Metabolic effects of fructose and glucose: implications for food intake

Differential effects of fructose and glucose preloads on carbohydrate metabolism and later food intake were examined in both lean and obese subjects. In study 1, a preload of either 50 g of fructose or glucose was administered in solution, and food intake at a buffet lunch presented 2.25 h after preload was assessed. Significant differences in caloric intake were observed between load conditions with the fructose group consuming fewer calories than the glucose group. Obese subjects demonstrated significantly greater insulin responses to the preload compared with lean subjects, and insulin levels of obese subjects at 15, 30, and 45 min after preload were found to correlate significantly with amount consumed. Incorporation of fructose or glucose into a mixed meal format in study 2 revealed no differences in subsequent caloric intake as a function of either type of preload or percent overweight. Differing insulin levels are discussed as a possible mechanism for differential food intake.     

Comparative effects of fructose, aspartame, glucose, and water preloads on calorie and macronutrient intake

Using a within-subjects design, we gave over-weight and normal-weight subjects a 500-mL drink of fructose, glucose, or aspartame diluted in lemon-flavored water or plain water in a randomized fashion at about weekly intervals. Food intake was assessed at a buffet lunch that began 38 min after the preload was completed. Blood was drawn throughout and assayed for concentrations of glucose, insulin, glucagon, and free fatty acid. When subjects drank the fructose preload, they subsequently ate fewer overall calories and fewer grams of fat than when they drank any of the other preloads. The aspartame load did not stimulate intake beyond the plain-water control. The effects of the oxidation of fructose as a possible mechanism for the reduction in food intake is discussed. The effects of insulin in stimulating intake are also discussed.     

Effects of fructose and glucose preloads on subsequent food intake

To determine how the nutrient content of one eating event might affect amount consumed at the next, we evaluated whether equicaloric fructose and glucose preloads differentially influence subsequent food intake. Subjects consumed 50 g of glucose or fructose in 500 ml of water or water alone and were given a "buffet" containing a variety of foods two and a quarter hours later. Subjects in glucose conditions ate, on the average, 252 X 7 calories more than subjects in the water condition, who in turn ate, on the average, 225 X 9 calories more than subjects in the fructose condition. The fructose and glucose preloads did not differentially affect the amount eaten of different types of nutrients (carbohydrate, fat and protein). This study, employing several sensory and cognitive controls, suggests that type of nutrient ingested, in and of itself, plays a role in determining subsequent intake for humans. The data are discussed in terms of possible physiological mechanisms that might account for these effects.     

Sex and cognitive dietary restraint influence cholecystokinin release and satiety in response to preloads varying in fatty acid composition and content

The aim of the study was to evaluate the effect of preloads differing in fatty acid composition, content, and delivery form on acute behavioral, subjective, and biological outcomes of satiety. Four energy- and volume-matched preloads were tested in normal weight men and women (n = 12 and 13, respectively), using a random, crossover design. Preloads were semisolid shakes differing in fat source [walnut or safflower (SAFF)], delivery [ground walnuts (WNT) or walnut oil (WOL)] or content [39% fat energy (SAFF, WNT, WOL) or 4% low-fat control (LFC)]. Blood was collected and subjective satiety assessed at 0 (fasting), 15, 30, and 45 min after preload consumption. Lunch (test meal) was provided thereafter. Energy intake at lunch was not affected by preload; however, subjects selected more carbohydrate, fiber-rich foods at the test meal lunch after walnut preloads than after LFC or SAFF preloads. Compared with the LFC preload, appetite satisfaction was significantly greater after SAFF and WNT, but not after WOL. Women were hungrier after SAFF than after WOL, whereas men were less hungry after SAFF and LFC than after WOL or WNT. Plasma cholecystokinin (CCK) concentrations reflected preload fat content and availability, particularly among men; CCK was higher after WOL and SAFF preloads than after LFC or WNT preloads. Plasma insulin was higher after LFC and SAFF preloads, corresponding to hunger suppression in men. Dietary restraint was associated with a blunted CCK response to preloads, whereas insulin was not affected by restraint. The results indicate that test meal energy intake after preloads containing approximately 40% walnut or safflower fat or 4% fat did not differ; however, walnut consumption may promote food patterns consistent with consuming diets higher in fiber.     

Role of protein and carbohydrate sources on acute appetite responses in lean and overweight men

Dietary protein induces greater satiety compared with carbohydrate in lean subjects, which may involve appetite-regulatory gut hormones. Little is known about the duration of effect, influence of protein and carbohydrate source and relevance to non-lean individuals. We compared the effect of various dietary proteins and carbohydrates on post-prandial appetite ratings, ad libitum energy intake (EI) and appetite hormones in lean and overweight men. Three randomised double-blinded cross-over studies examined appetite response (appetite ratings, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin) to liquid preloads over three to four hours followed by a buffet meal to assess ad libitum EI. The 1-MJ preloads contained ∼55 g of protein (whey, casein, soy and gluten), carbohydrate (glucose, lactose and fructose) or combined whey/fructose. EI was 10% higher following glucose preloads compared with protein preloads, observed at three hours but not four hours. Protein ingestion was followed by prolonged elevation of cholecystokinin and GLP-1 (two hours) and suppression of ghrelin (three to four hours) compared with glucose and independent of protein type. Replacing some whey with fructose attenuated the effect of protein on these hormones. Treatment effects on EI and appetite hormones were independent of bodyweight status, despite higher GLP-1 and lower ghrelin in overweight subjects. Protein-rich liquid preloads reduce EI over three hours in overweight men compared with glucose. These findings suggest a potential application for protein-rich drinks and/or foods to facilitate reduced EI. Future studies should explore additional dietary manipulations that may enhance this relationship, and confirm these effects within the context of energy-restricted dietary patterns.     

Day-to-day consistency in amount and source of carbohydrate intake associated with improved blood glucose control in type 1 diabetes.

OBJECTIVE: To determine if a relationship exists between blood glucose control and variability in nutrient intake from day-to-day in subjects with type 1 diabetes. METHODS: Two three-day diet records and one measurement of glycated hemoglobin (HbA1c) were obtained from 272 subjects with type 1 diabetes treated with a mixture of regular and NPH insulins before breakfast and supper and using a standardized algorithm to adjust insulin dose according to the results of self-monitoring of blood glucose two to four times daily. Day-to-day variation in nutrient intake was expressed as the coefficient of variation (CV = SDx100/mean). RESULTS: Nutrient intakes in the study population (mean +/- SD) were energy 8.35+/-2.43 MJ, fat 81+/-30 g, protein 94+/-28 g, carbohydrate 227+/-68 g, starch 126+/-38 g and dietary fiber 20+/-6 g with diet glycemic index being 84.2+/-7.4. Neither energy, nutrient intakes nor insulin dose was significantly related to HbA1c. Day-to-day variation of carbohydrate (p = 0.0097) and starch (p = 0.0016) intakes and diet glycemic index (p = 0.033) was positively related to HbA1c, and the associations remained significant when adjusted for age, sex, duration of diabetes and BMI. Day-to-day variation in energy, protein or fat intakes was not related to HbA1c. CONCLUSIONS: Consistency in the amount and source of carbohydrate intake from day-to-day is associated with improved blood glucose control in people with type 1 diabetes, a result which supports continued educational efforts to achieve adherence to a diabetes diet plan. This conclusion may not apply to people on intensified insulin therapy who adjust their insulin dose based on their actual carbohydrate intake at each meal.     

Protein source, quantity, and time of consumption determine the effect of proteins on short-term food intake in young men

The objective of these 4 studies was to describe the effects of protein source, time of consumption, quantity, and composition of protein preloads on food intake in young men. Young men were fed isolates of whey, soy protein, or egg albumen in sweet and flavored beverages (400 mL) and provided a pizza meal 1-2 h later. Compared with the water control, preloads (45-50 g) of whey and soy protein, but not egg albumen, suppressed food intake at a pizza meal consumed 1 h later. Meal energy intake after egg albumen and soy, but not after control or whey treatments, was greater when the treatments were given in the late morning (1100 h) compared with earlier (0830-0910 h). Suppression of food intake after whey protein, consumed as either the intact protein or as peptides, extended to 2 h. Altering the composition of the soy preload (50 g) by reducing the soy protein content to 25 g and by adding 25 g of either glucose or amylose led to a loss in suppression of food intake by the preload. Egg albumen, in contrast to whey and soy preloads, increased cumulative energy intake (sum of the energy content of the preload plus that in the test meal) relative to the control. We conclude that protein source, time of consumption, quantity, and composition are all factors determining the effect of protein preloads on short-term food intake in young men.     

Cholecystokinin-A receptors are involved in food intake suppression in rats after intake of all fats and carbohydrates tested

The hypothesis of these studies was that all fats and carbohydrates suppress food intake, at least in part, via cholecystokinin-A receptors (CCKAR). Fat (coconut oil, beef tallow, olive and safflower oil) and carbohydrate (cornstarch, sucrose, glucose and fructose) preloads were given intragastrically (1 g/4 mL) 30 min before feeding. Devazepide (0.25 mg/kg), a CCKAR antagonist, was given intraperitoneally at 60 or 30 min before or with each of the macronutrient preloads. Devazepide reversed food intake suppression caused by all fat and carbohydrate sources, but the effect was not consistently related to the time of devazepide administration or to any specific feeding interval. Among the fats, coconut and olive oil were most responsive to devazepide. The effect of all carbohydrates on food intake was decreased by devazepide. We conclude that CCKAR play a role in food intake suppression caused by all fats and carbohydrates, but their role is dependent upon the composition of the fat or carbohydrate.     

Thermogenesis in men and women induced by fructose vs glucose added to a meal

Energy expenditure (EE) was measured by indirect calorimetry in 20 subjects (10 men and 10 women) for 30 min before and 6 h after the ingestion of a mixed meal containing 20% protein, 33% fat, and either 75 g glucose or 75 g fructose as carbohydrate source (47%). Diet-induced thermogenesis (DIT) and the rate of carbohydrate oxidation were significantly greater with fructose (12.4 +/- 0.6% and 54.8 +/- 2.1 g/6 h, respectively) than with glucose (10.7 +/- 0.7%, p less than 0.01, and 48.3 +/- 2.4 g/6 h, p less than 0.01, respectively). The DIT of male (12.1 +/- 1% and 13.9 +/- 0.8% with glucose and fructose, respectively) was greater than that of female subjects (9.2 +/- 0.7%, p less than 0.05, and 11.0 +/- 0.7%, p less than 0.05, respectively). In contrast to the glucose meal, negligible changes in plasma levels of glucose and insulin were observed with the fructose meal but plasma levels of lactate increased more with fructose than with glucose (peak values: 3.3 +/- 0.6 vs 1.5 +/- 0.1 mmol/L, respectively). When fructose provides the only carbohydrate source of a mixed meal, it induces a larger increase in carbohydrate oxidation and thermogenesis than when glucose is the carbohydrate source.     

Dietary fructose but not starch is responsible for hyperlipidemia associated with copper deficiency in rats: effect of high-fat diet

OBJECTIVE: To test the hypothesis that copper deficiency in rats may be hyperlipidemic only when the diets consumed contain nutrients which contribute to blood lipids such as fructose and high fat. METHODS: Weanling male Sprague Dawley rats were fed diets which contained either starch or fructose as their sole carbohydrate source. The diets were either inadequate (0.6 microg Cu/g) or adequate (6.0 microg Cu/g) in copper and contained either high (300 g/kg) or low (60 g/kg) fat. At the end of the 4th week the rats were killed. Livers were analyzed for copper content. Plasma was analyzed for cholesterol and triglyceride concentrations. RESULTS: High-fat diet did not increase blood lipids in rats fed a copper-deficient diet containing starch. In contrast, the combination of high-fat diet with fructose increased blood triglycerides and fructose with copper deficiency resulted in a significant increases in blood cholesterol. CONCLUSIONS: Hyperlipidemia of copper deficiency in rats is dependent on synergistic effects between dietary fructose and copper deficiency and fructose and amount of dietary fat. Hyperlipidemia does not develop if starch is the main source of dietary carbohydrate in a copper-deficient diet even if a high-fat diet is fed.     

Differential effect of protein and fat ingestion on blood glucose responses to high- and low-glycemic-index carbohydrates in noninsulin-dependent diabetic subjects

Six noninsulin-dependent diabetic subjects received meals containing 25 g carbohydrate either as potato or as spaghetti. The meals were repeated with the addition of 25 g protein and with 25 g protein and 25 g fat. Blood glucose and insulin responses were measured for 4 h after the test meal. When carbohydrate was given alone, the blood glucose and serum insulin increments were higher for the potato meal. The addition of protein increased the insulin responses to both carbohydrates and slightly reduced the glycemic response to mashed potato (F = 2.04, p less than 0.05). The further addition of fat reduced the glycemic response to mashed potato (F = 14.63, p less than 0.001) without any change in the blood glucose response to spaghetti (F = 0.94, NS). The different responses to coingestion of protein and fat reduced the difference between the glycemic responses to the two carbohydrates.     

Reassessing the effects of simple carbohydrates on the serum triglyceride responses to fat meals

The effects of glucose, sucrose, and fructose ingestion on the serum triglyceride responses to meals containing 40 g fat were studied in 21 normolipidemic, nonobese medical students (9 men, 12 women). Mean postprandial lipemia was not significantly lower after meals containing 50 g glucose and 40 g fat than after meals containing 40 g fat alone (2.11 vs 2.42 mmol.L-1.7 h-1, p greater than 0.45) despite a substantial increase in plasma insulin concentrations after the glucose-containing meal. Ingestion of 50 g fructose and 40 g fat (4.23 mmol.L-1.7 h-1, p less than 0.0001) and 100 g sucrose and 40 g fat (3.77 mmol.L-1.7 h-1, p less than 0.001) resulted in significantly greater lipemia than did the ingestion of fat alone. These findings suggest that the ingestion of insulinogenic carbohydrates does not reduce postprandial lipemia in normolipidemic subjects and that the ingestion of fructose and fructose-containing carbohydrates may augment the postprandial lipemia induced by a fat-containing meal.     

Refeeding of rats fasted 36 hours with five different carbohydrates and with malt extract: differential effects on glycogen deposition in liver and muscle, on plasma insulin and on plasma triglyceride levels

Rats fasted for 36 h were refed for 1, 2, 4 or 6 h with a diet containing 12 g/100 g casein, 2 g/100 g NaCl and 86 g/100 g glucose, fructose, maltose, sucrose, starch or malt extract. Blood glucose reached constant levels after 1 to 2 h of refeeding. The increase in plasma insulin paralleled food intake rather than the increase in blood glucose. Plasma triglycerides decreased upon refeeding starch, maltose and malt extract and increased with sucrose and fructose. Recovery of absorbed carbohydrates was highest in rats refed malt extract. Glycogen deposition in muscle was highest in rats fed malt extract and lowest in those fed fructose; sucrose yielded intermediate values. Glucose, maltose and starch resulted in muscle glycogen depositions slightly lower than those obtained with malt extract. In liver, sucrose and fructose were better precursors for glycogen than glucose and starch. With carbohydrates containing only glucose units, much more glycogen was found to be deposited in total muscle than in liver. This asymmetry was less notable or even was reversed with sucrose and fructose. Glycogen deposition in muscle and in liver is influenced by the carbohydrate used for refeeding, and muscle, rather than liver, is the main glycogen storing tissue.     

Effect of fat sources on satiety

OBJECTIVE: There are inconsistent reports on the satiety value of different fatty acids. This study compared the appetitive effects of two fat sources rich in monounsaturated fatty acids (peanut oil and canola oil) with a source rich in saturated fatty acids (butter). RESEARCH METHODS AND PROCEDURES: After an overnight fast, lean participants completed a questionnaire eliciting information about hunger, fullness, desire to eat, and prospective consumption. They then consumed one of the preloads (muffins containing 40 g of each fat source or no fat) and 150 mL of water within 15 minutes. Questionnaires were completed again 30, 60, and 120 minutes after preload ingestion. Participants kept dietary records during the subsequent 24 hours. RESULTS: Canola and peanut oil muffins resulted in higher fullness, and butter, canola, and peanut oil muffins resulted in lower hunger ratings 30, 60, and 120 minutes after preload ingestion compared with the fat-free preload. No differences were observed among the fat-containing loads. Although energy intake 24 hours after consumption of the preloads was also comparable on days the three fat-containing loads were consumed, energy consumption after each study session was higher when the fat-free muffins were provided. However, total energy intake, including the calories provided by the preloads, was similar across treatments. DISCUSSION: These data do not support a differential satiety effect of fat sources rich in monounsaturated fatty acids relative to one rich in saturated fatty acids.     

Effects of starch, sucrose, fructose and glucose on chromium absorption and tissue concentrations in obese and lean mice

Forty-eight male genetically obese (OB) mice (C57BL/6J-OB) and 48 lean male littermates were randomly assigned within main plots (OB or lean) to one of eight diets. Diets were low chromium or supplemented with 1 mg chromium as CrCl3 per kg. Starch, sucrose, fructose or glucose comprised 50% of the diet, which met AIN recommendations except for chromium. Experimental diets and deionized water were available ad libitum for 26 d. Mice were fasted 10 h and were intubated 2 h before killing with 15 microCi of 51CrCl3 in a 25% carbohydrate solution (2 mg carbohydrate/g body wt) of either starch, sucrose, glucose or fructose corresponding to the diet previously fed. 51Cr concentrations were significantly higher in the blood, liver, spleen, epididymal fat pad, testes and femur of animals given their carbohydrate load as starch than in animals fed sucrose, fructose or glucose. Carbohydrate had a significant effect on chromium concentrations of testes, spleen, kidney and liver with values generally being higher with the starch diet. Chromium supplementation increased bone and kidney chromium concentrations and heart and muscle glycogen. These data indicate that the source of carbohydrate can alter chromium absorption and retention.     

Urinary chromium excretion and insulinogenic properties of carbohydrates

Eleven male and nine female adult subjects were given one of the following five carbohydrate-drink combinations (per kg body wt) on five mornings separated by greater than or equal to 2 wk: 1) 1.0 g glucose, 2) 0.9 g uncooked cornstarch, 3) 1.0 g glucose followed 20 min later by 1.75 g fructose, 4) 0.9 g uncooked cornstarch followed 20 min later by 1.75 g fructose, and 5) water followed 20 min later by 1.75 g fructose. Glucose plus fructose was the most insulinogenic followed by glucose alone, starch plus fructose, starch alone, and water plus fructose. The urinary losses of chromium followed a similar pattern. Subjects with the highest concentrations of circulating insulin displayed decreased ability to mobilize chromium on the basis of urinary chromium excretion. Therefore, urinary chromium losses are related to the insulinogenic properties of carbohydrates.     

Glycemic responses in insulin-dependent diabetic patients: effect of food composition

This study examined the hypothesis that the glucose component of food and not the total carbohydrate is the major determinant of the glycemic response in patients with insulin-dependent diabetes mellitus. Patients were given glucose alone, fructose alone, glucose + fructose, lactose, and glucose + fat + protein. Fructose given alone increased the blood glucose almost as much as a similar amount of glucose (78% of the glucose-alone area, p less than 0.05). However, the same amount of fructose given with glucose produced no greater glycemic response than did glucose alone (108%). Similarly, galactose contributed only slightly to the glycemic response when given as lactose (122%, p less than 0.01) whereas protein and fat had no additional glycemic effect (101%). To test the above hypothesis in natural foods, patients were fed an amount of bread (high glycemic index) or apple (low glycemic index) that contained 25 g glucose. Both challenges produced glycemic responses very similar to 25 g purified glucose.     

Short-term regulation of food intake in children, young adults and the elderly

OBJECTIVE: The present study investigated the effects of consuming preloads with different macronutrient and energy contents on subsequent intake and subjective feelings of hunger and satiety in children, young adults and the elderly. SUBJECTS: 30 Children (4-6 y), 33 young adults (18-26 y) and 24 elderly (61-86 y). DESIGN: A 'preload test meal' design was applied. Subjects were given four different strawberry yoghurt preloads that varied in energy and macronutrient content, or no yoghurt. Children, young adults and elderly consumed 200, 340 and 300 g of the preload, respectively. One yoghurt was low-fat, low-carbohydrate and low in energy (the control; 0.7 MJ/500 g serving), one yoghurt was high-fat and medium in energy (71% of energy (en%) of fat; 2 MJ/500 g serving), one yoghurt was high-carbohydrate and medium in energy (87 en% of carbohydrate; 2 MJ/500 g serving) and the fourth yoghurt was high-fat and high-carbohydrate and high in energy (42 en% of fat and 53 en% of carbohydrate; 3 MJ/500 g serving). Ninety minutes after preload consumption, subjects had an attractive ad libitum lunch-buffet. Energy intake at lunch and subjective feelings of hunger and satiety were analysed. RESULTS: The ability to compensate at lunch did not differ among the three age groups. Compared to the no-preload condition, all children, young adults and elderly ate significantly less after the high-fat and high-carbohydrate yoghurt. The energy compensation observed in the children ranged between -21% and 34%, in the young adults between 15% and 44% and in the elderly between 17% and 23%. Hunger responses were clearly different between young adults and the elderly. Compared to the no-preload condition, the young adults showed larger differences in their appetite ratings than the elderly, indicating that the elderly were less sensitive to the energy content of the preload than the young adults. CONCLUSION: We conclude that the ability to regulate the food intake within a preload 90 min test meal paradigm did not differ among children, young adults and the elderly. Sponsorship: This study was funded by the European Commission as part of project FAIR-CT95-0574.     

Plasma glucose and insulin reduction after consumption of breads varying in amylose content

OBJECTIVE: Consumption of a meal high in amylose starch (70%) decreases peak insulin and glucose levels and area under the curve (AUC). The objective was to determine the amount of amylose necessary in a meal for the beneficial decrease in glucose or insulin to occur. DESIGN: Twenty-five subjects, 13 men (averaging 88.1 kg, 41 y, and 27.9 body mass index) and 12 women (averaging 72.4 kg, 41 y and 27.1 body mass index) were given six tolerance tests in a Latin Square design: glucose alone (1 g glucose/kg body weight) and five breads (1 g carbohydrate/kg body weight) made with 70% amylose cornstarch, standard cornstarch (30% amylose), and blends of the two starches (40, 50 and 60% amylose starch). A standard menu was fed for 3 days. One subject withdrew from the study. RESULTS: Glucose, insulin and glucagon response to the carbohydrate loads was similar in men and women. Peak glucose response was lowest after the breads containing 50-70% amylose starch. AUC was significantly higher after the glucose load than after all bread loads. The lowest AUCs occurred after the 60 and 70% amylose starch breads. Insulin response and AUC were significantly lower after the 60 and 70% amylose starch breads than after the glucose or the other breads. CONCLUSION: Results indicate that the amylose content of the starch used in the acute meal needs to be greater than 50% to significantly reduce plasma glucose and insulin in men and women.     

Impairment of glucose tolerance in copper-deficient rats: dependency on the type of dietary carbohydrate

Copper deficiency was induced in weanling rats in order to study the possible interaction between the types of dietary carbohydrate and copper deficiency on glucose tolerance. Weanling male rats were fed copper-deficient or copper-supplemented diets containing either 62% starch, fructose or glucose. During week 5 the fructose portion of the copper-deficient diet was replaced (20 rats) by starch (10 rats) or glucose (10 rats). During the 9th week, an oral glucose tolerance test weas performed. Copper deficiency was associated with impaired glucose tolerance characterized by increased blood glucose and decreased insulin levels only in copper-deficient rats fed the monosaccharides fructose or glucose but not the polysaccharide starch. Changing the dietary carbohydrates in the copper-deficient diet from fructose to starch increased insulin levels and decreased blood glucose in response to the glycemic stress when compared to rats continuously fed fructose. Although both glucose and fructose feeding impaired the glucose tolerance, fructose was more diabetogenic. This could be demonstrated by some improvements in glucose tolerance when the copper-deficient rats were switched from the fructose to the glucose diet. The data indicate that copper deficiency per se does not impair glucose tolerance.