Twenty men completed both arms of the intervention. Mean age was 23 (4.1, sd) years, body mass index (BMI) was 21.6 (2.6, sd) kg/m2 and all were healthy as assessed by self-report and a biochemical screening panel. The diet was designed to be of typical of western composition, with 40 % of total energy derived from fat, 47 en% carbohydrate and 13 en% protein. There was no significant difference between total energy intake or macronutrient composition between treatments (P > 0.05, Table ) in this cross-over trial. The high-SFA and high-USFA dairy lipids used in the two diets resulted in a significant difference between dietary treatments for all fatty acids measured (paired t-test, P < 0.05; C10:0, C12:0, C14:0, C15:0, C16:0, C17:0, C18:0, C18:1, C18:2, C18:3, C20:4, C22:6, see Table ) other than C16:1 trans and the n-3 PUFA marine oil ecosapentaenoic acid (EPA, C20:5). The major changes in SFA were in myristic (C14:0, -1.9 g/d, -24%), palmitic (C16:0, -6.8 g/d, -28%) and stearic (C18:0, +3.0 g/d, +36%) acids. The major changes in USFA were in oleic (C18:1, +8.2 g/d, +39%), linoleic (LA, C18:2n-6, +6.9 g/d, +30%), α-linolenic (ALA, C18:3n-3, +0.6 g/d, +33%) and arachidonic (AA, C20:4n-6, +0.5 g/d, +14%) acids.
Composition of the two intervention diets as measured by direct chemical analysis
The erythrocyte fatty acid profile measured on day 21, following 3 weeks of high-SFA and high-USFA treatment are shown in Table . There was a significant difference in red blood cell (RBC) fatty acid profile between dietary treatments for C14:0, C16:0, C18:0, C18:1 and C20:4 (paired t-test, P < 0.05). C10:0 and C16:1 could not be detected as individual peaks on the FAME plots on either diet. Throughout the 21 day intervention period, RBC fatty acid profile (Figures &, middle and right panels) tended to mimic dietary profile (Figures &, left panel) for the majority of fatty acids measured but the relationships were weak.
Erythrocyte fatty acid profile in 20 healthy men following 21 days on a high saturated or a high unsaturated fat diet
Figure 1 Dietary (left panel) and red blood cell (RBC, centre and right panels) saturated fatty acid composition during the 3 week high-saturated (high-SFA) and high-unsaturated (high-USFA) dietary treatments. Diet was strictly controlled by providing subjects (more ...)
Figure 2 Dietary (left panel) and red blood cell (RBC, centre and right panels) mono- and polyunsaturated fatty acid composition during the 3 week high-saturated (high-SFA) and high-unsaturated (high-USFA) dietary treatments. Diet was strictly controlled by providing (more ...)
Not all individual SFAs were higher on the high-SFA diet, although the design of the trial ensured that total SFA content was higher on this treatment. Dietary C14:0, C15:0 and C16:0 were higher on the high-SFA treatment (P < 0.01), yet RBC analyses showed palmitic acid (C16:0) to be the single SFA which was greater following 21 days of the high-SFA diet compared with 21 days of high-USFA treatment (Figure , ANOVA, diet*time, P < 0.05). In contrast, dietary C12:0, C17:0 and C18:0 were all lower on the high-SFA treatment (P < 0.05), but RBC analyses showed stearic acid (C18:0) to be the single SFA significantly lower on the high-SFA relative to high-USFA treatment (ANOVA, diet*time, P < 0.05). With the exception of C16:0 there were significant increases above baseline RBC values in response to both treatments in all RBC SFAs over the 21 day intervention, possibly due to the change from habitual home diet (ANOVA, time, P < 0.01). RBC palmitic acid decreased on both treatments over time (ANOVA, time, P < 0.001).
Dietary oleic acid (C18:1) content was significantly higher on the high-USFA treatment (Figure , left panel, P < 0.001), which induced a significantly greater RBC oleic acid content over 21 days compared to high-SFA diet (Figure , middle and right panels, ANOVA, diet*time, P < 0.05). Both diets caused a decrease in RBC C18:1 content between baseline and follow-up which was independent of treatment group (ANOVA, time, P < 0.001).
Dietary linoleic (LA, C18:2), α-linolenic (ALA, C18:3), arachidonic (AA, C20:4) and docosahexaenoic acid (DHA, C22:6) were all significantly greater on the high-USFA treatment (Figure , left panel, P < 0.05), but only in the long chain PUFAs AA (C20:4) and DHA (C22:6) did RBC content differentially increase in response to the high PUFA diet (Figure , middle and right panels, ANOVA, diet*time, P < 0.01). There was a significant increase in RBC LA (C18:2) and a decrease in EPA (C20:5) and DHA (C22:6) content relative to baseline levels over the 3 weeks of dietary intervention, independent of treatment group (ANOVA, time, P < 0.001), but no significant change in RBC levels of ALA (C18:3) or AA (C20:4) over time (ANOVA, time, P > 0.05).
Table shows the Pearson correlations of dietary and RBC fatty acid composition throughout the 3 week intervention on both dietary treatments. There were significant correlations between dietary and RBC C14:0 and C18:1 on day 1 of high SFA, and C17:0 and C22:6 on day 1 of high-USFA diet (P < 0.05) both of which were pre-intervention. During the controlled intervention the analyses revealed a significant correlation between diet and blood markers for the MUFA oleic acid on day 14 of the high-SFA and day 21 of the high-USFA diets respectively (P < 0.05), for EPA throughout the high-SFA treatment (P < 0.05) and DHA throughout both treatments (P < 0.05). The correlation between diet and RBC fatty acid composition was by far the strongest and most consistent for the LCPUFA DHA despite the gradual decrease in RBCs over time on both high-SFA and high-USFA diets (ANOVA, time, P < 0.001).
Pearson correlations between diet and RBC fatty acid composition for the 2 dietary treatments (r values)