutrition may accentuate the beta cell dysfunction of type 2 diabetes

Seven undernourished and seven obese, insulin-requiring type 2 diabetic subjects, who were matched for age, sex, and duration of diabetes, were subjected to oral glucose tolerance tests. Although fasting glucose and free insulin levels were similar in both groups, glucose tolerance was markedly worse in the undernourished subjects, with a mean incremental glucose area (+/- SE) of 22.8 +/- 2.3 mmol/l.h vs. 12.4 +/- 1.3 in the obese diabetic subjects (P less than 0.001). The incremental insulin response (area under the curve) to oral glucose in the undernourished group (39.3 +/- 7.9 mU/l.h) was 50% lower than the response in both the obese group (89.2 +/- 19.9, P less than 0.001) and a group of non-diabetic, normal weight-for-height subjects (77.1 +/- 5.7, P less than 0.01). Peak insulin levels were similarly reduced to approximately half the levels seen in the obese and control groups (P less than 0.01). Undernutrition is known to impair both glucose tolerance and insulin secretory reserve by reducing the beta cell number, size, and granulation. It is concluded that chronic undernutrition accentuates beta cell dysfunction in undernourished diabetics, leading to increased glucose intolerance.

Effect of nutritional status on insulin sensitivity in vivo and tissue enzyme activities in the rat

The hyperinsulinaemic-glucose-clamp technique, in combination with measurement of glucose turnover in conscious unrestrained rats, was used to assess the effects of nutritional status on insulin sensitivity in vivo and glucose metabolism. Liver, heart and quadriceps skeletal-muscle glycogen content and activities of pyruvate dehydrogenase (PDH) and glycogen synthase were measured both basally and at the end of a 2.5 h glucose clamp (insulin 85 munits/h) in rats 6, 24 and 48 h after food withdrawal. Clamp glucose requirement and glucose turnover were unchanged by fasting. Activation of glycogen synthase and glycogen deposition in liver and skeletal muscle during the clamps were also not impaired in rats after a prolonged fast. By contrast with skeletal muscle, activation of cardiac-muscle glycogen synthase and glycogen deposition during the clamps were markedly impaired by 24 h of fasting and were undetectable at 48 h. Skeletal-muscle PDH activity fell with more prolonged fasting (6 h, 15.3 +/- 3.4%; 24 h, 4.7 +/- 0.7%; 48 h, 4.3 +/- 0.6% active; P less than 0.005), but at 24 and 48 h was stimulated by the clamp to values unchanged by the duration of fasting. Stimulation of cardiac PDH activity by the clamp was, however, impaired in rats fasted for 24 or 48 h. Basal hepatic PDH did not change significantly with fasting (6 h, 5.3 +/- 1.1%; 24 h, 4.6 +/- 0.7%; 48 h, 3.9 +/- 0.5%), and, although it could be partly restored at 24 h, very little stimulation occurred at 48 h. Hepatic pyruvate kinase and acetyl-CoA carboxylase activity were both stimulated by the clamps, and this was not impaired with more prolonged fasting. During the glucose clamps, blood concentrations of lactate, pyruvate and alanine were increased to a greater extent in rats fasted for 24 and 48 h than in rats studied 6 h after food withdrawal. The findings suggest that, although sensitivity to insulin of whole-body glucose disposal is unchanged with fasting, there may be qualitative differences in the metabolism of glucose.

Impaired glucose metabolism in surgical patients improved by intravenous nutrition: assessment by the euglycemic-hyperinsulinemic clamp

Malnutrition is associated with glucose intolerance. This could be related to decreased pancreatic insulin secretion and/or peripheral insulin resistance. We have used the euglycemic-hyperinsulinemic clamp and continuous indirect calorimetry to assess the disposal of an intravenous glucose load in 13 malnourished patients with benign disease (median age, 55 years; mean weight loss 21 kg +/- 8 SD). Seven normally nourished controls were also studied (median age, 62 years) and eight patients were restudied after 14 days on continuous glucose-based intravenous nutrition (IVN). With hyperinsulinemia of 90 microU/mL, malnourished patients disposed of 6.1 mg glucose/kg fat-free body (FFB).min +/- 1.7 SD and oxidized 1.9 mg/kg FFB.min +/- 1.4 SD. Controls disposed of a similar amount of glucose (6.6 mg/kg FFB.min +/- 3.5 SD) but oxidized significantly more (3.0 mg/kg FFB.min +/- 2.3 SD). After two weeks of glucose-based IVN, both glucose disposal rate (9.5 mg/kg FFB.min + 2.3 SD) and oxidation rate (3.9 mg/kg FFB min +/- 1.0 SD) increased significantly. Respiratory quotient was low in malnourished patients (.88 +/- .12), but above 1.0 in controls (1.07 +/- 0.18) and patients after IVN (1.10 +/- 0.11), showing net lipogenesis in these groups. Malnourished patients can metabolize normal amounts of glucose under conditions of hyperinsulinemia and, although carbohydrate oxidation rate is initially impaired, it becomes normal after 2 weeks of IVN.

Insulin resistance in patients with colorectal cancer

The euglycaemic glucose clamp technique has been used to assess insulin resistance in patients with colorectal adenocarcinoma. Ten cancer patients were studied and compared with control subjects matched for age, sex and nutritional status. Forty-one euglycaemic clamps were performed at one of five different insulin infusion rates (20, 30, 40, 100 or 200 milliunits min-1 m-2). Glucose disposal was significantly decreased in the cancer group at all insulin infusion rates, whilst attained insulin levels and metabolic clearance rates of insulin were comparable in the control and cancer groups. Analysis of dose-response data allowed assessment of sensitivity (insulin concentration of half maximal glucose disposal) and responsiveness (maximal glucose disposal). Responsiveness was significantly reduced in the cancer group (40.3 versus 71.5 mumol kg-1 min-1; P less than 0.001), whilst sensitivity was similar (93.7 milliunits l-1 in controls versus 90.8 milliunits l-1 in cancer patients), suggesting a postreceptor defect in insulin action in the cancer group.

C-peptide secretion in calcific tropical pancreatic diabetes

Serum C-peptide levels were measured during a glucagon stimulation test in ten normal nonobese controls and 54 diabetic patients with recent onset of diabetes under 30 years of age. Diabetic patients were comprised of 13 CTPD, 23 IDDM, and 18 NIDDM. As similar to IDDM patients, serum C-peptide concentrations did not rise significantly (P greater than 0.05) in response to glucagon administration in CTPD-patients. Mean baseline and peak serum C-peptide concentrations in CTPD-patients were significantly lower (P less than 0.001) than the values in normal controls and NIDDM patients, but were significantly higher (P less than 0.05) than those in IDDM patients. We conclude that CTPD patients have partial C-peptide reserve, which may protect against ketosis and contribute to ketosis resistance in CTPD. Our results also suggest that CTPD patients require insulin treatment. Neither baseline nor peak C-peptide levels after glucagon could discriminate CTPD from IDDM and CTPD from NIDDM.

Tropical or malnutrition-related diabetes: a real syndrome?

The syndrome known as tropical diabetes seems to be distinct from the two main types common in developed countries. Major pancreatic exocrine disease may or may not be present, and within these two groups there are clinical and biochemical variants. For these conditions the term malnutrition-related diabetes has been proposed. Although malnutrition is a plausible unifying factor, there is a good case for retaining the term tropical diabetes until there is more information on clinical and biochemical features and on aetiology.

Abnormalities of muscle metabolism and histology in malnourished patients awaiting surgery: effects of a course of intravenous nutrition

Malnourished surgical patients have metabolic and functional abnormalities of skeletal muscle and it has been suggested that these are due to reduced activities of glycolytic enzymes associated with abnormalities of muscle fibres. We have measured the activities of four key enzymes of glucose utilization and the size and distribution of muscle fibre types in vastus lateralis biopsies from 14 undernourished patients awaiting surgery (mean weight loss 24 +/- 10 per cent). These results were compared with those from 14 normally nourished controls, comparable in age, sex, race and habitual activity. Fructose bisphosphatase activity was reduced in undernourished patients by 44 per cent (P less than 0.01), phosphofructokinase by 40 per cent (P = 0.005) and hexokinase by 37 per cent (P less than 0.001). Both fibre types were smaller in patients than controls (area I, 41.4 micron2 X 10(-2) +/- 0.4 vs. 73.3 micron2 X 10(-2) +/- 0.6, less than 0.001; area II, 27.7 micron2 X 10(-2) +/- 0.4 vs. 72.5 micron2 X 10(-2) +/- 0.5, P less than 0.001), and there was a smaller proportional number of type II fibres in patients (35 per cent vs. 65 per cent, P less than 0.01). This loss of type II fibre numbers and preferential type II atrophy may account for the enzyme depression associated with it and could produce the syndrome of impaired glucose tolerance, muscle weakness and fatigue seen in undernourished patients. In a subgroup of 11 patients, biopsy was repeated after 14 days of intravenous nutrition. Only phosphofructokinase activity rose significantly (19.62 +/- 1.85 to 30.74 +/- 2.99 mumol min-1 g-1, P less than 0.01) and both type II fibre size (40.6 +/- 18.5 to 47.4 micron2 +/- 20.3 X 10(-2), P less than 0.05) and number (42 per cent +/- 6 to 56 per cent +/- 5, P less than 0.05) also rose. Intravenous nutrition may therefore increase maximum glycolytic rate and improve muscle function in undernourished surgical patients.

Energy and protein requirements of general surgical patients requiring intravenous nutrition

General surgical patients require intravenous nutrition either because their gastrointestinal tract is blocked, too short or inflamed or because it cannot cope. Such patients can be grouped into four nutritional/metabolic categories: normal and unstressed; normal and stressed; depleted and unstressed; depleted and stressed. The energy requirements of patients in each of these groups vary according to their energy expenditure. Normally nourished and stressed patients have the highest energy expenditure and therefore require the highest energy input (45-55 kcal.kg-1day-1). Other groups of patients rarely require more than 40 kcal.kg-1day-1. Energy can be given mainly as dextrose although calories needed above 40 kcal kg-1day-1 should be given as fat (unless lipogenesis is desirable). In very stressed patients high rates of glucose infusion can themselves constitute a metabolic stress and fat may play a bigger role as a calorie source. For long term feeding, 1 litre of 10 per cent fat emulsion should be given weekly to avoid essential fatty acid deficiency. The level of nitrogen intake required to maintain a positive nitrogen balance is a lot higher in surgical patients than the suggested recommended dietary allowances for normal subjects. It is dependent not only on the nutritional and clinical state of the patient but also on the levels of energy and nitrogen intake given. When energy intake is below energy needs, normally nourished patients cannot retain nitrogen, although depleted patients can. When energy intake exceeds energy needs, both normally nourished and depleted patients retain nitrogen at levels of nitrogen intake ranging from 250 mg kg-1day-1 (depleted and unstressed) to over 400 mg kg-1day-1 (stressed). Depleted patients can maintain a positive nitrogen balance at lower levels of calorie and nitrogen intake than normally nourished patients and in this respect are analogous to a growing child. In all surgical patients, energy and nitrogen intakes can be manipulated to provide for a controlled maintenance or restoration of either wet lean tissue and/or fat. There is little place for protein sparing therapy or the use of insulin and anabolic steroids to promote nitrogen retention in surgical patients requiring intravenous feeding.

Insulin secretion and carbohydrate metabolism in experimental protein malnutrition

In order to study the evolution of endocrine and metabolic changes in protein malnutrition, we created a replica of this human syndrome in a primate model. This model was free from stress factors like infestations, and infections and provided an opportunity to study the details more closely. Our results showed that definite endocrine and metabolic changes are established by six weeks of protein deprivation. The study demonstrated that protein deprivation results in decreased fasting blood glucose levels associated with diminution in fasting, and total insulin output when presented with a glucose load. There is also deterioration of carbohydrate tolerance. It is suggested that decreased fasting blood glucose is a consequence of impaired breakdown and/or depletion of glycogen stores, and hepatic dysfunction secondary to fatty infiltration. The exact cause of decrease in insulin output remains to be clearly elucidated. The carbohydrate intolerance is attributed to insulin lack, hepatic dysfunction and decreased glucose disposal consequent to protein deprivation.

Suppression of insulin secretion by protein deprivation in obesity

1) Protein restricted diets decrease basal plasma insulin levels in obesity. 2) This effect occurs even in the presence of sufficient calories to maintain body weight and while the diet is high in carbohydrate. 3) The decrease in insulin is accompanied by a fall in plasma glucose and in the I/G ratio, suggesting an increase in insulin sensitivity. 4) Excessive protein intake, in addition to carbohydrate, may play a role in the pathogenesis of the hyperinsulinemia and insulin resistance found in obesity.

Mechanism of impaired glucose tolerance in patients with neoplasia

The disappearance rate (k) of i.v. glucose was measured in cachectic and non-cachectic cancer patients and tumour-free controls. The respective k values were found to be 1.06 +/- 0.27 (mean +/- s.d.), 1.64 +/- 0.34 and 1.63 +/- 0.23. Of the other parameters measured, only plasma albumin level was found to vary significantly amongst the 3 categories, the mean level being the lowest in cachectic cancer patients. The means of total plasma protein, fasting blood glucose and plasma liver enzyme concentrations were similar in the 3 groups. Glucagon, a potent insulin secretogogue, failed to augment the fasting insulin level in cachectic but did so in non-cachectic cancer patients. Taken together, the findings suggest that the reduced glucose tolerance in patients with neoplasia is due to impairment of insulin release exhibited predominantly by ill-nourished advanced cancer patients having a moderate to sever degree of hypoalbuminemia.