Peter C. Taylor

Arachidonic acid supplementation enhances synthesis of eicosanoids without suppressing immune functions in young healthy men

This study was conducted to determine the effects of arachidonic acid (AA) supplementation on human immune response (IR) and on the secretion of prostaglandin E2 (PGE2) and leukotriene B4 (LTB4). Ten healthy men (20–38 yr) participated in the study and lived at the Metabolic Suite of the Western Human Nutrition Research Center. They were fed a basal diet (57, 27, and 16 energy percentage from carbohydrate, fat, and protein, respectively, and AA 200 mg/d) for the first 15 d of the study. Additional AA (1.5 g/d) was added to the diet of six men from day 16 to 65, while the remaining four subjects remained on the basal diet. The diets of the two groups were crossed-over from day 66 to 115. In vitro indices of IR were examined using blood drawn on days 15, 58, 65, 108, and 115. Influenza antibody titers were determined in the sera prepared from blood drawn on days 92 and 115 (23 d postimmunization). AA supplementation caused significant increases in the in vitro secretion of LTB4, and PGE2, but it did not alter the in vitro secretion of tumor necrosis factor α; interleukins 1β, 2, 6; and the receptor for interleukin 2. Nor did it change the number of circulting lymphocytes bearing markers for specific subsets (B, T, helper, suppressor, natural killer) and the serum antibody titers against influenza vaccine. The opposing effects of PGE2 and LTB4 may have led to the lack of change in immune functions tested.

Dietary α-linolenic acid alters tissue fatty acid composition, but not blood lipids, lipoproteins or coagulation status in humans

We examined the effect of dietary α-linolenic acid (ALA) on the indices of lipid and coagulation status and on the fatty acid composition of serum and peripheral blood mononuclear cell (PBMNC) lipids in ten healthy men (age 21–37 yr) who consumed all their meals at the Western Human Nutrition Research Center for 126 d. There was a stabilization period of 14 d at the start when all 10 subjects consumed the basal diet (BD) containing 23.4 energy percent (en%) fat and two intervention periods of 56 d each. During the first intervention period, 5 subjects consumed the BD containing 23.4 en% fat, and 5 subjects consumed a diet providing 6.3% calories from α-linolenic acid [flaxseed oil (FSO) diet containing 28.8 en% fat]. Diets were crossed over between the two groups during the second intervention period. Feeding the FSO diet did not nignificantly alter serum triglycerides, cholesterol, highdensity lipoproteins, low-density lipoproteins, apoprotein A-I and apoprotein B when compared to the corresponding values in the subjects fed the BD, nor was there any effect of the FSO diet on the bleeding time, prothrombin time and partial prothrombin time for these subjects. Feeding the ALA-containing diet did cause a significant increase in ALA concentration in serum (P<0.001) and PBMNC lipids (P<0.05). It also caused a significant increase (P<0.05) in the eicosapentaenoic and docosapentaenoic acid contents of PBMNC lipids, and a decrease (P<0.01) in linoleic and eicosatrienoic acid contents of serum lipids. Thus, dietary ALA, fed for 56 d at 6.3% of calories, had no effect on plasma triglyceride or very low density lipoprotein levels or the common risk factors associated with atherosclerosis, although these parameters have been reported by others to be influenced by fatty acids, such as palmitic or linoleic acids, in the diet. Dietary ALA did significantly alter the fatty acid composition of plasma and PBMNC.

Dietary conjugated linoleic acid did not alter immune status in young healthy women

The purpose of this study was to examine whether conjugated linoleic acid (CLA) supplementation in human diets would enhance indices of immune status as reported by others for animal models. Seventeen women, 20–41 yr, participated in a 93-d study conducted in two cohorts of 9 and 8 women at the Metabolic Research Unit of Western Human Nutrition Research Center. Seven subjects were fed the basal diet (19, 30 and 51% energy from protein, fat, and carbohydrate, respectively) throughout the study. The remaining 10 subjects were fed the basal diet for the first 30 d, followed by 3.9 g CLA (Tonalin)/d for the next 63 d. CLA made up 65% of the fatty acids in the Tonalin capsules, with the following isomeric composition: t10, c12, 22.6%; c11, t13, 23.6%; c9, t11, 17.6%; t8, c10, 16.6%; and other isomers 19.6%. Most indices of immune response were tested at weekly intervals, three times at the end of each period (stabilization/intervention); delayed-type hypersensitivity (DTH) to a panel of six recall antigens was tested on study day 30 and 90; all subjects were immunized on study day 65 with an influenza vaccine, and antibody titers were examined in the sera collected on day 65 and 92. None of the indices of immune status tested (number of circulating white blood cells, granulocytes, monocytes, lymphocytes, and their subsets, lymphocytes proliferation in response to phytohemagglutinin, and influenza vaccine, serum influenza antibody titers, and DTH response) were altered during the study in either dietary group. Thus, in contrast to the reports with animal models, CLA feeding to young healthy women did not alter any of the indices of immune status tested. These data suggest that short-term CLA supplementation in healthy volunteers is safe, but it does not have any added benefit to their immune status.

Effects of dietary arachidonic acid on human immune response

Arachidonic acid (AA) is a precursor of eicosanoids, which influence human health and the in vitro activity of immune cells. We therefore examined the effects of dietary AA on the immune response (IR) of 10 healthy men living at our metabolic suite for 130 d. All subjects were fed a basal diet containing 27 energy percentage (en%) fat, 57 en% carbohydrate, and 16 en% protein (AA, 200 mg/d) for the first and last 15 d of the study. Additional AA (1.5 g/d) was incorporated into the diet of six men from day 16 to 65 while the remaining four subjects continued to eat the basal diet. The diets of the two groups were crossed-over from day 66 to 115. In vitro indexes of IR were examined using the blood samples drawn on days 15, 58, 65, 108, 115, and 127. The subjects were immunized with the measles/mumps/rubella vaccine on day 35 and with the influenza vaccine on day 92. Dietary AA did not influence many indexes of IR (peripheral blood mononuclear cell proliferation in response to phytohemagglutinin, Concanavalin A, pokeweed, measles/mumps/rubella, and influenza vaccines prior to immunization, and natural killer cell activity). The postimmunization proliferation in response to influenza vaccine was about fourfold higher in the group receiving high-AA diet compared to the group receiving low-AA diet (P=0.02). Analysis of variance of the data pooled from both groups showed that the number of circulating granulocytes was significantly (P=0.03) more when the subjects were fed the high-AA diet than when they were fed the low-AA diet. The small increases in granulocyte count and the in vitro proliferation in response to influenza vaccine caused by dietary AA may not be of clinical significance. However, the lack of any adverse effects on IR indicates that supplementation with AA may be done safely when needed for other health reasons.

Concentration of dietary n-6 polyunsaturated fatty acids and the human immune status

We examined the effect of the dietary concentration of total fat and n-6 polyunsaturated fatty acids (PUFA) on the immune status of seven healthy women (age 30-65 years) who lived at our metabolic suite. During the first 20 days all subjects consumed a stabilization diet that contained 5.2 energy percent (en%) PUFA and 41.1 en% fat. For the next 40 days, three subjects consumed a diet with 3.2 en% PUFA and 26.1 en% fat, while the remaining four subjects consumed a diet with 9.1 en% PUFA and 31.1 en% fat. For the next 40 days, the diets of the two groups were crossed over. Blastogenesis of peripheral blood mononuclear cells cultured with phytohemagglutinin, concanavalin A, protein A, and pokeweed, and the serum concentrations of complement fractions C3 and C4 were significantly increased upon the feeding of both low fat (26.1 or 31.1 en%) diets compared to the values when the high fat (41.1 en%) diet was fed. None of the indices tested were different when the high PUFA (9.1 en%) and low PUFA (3.1 en%) diets were compared. Our results indicate that low fat diets improve some of the indices of human immune status and that a moderate increase in the level of n-6 PUFA in an otherwise low fat diet does not suppress the human immune system.

Energy restriction and immunocompetence in overweight women

Abstract The purpose of this study was to examine the effects of energy restriction on human immune functions and the mechanisms involved. Eight overweight (30–50%) women, 28–41 y, were fed a weight stabilization diet for 3 weeks; for the next 15 weeks their energy intake was reduced by 50%, while still providing adequate protein, vitamins and minerals. Indices of immune response were determined twice at the end of each metabolic period. Energy restriction caused a mean weight loss of 13.2 Kg, 25% decrease in NK cells numbers, and a 20–30 % decrease in their In vitro activity determined at different effector to target cell ratios (p In vitro secretion of IL1, IL2, and IL2R by peripheral blood mononuclear cells stimulated with LPS or PHA were not altered by energy restriction. There was a 38% increase in the concentration of serum cortisol associated with energy restriction (p=0.001), which may have lead to the decline in immune functions. Although, there were no obvious health risks to participants of this study, potentially they could be at increased risk for viral infections and tumor growth.