The relationships between dietary alpha-linolenic:linoleic acid and rat platelet eicosapentaenoic and arachidonic acids

Increased dietary intake of alpha-linolenic acid (ALA) may be desirable to enrich tissue eicosapentaenoic acid (EPA; 20:5n-3) but competition between n-3 and n-6 fatty acids for enzymes involved in elongation and subsequent acylation will determine the relative proportions of phospholipid fatty acids. The aim of the present study was to examine the effects of altering the dietary ALA:linoleic acid (LA) ratio on rat platelet EPA and arachidonic acid (AA; 20:4n-6) concentrations. Sprague-Dawley rats were fed on diets containing 30% total energy as fat with approximately 10% each of saturated, monounsaturated and polyunsaturated fatty acids with one of the following ALA:LA values; 1:7, 1:4, 1:1 or 1.3:1 (nine rats per group). After 4 weeks, blood was withdrawn from the abdominal aorta and platelet fatty acids analysed. The proportion of EPA was greater at the 1:1 and 1.3:1 ratios compared with the 1:7 and 1:4 (P < 0.05), and a decrease in AA was observed (P < 0.05) at the higher ratios. It was established that the platelet EPA:AA value increased (P < 0.05) as the dietary ALA:LA value increased.

Effects of diets containing high or low amounts of stearic acid on plasma lipoprotein fractions and fecal fatty acid excretion of men

Ten middle-aged males participated in a crossover study to determine the cholesterolemic effect of high amounts of stearic acid in a natural diet. They consumed a 20-d stabilization diet followed by two 40-d intervention diets containing either 1.5% of energy as stearic (18:0) acid and 7.3% of energy as palmitic (16:0) acid (low stearate: LS) or 2.4% of energy as 16:0 and 7.3% of energy as 18:0 (high stearate: HS). The experimental diets also contained approximately 10% of energy each as saturated and monounsaturated fatty acids and 7.2-8% of energy as polyunsaturated fatty acids. The primary source of 18:0 in the HS diet was sheanut oil (commercially referred to as shea butter) and palm oil and butter in the LS diet. Plasma total, low-density-lipoprotein, and high-density-lipoprotein cholesterol were significantly lower with the HS than with the LS diet. Total fecal fatty acid excretion was higher throughout the HS period. Apparent digestibility of the major dietary fatty acids showed that all of the selected fatty acids, except 18:0, were > or = 95% absorbed. These data demonstrate that feeding diets containing about two times the usual amount of stearic acid consumed in the United States, contributed to an increase in plasma lipoprotein concentrations at 40 d from an earlier decrease at 20 d. The time required to achieve stable cholesterol concentrations appears to vary depending on the kind of saturated fatty acids present in the diet.

Supplementation with flaxseed oil versus sunflowerseed oil in healthy young men consuming a low fat diet: effects on platelet composition and function

OBJECTIVE

To compare the effects of supplementing a low fat diet with an alpha-linolenic acid-rich (C18:3 n-3) oil with a linoleic acid-rich (C18:2 n-6) oil on platelet composition and function.

DESIGN

Prospective study with random allocation to one of the two oils.

SETTING

Free-living study.

SUBJECTS

Eleven healthy young males recruited from within the University.

INTERVENTIONS

Subjects were allocated to consume 40 g of either flaxseed oil (n = 5) or sunflowerseed oil (n = 6) daily for 23 days. Fasting blood samples were collected at commencement and completion of supplementation for analysis of platelet fatty acids and platelet aggregation.

RESULTS

The platelet eicosapentaenoic acid (EPA) more than doubled in the group taking flaxseed oil (P < 0.05) but was unchanged in the sunflowerseed group. As a result the platelet EPA:arachidonic acid ratio, considered a marker for thromboxane production and platelet aggregation potential, increased in the flaxseed group (P < 0.05). The aggregation response induced by 0.75 and 2 micrograms of collagen was decreased in those taking flaxseed oil (P < 0.05).

CONCLUSION

This study provides further evidence that consumption of alpha-linolenic acid-rich oils may offer protective effects against cardiovascular disease over linoleic acid-rich oils via their ability to decrease the tendency of platelets to aggregate.

Elevated plasma vitamers of vitamin B6 in patients with chronic renal failure on regular haemodialysis

Plasma pyridoxal-5'-phosphate (PL-5'-P), pyridoxal (PL), pyridoxine (PN), and 4-pyridoxic acid (4-PA) were measured by high-performance liquid chromatography (HPLC) in 39 patients (15 male, 24 female) with chronic fenal failure undergoing regular haemodialysis and 46 healthy controls (28 male, 18 female). All three vitamers of vitamin B6 and the metabolite were significantly elevated in the haemodialysis patients. Mean PL-5'-P and PN concentrations were 20 times the mean in controls. Only one patient took a vitamin B6 supplement. In view of the neurotoxicity of supranutritional intakes of PN in normal humans we suggest that supplements of PN be carefully monitored when administered to patients with chronic renal failure.

Energy supplementation and the nutritional status of hemodialysis patients

Twenty-one patients undergoing regular hemodialysis completed a trial of energy supplementation. Nine patients added the glucose polymer Polycose to their usual diet and 12 acted as control subjects. The supplemented patients were asked to incorporate 100 or 150 g polymer, equivalent to 1600 or 2400 kJ (400 or 600 kcal) into their usual diet, daily for 6 mo. This resulted in a mean increase in energy intake of 1630 kJ (p less than 0.05) and a mean weight gain of 3.1 kg (p less than 0.005). The addition of glucose polymer to the diet resulted in a mean increase in body fat of 1.8 kg and the lean body mass increased by 1.3 kg. No significant effect on plasma triglycerides, urea, or creatinine was detected. The intake of macro- and micronutrients was not adversely affected and no clinical or psychological side effects were reported. Follow-up of these patients showed that the weight gain was maintained after 6 mo. Glucose polymer was an effective energy supplement that had beneficial effects on the nutritional status of hemodialysis patients.

Body protein of patients undergoing haemodialysis

The total body protein status of 18 patients undergoing regular haemodialysis was assessed by measuring total body nitrogen (TBN) using in vivo neutron activation analysis (NAA). Eighteen healthy controls, who were selected according to their height, age and sex match with the patients were also measured. The male and female patients were both found to have lower mean values for total body protein (P less than 0.01, P less than 0.025 respectively) although they had similar weights compared with their matched controls. Seven patients were measured on further occasions and only two patients showed a change in their body protein. One female showed an increase of 11 per cent in body protein (with an increase of 25 per cent in body weight) after intensive nutritional repletion therapy. In vivo NAA provides a direct means of measuring body protein and is a reliable method to monitor changes with treatment regimes.

Vitamin supplementation of patients receiving haemodialysis

In order to assess the necessity of vitamin supplementation for patients who are receiving haemodialysis, measurements of vitamin status were made, and both dietary and supplementary intakes were assessed, in 26 patients who were undergoing haemodialysis. Blood samples were collected from these patients before they underwent haemodialysis, after an overnight fast, for the measurement of plasma retinol, alpha-tocopherol and ascorbate levels. Serum and erythrocyte folate levels were measured also. Thiamin status was assessed by the effect of added thiamin pyrophosphate on erythrocyte transketolase activity and pyridoxine status was assessed by the effect of added pyridoxal-5'-phosphate on erythrocyte aminotransferase activity. All patients had elevated plasma retinol levels; 48% of patients had elevated plasma alpha-tocopherol levels; the plasma ascorbate level was low in 50% of patients but was elevated in 25% of patients; and plasma and erythrocyte folate levels were elevated in 76% and 91% of patients, respectively. Thiamin status was normal in all but one patient and the pyridoxine level appeared to be low in two other patients. Many patients had low dietary intakes of vitamin C, folate and vitamin B6. We conclude that supplements of vitamins A and E are not required and, when dietary intakes of water-soluble vitamins are marginal, these should be supplemented at a dose as near as possible to the recommended dietary intake.