Effect of acute lactulose administration on serum acetate levels in cirrhosis

Lactulose has been used successfully in the treatment of portal-systemic encephalopathy but its exact mechanism of action is not known. The aim of this study was to observe the systemic effects of the colonic fermentation of an acute lactulose dose in cirrhotics and normal subjects. Six cirrhotic patients and 6 normal subjects were placed on 2 identical 2-d metabolic diets, 1 of which was supplemented with lactulose (1 g/100 kcals to a maximum of 28 g/d). Lactulose increased colonic fermentation in cirrhotic and normal subjects as evidenced by higher breath hydrogen and serum acetate levels. The increase in serum acetate levels after lactulose compared to control was similar in cirrhotic compared to normal subjects. However, the mean serum acetate concentration in the cirrhotics was significantly greater than that in the control subjects (p = 0.039), indicating increased endogenous production, or decreased peripheral utilization of acetate by the cirrhotic liver, or both. No change was observed in blood ammonia, glucose, insulin, or free fatty acid levels with lactulose.

Determinants of diet glycemic index calculated retrospectively from diet records of 342 individuals with non-insulin-dependent diabetes mellitus

Controlled trials have shown that a diet with a low glycemic index improves blood glucose and lipid control in patients with diabetes. To study the distribution and determinants of diet glycemic index, we obtained two 3-d diet records from 342 free-living subjects with non-insulin-dependent diabetes. Mean +/- SD 24-h intakes were as follows: energy, 7170 +/- 1890 kJ; fat, 33.6 +/- 6.5% of energy; protein, 20.1 +/- 3.2% of energy; available carbohydrate, 45.3 +/- 7.2% of energy; and dietary fiber, 17.2 +/- 6.4 g. Diet glycemic index values (85.4 +/- 4.55, range, 70-97.8) were normally distributed. Diet glycemic index was inversely associated with intake of simple sugars, whether expressed in grams (r = -0.426), percent of energy (r = -0.446), or percent of carbohydrate (r = -0.453, P < 0.001). By step-wise-multiple-linear regression, grams carbohydrate and percent protein were also independently related to diet glycemic index. Differences in diet glycemic index between men and women, and between subjects on different types of diabetes therapy were explained by differences in intake of simple sugars.

Method of administration influences the serum cholesterol-lowering effect of psyllium

To determine whether psyllium must be mixed with food to lower serum cholesterol, 18 modestly hypercholesterolemic subjects were studied for three 2-wk periods, in random order, separated by a 2-wk return to a National Cholesterol Education Program Step 2 diet. Compared with values for subjects consuming control wheat-bran cereal (63 g/d), after 2 wk of 54 g psyllium-enriched cereal/d containing 7.3 g psyllium, serum total, LDL, and HDL cholesterol, respectively, were reduced by 8% (6.15 +/- 0.15 vs 6.71 +/- 0.19 mmol/L, P < 0.01), 11% (4.24 +/- 0.15 vs 4.78 +/- 0.19 mmol/L, P < 0.02), and 7% (0.99 +/- 0.05 vs 1.07 +/- 0.05 mmol/L, P < 0.01). When 7.6 g of the same type of psyllium as in the test cereal was taken between meals, serum total (6.50 +/- 0.19 mmol/L), LDL (4.50 +/- 0.21 mmol/L), and HDL (1.06 +/- 0.06 mmol/L) cholesterol were no different from control values, and total cholesterol was greater than after psyllium cereal (P < 0.05). We conclude that psyllium must be mixed with foods to have the maximum effect on serum cholesterol.

Psyllium reduces blood lipids in men and women with hyperlipidemia

To see if a modest amount of soluble fiber reduced blood lipids in subjects with hyperlipidemia who were on a low-fat diet, 42 subjects (21 men, 21 women) consuming an American Heart Association step 2 diet took two servings of breakfast cereal daily for two 2-week periods in a randomized crossover trial. There were two types of test cereals, each providing 6.7 g psyllium fiber daily, and two types of wheat bran control cereals, matched for available carbohydrate and total fiber. Half the subjects tested each type of cereal, and the results were pooled because the psyllium cereals had similar effects on serum cholesterol levels. Comparing values at the end of 2 weeks, psyllium reduced serum total (6.33 +/- 0.12 mmol/L versus 6.76 +/- 0.12 mmol/L, p < 0.001), low-density lipoprotein (LDL; 4.36 +/- 0.11 mmol/L versus 4.73 +/- 0.12 mmol/L, p < 0.001) and high-density lipoprotein cholesterol levels (HDL; 1.10 +/- 0.05 mmol/L versus 1.14 +/- 0.05 mmol/L, p < 0.05) and the LDL/HDL cholesterol ratio (4.27 +/- 0.20 versus 4.48 +/- 0.22, p < 0.02) with no effect on triglycerides. There was no significant interaction between the effects of treatment and sex for any of the blood lipid variables. Women tended to have greater decreases in total, LDL, and HDL cholesterol levels than men, but the percent decrease in LDL/HDL ratio on psyllium was similar in men, 4.9%, and women, 4.7%. It is concluded that 6.7 g of psyllium fiber daily, with a low-fat diet, reduces serum cholesterol levels in both men and women with hyperlipidemia.

Low glycemic index: lente carbohydrates and physiological effects of altered food frequency

Many factors influence carbohydrate absorption. Slower rates of absorption may have advantages in reducing postprandial glycemia and insulinemia and, in time, reduce serum low-density-lipoprotein (LDL) cholesterol and apolipoprotein B concentrations. Foods high in viscous fiber or antinutrients, or foods that are resistant to gelatinization, show slower rates of digestion and absorption and may be called low glycemic index or lente carbohydrate foods. Specific enzyme inhibitors may also cause lente effects. Certain small-intestinal effects of lente carbohydrate may be mimicked by altering feeding frequency (eg, nibbling vs gorging). Increased meal frequency reduces post-prandial insulin and glucose responses in people with non-insulin-dependent diabetes and in nondiabetic volunteers and lowers serum concentrations of LDL cholesterol and apolipoprotein B. Reduced hepatic cholesterol synthesis has been reported. Increased meal frequency may also slow small-intestinal absorption in the treatment of conditions such as diabetes, hyperlipidemia, and possibly obesity.

Effect of meal frequency on serum amino acids and creatinine clearance in young men

Seven healthy men consumed a liquid formula diet either as 3 meals taken at 0, 4, and 8 hours, or as 72 equal portions taken at 10-minute intervals (sipping). Day-long mean serum amino acids were similar on both treatments. Sipping reduced the fall in serum creatinine levels by more than 50% (p < 0.01), and reduced urine creatinine output and creatinine clearance by 11% (p < 0.05). These results suggest that increased meal frequency warrants investigation as a potentially beneficial maneuver in the dietary management of chronic renal failure.

Response of individual serum free fatty acids to oral and intravenous glucose: relation to adipose tissue composition

The rate of oral glucose delivery determines whether serum total free fatty acids remain low (glucose sipping over 210 min) or rebound 120-180 min after initial suppression (via glucose bolus), but the response of individual serum free fatty acids to glucose ingestion is largely unknown. In this study, we measured the changes over 240 min in the levels of individual serum free and esterified fatty acids after bolus or sipped glucose ingestion and determined the extent to which the changes are related to abdominal subcutaneous adipose tissue composition. In eight healthy volunteers, 74% of the prolonged suppression of total serum free fatty acids resulting from sipping 50 g glucose over 210 min was caused by a decrease in free linoleic and oleic acids, whereas 92% of the rebound in total free fatty acids 240 min after consuming 50 g of glucose as a bolus was caused by increases in free oleic and linoleic acids. Two hundred forty minutes after the oral glucose, slower intravenous clearance of 5 g glucose was directly correlated to higher total serum free fatty acids and free stearic acid and higher oleic but lower linoleic acid in adipose tissue. We conclude that the net response of serum free fatty acids to an oral glucose load is mediated primarily by oleic and linoleic acids in a manner largely unrelated to adipose tissue composition.

Effect on blood lipids of very high intakes of fiber in diets low in saturated fat and cholesterol

BACKGROUND

It is known that soluble fiber in the diet can lower blood lipid levels. It is less certain, however, that eating foods with soluble fiber will further lower blood lipids when the intake of saturated fat and cholesterol has already been reduced to very low levels. Furthermore, the mechanism of the lipid-lowering effect of fiber has not been elucidated.

METHODS

To address these questions, we studied 43 volunteers with hyperlipidemia in a crossover study involving two four-month dietary periods. The two metabolic diets contained foods high in either soluble or insoluble fiber and were separated by a two-month National Cholesterol Education Program Step 2 diet. The metabolic diets were low in saturated fat (< 4 percent of total calories) and cholesterol (< 25 mg per 1000 kcal), high in carbohydrate (> or = 60 percent of total calories), and very high in fiber (> 24 g per 1000 kcal).

RESULTS

Blood lipids fell to their lowest levels by week 4 of both study diets. When the soluble-fiber period was compared with the insoluble-fiber period, the subjects' total, low-density lipoprotein (LDL), and high-density lipoprotein (HDL) cholesterol levels were found to be lower by a mean (+/- SE) of 4.9 +/- 0.9 percent (P < 0.001), 4.8 +/- 1.3 percent (P < 0.001), and 3.4 +/- 1.3 percent (P = 0.014), respectively. In contrast, the ratio of total to HDL cholesterol was not significantly different during the two dietary periods. The loss of fecal bile acids was 83 +/- 14 percent greater during the soluble-fiber period than during the insoluble-fiber period (P < 0.001) and was related to the differences in total and LDL cholesterol and apolipoprotein B levels (r = 0.42, P = 0.005; r = 0.49, P < 0.001; and r = 0.33, P = 0.035, respectively). The difference in serum cholesterol levels between the two dietary periods was greater among the men (7.5 +/- 1.2 percent, P < 0.001) than among the women (3.4 +/- 1.2 percent, P = 0.008).

CONCLUSIONS

Very high intakes of foods rich in soluble fiber lower blood cholesterol levels even when the main dietary modifiers of blood lipids--namely, saturated fat and cholesterol--are greatly reduced.

Interaction between methane-producing status and diet on serum acetate concentration in humans

About half the population excretes methane in the breath. To see if methane producing status influenced serum acetate, we studied six methane producers and six nonproducers on three separate days. For 36 h they ate a polysaccharide-free diet alone, or with 20 g of unabsorbed sugar lactulose, or 20 g of fermentable fiber, guar, in random order. The mean fasting serum acetate concentration on the three test days in producers was higher than in nonproducers, 84 +/- 5 vs. 69 +/- 5 mumol/L (P < 0.05). Compared to the control diet, both lactulose and guar raised serum acetate concentration significantly in both groups of subjects. However, there was a significant interaction between methane producing status and diet. After lactulose consumption, postprandial serum acetate was similar in both groups of subjects, but guar consumption had a significantly greater effect in producers than nonproducers (98 +/- 8 vs. 73 +/- 5 mumol/L; P < 0.05). We conclude that methane producing status may influence serum acetate concentrations in humans, depending upon the type of fermentable carbohydrate in the diet.

High alpha-linolenic acid flaxseed (Linum usitatissimum): some nutritional properties in humans

Although high alpha-linolenic acid flaxseed (Linum usitatissimum) is one of the richest dietary sources of alpha-linolenic acid and is also a good source of soluble fibre mucilage, it is relatively unstudied in human nutrition. Healthy female volunteers consumed 50 g ground, raw flaxseed/d for 4 weeks which provided 12-13% of energy intake (24-25 g/100 g total fat). Flaxseed raised alpha-linolenic acid and long-chain n-3 fatty acids in both plasma and erythrocyte lipids, as well as raising urinary thiocyanate excretion 2.2-fold. Flaxseed also lowered serum total cholesterol by 9% and low-density-lipoprotein-cholesterol by 18%. Changes in plasma alpha-linolenic acid were equivalent when 12 g alpha-linolenic acid/d was provided as raw flaxseed flour (50 g/d) or flaxseed oil (20 g/d) suggesting high bioavailability of alpha-linolenic acid from ground flaxseed. Test meals containing 50 g carbohydrate from flaxseed or 25 g flaxseed mucilage each significantly decreased postprandial blood glucose responses by 27%. Malondialdehyde levels in muffins containing 15 g flaxseed oil or flour/kg were similar to those in wheat-flour muffins. Cyanogenic glycosides (linamarin, linustatin, neolinustatin) were highest in extracted flaxseed mucilage but were not detected in baked muffins containing 150 g flaxseed/kg. We conclude that up to 50 g high-alpha-linolenic acid flaxseed/d is palatable, safe and may be nutritionally beneficial in humans by raising n-3 fatty acids in plasma and erythrocytes and by decreasing postprandial glucose responses.

Evidence for colonic conservation of malabsorbed carbohydrate in short bowel syndrome

The purpose of this study was to determine whether energy from malabsorbed carbohydrate could be conserved through colonic fermentation in short bowel syndrome. Seven patients with short bowel anastomosed to the remaining colon and five patients with short bowel without a colon were selected from the home total parenteral nutrition (TPN) program. Six normal volunteers also were studied. After an overnight fast, subjects consumed a 50-g carbohydrate bread meal and were studied hourly over the next 6 h. Carbohydrate malabsorption, estimated by lactulose breath hydrogen testing, was 48 +/- 13% in short bowel patients. After the bread meal, breath hydrogen was higher in short bowels with colons (69 +/- 20 ppm) than in either short bowels without colons (11 +/- 7 ppm) or normal subjects (10 +/- 3 ppm) (p less than 0.01). Blood acetate levels also were higher in short bowels with colons than in those without colons, reaching a peak of 167 +/- 27 mumol/L at 4 h (p less than 0.05). We conclude that in patients with a short bowel and a colon, malabsorbed carbohydrate is fermented and there is a rise in blood acetate, suggesting that the colon has a role in salvaging malabsorbed carbohydrate as a source of energy through carbohydrate fermentation.

Beneficial effect of a low glycaemic index diet in type 2 diabetes

Low glycaemic index foods produce low blood glucose and insulin responses in normal subjects, and improve blood glucose control in Type 1 and well-controlled Type 2 diabetic patients. We studied the effects of a low glycaemic index diet in 15 Type 2 diabetic patients with a mean fasting blood glucose of 9.5 mmol l-1 using a randomized, crossover design. Patients were given pre-weighed diets (59% energy as carbohydrate, 21% fat, and 24 g 1000-kcal-1 dietary fibre) for two 2-week periods, with a diet glycaemic index of 60 during one period and 87 during the other. On the low glycaemic index diet, the blood glucose response after a representative breakfast was 29% less than on the high glycaemic index diet (874 +/- 108 (+/- SE) vs 204 +/- 112 mmol min l-1; p less than 0.001), the percentage reduction being almost identical to the 28% difference predicted from the meal glycaemic index values. After the 2-week low glycaemic index diet, fasting serum fructosamine and cholesterol levels were significantly less than after the high glycaemic index diet (3.17 +/- 0.12 vs 3.28 +/- 0.16 mmol l-1, p less than 0.05, and 5.5 +/- 0.4 vs 5.9 +/- 0.5 mmol l-1, p less than 0.02, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Beneficial effect of low-glycemic index diet in overweight NIDDM subjects

OBJECTIVE

To determine whether low-glycemic index (GI) diets have clinical utility in overweight patients with non-insulin-dependent diabetes mellitus (NIDDM).

RESEARCH DESIGN AND METHODS

Six patients with NIDDM were studied on both high- and low-GI diets of 6-wk duration with metabolic diets with a randomized crossover design. Both diets were of similar composition (57% carbohydrate, 23% fat, and 34 g/day dietary fiber), but the low-GI diet had a GI of 58 compared with 86 for the high-GI diet.

RESULTS

Small and similar amounts of weight were lost on both diets: 2.5 kg on high-GI diet and 1.8 kg on low-GI diet. On the low-GI diet, the mean level of serum fructosamine, as an index of overall blood glucose control, was lower than on the high-GI diet by 8% (P less than 0.05), and total serum cholesterol was lower by 7% (P less than 0.01).

CONCLUSIONS

In overweight patients with NIDDM, reducing diet GI improves overall blood glucose and lipid control.

Guar, but not psyllium, increases breath methane and serum acetate concentrations in human subjects

Guar and psyllium are fermented by human fecal bacteria in vitro. To see if they were fermented in vivo, eight subjects were studied over 3 separate days, in random order, while eating a polysaccharide-free diet. Twenty grams guar or psyllium, taken at breakfast, had no effect on breath hydrogen levels over 14 h. Mean breath methane and serum acetate concentrations after guar, 37 +/- 1 ppm and 93 +/- 6 mumol/L, respectively, were significantly greater than after control, 20 +/- 2 ppm (P less than 0.05) and 62 +/- 4 mumol/L (P less than 0.01), and psyllium, 20 +/- 2 ppm (P less than 0.05) and 78 +/- 6 mumol/L (P less than 0.05). Serum acetate increased after guar (area under curve 193 +/- 56 mumol.h/L; P less than 0.02) but decreased after psyllium and control. We conclude that guar is fermented in the human colon, producing rises in breath methane and serum acetate but not hydrogen. Although psyllium had no effect on hydrogen, methane, or acetate, this does not prove that it is not fermented.

Effect of guar, pectin, psyllium, soy polysaccharide, and cellulose on breath hydrogen and methane in healthy subjects

Different types of dietary fiber are fermented to various extents in vitro, but little is known about the effects of fiber on breath hydrogen and methane levels in vivo. Therefore, we studied the effects on breath hydrogen and methane of 15 g of guar, pectin, psyllium, soy polysaccharide, or cellulose in eight healthy subjects over a 12-h period. None of the fibers had a significant effect on breath hydrogen or methane concentrations, compared with the control (fasting). The four methane producers had lower breath hydrogen levels than the nonproducers 1 h after 15 g of lactulose (3 +/- 1 vs. 42 +/- 9, p less than 0.005) and 5-12 h after the different fibers (3.3 vs. 4.8 ppm; pooled SEM = 0.8; p less than 0.025). When the methane responses of the methane producers were expressed as increments relative to the control, there were small differences between treatments, with guar producing a larger response, 8.2 +/- 3.3 ppm, than cellulose, -2.9 +/- 2.3 ppm (p less than 0.05). The incremental methane responses of the different fibers in vivo were related to the previously reported production of propionic acid (r = 0.94, n = 5, p less than 0.02) and methane (r = 0.93, n = 4, NS) from in vitro fermentation of the same fibers. We conclude that methane producers have lower breath hydrogen levels than nonproducers. Purified fermentable and nonfermentable dietary fibers have no effect on breath hydrogen levels over 12 h in subjects previously consuming a normal diet. However, fermentable fibers may produce small increases in breath methane in methane-producing subjects.

Metabolic advantages of spreading the nutrient load: effects of increased meal frequency in non-insulin-dependent diabetes

The acute effect of increasing meal frequency as a model of slow absorption was studied for 1 d in 11 patients with non-insulin-dependent diabetes. On 1 d they took 13 snacks (the nibbling diet) and on another day the same diet was taken as three meals and one snack (the three-meal diet). The nibbling diet reduced mean blood glucose, serum insulin, and C peptide concentrations over the 9.5 h of observation and 24-h urinary C peptide output by 12.7 +/- 3.7% (mean +/- SE) (P = 0.0062), 20.1 +/- 5.8% (P = 0.0108), 9.2 +/- 2.6% (P = 0.0073), and 20.37 +/- 8.12% (P = 0.039), respectively, compared with the three-meal diet. Serum triglyceride concentrations were lower by 8.5 +/- 3.2% (P = 0.037). Despite lower insulin concentrations on the nibbling diet, the concentrations of free fatty acids, 3-hydroxybutyrate, and the insulin-sensitive branched-chain amino acids responded similarly on both treatments. Metabolic benefits seen with increased meal frequency may explain the success of similar agents that prolong absorption, including fiber and enzyme inhibitors.

The glycemic index: methodology and clinical implications

There is controversy regarding the clinical utility of classifying foods according to their glycemic responses by using the glycemic index (GI). Part of the controversy is due to methodologic variables that can markedly affect the interpretation of glycemic responses and the GI values obtained. Recent studies support the clinical utility of the GI. Within limits determined by the expected GI difference and by the day-to-day variation of glycemic responses, the GI predicts the ranking of the glycemic potential of different meals in individual subjects. In long-term trials, low-GI diets result in modest improvements in overall blood glucose control in patients with insulin-dependent and non-insulin-dependent diabetes. Of perhaps greater therapeutic importance is the ability of low-GI diets to reduce insulin secretion and lower blood lipid concentrations in patients with hypertriglyceridemia.

Effect of method of administration of psyllium on glycemic response and carbohydrate digestibility

To determine whether there was any advantage to taking a soluble fiber supplement separate from food, as opposed to incorporated into a food, we used psyllium as a model, either taken in water just before a flaked bran cereal test meal, sprinkled on top of the cereal, or actually incorporated into the flake. In normal subjects, psyllium reduced the glycemic response when sprinkled onto or incorporated into the cereal, but not when taken before the cereal. Varying the amount of psyllium incorporated into the cereal from 0 to 20% resulted in a linear dose-dependent reduction of the glycemic index (GI) (GI = 101 -2.2 x % psyllium; r = 0.950; p less than 0.002). In subjects with diabetes, the blood-glucose-lowering effect of the psyllium flake cereal was similar to that in normal subjects. Mixing psyllium with the cereal or incorporating it into the cereal reduced the rate of digestion of bran flakes in vitro but was not associated with increased breath hydrogen levels in vivo as an index of rapid colonic fermentation. The bran flakes with psyllium incorporated was rated as no less palatable than the bran flakes cereal alone, and significantly more palatable (p less than 0.05) than taking psyllium in water before the cereal or sprinkling psyllium onto the cereal. These studies confirm earlier reports that viscous fibers must be intimately mixed with the food to have the effect of reducing blood glucose responses, and that the mechanism of action relates to a reduced rate of digestion rather than carbohydrate malabsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Specific types of colonic fermentation may raise low-density-lipoprotein-cholesterol concentrations

To assess the effects of increased colonic fermentation on serum lipids, eight healthy volunteers were placed on two identical 2-wk metabolic diets, one of which was supplemented with lactulose (18-25 g/d). Lactulose raised day-long concentrations of breath hydrogen and serum glutamine as indicators of increased colonic fermentation by 78 +/- 13% (P less than 0.001) and 24.7 +/- 9.5% (P less than 0.05), respectively). Unexpectedly, however, fasting serum total and low-density-lipoprotein cholesterol and apolipoprotein B concentrations were higher at 2 wk by 8.9 +/- 1.5% (P less than 0.001), 10.9 +/- 2.2% (P less than 0.005), and 18.9 +/- 5.9% (P less than 0.02), respectively, compared with the control diet. With lactulose, mean free fatty acid concentrations were reduced over the day by 19.5 +/- 5.9% (P less than 0.02), with no change in mean day-long blood glucose, serum insulin, or C-peptide concentrations. We conclude that certain rapidly fermented substrates may raise rather than lower serum lipids, possibly through increasing the amount of acetate absorbed from the colon.

Is colonic fermentation minimized by increasing meal frequency?

It has been suggested that, although increasing meal frequency has metabolic advantages in terms of carbohydrate and lipid metabolism, the efficiency of small intestinal absorption may be enhanced, thus reducing the extent of colonic fermentation. Since this may be undesirable, we have tested whether increasing meal frequency reduces the amount of carbohydrate fermented into the colon. Accordingly, seven healthy male volunteers took, in random order, two identical 2-week metabolic diets divided into either seventeen or three meals daily. On day 13 of each period measurements were made throughout the day of breath H2 and serum acetate, as markers of colonic fermentation. Mean levels of both breath H2 and acetate were similar on both diets, being lower on nibbling by 3.2 +/- 0.8 ppm and 25 +/- 9 mumols/l respectively (not significant). This study failed to demonstrate an effect of more efficient carbohydrate absorption with increased meal frequency.