The effect of dietary docosahexaenoic acid on plasma lipoproteins and tissue fatty acid composition in humans.
Level 3 - non-randomized controlled study
Controlled dietary trial without reported randomization
PubMed 9397398 · doi:10.1007/s11745-997-0146-5
What was done
Healthy male volunteers were fed a 30-day stabilization diet low in docosahexaenoic acid (<50 mg/day DHA). Following stabilization, 6 participants received a high-DHA diet (6 g/day) for 90 days, while 4 control participants remained on the low-DHA diet for the full 120 days. Blood samples were collected at days 30, 75, and 120, and subcutaneous adipose tissue biopsies were taken at days 30 and 120 to assess plasma lipids, apolipoproteins, and tissue fatty acid composition.
What was found
In the high-DHA group (n = 6): - Plasma triglycerides decreased from 76.67 ± 24.32 to 63.83 ± 16.99 mg/dL (p < 0.007). - HDL cholesterol increased from 34.83 ± 4.38 to 37.83 ± 3.32 mg/dL (p < 0.017). - Apo-E increased from 7.06 ± 4.47 to 12.01 ± 4.96 mg/dL (p < 0.002); control apo-E was unchanged (8.46 ± 2.90 to 8.59 ± 2.97 mg/dL). - Total cholesterol, LDL-C, apo A-I, apo B, and lipoprotein(a) were unchanged. - Plasma DHA weight percentage rose from 1.83 ± 0.22% to 8.12 ± 0.76%. - Plasma EPA weight percentage rose from 0.38 ± 0.05% to 3.39 ± 0.52%, despite an EPA-free diet. - Adipose tissue DHA increased from 0.10 ± 0.02% to 0.31 ± 0.07% (p < 0.001), while adipose tissue EPA did not change. - The control group (n = 4) showed no significant changes in plasma triglycerides, apo-E, DHA, or EPA.
Why it matters
This study demonstrates in humans that isolated dietary DHA lowers triglycerides independently of EPA, raises apo-E, and undergoes substantial retroconversion to EPA in plasma.
Limits
The sample size is extremely small (n = 6 intervention, n = 4 control), limited entirely to healthy men, and the abstract does not report randomization or blinding. The 6 g/day dose of DHA is far higher than typical dietary or standard supplemental intakes.
Cited by
- supports In normal human red blood cells and most other tissues, DHA is naturally present at approximately four times the concentration of EPA.