Butter-enriched diets reduce arterial prostacyclin production in rats

Rats were fed diets containing 10%, 30% or 50% energy as fat derived predominantly from butter or lard. The protein content of the diets was maintained at 20%. After three weeks on the diets, the rats were killed and the following parameters measured: prostacyclin production in vitro from abdominal aorta and mesenteric artery; platelet aggregation to ADP and thrombin; fatty acid composition of the phospholipids in plasma, thoracic aorta and liver; smooth muscle reactivity and release of endothelial derived relaxing factor (EDRF) from aortic endothelium stimulated by acetylcholine. There was no significant effect of increasing fat content of the diets (neither lard nor butter) on platelet aggregation. In contrast, prostacyclin production in both the mesenteric artery and the abdominal aorta fell in a concentration-dependent manner in the butter-supplemented rats. However, no effect on prostacyclin production was detected in arteries from the lard-supplemented animals. The effects of the diets on prostacyclin (PGI2) production correlated very well with the changes in plasma, aortic and liver phospholipid arachidonic acid (AA) and eicosapentaenoic acid (EPA) contents. AA decreased in a concentration-dependent manner in the rats fed the butter-enriched diets but did not change in those fed the lard-enriched diets, whereas EPA rose in a concentration-dependent manner in the butter-fed rats and was unchanged in the lard-fed animals. The clear-cut effects of the butter-enriched diets on aortic phospholipid fatty acid composition and aortic PGI2 production were accompanied by a significant reduction in smooth muscle relaxation to EDRF.(ABSTRACT TRUNCATED AT 250 WORDS)

An investigation of nutrition-related risk factors in an isolated Aboriginal community in northern Australia: advantages of a traditionally-orientated life-style

Australian Aborigines develop a high frequency of type-2 diabetes mellitus when they make the transition from a traditional to an urban life-style. Preliminary studies were conducted at an outstation in northeastern Arnhem Land where the Aborigines have been exposed to Western influence for approximately 20 years only and where they continue to follow a life-style that is largely traditional. At the time of the study 31 persons were resident at the outstation, 20 persons were over 15 years of age (adults) and 11 persons were under 15 years of age (children). Eighteen adults and six children were tested. By standard criteria for body mass index these persons were all underweight (less than 20 kg/m2). In spite of this, they displayed no biochemical evidence of malnutrition. Their plasma fatty-acid profiles were consistent with a low dietary fat intake and a high consumption of lean meat. Levels of linoleic acid were much lower and those of arachidonic acid were much higher than are those in persons who consume a Western diet. Fasting glucose and cholesterol concentrations were low relative to those of urbanized Aborigines and white Australians. However, their fasting insulin and triglyceride levels were inappropriately high for their very low body mass index and fasting glucose levels. The mild elevation of triglyceride and fasting insulin levels is consistent with insulin resistance and suggests that these Aborigines (in common with other Aborigines) may become susceptible to obesity and diabetes if they became urbanized further.

Impaired glucose tolerance, hyperinsulinemia, and hypertriglyceridemia in Australian aborigines from the desert

A cross section of adult full-blooded Aborigines from three small isolated communities in the desert region of northwest Australia was surveyed for diabetes, impaired glucose tolerance (IGT), insulin levels, and lipoprotein lipids. Sixty-three men and 86 women from a total adult population of 330 were tested. Of the people tested, 67.6% had normal glucose tolerance, 25% had IGT, and 7.4% had diabetes. Both diabetes and IGT were strongly age related. Fasting insulin levels and insulin responses to oral glucose (elevation above basal) were elevated. Although fasting insulin rose with age, insulin response did not rise after adjustment for body mass index (BMI). Plasma triglyceride levels were high, particularly in men greater than 35 yr old (3.13 +/- 0.32 mM), but cholesterol levels were not elevated. Multiple regression analysis of fasting glucose, 2-h glucose, plasma triglyceride, fasting insulin, and insulin response for the nondiabetic subjects revealed 1) BMI was an independent risk factor for elevated 2-h glucose levels in women but not in men and was strongly related to fasting insulin concentrations in both genders; 2) fasting insulin concentration was an independent risk factor for increases in fasting glucose, insulin response, and triglyceride levels; 3) insulin response was related to the 2-h glucose level; 4) fasting and 2-h glucose levels and fasting insulin and triglyceride concentrations all rose with age in both genders, with the rate of increase generally greater in men. The most striking difference between these desert Aborigines and previously studied coastal Aborigines from the same geographical region was the significantly higher insulin response.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of short-term consumption of a high fat diet on glucose tolerance and insulin sensitivity in the rat

The mechanism by which the consumption of high fat, low carbohydrate diets impair glucose tolerance and decrease insulin sensitivity is poorly understood. In an attempt to clarify this question, intravenous glucose tolerance and insulin action in the liver and skeletal muscle were examined in rats after two weeks feeding of either a high fat (HF: 66% energy as fat) or a low fat (LF: 12% energy as fat) diet. Both diets had a P/S ratio (ratio of polyunsaturated to saturated fat in the diet) of 1.3. The high fat diet resulted in mild impairment of intravenous glucose tolerance. Postprandial glucose levels were elevated in the presence of a sustained insulin response. In vitro insulin-stimulated glucose utilisation was decreased significantly in soleus muscle of HF rats, as indicated by decreased [14C]glucose incorporation into muscle glycogen. In contrast, muscle lipogenesis from glucose was not affected by dietary composition. There was no difference in insulin binding to soleus muscle of HF and LF rats, indicating a dissociation between insulin receptor binding and post-receptor metabolic events. Dietary composition did not influence the incorporation of increasing [14C]glucose loads into muscle glycogen or lipid in vivo. However, the HF diet was associated with reduced incorporation of [14C]glucose into lipids and glycogen in the liver and, to a smaller extent, reduced incorporation into adipose tissue lipids in vivo. These results suggest that the mechanism by which HF diets impaired glucose tolerance was mainly hepatic in origin. Decreased glucose uptake, secondary to reduced glucokinase activity, may result in a reduction in glucose utilisation in the liver.

Plasma glucose and insulin responses to starchy foods in Australian aborigines: a population now at high risk of diabetes

We compared plasma glucose and insulin responses to an Aboriginal bushfood and its western equivalent in healthy Aborigines and Caucasians. Bush potato (Ipomoea costata), an Aboriginal bushfood which is slowly digested in vitro, and potato (Solanum tuberosum), which has a high glycemic index, were studied. The areas under the glucose and insulin curves for Aborigines were 34% and 42% smaller, respectively, after bush potato than after potato (p less than 0.05). In Caucasians only the insulin response to bush potato was lower (by 19%) than that to potato (p less than 0.05). Compared with Caucasians, Aborigines produced 2.5 times greater glucose and insulin responses to potato (p less than 0.025). Their insulin responses to bush potato were also twice as large (p less than 0.05) although glucose responses were not significantly different. These findings add weight to the hypothesis that rapidly digested carbohydrate in western diets may be one of the factors in the lifestyle change which precipitates diabetes in indigenous populations.

Effects on plasma lipids and fatty acid composition of very low fat diets enriched with fish or kangaroo meat

The effects of very low fat diets (less than 7% energy) enriched with different sources of long chain (C20 and C22) polyunsaturated fatty acids (PUFA) on plasma lipid levels and plasma fatty acid composition were studied in 13 healthy volunteers. Three diets provided 500 g/day of tropical Australian fish (rich in arachidonic acid and docosahexaenoic acid), southern Australian fish (rich in docosahexaenoic acid) or kangaroo meat (rich in linoleic and arachidonic acids). The fourth diet was vegetarian, similarly low in fat but containing no 20- and 22-carbon PUFA. Subjects ate their normal or usual diets on weeks 1 and 4 and the very low fat diets in weeks 2 and 3. Weighed food intake records were kept, and weeks 2, 3 and 4 were designed to be isoenergetic with week 1. Plasma cholesterol levels fell significantly on all diets within one week. There were reductions in both low density (LDL) and high density lipoprotein (HDL) cholesterol levels, with effects on HDL cholesterol being more consistent. There were no consistent or significant effects on total triglyceride levels despite the high carbohydrate content of the diets. On all diets the percentage of linoleic acid fell in the plasma phospholipid and cholesteryl ester fractions, while the percentage of palmitic acid in the phospholipids and cholesteryl esters and palmitoleic acid in the cholesteryl ester fraction rose on all diets. The percentage of arachidonic acid rose in the phospholipid and cholesteryl esters on the two diets that were good sources of this fatty acid (tropical fish and kangaroo meat).(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of T4 and T3 binding kinetics in the thyroxine binding globulin abnormality of Australian aborigines

Low serum total T4 associated with subnormal concentrations of thyroxine binding globulin (TBG) has been reported in up to 40% of euthyroid Australian aborigines. It has been suggested that these subjects show both diminished concentration of TBG and reduced TBG affinity for T4 (Sarne et al., 1985). We have compared 12 euthyroid aborigines with low T4 (total T4 44 +/- 5 nmol/l) and aborigines with normal T4 (T4 99 +/- 9 nmol/l, n = 12) using measurements of free T4 and T3 by equilibrium dialysis. TBG was measured both by RIA (Henning, Berlin, FRG) and a method dependent on T4 binding (Corning Immophase). Aborigines with low T4 showed lower levels of free T4 (12.6 +/- 0.6 cf. 18.7 +/- 1.0 pM), free T4 index (66 +/- 8 cf. 98 +/- 13), total T3 (1.1 +/- 0.2 cf. 1.6 +/- 0.3 nmol/l), TBG RIA (14.0 +/- 0.6 cf. 25.0 +/- 1.2 ng/l), and TBG Immophase (9.0 +/- 0.5 cf. 22.0 +/- 1.2 mg/l) (P less than 0.01), but free T3 (5.3 +/- 0.4 cf. 4.7 +/- 0.4 pM) and TSH (1.9 +/- 0.2 cf. 1.8 +/- 0.2 mU/l) were not significantly different from the values found in aborigines with normal T4. Scatchard analysis of T4 and T3 binding was performed using serum diluted 1 : 20,000 for T4 and 1 : 500 for T3 (barbitone buffer pH 8.6, 4 degrees C, dextran-coated charcoal separation). In euthyroid low T4 aborigines compared to those with normal T4, both T4 capacity (106 +/- 14 cf. 238 +/- 13 nM, P less than 0.01) and affinity (5.05 X 10(10) cf. 8.47 X 10(10) M-1, P less than 0.05) were significantly reduced. Similarly, both T3 capacity (62 +/- 10 cf. 154 +/- 16 nM, P less than 0.01) and affinity (1.67 X 10(9) cf. 2.28 X 10(9) M-1, P less than 0.02) were reduced. A substantial minority of euthyroid Australian aborigines have a TBG variant characterized by both reduced capacity and affinity of T4 and T3. These findings suggest that TBG may be both qualitatively and quantitatively abnormal in these subjects.

Effect of short-term consumption of a high-fat, low-carbohydrate diet on metabolic control in insulin-deficient diabetic rats

This study examined the effect of changing the proportion of dietary fat on metabolic control in rats rendered mildly diabetic with streptozotocin (STZ). The high-fat (HF) diet contained 66% energy as fat and 12% as carbohydrate while the low-fat (LF) diet contained 12% energy as fat and 66% as carbohydrate. Both diets had a P/S ratio of 1:3. Young male rats weighing 100 g were treated with STZ (60 mg/kg IV) and randomly allocated to either the LF of HF diet. After 2 weeks, the fasting plasma glucose concentrations were significantly higher in the HF-STZ rats than in the LF-STZ rats (13.2 +/- 1.2 mmol/L v 7.1 +/- 0.8 mmol/L, respectively, P less than 0.001). The increase in plasma glucose above the basal level following the intravenous glucose load (0.5 g/kg body wt) was similar in both groups of STZ-treated rats and glucose clearance was similarly impaired. The fall in glucose concentrations in the 30 minutes following the IV insulin (0.5 U Actrapid insulin/kg body wt) was greater in the LF-STZ rats (delta AUC = -1.60 +/- 0.20 mmol/L 0.5h) than in the HF-STZ group (delta AUC = -0.97 +/- 0.20 mmol/L 0.5 h, P less than 0.05) and either of the control groups (delta AUC = -0.94 +/- 0.37, -0.83 +/- 0.09 mmol/L 0.5 h for LF and HF rats, respectively, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animal foods in traditional Australian aboriginal diets: polyunsaturated and low in fat

Australian Aborigines develop high frequencies of diabetes and cardiovascular diseases when they make the transition to an urban lifestyle. The composition of the traditional diet, particularly its lipid components, is a most important aspect of the hunter-gatherer lifestyle that would bear on the risk of these diseases. We have examined the fat content and fatty acid composition of a variety of animal foods eaten traditionally by Aborigines from different regions of Australia. The muscle samples of the wild animals from all over Australia were uniformly low in fat (less than 2.6% wet weight) with a high proportion of polyunsaturated fatty acids (greater than or equal to 20% PUFA). Liver samples had a higher range of fat content (5-10% wet weight) but were also rich in PUFA (33-42%). Depot fat samples varied widely in their PUFA content (5-40%). In terms of their PUFA composition the foods tended to fall into three groups: (i) those rich in both n-3 and n-6 PUFA, which included land-based, coastal and freshwater animals; (ii) those rich in n-3 PUFA, i.e., marine species; (iii) those rich in n-6 PUFA, mainly land-based species. The results of these analyses suggest that even when the traditional Aboriginal diet contained a high proportion of animal foods it would have been low in fat with a high proportion of PUFA and thereby could have protected Aborigines against cardiovascular diseases and related conditions through a combination of factors: low energy density, low saturated fat and relatively high PUFA content.

Commercial canning increases the digestibility of beans in vitro and postprandial metabolic responses to them in vivo

Six weight-stable subjects consumed three test meals containing 50 g carbohydrate in random order after a 12-h fast: D-glucose, canned baked beans, or home-cooked (boiled) baked beans. Postprandial glucose and insulin responses were greatest to glucose, lowest to home-cooked baked beans, and intermediate to canned baked beans. Profiles of glucose and insulin responses to home-cooked beans were flatter and more attenuated than responses to canned beans or glucose, which correlates with the in vitro data showing a six-to-eight times higher rate of starch hydrolysis in canned beans relative to boiled beans. Increases in temperature (pressure) and duration of pressure-cooking resulted in increased starch digestibility, whereas even mildly acidic conditions (pH 5.0) markedly reduced it. None of the processes studied affected the total amount of available carbohydrate.

Glucose tolerance and insulin sensitivity in ponies and Standardbred horses

The existence of an innate insulin insensitivity in ponies was investigated and compared with the situation in larger breeds of horse. Ponies that were fat or had previously suffered laminitis were found to be far more intolerant to oral glucose loading (1 g/kg bodyweight [bwt]) than normal ponies or Standardbreds. These ponies also exhibited a far greater response in plasma insulin levels after glucose loading. Insulin response tests (0.4 iu/kg bwt insulin intravenously) showed only a minimal and very protracted response in both the fat and laminitic groups. The relevance of these findings in regulation of carbohydrate and lipid metabolism, and their role in the pathogenesis of hyperlipaemia, are discussed.

More severe impairment of oral than intravenous glucose tolerance in rats after eating a high fat diet

Glucose and insulin responses to oral and intravenous glucose (1 g/kg body weight) were measured after consumption of a high fat (HF) or low fat (LF) diet for 3 wk in conscious rats with implanted intravenous and intra-arterial catheters. The HF diet resulted in impaired glucose tolerance and insulin resistance after both oral and intravenous glucose; the effect was more pronounced after oral glucose. In an attempt to understand the basis of the impairment of glucose tolerance after consuming the HF diet, the activity of hepatic glucokinase and the rate of intestinal glucose uptake were also measured. The more severe impairment of glucose tolerance by oral rather than intravenous administration was not explained by an increased rate of intestinal glucose uptake. Indeed, there was a small but significant reduction in the rate of jejunal glucose uptake in the HF rats. However, the greatly reduced activity of hepatic glucokinase in the HF rats was consistent with a reduced capacity for hepatic glucose uptake, which may have contributed significantly to the impaired glucose tolerance. The effects of the HF diet on the insulin response to glucose were much more pronounced after oral rather than intravenous glucose administration. This indicated that the HF diet may have stimulated the enteroinsular axis. However, it is also possible that the particularly high circulating insulin levels, resulting from oral glucose in the HF rats, were a direct response to hyperglycemia, secondary to reduced glucose removal.

The effects of low-fat diets rich in arachidonic acid on the composition of plasma fatty acids and bleeding time in Australian aborigines

In the present study we measured the bleeding times in fourteen Aborigines (10 diabetic, 4 non-diabetic) before and after 2 weeks on a diet of tropical seafood (rich in both arachidonic acid and the omega 3 PUFA), followed by 3 weeks on a diet in which kangaroo and freshwater fish (linoleic and arachidonic acid-rich) were the major fat sources. Both diets were very low in fat. Bleeding times increased in all subjects after the 2 weeks of tropical seafood and continued to rise on the mixed diet. The increase over 5 weeks from 4.1 +/- 0.4 to 5.9 +/- 0.4 min was highly significant (p less than 0.01). Due to the extreme isolation of the study location it was only possible to measure the plasma fatty acid composition at the beginning and end of the study. The concentration of arachidonic acid in the plasma lipids doubled whereas that of linoleic acid was almost halved, despite the fact that the diet in the second part of the study contained considerably more linoleic than arachidonic acid. That there appeared to be preferential incorporation of arachidonic acid into the plasma lipids is further supported by the observation that the rise in arachidonic acid in the cholesterol ester and phospholipid fractions was almost exactly counter-balanced by the fall in linoleic acid. In conclusion, the present study demonstrated a rise in bleeding time associated with an increased concentration of arachidonic acid and decreased concentration of linoleic acid in plasma lipids, and suggests that the mechanism by which diet modulates haemostatic function may be more complex than currently assumed.

Factors affecting the rate of hydrolysis of starch in legumes

In an attempt to understand the mechanism for the extremely slow rate of digestion and absorption of carbohydrate from legumes, we have examined a number of factors which could potentially affect the process in vitro. The rate of hydrolysis of legume starch in vitro was not affected by the presence of fat (as either butter or an emulsion). However, it was significantly increased in commercially available canned bean preparations, suggesting that the high temperatures used in the canning process may alter the availability of starch in legumes. In vitro starch hydrolysis rate was also significantly increased by grinding legumes finely prior to cooking. Finally, the slow rate of digestion and absorption of legume carbohydrate does not appear to be due to viscosity since a) increasing the shaking rate of viscous mixture of either red kidney beans or lentils from 0 to 120 oscillations per minute did not affect the hydrolysis rate, and b) a thick viscous mixture of either of these legumes did not retard the diffusion of free glucose from a dialysis sac into the dialysate.

Optimum effectiveness of intestinal alpha-glucosidase inhibitors: importance of uniform distribution through a meal

A major barrier to the widespread clinical use of an alpha-glucosidase inhibitor such as Acarbose, is the unpleasant gastrointestinal symptoms of carbohydrate malabsorption associated with its use. Acarbose is usually administered as a tablet and eaten with the first mouthful of the meal, making its uniform distribution through the meal unlikely. In the present study, Acarbose was crushed to a powder and mixed through a test meal before it was consumed. Six healthy young men consumed test meals containing 75 g carbohydrate either as whole brown rice or as ground brown rice. When Acarbose was uniformly mixed through a ground rice meal prior to digestion it produced dose-dependent reductions in the postprandial glucose, insulin and GIP responses which were evident at doses as low as 12.5 mg. The responses to whole brown rice were intermediate between those to 12.5 and 25 mg Acarbose in ground brown rice. In tablet form Acarbose was only one quarter as effective in flattening the post prandial glucose and insulin responses as it was in powder form. These results highlight the importance of uniform distribution of Acarbose through a carbohydrate meal in order to achieve maximum effectiveness in delaying digestion and absorption and yet not promoting carbohydrate malabsorption.

Blunted norepinephrine responsiveness to changing energy states in obese subjects

We have previously reported in lean subjects a significant relationship between plasma norepinephrine metabolism and energy state. The present study has examined in six obese men the response in plasma norepinephrine flux to ten day periods of overeating (+ 1000 kcal/m2 above isocaloric requirements) or undereating (400 kcal/d). Despite significant gains or losses in body weight, norepinephrine flux, measured during constant infusions of 3H-l-norepinephrine, failed to change significantly. Measurements of glucose utilization during constant infusions of insulin, showed significant changes with changing energy state, falling with overeating and rising with undereating. Insulin sensitivity was not correlated with plasma norepinephrine metabolism.

Marked improvement in carbohydrate and lipid metabolism in diabetic Australian aborigines after temporary reversion to traditional lifestyle

The rationale for the present study was that temporarily reversing the urbanization process in diabetic Aborigines should improve all aspects of their carbohydrate and lipid metabolism that are linked to insulin resistance. Ten full-blood, diabetic Aborigines from the Mowanjum Community (Derby, Western Australia) agreed to be tested before and after living for 7 wk as hunter-gatherers in their traditional country in north-western Australia. They were middle aged (53.9 +/- 1.8 yr) and overweight (81.9 +/- 3.4 kg), and all lost weight steadily over the 7-wk period (average, 8 kg). A detailed analysis of food intake over 2 wk revealed a low-energy intake (1200 kcal/person/day). Despite the high contribution of animal food to the total energy intake (64%), the diet was low in total fat (13%) due to the very low fat content of wild animals. Oral glucose tolerance tests (75 g glucose) were conducted in the urban setting and repeated at the end of 7 wk of traditional lifestyle. The marked improvement in glucose was due to both a fall in fasting glucose (11.6 +/- 1.2 mM before, 6.6 +/- 0.8 mM after) and an improvement in postprandial glucose clearance (incremental area under the glucose curve: 15.0 +/- 1.2 mmol/L/h before, 11.7 +/- 1.2 mmol/L/h after). Fasting plasma insulin concentration fell (23 +/- 2 mU/L before, 12 +/- 1 mU/L after) and the insulin response to glucose improved (incremental area under the insulin curve: 61 +/- 18 mU/L/h before, 104 +/- 21 mU/L/h after). The marked fall in fasting plasma triglycerides (4.0 +/- 0.5 mM before, 1.2 +/- 0.1 mM after) was due largely to the fall in VLDL triglyceride concentration (2.31 +/- 0.31 mM before, 0.20 +/- 0.03 mM after.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of co-ingestion of fat on the metabolic responses to slowly and rapidly absorbed carbohydrates

The present study examined the acute effects of co-ingestion of fat (37.5 g) on the post-prandial metabolic responses to 75 g of carbohydrate which was either slowly absorbed (lentils) or rapidly absorbed (potatoes). Co-ingestion of fat resulted in a significant flattening of the post-prandial glucose curves, the effect being more pronounced for the rapidly absorbed potatoes. This was probably due to delayed gastric emptying. However, the post-prandial insulin responses to either carbohydrate were not significantly reduced by fat, suggesting that the insulin response to a given glucose concentration was potentiated in the presence of fat. The gastric inhibitory polypeptide (GIP) responses to both carbohydrates were greatly increased in the presence of fat. To investigate further the possible roles of GIP in the entero-insular axis, a 5-g bolus of glucose was injected intravenously 1 h after lentils +/- fat. This was sufficient to raise the glucose levels above the threshold reported for GIP to potentiate insulin secretion. However, despite the large differences in circulating GIP levels, the insulin response to glucose was not affected by the presence of fat. These results suggest that (1) the rate of absorption of carbohydrate is a major determinant of post-prandial metabolic responses even in the presence of fat, (2) fat-stimulated GIP secretion does not potentiate glucose-induced insulin secretion, and (3) the potentiation of the insulin response to glucose when carbohydrate is co-ingested with fat is consistent with the well-documented insulin resistance associated with high fat diets.

Elevated levels of arachidonic acid in fish from northern Australian coastal waters

The fatty acid composition of 10 species of fish caught off the northwest coast of Australia (latitude 17 degrees S) was examined. All species contained high levels of omega 6 fatty acids (9.6-23.1% of total fatty acids) with arachidonic acid being the major omega 6 fatty acid (5.9-14.8% of fatty acids). Docosatetraenoic and docosapentaenoic acids of the omega 6 series accounted for 3-8% of the total fatty acids. The ratio of omega 6 to omega 3 fatty acids in these fish varied from 0.38 to 0.93, compared with an average ratio of 0.16 for fish from the northern hemisphere (latitude greater than 30 degrees N). The present data and figures from the literature indicate that the marine food chain in the southern hemisphere contains significant quantities of omega 6 fatty acids.

The rate of starch hydrolysis in vitro does not predict the metabolic responses to legumes in vivo

The aim of this study was to determine whether legumes in a physical form which is rapidly digested in vitro give rise to proportionately greater metabolic responses in vivo than legumes which are slowly digested in vitro. Samples of cooked whole and ground lentils were incubated in vitro with pancreatic amylase for 30 min and the percentage starch hydrolysis determined. Grinding the lentils before cooking resulted in a 5-fold increase in the rate of starch hydrolysis (whole lentils 12.1%, ground lentils 60.9%). For the in vivo studies six healthy, young, lean subjects consumed two test meals containing 50 g starch: whole lentils and lentils that had been ground finely before cooking. Postprandial glucose and insulin responses were measured over 4 h. Peak glucose and insulin responses occurred 60 min postprandially for the whole lentils and 30 min postprandially for ground lentils. Although the increase in plasma glucose after ground lentils (1.6 mM) was significantly higher (p less than 0.025) than that after whole lentils (0.9 mM), there was no difference in the magnitude of the insulin responses. These results indicate that, unlike for cereals, the rate of intestinal starch hydrolysis is not the major factor determining the metabolic responses to legumes. By virtue of their low postprandial glucose and insulin responses, irrespective of their physical form and digestibility, legumes would appear to be ideal for inclusion in the diet of diabetics.