A low fat-high vegetable diet might increase CVD risk

20 07 2010

Another study that shows the “safety” of the proposed healthy guidelines. This one was published in the Journal of Arteriosclerosis, Thrombosis and Vascular Biology from the American Heart Association. The authors wanted to measure the levels of oxLDL and Lp (a) in a group of women after a dietary intervention. Women were told to follow one of two diets:

Group A: Low fat, high vegetable

Group B: Low fat, low vegetable

A crossover design was used, so all women followed both diets at the end of the study. From baseline:

  • Both groups increased their carbohydrate (3-4%) and protein (3%) intake.
  • Total fat intake was reduced (but only 5%).
  • Saturated fat was reduced 4% in group B and 5.5% in group A.
  • Monounsaturated fat decreased 1 and 2% in group A and group B, respectively.
  • Polyunsaturated fat increased 1% in group B and 3.5% in group A.
  • Dietary fiber increased from 21g to 25g in group B and a whopping 40g in group A.
  • All micro nutrients and antioxidants were higher in group A than in group B.


Plasma Lipids

Both diets lowered triglycerides. Total cholesterol was only reduced in Group A. Not surprisingly (at least for me) HDL was reduced with both diets, having the lowest value on the low fat-high vegetable diet. LDL cholesterol was reduced only in Group A but increased in Group B.

Plasma Antioxidant Levels

All antioxidants were increased in Group A, except for lycopene and α-tocopherol.

oxLDL and Lp (a)

Both markers increased in both groups:

OxLDL-EO6* Lp (a)*
Group A 19% 9%
Group B 27% 7%

* % of increase from baseline (median value).

The levels of oxLDL-EO6 and Lp (a) and the relative changes were strongly correlated in both groups. The authors concluded (my remarks):

In conclusion, we found that a diet traditionally considered to be anti-atherogenic (low in saturated fat and high in polyunsaturated fat and naturally occurring antioxidants) increased plasma levels of circulating oxidized LDL and Lp(a). The question of whether the changes observed in the present study are, in fact, pro-atherogenic or anti-atherogenic remains to be solved. (Italics added)

A clear bias towards the lipid hypothesis is seen, beginning with the title of the study (I wonder how the study would have been called if the results showed the opposite). But are these changes in fact, pro-atherogenic? Lets see:

  • LDL oxidation is an important factor in atherogenesis, as it attracts monocytes into the vascular intima and transform them into foam cells. This process contributes to cholesterol accumulation in arterial wall macrophages and promotes pro-inflammatory events that accelerate lesion development and plaque rupture (1). Because of this, LDLox is a strong marker for CVD (2).
  • Lp (a) is also a strong risk factor for CAD and its believed to be an independent one (3, 4).

So, it seems that increased levels of oxLDL and Lp (a) are in fact pro-atherogenic. But why do a “healthy” low fat-high vegetable diet would cause pro-atherogenic results? We have to consider that:

  • Saturated fat intake and Lp (a) are inversely correlated (so more saturated fat intake = less Lp (a)) (5).
  • Polyunsaturated fat intake increases LDL susceptibility to oxidation (6).
  • Antioxidants have not shown positive results in vivo reducing CVD (7)

The lack of effect of fiber and vegetables in reducing the risk of CVD might be due to the low fat intake. Studies like this one have shown that vegetable and fruit intake might reduce CVD and CAD risk only when combined with a high fat diet.

Even though the changes in fat composition between the baseline diet and the intervention diet weren’t that drastic, the results speak for themselves. The diet wasn’t that low fat either, so the results could be worst when following a recommended “healthy balanced” diet with a more drastic reduction in total fat intake and saturated fat.




One response

1 08 2010
NU's Quest for Carnivory!

[…] balanced” diet with a more drastic reduction in total fat intake and saturated fat. A low fat-high vegetable diet might increase CVD risk Somatotropin (Follow link for original included embedded link to references) Disclaimer: All posts on […]

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