Role of catecholamines in hypotensive response to dieting.

The effect of dieting on blood pressure and catecholamine metabolism was assessed in 11 normotensive obese women by providing first a weight-maintenance regimen high in carbohydrate and then a low-energy diet. All dietary constituents other than carbohydrate were maintained constant throughout the 18-day study. The low-carbohydrate diet led within 48 hours to a 41% fall in the urinary output of 4-hydroxy-3-methoxy mandelate and a significant fall in systolic and diastolic blood pressure. Plasma noradrenaline concentrations also fell and the hypotensive effect of the diet continued despite a maintained total body sodium. Thus the fall in blood pressure appeared to be mediated by changes in catecholamine metabolism independent of sodium intake. This may explain both the usefulness of weight reduction in hypertensive patients and the fainting that occurs in some normotensive obese subjects taking slimming regimens low in carbohydrate.     

Nutritional management of hypertension: past, present, and future

A succinct overview of the nutritional management of hypertension, past, present, and future is presented. Prior to 1945, the low sodium diet and the rice-fruit diet were shown to be effective in reducing the blood pressure to normal levels in 35-40% of hypertensive patients. Between 1945 and the present, many studies were made on the effects of alcohol, water hardness, obesity, moderate restriction of sodium with increased potassium intake, increased dietary calcium, low animal and high unsaturated fat intake, and increased amounts of fiber in the diet. Criticisms are made of the very small magnitude, even if statistically significant, of blood pressure decreases and the too-short control periods in many instances, and also concerning the assumption of use of 24-h urinary sodium as an accurate index of the sodium intake, and of urinary creatinine as a physiological reference standard against the excretion of sodium. The author mentions, for possible future research, long-term studies of the effects of diets moderately restricted in sodium and high in potassium, of reducing weight and increasing physical activity in obese hypertensives, and of low animal and high polyunsaturated fat diets in patients with mild essential hypertension.     

Changes in nutrient intakes of conditioned men during a 5-day period of increased physical activity and other stresses

Nutrient intakes and selected blood and urinary constituents of 16 Navy servicemen were obtained before and during a period of 113 hours of physical activity, sleep deprivation, and psychological stress, to document the dietary adaptation of physically conditioned men to an extended period of hard physical work and other stresses. Food intakes were monitored by 1-day diet records prior to and by direct observation during the period. The factorial method was used to calculate energy expenditure. Carbohydrates provided 45 and 43% of the total energy intake before and during the experiment. Protein intakes and intakes of all the vitamins and minerals studied exceeded the Recommended Dietary Allowances, both before and during the period. Total energy intake averaged 18.7 MJ.d-1 before and 24.4 MJ.d-1 during the experiment. Body weight increased significantly by 2.7 +/- 0.4 kg (mean +/- s.e.) during the experiment (p less than 0.0001). There was a significant correlation (r = 0.74; p less than 0.001) between the change in body weight and urinary sodium from before to after the experiment suggesting that increased dietary sodium may have contributed to the weight gain. A significant increase in plasma volume (11.9 +/- 3.2%; p less than 0.0003) provided further support that the observed weight gain was due to sodium intake rather than a positive energy balance. In conclusion, conditioned men increased food consumption adequately to meet increased energy demands.     

Sodium restriction and blood pressure in hypertensive type II diabetics: randomised blind controlled and crossover studies of moderate sodium restriction and sodium supplementation.

OBJECTIVE--To determine the effect of moderate dietary sodium restriction on the hypertension of non-insulin-dependent (type II) diabetes. DESIGN--Randomised parallel controlled study of moderate sodium restriction for three months compared with usual diabetic diet, followed by randomised double blind crossover trial of sustained release preparation of sodium for one month versus placebo for one month in patients continuing with sodium restriction. SETTING--Patients attending diabetic outpatient clinic of city hospital. PATIENTS--Thirty four patients with established type II diabetes complicated by mild hypertension (systolic blood pressure greater than 160 mm Hg or diastolic pressure greater than 95 mm Hg on three consecutive occasions). Patients already taking antihypertensive agents (but not diuretics) not barred from study provided that criteria for mild hypertension still met. Conditions precluding patients from study were diabetic or hypertensive nephropathy, cardiac failure, and pregnancy. INTERVENTIONS--After run in phase with recordings at seven weeks, three weeks, and time zero patients were allocated at random to receive moderate dietary sodium restriction for three months (n = 17) or to continue with usual diabetic diet. Subsequently nine patients in sodium restriction group continued with regimen for a further two months, during which they completed a randomised double blind crossover trial of sustained release preparation of sodium (Slow Sodium 80 mmol daily) for one month versus matching placebo for one month. END POINT--Reduction in blood pressure in type II diabetics with mild hypertension. MEASUREMENTS AND MAIN RESULTS--Supine and erect blood pressure, body weight, and 24 hour urinary sodium and potassium excretion measured monthly during parallel group and double blind crossover studies. After parallel group study sodium restriction group showed significant reduction in systolic blood pressure (supine 19.2 mm Hg, erect 21.4 mm Hg; p less than 0.001) and mean daily urinary sodium excretion (mean reduction 60 mmol/24 h). There were no appreciable changes in weight, diabetic control, or diastolic pressure. No significant changes occurred in controls. In double blind crossover study mean supine systolic blood pressure rose significantly (p less than 0.005) during sodium supplementation (to 171 mm Hg) compared with value after three months of sodium restriction alone (159.9 mm Hg) and after one month of placebo (161.8 mm Hg). CONCLUSIONS--Moderate dietary restriction of sodium has a definite hypotensive effect, which may be useful in mild hypertension of type II diabetes.     

Dietary sodium restriction for mild hypertension in general practice.

Eighteen patients with stable mild hypertension (mean blood pressure 144/93 mm Hg) restricted their sodium intake for eight weeks while taking part in a double blind randomised crossover trial of slow sodium and placebo tablets. Mean 24 hour urinary sodium excretion was 143 mmol(mEq) during the period on slow sodium and 87 mmol during the period on placebo. Five patients were unable to reduce their sodium intake below 120 mmol, but the others had a mean 24 hour urinary sodium excretion of 59 mmol during the period on placebo. There was no significant difference in blood pressure between the slow sodium and placebo treatment periods, although the study had a power of 99% to detect a difference of 5 mm Hg in mean arterial pressure between the two periods. Moderate dietary sodium restriction does not lower blood pressure in patients with this degree of hypertension.     

Antihypertensive effect of diet compared with drug treatment in obese men with mild hypertension.

OBJECTIVE--To determine whether dietary treatment has a similar antihypertensive effect to conventional drug treatment while being superior to drugs in improving serum lipid concentrations in obese men with mild hypertension. DESIGN--Six week run in period followed by randomisation to either diet or drug treatment groups for one year. SETTING--Outpatient clinic in city hospital. PATIENTS--61 Men aged 40-69 years, body mass index greater than or equal to 26, diastolic blood pressure 90-104 mm Hg when untreated. Exclusion criteria were signs of organ damage secondary to hypertension and diseases that might have interfered with compliance or with interpretation of results. INTERVENTIONS--Dietary treatment was based on weight reduction, restriction of sodium, and decrease of excess alcohol intake (defined as greater than or equal to 250 g alcohol per week). Drug treatment used a stepped care approach with atenolol as drug of first choice. MAIN OUTCOME MEASURES--Diastolic blood pressure less than 90 mm Hg; absolute reductions in blood pressure and serum lipid concentrations. RESULTS--Mean body weight decreased 7.6 kg in the diet group and increased 0.9 kg in the drug treatment group (p less than 0.0001), and mean sodium excretion decreased 42 and 10 mmol/24 h respectively (p = 0.019). There was no difference in reported alcohol intake. Mean systolic blood pressure decreased 4 mm Hg in the diet group and 16 mm Hg in the drug group (p = 0.003) and diastolic blood pressure 3 and 11 mm Hg respectively (p = 0.002). Diastolic blood pressure of 90 mm Hg was attained by 29% of the diet group (nine men) and 73% (22) of those receiving drug treatment (mean difference 44%, 95% confidence interval 21 to 67%, p = 0.001). Dietary treatment produced decreases in mean serum concentrations of total and low density lipoprotein cholesterol as well as triglycerides and an increase in high density lipoprotein cholesterol concentration. In the drug treatment group the changes were in the opposite direction, and the groups differed significantly in all but total cholesterol. CONCLUSIONS--Dietary treatment was inferior to conventional drug treatment in controlling mild hypertension but superior in lowering serum concentrations of lipids.     

Effect of "no added salt diet" on blood pressure control and 24 hour urinary sodium excretion in mild to moderate hypertension

Background

The incidence of Hypertension as a major cardiovascular threat is increasing. The best known diet for hypertensives is 'no added salt diet'. In this study we evaluated the effect of 'no added salt diet' on a hypertensive population with high dietary sodium intake by measuring 24 hour urinary sodium excretion.

Methods

In this single center randomized study 80 patients (60 cases and 20 controls) not on any drug therapy for hypertension with mild to moderate hypertension were enrolled. 24 hour holter monitoring of BP and 24 hour urinary sodium excretion were measured before and after 6 weeks of 'no added salt diet'.

Results

There was no statistically significant difference between age, weight, sex, Hyperlipidemia, family history of hypertension, mean systolic and diastolic BP during the day and at night and mean urinary sodium excretion in 24 hour urine of case and control groups. Seventy eight percent of all patients had moderate to high salt intake. After 6 week of 'no added salt diet' systolic and diastolic BP significantly decreased during the day (mean decrease: 12.1/6.8 mmhg) and at night (mean decrease: 11.1/5.9 mmhg) which is statistically significant in comparison to control group (P 0.001 and 0.01). Urinary sodium excretion of 24 hour urine decreased by 37.1 meq/d ± 39,67 mg/dl in case group which is statistically significant in comparison to control group (p: 0.001). Only 36% of the patients, after no added salt diet, reached the pretreatment goal of 24 hour urinary sodium excretion of below 100 meq/dl (P:0.001).

Conclusion

Despite modest effect on dietary sodium restriction, no added salt diet significantly decreased systolic and diastolic BP and so it should be advised to every hypertensive patient.

Trial Registration

Clinicaltrial.govnumber NCT00491881     

Short term effects of a low-carbohydrate diet in overweight and obese subjects with low HDL-C levels

Background

The aim of this study was to evaluate short-term effects of a low-carbohydrate diet in overweight and obese subjects with low HDL-C levels.

Methods

Overweight (BMI between 25-30 kg/m²) or obese (BMI over 30 kg/m²) subjects with low HDL-C levels (men with HDL-C <1.03, women <1.29 mmol/l) were invited to the study. A 1400 kcal 75-gram carbohydrate (CHO) diet was given to women and an 1800 kcal 100-gram CHO diet was given to men for four weeks. The distribution of daily energy of the prescribed diet was 21-22% from CHO, 26-29% from protein and 49-53% from fat. Subjects completed a three-day dietary intake record before each visit. Anthropometric indices, body fat ratio, blood lipids, glucose and insulin were measured. Baseline and week-four results were compared with a Wilcoxon signed ranks test.

Results

Twenty-five women and 18 men participated. Basal median LDL-C level of men was 3.11 and basal median LDL-C level of women was 3.00 mmol/l. After four weeks of a low-carbohydrate diet, the median energy intake decreased from 1901 to 1307 kcal/day, daily energy from carbohydrate from 55% to 33%, body weight from 87.7 to 83.0 kg and HDL-C increased from 0.83 to 0.96 mmol/l in men (p < 0.002, for all). After four weeks of a low-carbohydrate diet, the median energy intake tended to decrease (from 1463 to 1243 kcal, p = 0.052), daily energy from carbohydrate decreased from 53% to 30% (p < 0.001) and body weight decreased from 73.2 to 70.8 kg (p < 0.001) in women, but HDL-C did not significantly change (from 1.03 to 1.01 mmol/l, p = 0.165). There were significant decreases in body mass index, waist circumference, body fat ratio, systolic blood pressure, total cholesterol, triglyceride and insulin levels in all subjects.

Conclusions

HDL-C levels increased significantly with energy restriction, carbohydrate restriction and weight loss in men. HDL-C levels didn't change in women in whom there was no significant energy restriction but a significant carbohydrate restriction and a relatively small but significant weight loss. Our results suggest that both energy and carbohydrate restriction should be considered in overweight and obese subjects with low HDL-C levels, especially when LDL-C levels are not elevated.     

Moderate sodium restriction with angiotensin converting enzyme inhibitor in essential hypertension: a double blind study.

Fifteen unselected patients who had essential hypertension and whose average supine blood pressure when they were not receiving any treatment and their usual sodium intake was 162/107 mm Hg were treated with captopril 50 mg twice daily. After one month''s treatment their supine blood pressure had decreased to 149/94 mm Hg. They were then instructed to reduce their sodium intake to about 80 mmol(mEq)/day. After two weeks of moderate sodium restriction they were entered into a double blind randomised crossover study comparing the effect of 10 Slow Sodium tablets (100 mmol sodium chloride) with matching placebo tablets while continuing to take captopril and restrict sodium in their diet. After one month of taking placebo their mean supine blood pressure was 137/88 mm Hg with a urinary sodium excretion of 83 mmol/24 h, while after one month of taking Slow Sodium tablets their mean supine blood pressure was 150/97 mm Hg (p less than 0.001) with a sodium excretion of 183 mmol/24 h. The mean supine blood pressure during moderate sodium restriction therefore decreased by 9% and correlated significantly with the reduction in urinary sodium excretion. These results suggest that the combination of treatment with a moderate but practical reduction in sodium intake and an angiotensin converting enzyme inhibitor is effective in decreasing the blood pressure in patients with essential hypertension. This combined approach overcomes some of the objections that have been made to salt restriction alone and to converting enzyme inhibitors alone.     

Effect of dietary energy intake on tubular reabsorption of urea in sheep

The aim of the experiment was to determine the effect of dietary energy intake on renal urea excretion in sheep with different nitrogen intakes. The control sheep, with a high nitrogen and energy intake, were given a daily feed dose of 21.18 g N and 15.2 MJ digestible energy (DE). The two experimental groups, with an equal, low nitrogen intake, were given diets with a different energy content. The high energy diet contained 3.63 g N and 14.18 MJ DE, the low energy diet 3.4 g N and 6.44 MJ DE. After nine weeks' adaptation to the diets, renal functions were measured by a standard clearance technique. It was found that, under stable urine flow conditions, both groups given the low nitrogen diet had a significantly lower glomerular filtration rate, fractional urea excretion and total urea excretion. A reciprocal comparison of these two groups showed that fractional urea excretion by the sheep with a high energy intake was significantly lower than in the group with a low energy intake. There were no differences in the glomerular filtration rate. A raised dietary energy intake in the presence of a low nitrogen intake caused marked natriuresis and kaliuresis. The results indicate that a raised dietary energy intake can be a significant factor in potentiating the renal effect of urea retention in sheep with a low nitrogen intake.     

Lifestyle modifications to prevent and control hypertension. 5. Recommendations on dietary salt. Canadian Hypertension Society,Canadian Coalition for High Blood Pressure Prevention and Control,Laboratory Centre for Disease Control at Health Canada,Heart and Stroke Foundation of Canada

OBJECTIVE: To provide updated, evidence-based recommendations concerning the effects of dietary salt intake on the prevention and control of hypertension in adults (except pregnant women). The guidelines are intended for use in clinical practice and public education campaigns. OPTIONS: Restriction of dietary salt intake may be an alternative to antihypertensive medications or may supplement such medications. Other options include other nonpharmacologic treatments for hypertension and no treatment. OUTCOMES: The health outcomes considered were changes in blood pressure and in morbidity and mortality rates. Because of insufficient evidence, no economic outcomes were considered. EVIDENCE: A MEDLINE search was conducted for the period 1966-1996 using the terms hypertension, blood pressure, vascular resistance, sodium chloride, sodium, diet, sodium or sodium chloride dietary, sodium restricted/reducing diet, clinical trials, controlled clinical trial, randomized controlled trial and random allocation. Both trials and review articles were obtained, and other relevant evidence was obtained from the reference lists of the articles identified, from the personal files of the authors and through contacts with experts. The articles were reviewed, classified according to study design and graded according to level of evidence. In addition, a systematic review of all published randomized controlled trials relating to dietary salt intake and hypertension was conducted. VALUES: A high value was placed on the avoidance of cardiovascular morbidity and premature death caused by untreated hypertension. BENEFITS, HARMS AND COSTS: For normotensive people, a marked change in sodium intake is required to achieve a modest reduction in blood pressure (there is a decrease of 1 mm Hg in systolic blood pressure for every 100 mmol decrease in daily sodium intake). For hypertensive patients, the effects of dietary salt restriction are most pronounced if age is greater than 44 years. A decrease of 6.3 mm Hg in systolic blood pressure and 2.2 mm Hg in diastolic blood pressure per 100 mmol decrease in daily sodium intake was observed in people of this age group. For hypertensive patients 44 years of age and younger, the decreases were 2.4 mm Hg for systolic blood pressure and negligible for diastolic blood pressure. A diet in which salt is moderately restricted appears not to be associated with health risks. RECOMMENDATIONS: (1) Restriction of salt intake for the normotensive population is not recommended at present, because of insufficient evidence demonstrating that this would lead to a reduced incidence of hypertension. (2) To avoid excessive intake of salt, people should be counselled to choose foods low in salt (e.g., fresh fruits and vegetables), to avoid foods high in salt (e.g., pre-prepared foods), to refrain from adding salt at the table and minimize the amount of salt used in cooking, and to increase awareness of the salt content of food choices in restaurants. (3) For hypertensive patients, particularly those over the age of 44 years, it is recommended that the intake of dietary sodium be moderately restricted, to a target range of 90-130 mmol per day (which corresponds to 3-7 g of salt per day). (4) The salt consumption of hypertensive patients should be determined by interview. VALIDATION: These recommendations were reviewed by all of the sponsoring organizations and by participants in a satellite symposium of the fourth International Conference on Preventive Cardiology. They have not been clinically tested. SPONSORS: The Canadian Hypertension Society, the Canadian Coalition for High Blood Pressure Prevention and Control, the Laboratory Centre for Disease Control at Health Canada, and the Heart and Stroke Foundation of Canada.     

Sodium and potassium intake and blood pressure change in childhood.

OBJECTIVE--To assess the association between sodium and potassium intake and the rise in blood pressure in childhood. DESIGN--Longitudinal study of a cohort of children with annual measurements during an average follow up period of seven years. SETTING--Epidemiological survey of the population of a suburban town in western Netherlands. SUBJECTS--Cohort of 233 children aged 5-17 drawn at random from participants in the population survey. MAIN OUTCOME MEASURES--At least six annual timed overnight urine samples were obtained. The mean 24 hour sodium and potassium excretion during the follow up period was estimated for each participant and the sodium to potassium ratio calculated. Individual slopes of blood pressure over time were calculated by linear regression analysis. RESULTS--No significant association was observed between sodium excretion and the change in blood pressure over time. The mean systolic blood pressure slopes, however, were lower when potassium intake was higher (coefficient of linear regression -0.045 mm Hg/year/mmol; 95% confidence interval -0.069 to -0.020), and the change in systolic pressure was greater when the urinary sodium to potassium ratio was higher (0.356 mm Hg/year/unit; 95% confidence interval 0.069 to 0.642). In relation to potassium this was interpreted as a rise in blood pressure that was on average 1.0 mm Hg (95% confidence interval -1.65 to -0.35) lower in children in the upper part of the distribution of intake compared with those in the lower part. The mean yearly rise in systolic blood pressure for the group as a whole was 1.95 mm Hg. Urinary electrolyte excretion was not associated with diastolic blood pressure. CONCLUSION--Dietary potassium and the dietary sodium to potassium ratio are related to the rise in blood pressure in childhood and may be important in the early pathogenesis of primary hypertension.     

High Dietary Calcium Reduces Body Fat Content,Digestibility of Fat,and Serum Vitamin D in Rats

Objective: This study investigated which aspect of energy balance was responsible for the decrease in body fat content of rats fed a high‐calcium, high—dairy protein diet. Research Methods and Procedures: Male Wistar rats were fed a control diet (25% kcal fat, 14% kcal protein from casein, 0.4% by weight calcium) or high‐calcium diet (25% kcal fat, 7% kcal protein from nonfat dry milk, 7% kcal protein from casein, 2.4% calcium) for 85 days. Body weights, digestible energy intakes, energy expenditures, rectal temperatures, body composition, and serum glucose, insulin, free fatty acids, triglycerides, and 1, 25‐dihydroxyvitamin D were measured. Results: Rats fed high‐calcium diet gained significantly less weight than controls and had 29% less carcass fat. Gross energy intake was not significantly different between groups, but digestible energy was 90% of gross energy in the high‐calcium diet compared with 94% in the control diet because of increased fecal excretion of dietary lipid. The difference in digestible energy intake accounted for differences in carcass energy. Body temperatures and energy expenditures of the rats were not different. The high‐calcium diet reduced serum triglycerides by 23% and serum 1, 25‐dihydroxyvitamin D by 86%. Discussion: These results confirm that a high‐calcium diet decreases body weight and fat content due to a lower digestible energy intake caused by increased fecal lipid and a nonsignificant reduction in gross energy intake.     

Failure of renal denervation to attenuate hypertension in Dahl NaCl-sensitive rats

In previous experiments we have demonstrated that the renal nerves play a significant role in all genetic and (or) induced models of hypertension that we have studied. The current experiments extended this research by investigating the contribution of the renal nerves to hypertension in the Dahl NaCl-sensitive rat. This was investigated by assessing the effect of bilateral phenol renal denervation carried out prior to initiation of a high NaCl (8% NaCl) diet. In two separate studies, renal denervation did not affect systolic blood pressure in either Dahl NaCl-sensitive rats or their normotensive counterparts, Dahl NaCl-resistant rats. Further, denervation did not increase absolute urinary sodium excretion, percent urinary sodium excretion, urinary volume output, or food or water intake; nor did it differentially alter creatinine clearance or body weight. Denervation was verified at the termination of each study by a greater than 80% depletion of renal noradrenaline stores. These results indicate that the renal nerves do not provide a major contribution to hypertension in the Dahl NaCl-sensitive rat.     

Effects of Calcium and Dairy on Body Composition and Weight Loss in African‐American Adults

Objective: Our objective was to determine the effects of dairy consumption on adiposity and body composition in obese African Americans. Research Methods and Procedures: We performed two randomized trials in obese African‐American adults. In the first (weight maintenance), 34 subjects were maintained on a low calcium (500 mg/d)/low dairy (<1 serving/d) or high dairy (1200 mg Ca/d diet including 3 servings of dairy) diet with no change in energy or macronutrient intake for 24 weeks. In the second trial (weight loss), 29 subjects were similarly randomized to the low or high dairy diets and placed on a caloric restriction regimen (?500 kcal/d). Results: In the first trial, body weight remained stable for both groups throughout the maintenance study. The high dairy diet resulted in decreases in total body fat (2.16 kg, p < 0.01), trunk fat (1.03 kg, p < 0.01), insulin (18.7 pM, p < 0.04), and blood pressure (6.8 mm Hg systolic, p < 0.01; 4.25 mm Hg diastolic, p < 0.01) and an increase in lean mass (1.08 kg, p < 0.04), whereas there were no significant changes in the low dairy group. In the second trial, although both diets produced significant weight and fat loss, weight and fat loss on the high dairy diet were ～2‐fold higher (p < 0.01), and loss of lean body mass was markedly reduced (p < 0.001) compared with the low dairy diet. Discussion: Substitution of calcium‐rich foods in isocaloric diets reduced adiposity and improved metabolic profiles in obese African Americans without energy restriction or weight loss and augmented weight and fat loss secondary to energy restriction.     

Effect of a moderate variation in dietary energy intake on the retention and excretion of zinc,calcium, and magnesium

Mineral balance was studied by metabolic balance techniques in 13 healthy college females aged 21–23 yr. They were fed diet containing 1780 kcal, 2580 kcal, and 25 g protein in a 20-d experiment period. Both diets contained approximately 5.28 mg zinc, 216.85 mg calcium, and 364.3 mg magnesium. The diet consisted of habitually consumed foods. Blood, urine and fecal samples were collected for mineral analysis using atomic absorption spectrophotometry. Plasma mineral levels were not affected by the change in dietary energy intake. Fecal calcium and magnesium were significantly higher when subjects were fed the low calorie (1780 kcal) diet, whereas there was no significant difference in fecal zinc for the two levels of dietary energy. Urinary calcium and magnesium were also significantly higher when the diet provided 1780 kcal though, on the other hand, urinary zinc was significantly higher when the diet provided 2680 kcal (P<0.05). Urinary calcium and magnesium correlated negatively, whereas urinary zinc correlated positively, with the dietary energy intake (P ^o<0.05). Dietary energy intake has a significant effect on the mineral balance of the subjects.     

Evaluation of methods used to assess dietary intake: simulation analyses

The choice of dietary methodology can affect the ability to detect and describe the relationship between dietary sodium intake and blood pressure. This is illustrated in this paper through the use of simulation modelling of the effect of using different dietary methods (food recalls or records covering different numbers of days, food frequency questionnaire estimates of a single diet component) and using urinary excretion as a proxy for intake. Both epidemiologic studies and experimental interventions are simulated. Although the data base used was simulated rather than real, an attempt was made to keep it realistic in relation to what might be seen in actual populations. From these analyses it can be inferred that with appropriate choice of methodology and study design, even low order relationships between sodium intake and blood pressure should be detectable. At a more general level, it may be concluded that while there is no perfect dietary methodology, there are preferred methodologies for defined purposes.     

Dietary fat increases energy intake across the range of typical consumption in the United States

Objective: The fat content of a diet has been shown to affect total energy intake, but controlled feeding trials have only compared very high (40% of total calories) fat diets with very low (20% of total calories) fat diets. This study was designed to measure accurately the voluntary food and energy intake over a range of typical intake for dietary fat. Methods and Procedures: Twenty‐two non‐obese subjects were studied for 4 days on each of three diets, which included core foods designed to contain 26, 34, and 40% fat, respectively of total calories and ad lib buffet foods of similar fat content. All diets were matched for determinants of energy density except dietary fat. Subjects consumed two meals/day in an inpatient unit and were provided the third meal and snack foods while on each diet. All food provided and not eaten was measured by research staff. Results: Voluntary energy intake increased significantly as dietary fat content increased (P = 0.008). On the 26% dietary fat treatment, subjects consumed 23.8% dietary fat (core and ad lib foods combined) and 2,748 ± 741 kcal/day (mean ± s.d.); at 34% dietary fat, subjects consumed 32.7% fat and 2,983 ± 886 kcal/day; and at 40% dietary fat subjects consumed 38.1% fat and 3,018 ± 963 kcal/day. Discussion: These results show that energy intake increases as dietary fat content increases across the usual range of dietary fat consumed in the United States. Even small reductions in dietary fat could help in lowering total energy intake and reducing weight gain in the population.     

Intersalt revisited: further analyses of 24 hour sodium excretion and blood pressure within and across populations. Intersalt Cooperative Research Group.

OBJECTIVES--To assess further the relation in Intersalt of 24 hour urinary sodium to blood pressure of individuals and populations, and the difference in blood pressure from young adulthood into middle age. DESIGN--Standardised cross sectional study within and across populations. SETTING--52 population samples in 32 countries. SUBJECTS--10,074 men and women aged 20-59. MAIN OUTCOME MEASURES--Association of sodium and blood pressure from within population and cross population multiple linear regression analyses with multivariate correction for regression dilution bias. Relation of sample median daily urinary sodium excretion to difference in blood pressure with age. RESULTS--In within population analyses (n = 10,074), individual 24 hour urinary sodium excretion higher by 100 mmol (for example, 170 v 70 mmol) was associated with systolic/diastolic blood pressure higher on average by 3/0 to 6/3 mm Hg (with and without body mass in analyses). Associations were larger at ages 40-59. In cross population analyses (n = 52), sample median 24 hour sodium excretion higher by 100 mmol was associated with median systolic/diastolic pressure higher on average by 5-7/2-4 mm Hg, and estimated mean difference in systolic/diastolic pressure at age 55 compared with age 25 greater by 10-11/6 mm Hg. CONCLUSIONS--The strong, positive association of urinary sodium with systolic pressure of individuals concurs with Intersalt cross population findings and results of other studies. Higher urinary sodium is also associated with substantially greater differences in blood pressure in middle age compared with young adulthood. These results support recommendations for reduction of high salt intake in populations for prevention and control of adverse blood pressure levels.     

High dietary salt intake increases carotid blood pressure and wave reflection in normotensive healthy young men

Dietary salt intake is associated with high brachial blood pressure (BP) and increased risk of cardiovascular disease. We investigated whether changes in dietary salt intake are associated with changes in central BP and wave reflection in healthy volunteers. Ten healthy normotensive male volunteers (22-40 yr) participated in a 6-wk double-blind randomized crossover study to compare a low-dietary salt intake (60-80 mmol sodium/day) with a high-salt intake (low salt intake supplemented with 128 mmol sodium/day) on central BP and wave reflection. Brachial and carotid BP, carotid blood flow velocity, forward (P(f)) and backward (P(b)) pressure, wave intensity, body weight, and urinary electrolyte excretion were measured at the end of each crossover period. High salt intake significantly increased carotid systolic BP [98 (SD 11) vs. 91 mmHg (SD 13), P < 0.01] and increased wave reflection [ratio of backward to forward pressure (P(b)/P(f)) 0.13 (SD 0.02) vs. 0.11 (SD 0.03), P = 0.04] despite only small effects on brachial BP [114 (SD 9) vs. 112 mmHg (SD 6), P = 0.1]. Urinary sodium excretion and body weight were also increased following high salt intake. High salt intake disproportionately increases central BP compared with brachial BP as a result of enhanced wave reflection. These effects may contribute to the adverse effect of high dietary salt intake on the risk of cardiovascular disease.