THE EFFECT OF DIETARY DOCOSAHEXAENOIC ACID ON PLASMA-LIPOPROTEINS ANDTISSUE FATTY-ACID COMPOSITION IN HUMANS

Normal, healthy male volunteers (n = 6) were fed diets [high docosahex aenoic acid-DHA] containing 6 g/d of DHA for 90 d. The stabilization ( low-DHA) diet contained less than 50 mg/d of DHA. A control group (n = 4) remained on the low-DHA diet for the duration of the study (120 d) . Blood samples were drawn on study days 30 (end of the stabilization period), 75 (midpoint of the intervention period), and 120 (end of the intervention period). Adipose tissue (AT) samples were taken on days 30 and 120. The plasma cholesterol (C), low density lipoprotein (LDL)- C and apolipoproteins. (ape) [Al, B, and lipoprotein (all were unchang ed after 90 d, but the triglycerides (TAG) were reduced from a mean va lue of 76.67 +/- 24.32 to 63.83 +/- 16.99 mg/dL (n = 6, P < 0.007 usin g a paired t-test) and the high density lipoprotein (HDL)-C increased from 34.83 +/- 4.38 mg/dL to 37.83 +/- 3.32 mg/dL (n = 6, P < 0.017 us ing a paired t-test), The control group showed no significant reductio n in plasma TAG levels. Apo-E, however, showed a marked increase in th e volunteers' plasma after 90 don the high-DHA diet, from 7.06 +/- 4.4 7 mg/dL on study day 30 to 12.01 +/- 4.96 mg/dL on study day 120 (P < 0.002 using a paired t-test). The control subjects showed no significa nt change in the apo-E in their plasma (8.46 +/- 2.90 on day 30 vs. 8. 59 +/- 2.97 on day 120). The weight percentage of plasma DHA rose from 1.83 +/- 0.22 to 8.12 +/- 0.76 after 90 d on the high-DHA diet. Altho ugh these volunteers were eating a diet free of eicosapentaenoic acid (EPA), plasma EPA levels rose from 0.38 +/- 0.05 to 3.39 +/- 0.52 (wt% ) after consuming the high-DHA diet, The fatty acid composition of pla sma lipid fractions-cholesterol esters, TAG, and phospholipid-showed m arked similarity in the enrichment of DHA, about 10%, after the subjec ts consumed the high-DHA diet. The DHA content of these plasma lipid f ractions varied from less than 1% (TAG) to 3.5% (phospholipids) at bas eline, study day 30. EPA also increased in all plasma lipid fractions after the subjects consumed the high-DHA diet. There were no changes i n the plasma DHA or EPA levels in the control group. Consumption of DH A also caused an increase in AT levels of DHA, from 0.10 +/- 0.02 to 0 .31 +/- 0.07 (wt%) (n = 6, P < 0.001 using a paired t-test), but the a mount of EPA in their AT did not change. Thus, dietary DHA will lower plasma TAG without EPA, and-DHA is retroconverted to EPA in significan t amounts. Dietary DHA appears to enhance apo-E synthesis in the liver . It appears that DHA can be a safe and perhaps beneficial supplement to human diets.