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The story of research in dietary fat.
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Body fat deposition: effects of dietary fat and two exercise protocols.
OBJECTIVE: We evaluated the effects of two levels of dietary fat (0 and 20g beef tallow/100g diet) and two treadmill exercise protocols (low-intensity, high-intensity) on fat deposition in rats. DESIGN: Male Wistar rats (n = 50) remained sedentary or were forced to run 840 meters/day, 5 days/week, on a rodent treadmill. Those on the high-intensity protocol covered this distance in less time (38 min) than those on the low-intensity program (60 min). Responses to high-fat (HF) and low-fat (LF) diets were compared within each exercise group for this 8-week study. RESULTS: High fat feeding, as a single factor, did not affect energy intake, carcass fat, intramuscular fat, or fat associated with any tissue studied. The HF diet also did not affect responses to either exercise protocol. The high-intensity-exercised animals had less carcass fat (LF: 21% less; HF: 33% less), smaller omental fat pads (LF: 20% less; HF: 37% less), and retroperitoneal fat pads (LF: 19% less; HF: 38% less), and lower serum triglyceride levels (LF: 26% less; HF: 41% less) than sedentary rats. Those differences were less marked for the low-intensity-exercise rat. Neither mode of exercise or diet affected lipid concentrations in hindlimb muscles, livers, hearts, or kidneys. CONCLUSION: Exercised animals generally had less fat deposition than sedentary rats but this was more pronounced for high-intensity than low-intensity-exercised rats, and was not affected by feeding a 20% beef tallow diet.
[Determination of trace elements in dietary fats and emulsifiers by non-flame atomic absorption spectrometry (AAS). 2. Determination of mercury in dietary fats and emulsifiers].
Of the trace elements, mercury holds an exceptional position as to its chemico-physical and toxic properties. In the light of the special analytical problem, the methods used (cold-steam AAS in combination with the addition method) are discussed. The experimental conditions required for the digestion and the cold-steam AAS of samples of emulsifiers and dietary fats are indicated. The accuracy and the reproducibility of the procedure are dealt with, and the amounts of mercury found in products of the oil and margarine industries are reported.
Dietary fat and mammary cancer. II. Modulation of serum and tumor lipid composition and tumor prostaglandins by different dietary fats: association with tumor incidence patterns.
For investigation of the role of linoleic acid (LA) and its biologically significant metabolites in mammary tumor promotion by dietary fat, a detailed study of the fatty acid group composition of serum lipids, tumor neutral lipids, tumor phospholipids, and tumor prostaglandins (PG's) was conducted in female inbred F344 rats initiated with N-nitrosomethylurea (CAS: 684-93-5) and fed diets containing various types and amounts of fat. The oils, safflower [23%, high fat (HF); 5%, low fat], corn (23%, 5%), olive (23%, 5%), and coconut (23%) varied widely with respect to their LA content and their polyunsaturate:monounsaturate:saturate ratios (9:1:1, 4.6:2.6:1, 0.6:5.9:1, and 0.008:0.05:1, respectively, for safflower, corn, olive, and coconut oils). A modified hexane-based technique was used for extraction of serum and tumor lipids. Total tumor lipids ranged from a low of 5 to a high of 228 mg/g (wet wt) with no differences found among the 7 dietary groups. The phospholipid content of the tumors ranged from 27 to 47% of total tumor lipid, again with no differences seen among dietary groups. Total serum lipids varied from a low of 3.77 mg/ml (safflower oil, 23%) to a high of 6.11 mg/ml (coconut oil, 23%), and an overall inverse trend was observed between total serum lipids and tumor incidence for the 4 HF diet groups. Serum cholesterol levels were significantly depressed in the HF safflower oil and corn oil groups compared to those in all other dietary groups and, in general, varied inversely with respect to mammary tumor incidence. Serum and tumor neutral fatty acid profiles closely reflected those of the diet, while tumor phospholipids appeared more resistant to diet-induced changes. Olive oil-fed animals exhibited high levels of oleic acid in both serum and tumor lipids. The levels of the major metabolite of LA, arachidonic acid (AA), in tumor phospholipids were highly variable and did not equate with dietary or serum LA levels. A positive association was found among dietary LA, tumor PGE2, and mammary tumor incidence among the 4 HF groups; however, no association was found between tumor AA levels and either tumor PGE2 levels or mammary tumor incidence. The results of this study suggest that dietary LA may exert its effects on mammary tumor promotion by virtue of its role as a PG precursor; but the precise steps in this sequence and possible competitive interactions between essential fatty acids, monoenes, and saturates and the PG-synthesizing system remain to be determined.
Responses of milk fat composition to dietary fat or nonstructural carbohydrates in Holstein and Jersey cows.
Milk fat from Jersey cows contains less oleic acid (cis-C18:1) and more short- and medium-chain fatty acids than does milk fat from Holstein cows. The objective of this experiment was to determine responses in milk fat composition when Jersey and Holstein cows were fed diets either high (37% of dry matter) or low (27% of dry matter) in content of nonstructural carbohydrates (NSC) and supplemented with either 0 or 2.5% (of dry matter) of a mostly saturated fat source. Four Holstein cows and four Jersey cows were used in a Latin square design with 28-d periods; diets were in a 2 x 2 factorial arrangement. Fat supplementation decreased contents of fatty acids synthesized de novo within the mammary gland and increased contents of C18:0 and cis-C18:1. Low-NSC diets tended to increase C16:0 and to decrease C18:0, cis-C18:1, and C18:3. Despite the differences in fatty acid composition between breeds, both breeds generally responded similarly to dietary treatments. An interaction of breed and fat indicated that the content of cis-C18:1 in milk fat was increased more by supplemental fat in Holsteins than in Jerseys. Interactions of breed x fat and breed x carbohydrate type showed that the ratio of cis-C18:1 to C18:0 decreased when Jerseys were supplemented with fat but increased for Holsteins, and decreased when Jerseys were fed the low-NSC diet but increased when Holsteins were fed low NSC. The data are consistent with the hypothesis (Beaulieu and Palmquist, 1995, J. Dairy Sci. 78:1336-1344) that mammary activity of stearoyl-coenzyme A desaturase is lower in Jerseys than in Holsteins.
Use of qualitative and quantitative methods to define behavioral fat-reduction strategies and their relationship to dietary fat reduction in the Patterns of Dietary Change Study.
OBJECTIVE: The purposes of this study were to identify specific food choice behaviors used to decrease dietary fat intake in a community-dwelling population; assess how people categorize changes to diet; determine whether logical grouping of food intake changes revealed one or more common patterns or strategies used by these participants to decrease fat; and determine which strategies were responsible for the greatest decrease in dietary fat intake in the study population. DESIGN: Survey analysis and in-depth interviews were used to quantitatively and qualitatively define dietary change patterns retrospectively in a population who, according to self-report, had decreased their fat intake. Specific food changes made to decrease fat intake, interview statements, and participants' reduction of percentage energy from fat were examined. SETTING: Interviews were conducted from June 1993 through April 1994. SUBJECTS: Included in the study were 145 persons aged 30 to 55 years who reported that they had been decreasing their dietary fat intake for 5 years or more, maintained a healthful diet for at least 5 months, and resided in the United States while changing their diets. STATISTICAL ANALYSES PERFORMED: Confirmatory factor analysis, reliability analysis, and linear regression analysis were performed. RESULTS: Nine fat-reduction strategies were identified. Decrease fat flavorings, decrease "recreational foods," decrease cooking fat, replace meat, change breakfast, and use fat-modified foods accounted for significant reduction in fat intake. CONCLUSIONS: People use a variety of dietary changes to reduce their fat intake. These changes can be categorized into strategies according to the way people change their diets. Knowledge of these strategies and their importance in dietary fat reduction can improve and help nutritionists prioritize the messages they convey.
Tumor promotion by dietary fat in azoxymethane-induced colon carcinogenesis in female F344 rats: influence of amount and source of dietary fat.
The promoting effect of dietary corn oil (CO), safflower oil (SO), olive oil (OO), coconut oil (CC), and medium-chain triglycerides (MCT) on azoxymethane (AOM)-induced colon tumors was studied in female F344 rats. The animals were fed low-fat diets containing 5% CO, 5% SO, or 5% OO 2 weeks before, during, and 1 week after sc injection of 20 mg AOM/kg body weight. One week after the AOM treatment, groups of animals were transferred to high-fat diets containing 23.52% CO, 23.52% SO, 23.52% OO, and 23.52% CC, or 5.88% CO + 17.64% MCT; the remaining animals were continued on 5% fat diets. All animals were fed these diets until the termination of the experiment. Body weights and intakes of calories, protein, and micronutrients were comparable among the various dietary groups. The incidence of colon tumors was increased in rats fed diets containing high-CO and high-SO compared to those fed low-CO and low-SO diets, whereas the diets containing high OO, CC, or MCT had no promoting effect on colon tumor incidence. There was a significant increase in the excretion of fecal deoxycholic acid, lithocholic acid, and 12-ketolithocholic acid in animals fed the high-CO and high-SO diets and no difference in these secondary bile acids excretion in animals fed the high-OO and high-CC diets compared to those animals fed their respective 5% fat diets. This study thus indicates that not only the amount of dietary fat but also the fatty acid composition (type) of fat are important factors in the determination of the promoting effect in colon carcinogenesis.
Effect of high fat diet on insulin resistance: dietary fat versus visceral fat mass.
The purpose of the present study was to determine whether chronic high-fat diet (HF) induces insulin resistance independently of obesity. We randomly divided 40 rats into two groups and fed them either with a HF or with a high-carbohydrate diet (HC) for 8 weeks. Whole body glucose disappearance rate (Rd) was measured using a euglycemic hyperinsulinemic clamp. Firstly, we defined whether insulin resistance by HF was associated with obesity. Plasma glucose and triglyceride concentrations were significantly increased in HF. Rd was decreased (10.6+/-0.2 vs. 9.1+/-0.2 mg/kg/min in HC and HF, respectively) and the hepatic glucose output rate (HGO) was increased in HF (2.2+/-0.3 vs. 4.5+/-0.2 mg/kg/min in HC and HF, respectively). Rd was significantly correlated with %VF (p<0.01). These results implicate that visceral obesity is associated with insulin resistance induced by HF. In addition, to define whether dietary fat induces insulin resistance regardless of visceral obesity, we compared Rd and HGO between groups 1) after matching %VF in both groups and 2) using an ANCOVA to adjust for %VF. After matching %VF, Rd in HF was significantly decreased by 14% (p<0.001) and HGO was significantly increased by 110% (p<0.001). Furthermore, statistical analyses using an ANCOVA also showed Rd for HF was significantly decreased even after adjusting %VF. In conclusion, we suggest that dietary fat per se could induce insulin resistance in rats fed with chronic HF independently of obesity.
Comparison of dietary assessment methods in a low-fat dietary intervention program.
The food frequency questionnaire (FFQ) is commonly utilized for assessment of dietary fat intake, but its validity among individuals following a low-fat diet is unclear. We evaluated the agreement of nutrient estimates derived from FFQ, 24-h recall, and 3-day food records obtained from 104 participants in a randomized trial of a low-fat dietary intervention for women at elevated breast cancer risk. Comparisons were made for total calories, percent calories from fat, and total fat after 1 yr. Correlation was assessed using standard methods based on a null hypothesis of no agreement between instruments as well as by a methodology based on a null hypothesis that the instruments should be in agreement. With the use of standard methods, FFQ estimates for women on the low-fat diet were significantly correlated to records only for percent calories from fat (r = 0.39), whereas recall and record estimates were significantly correlated for all three dietary variables. Using the new method, we found no significant correlation between FFQ and either recalls or records for women following a low-fat diet but significant correlation between recall and record estimates for total calories (r = 0.67). Traditional correlation testing may overestimate the extent of agreement in dietary instruments among women on a low-fat diet. We found empirical support for the nontraditional method.
Role of dietary fat in human nutrition. IV. Experimental & clinical evidence relating to the effect of dietary fat upon health in man.
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DIETARY FAT AND THE STRUCTURE AND PROPERTIES OF RAT ERYTHROCYTES. III. RESPONSE OF ERYTHROCYTE FATTY ACIDS TO VARIOUS DIETARY FATS.
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An elemental diet controls inflammation in indomethacin-induced small bowel disease in rats: the role of low dietary fat and the elimination of dietary proteins.
Elemental diets (EDs) are effective in treating Crohn's disease. We hypothesize that low dietary fat and amino acids used as the sole nitrogen source are the major contributors for the success of EDs. We examined the influences of the addition of dietary fat and protein to an ED using an indomethacin-induced inflammation model in rat small intestine. In the ED-fed rats, the intestinal damage score was decreased compared with that in the standard chow group with decreasing intestinal permeability. By supplementing an ED with soybean oil (SO), intestinal permeability was increased to a level similar to that of the standard chow group. For this group, the intestinal damage score also increased compared with that of the ED group but did not reach the levels observed in the standard chow group. The addition of dietary proteins (using heat-denatured pancreatin) resulted in intestinal damage scores that were significantly higher than those of the ED+SO-fed group. The dietary protein increased the intestinal damage score. These results suggest that EDs control inflammation by decreasing intestinal permeability and the elimination of dietary proteins.
Dietary fat and health: the evidence and the politics of prevention: careful use of dietary fats can improve life and prevent disease.
Every year, more young people start the slow progressive injury that eventually becomes cardiovascular disease and death. It could be prevented with nutrition education, but medical efforts focus more on treatments for older people than on preventing primary causes of disease in young people. Two avoidable risks are prevented by simple dietary interventions: (1) Eat more omega-3 and less omega-6 fats, so tissues have less intense n-6 eicosanoid action, and (2) eat less food per meal to lower vascular postprandial oxidant stress. An empirical diet-tissue relationship was developed and put into an interactive personalized software program to aid informed food choices.
Lipid composition and peroxide levels of mucosal cells in the rat large intestine in relation to dietary fat.
To examine whether dietary fat alters membrane lipid composition and peroxidation of polyunsaturated fatty acids in "non-proliferative" and "proliferative" cells in the large intestine, Sprague-Dawley rats were fed diets providing a polyunsaturated-to-saturated fatty acid ratio of 1.2 or 0.3 at a high or low level of fat intake for a 25-day period. Cell populations were isolated and the effect of dietary fat on membrane polyunsaturated fatty acid content and peroxide levels was determined. Neither fat level nor fatty acid composition of diet influenced total cholesterol, total phospholipids, and percentage of phospholipid classes in membrane phospholipids. Feeding the high fat and/or high polyunsaturated-to-saturated fatty acid ratio diet increased polyunsaturated fatty acid content of mucosal cell phospholipids. Increase in polyunsaturated fatty acid content was paralleled by a decrease in the monounsaturated fatty acid content of mucosal cell phospholipids. Membrane content of total saturated fatty acids was not significantly affected by diet. Variation in phospholipid fatty acid composition between "non-proliferative" and "proliferative" cells was observed. Lipid peroxide levels in mucosal cell lipid fractions were altered by dietary fat treatment. Animals fed high fat diets, compared to groups fed low fat diets, exhibited higher membrane peroxide levels when results are expressed as nmol/mg protein. Higher peroxide levels were observed in mucosal cells for rats fed high polyunsaturated-to-saturated fatty acid ratio diets when results were expressed per nmol of phospholipid. It is concluded that changes in fat level and fatty acid composition of the diet alters the mucosal cell membrane lipid composition in the rat large intestine and influences susceptibility of mucosal cell lipid to peroxidation. Further research is required to delineate which dietary factors--fat level, polyunsaturated-to-saturated fatty acid ratio, or both--have a primary influence on the degree of lipid peroxidation.
The role of dietary fat in the prevention and treatment of obesity. Efficacy and safety of low-fat diets.
BACKGROUND: Does dietary fat play a central role in weight gain and development of obesity? Do low-fat diets have adverse effects on blood lipids? OBJECTIVE AND DESIGN: To answer these questions we have reviewed the evidence linking the dietary fat content to energy balance and obesity, and examined the efficacy and safety of ad libitum low fat, high carbohydrate/protein diets in the prevention and management of obesity. RESULTS: Physiological studies have provided insight into the mechanisms by which the macronutrients differ in their effect on energy balance: (1) energy from fat is less satiating than energy from carbohydrate, and a high fat/carbohydrate ratio in the diet promotes passive overconsumption, a positive energy balance and weight gain in susceptible individuals; (2) fat is more readily absorbed from the intestine and fecal energy loss is much lower with a high dietary fat/carbohydrate ratio; (3) carbohydrate is more thermogenic than fat and energy expenditure is lower during positive energy balance produced by a diet with a high fat/carbohydrate ratio than during positive energy balance produced by a diet with a low fat/carbohydrate ratio. Randomized intervention studies comparing low fat diets to normal fat diets show that low fat diets prevent weight gain in normal weight subjects and produce weight loss in overweight individuals. In our meta-analysis of ad libitum low fat interventions we included 16 trials involving 1728 individuals. The difference in weight loss between intervention and control groups was 2.5 kg (95% CI, 1.5-3.5; P<0.0001). Weight loss was positively related to pre-treatment body weight (r=0.52, P<0.05) and to reduction in percentage energy as fat (0.37 kg/%, P<0.005). Extrapolated to a body mass index (BMI) approximately 30 kg/m(2), and assuming a 10% reduction in dietary fat, the predicted weight loss would be 4.4 kg (95% CI, 2.0-6.8 kg), which has been confirmed in subsequent studies. Newer studies have shown that replacing some carbohydrate with protein may enhance weight loss. CONCLUSION: The American Paradox, the observation that obesity prevalence is increasing despite a slight decrease in population dietary fat consumption, is easily explained by the concomitantly decreasing physical activity, which reduces fat requirements and counteracts the beneficial effect of a slight reduction in dietary fat. Low fat diets with a high content of complex carbohydrates and protein do not produce any adverse effect on cardiovascular risk factors when weight loss is allowed to occur, and they have been shown to decrease mortality among high risk subjects.
The impact of usual dietary patterns, selection of significant foods and cuisine choices on changing dietary fat under 'free living' conditions.
Dietary guidelines for the general population and for the management of obesity, diabetes and heart disease suggest a reduction in dietary fat, and in particular dietary saturated fatty acids (SFA). In order to achieve the recommended levels, changes in food choice patterns are required. Foods are consumed in combination with other foods, and these combinations are often recognizable as cuisine patterns. In this study we examined the food choice patterns of a group of 63 adults with existing type 2 diabetes mellitus who completed a 12 month dietary intervention trial aimed at changing dietary fat under 'free living' conditions. In both lower fat (LF, 27%) and modified fat (MF, 37%E) groups, a reduction in dietary SFA and an increase in polyunsaturated fat were required, with an additional requirement to increase dietary monounsaturated fat in the MF group. The usual diets of the study sample were on average low in total fat (27%E), but high in saturated fat (12%E). Those already consuming total fat at the level concordant with their allocation (LF or MF) achieved targets faster than those with a discordant allocation, but there was no significant effect of usual diet on time of target achievement at 12 months. At 6 months, those achieving dietary fat targets had changed to low fat dairy products and leaner meats, were having more spreads, oils, and nuts and were consuming takeaway meals less than twice a week. Contributions to dietary fat shifted from takeaway foods, meat, dairy products and cakes to spreads, oils and nuts. The modified fat and low fat groups chose more Mediterranean and South East Asian cuisines respectively. In this study sample, usual dietary patterns had an initial impact on change in the diet, but identifiable changes in food choice patterns and the adoption of certain cuisines that combined foods indicative of the dietary guidelines resulted in successful achievement of dietary fat targets.
Dietary fat content influences uptake of hexoses and lipids into rabbit jejunum following ileal resection.
After 6 weeks' feeding on a high-fat or low-fat diet, the in vitro uptake of hexoses and lipids was measured in control rabbits with an intact intestinal tract, and in animals submitted to the surgical removal of the distal half of their small intestine. Jejunal villus height, villus surface area and mucosal surface area were higher in unresected control rabbits fed the low- as compared with the high-fat diet, whereas dietary fat content had no effect on villus morphology in resected animals. Mucosal surface area was similar in control and in resected animals fed the high-fat diet, but was lower in resected than in control animals fed the low-fat diet. The active and passive transport properties of the jejunum were influenced by dietary fat manipulation. These absorption changes were qualitatively and/or quantitatively different in animals with an ileal resection from those in animals with an intact small intestine. Dietary fat manipulation had a different effect on the uptake of each lipid probe. The effective resistance of the intestinal unstirred water layer also adapted to changes in the dietary content of fat, but the changes in uptake of hexoses, fatty acids and cholesterol cannot be simply explained by alterations in this diffusion barrier, or by changes in the villus morphology. These findings indicate the importance of dietary fat on villus structure and transport function and their adaptation to ileal resection.