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Biomedical subjects

D J Jenkins

Publications and source records attributed to D J Jenkins.

At least 145 records · Page 8Linked to original sources
PubMed1988

The acute effect of fat on insulin secretion.

Previous studies suggest that the rate of rise of the plasma glucose-dependent insulinotropic peptide (GIP) concentration, rather than the steady state level achieved, may be the stimulus of the increased insulin secretion that occurs when fat is ingested with carbohydrate. To test this hypothesis six normal men were given a 5-g iv bolus dose of glucose 15 min after a carbohydrate meal with or without fat. At the time of the iv glucose injection after the fat-containing meal, the rate of rise of plasma GIP was maximum, but the level was only 40% of the achieved by 30 min. Plasma GIP did not change after the meal without fat. After the fat meal, peak insulin and C-peptide levels in response to iv glucose were 60% greater than those after carbohydrate alone despite similar peak blood glucose levels. The calculated insulin clearance was not altered by the fat meal. We conclude that glucose-stimulated insulin secretion is increased early after fat ingestion, possibly due to a rise in GIP or other incretins.

Adult↗
PubMed1988

Starchy foods and glycemic index.

Different starchy foods produce different glycemic responses when fed individually, and there is some evidence that this also applies in the context of the mixed meal. A major reason appears to relate to the rate at which the foods are digested and the factors influencing this. A similar ranking in terms of glycemic response to specific foods is seen independent of the carbohydrate tolerance status of the groups tested. Potentially clinically useful starchy foods producing relatively flat glycemic responses have been identified. Many of these are considered ethnic or traditional and include legumes; pasta; grains such as barley, parboiled rice, and bulgur (cracked wheat); and whole-grain breads such as pumpernickel. Specific incorporation of these foods into diets has been associated with reductions in low-density lipoprotein cholesterol and triglyceride levels in hyperlipidemia and with improved blood glucose control in insulin-dependent diabetic patients. To facilitate identification of such foods, it has been suggested that the glycemic response should be indexed to a standard (e.g., white bread) to allow comparisons to be made between the glycemic index of foods tested in different groups of subjects. The scope of application of this principle is subject to further investigation. It may be used to expand the range of possibly useful starchy foods for trial in the diets of diabetic patients.

Blood Glucose↗
PubMed1988

Dietary fiber in management of diabetes.

Current evidence suggests that high-fiber diets, especially of the soluble variety, and soluble fiber supplements may offer some improvement in carbohydrate metabolism, lower total cholesterol and low-density lipoprotein (LDL) cholesterol, and have other beneficial effects in patients with non-insulin-dependent diabetes mellitus (NIDDM). Diets enriched with wheat bran and guar gum induce 10-20% reductions in serum cholesterol and LDL in both normo- and hypercholesterolemic subjects and have the ability to blunt the hypertriglyceridemic effects of diets high in carbohydrate and low in fiber. In insulin-dependent diabetes mellitus (IDDM) the situation is less clear, but a decrement of the circadian glucose profile has been shown. Americans, in general, consume too little fiber. With the need to restrict fat and reduce protein, an increase in carbohydrates is mandatory. A practical goal would be to establish the present level of fiber intake (15-30 g/day) and to gradually increase it. An intake of up to 40 g of fiber per day or 25 g/1000 kcal of food intake appears beneficial; in many individuals on weight-reducing diets higher levels may be unacceptable because of gastrointestinal side effects. The level of maximum benefit has not been determined. Fiber supplementation appears beneficial only if given with a diet comprising approximately half of the calories as carbohydrate. Foods should be selected with moderate to high amounts of dietary fiber from a wide variety of choices to include both soluble and insoluble types of fiber. Insufficient data are available on the long-term safety of high-fiber supplements. People at risk for deficiencies, such as postmenopausal women, the elderly, or growing children, may require supplements of calcium and trace minerals. People with upper gastrointestinal dysfunction are at risk of bezoar formation and cautioned against a diet high in fiber of the leafy vegetable type. Careful attention must be paid to insulin dose because hypoglycemia can result if there is a radical change in fiber intake and insulin dose is not reduced appropriately. Care must be exercised in the use of "novel" fibers, including the wood celluloses, because little is known of their safety and efficacy.

Diabetes Mellitus, Type 1↗
PubMed1988

Manipulation of gut hormone response to food by soluble fiber and alpha-glucosidase inhibition.

Preliminary data indicated that viscous fiber (guar) and alpha-glycosidase inhibition (acarbose) used in combination to slow carbohydrate absorption have an apparently additive effect in reducing the postprandial glycemic response. The full endocrine data reported here also demonstrate that reductions in insulin and gastric inhibitory polypeptide are most significant when guar and acarbose are used in combination. The results are divergent for enteroglucagon when guar and acarbose were given singly. Raised enterglucagon levels seen after acarbose are in keeping with inhibition of proximal absorption resulting in more distal absorption of carbohydrate. However, with viscous fiber, the enteroglucagon response was reduced, and this reduction was maintained even after addition of acarbose. The results demonstrate that the gut endocrine response can be manipulated by pharmacological interventions which alter the pattern of carbohydrate absorption.

Acarbose↗
PubMed1988

Comparison of ileal effluents, dietary fibers, and whole foods in predicting the physiological importance of colonic fermentation.

An in vitro fermentation system that simulates the human colon was used in conjunction with the human ileostomy model to determine whether whole foods or dietary fiber isolates from the same foods could be used in lieu of ileal effluent to estimate the daily colonic production of short chain fatty acids (SCFA). A basal diet and a test food were fed for 3 days to a healthy ileostomate, and the ileal effluent was collected. Dietary fiber intake significantly increased ileal dry matter, ash, protein, and available carbohydrate (total carbohydrate minus dietary fiber) (p less than 0.05). Basal diet, test foods, ileal effluents, and dietary fiber isolates then were fermented in vitro with mixed human fecal microflora for 24 h, and SCFA production (mmol SCFA/g organic matter) was measured. SCFA production from ileal effluent significantly correlated with that from dietary fiber isolates (r = 0.86, p less than 0.05), but not with that from whole foods. Therefore, dietary fiber isolates, rather than whole foods, can provide the closest estimates of colonic SCFA production when ileostomates are not available. Test foods significantly changed molar ratios of individual SCFA within the ileal effluent and dietary fiber isolate groupings (p less than 0.05). In view of the different ileal loads arriving in the colon, we conclude that large differences in SCFA production probably depend on the food consumed.

Colon↗
PubMed1988

Diet and cancer.

Explore the source record for details and available documents.

Diet↗
PubMed1988

Relationship between fasting serum tryptophan/large neutral amino acid ratio and reported hunger in subjects with diabetes.

Food intake regulation is influenced by serum amino acid (AA) ratios. The objectives of this study were to determine whether non-obese subjects with diabetes have normal serum AA ratios, and to see if AA ratios relate to perceived hunger. We therefore measured fasting serum AA in nine normal subjects on two occasions and 19 patients with diabetes on four occasions over a two month period. At the time of the blood samples, the subjects with diabetes were asked to rate how hungry they felt on a scale of -3 (very hungry) to +3 (very full). There were no significant differences between the mean AA ratios of normal and diabetic subjects. There was a positive correlation between reported hunger score and the ratio of serum tryptophan (TRP) to the sum of the concentrations of the other large neutral AA (LNAA) (r = 0.286, n = 78, p less than 0.05). The relationships between hunger and other AA ratios were not significant. Variations of the TRP/LNAA ratio within each subject did not relate to differences in hunger from day-to-day. However, there was a positive correlation between the mean TRP/LNAA ratio and mean hunger score of the different subjects (r = 0.495, n = 19, p less than 0.05). The relationships between TRP/LNAA ratio and body weight or hunger score were not significant. It is concluded that the serum AA ratios are normal in patients with diabetes. The data is consistent with the hypothesis that a low serum TRP/LNAA ratio causes increased feelings of hunger in different individuals.

Adult↗
PubMed1988

The glycaemic index: effect of age in insulin dependent diabetes mellitus.

It has been suggested that age effects the glycaemic index value of foods, although there is no data to support this. We therefore studied the blood glucose responses of bread and lentils in seven children (aged 7-17 years) and 10 adults (aged 27-74 years) with insulin dependent diabetes (IDDM). Although there were small differences in the shape of the blood glucose response curves in adults and children, the mean glycaemic index value for lentils was virtually identical in the two groups being 43 +/- 7 in the children and 44 +/- 10 in the adults. We conclude that, in IDDM, the glycaemic index is not affected by age.

Adolescent↗
PubMed1987

Starchy foods, type of fiber, and cancer risk.

Fibers have been classified broadly as predominantly "soluble" or "insoluble," The soluble fibers have little effect on fecal bulk because they are largely fermented to short-chain fatty acids, so lowering colonic pH, and their influence on cancer risk is in relation to these variables. They are associated with increased fecal bile acid losses. Insoluble fibers are much less fermented and enhance fecal bulk without greatly increasing bile acid losses. Their effect in diluting carcinogens or bile acid promoters relates to their protective role in colon cancer. However, high-fiber foods not only contain combinations of different fiber types but also usually contain starch. Under various conditions, and possibly influenced by fiber, substantial amounts of starch (3-20% of dietary intake) may also enter the colon depending on the nature of the foods eaten. These carbohydrates will contribute to the effective fiber load. In considering the action of fiber in the human gut, fiber type, starch, and other components as well as the nature of foods making up the diet must be assessed. These factors are of importance both in interpreting epidemiological leads and in devising logical trials of fiber in terms of intervention.

Carcinogens↗
PubMed1987

The glycemic index: similarity of values derived in insulin-dependent and non-insulin-dependent diabetic patients.

To see whether relative differences in the glycemic responses to different foods were similar in insulin-dependent (IDDM) and non-insulin-dependent diabetic patients (NIDDM) we determined the glycemic index (GI) of a total of 20 foods and mixed test meals in groups of IDDM and NIDDM volunteers. The mean GI values ranged from 32 in NIDDM and 41 in IDDM (pearled barley) to 105 in NIDDM and 111 in IDDM (bread with cheese and tomato). The correlation between the mean GI values in IDDM and NIDDM was highly significant (r = 0.927, p less than 0.001). The mean GI values for 15 of the 20 test meals was greater in IDDM than in NIDDM (mean of GI for all 20 foods, 76 in IDDM compared with 68 in NIDDM, p less than 0.005). However, the difference in GI between IDDM and NIDDM was t statistically significant for 19 of the 20 individual test meals. Greater within-individual variability of glycemic responses in IDDM probably accounts for the slightly greater mean GI value seen in IDDM compared with NIDDM. The addition of 32 g cheddar cheese to four foods which were also fed without cheese had no significant effect on the GI in NIDDM (mean GI of 68 without cheese compared with 72 for the meals with cheese), but had a small effect in IDDM where the mean GI was increased from 72 to 87 (p less than 0.05). However, despite small increases in glycemic response to foods with added cheese, the relative differences between foods were unaffected by the addition of cheese in both IDDM and NIDDM. It is concluded that mean GI values for foods are very similar in IDDM and NIDDM patients.

Adult↗
PubMed1987

The effect of starch-protein interaction in wheat on the glycemic response and rate of in vitro digestion.

To determine the effect on blood glucose of removal of protein from wheat products, healthy volunteers took test meals of white bread made from either regular or gluten-free flour. After bread made from gluten-free flour, the blood-glucose rise was significantly greater. This corresponded with a significantly more rapid rate of digestion in vitro and reduced starch malabsorption in vivo as judged by breath-H2 measurements. Addition of gluten to the gluten-free bread mix did not reverse these effects. Factors associated with unprocessed wheat flour, such as the natural starch-protein interaction, may therefore be important in wheat products in reducing both their rate of absorption and glycemic response. They may have implications in the dietary management both of diabetes and of diseases where small intestinal absorptive capacity is impaired.

Adult↗
PubMed1987

Concurrent ingestion of fat and reduction in starch content impairs carbohydrate tolerance to subsequent meals.

We examined the effect of breakfasts of different macronutrient compositions on blood glucose and insulin levels after a standard lunch fed 4 h later. Fat-containing breakfasts were compared with a breakfast of equal carbohydrate and protein content and another with higher carbohydrate but equal calorie content. Concurrent ingestion of fat resulted in a large impairment of glucose tolerance following the standard lunch 4 h later. There was no significant difference in glucose and insulin if the fat eaten was butter or peanut butter. When the fat breakfast was compared with the isocaloric larger carbohydrate meal, the effect of fat on carbohydrate tolerance at lunch was even greater. Part of the reason for this additional difference is an improved glucose tolerance at lunch due to the higher carbohydrate content of the breakfast. Concurrent ingestion of fat and reduction of starch content have a persistent effect on carbohydrate tolerance to subsequent meals.

Adult↗
PubMed1987

Low-glycemic index diet in hyperlipidemia: use of traditional starchy foods.

To define those patients most likely to benefit from the hypolipidemic effect of low-glycemic-index (GI) traditional starchy foods, 30 hyperlipidemic patients were studied for 3 mo. During the middle month, low-GI foods were substituted for those with a higher GI with minimal change in dietary macronutrient and fiber content. Only in the group (24 patients) with raised triglyceride levels (types IIb, III, and IV) were significant lipid reductions seen: total cholesterol 8.8 +/- 1.5% (p less than 0.001), LDL cholesterol 9.1 +/- 2.4% (p less than 0.001), and serum triglyceride 19.3 +/- 3.2% (p less than 0.001) with no change in HDL cholesterol. The percentage reduction in serum triglyceride related to the initial triglyceride levels (r = 0.56, p less than 0.01). The small weight loss (0.4 kg) on the low-GI diet did not relate to the lipid changes. Low-GI diets may be of use in the management of lipid abnormalities associated with hypertriglyceridemia.

Adult↗
PubMed1987

Phytic acid and calcium affect the in vitro rate of navy bean starch digestion and blood glucose response in humans.

Carbohydrate foods that are slowly digested appear beneficial in the management of diabetes and hyperlipidemia. This study determined the effect of endogenous and added phytic acid as well as Ca on the in vitro rate of starch digestion and in vivo blood glucose response to navy bean flour, prepared as unleavened bread. Removal of phytic acid from and addition of Ca to navy bean flour increased the starch digestion in vitro and raised the glycemic response in vivo while readdition of phytic acid to dephytinized flour produced the opposite effect. Carbohydrate malabsorption assessed by breath H2 measurement related negatively to glycemic response but the changes observed were much lower than the changes in glycemic response. This study confirmed the role of both added and endogenous phytic acid in slowing the in vitro rate of starch digestibility and in vivo glycemic response to legumes and the ability of Ca to modify this effect.

Blood Glucose↗
PubMed1987

Metabolic effects of a low-glycemic-index diet.

Six healthy male volunteers underwent 2-wk metabolically controlled high-glycemic-index (GI) and low-GI diets in random order. Over the low-GI diet significant reductions were seen in serum fructosamine (7.0 +/- 1.0%, p less than 0.01), 12-h blood glucose profile (37 +/- 7%, p less than 0.01), and total serum cholesterol (15 +/- 3%, p less than 0.01). As a measure of insulin secretion, 24-h urinary C-peptide levels were 32 +/- 10% lower (p less than 0.05) after the low-GI than after the high-GI diet. Lower C-peptide levels were maintained after a standard carbohydrate challenge after the low-GI diet despite higher blood glucose levels. Differences in blood glucose were not seen after a 5-g intravenous glucose challenge. These results are of interest with respect to the effect that prolonged postprandial reductions in nutrient fluxes and insulin secretion may have on carbohydrate and lipid metabolism and renal function.

Adult↗
PubMed1987

Starchy foods and fiber: reduced rate of digestion and improved carbohydrate metabolism.

The rate of the small intestine amylolytic digestion appears to be a major determinant of the glycemic response. Foods such as legumes appear to be digested less rapidly than many cereal foods although even amongst these large differences in rates of in vitro digestion exist. Studies of diabetes using high fibre, high legume diets have almost uniformly noted improvements in glycemic control and blood lipid profile. However, diets where changes in fibre content have been relatively small, but where the foods were selected on the basis of their slow rates of digestion and flatter glycemic response, have also produced similar beneficial effects. The reasons for the altered rates of digestion include fibre, food form, the nature of the starch, antinutrients etc. Through reducing the rate of digestion of starchy foods post prandially "slow release" starchy foods blunt many gut hormone responses, and prolong FFA and ketone body suppression. In addition increased starch losses to the colon may enhance production of SCFA. All these events may modify carbohydrate and lipid metabolism. Many foods which produce these effects are traditional starchy foods and so strengthen current recommendations of the diabetes association, heart foundations and cancer institutes to increase the use of starchy foods through reducing fat intake. Recognition of the nutritional value of these foods is however not new, but was well accepted in the ancient world and is still preserved in traditional cultures where freedom from many of the major non-infective Western diseases is a notable phenomenon.

Animals↗