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Walnuts and cholesterol

 

Clinical bottom line

Eating 40 to 84 g walnuts/day, equivalent to approximately 8 to 16 walnuts, appears to reduce total and LDL cholesterol by 5% to 10%.


Background

A recent study from Ros et al [1] reported favourable changes in total and LDL-cholesterol and endothelial-dependent vasodilation associated with a diet rich in walnuts. But the study was small (21 individuals) and of short duration (four weeks on each diet), so Bandolier looked for other reports of diets rich in walnuts. There is a comprehensive, but lengthy, review of the relationship between walnuts and coronary heart disease [2], and for those who want something a little more digestible Bandolier has summarised the cholesterol changes found in clinical trials of diets rich in walnuts.

Results


Table 1: Changes in cholesterol levels with walnut-rich diets

         
% change
% change
% change
% change
Study
n
Duration
walnuts/day
Comparison diet
TC
LDL-C
HDL-C
LDL:HDL
Sabate [3]
18
4 weeks
84g
NCEP Step 1
-12
-16
-5
red
Abbey [4]
16
3 weeks
68g
Peanut diet
-5
-9
NSC
Chisholm [5]
21
4 weeks
78g
baseline
-4
-8
42
Zambon [6]
49
6 weeks
41-56g
baseline
-9
-11
NSC
-8
 
Meditteranean diet
-4
-5
NSC
NS
Almario [7]
18
6 weeks
48g
habitual diet
(red TF, SFA, inc MUFA)
NSC
NSC
dec
Iwamoto [8]
40
4 weeks
48-57g
average Japanese diet
-5
-11
NSC
-9
Morgan [9]
67
6 weeks
64g
low fat, low cholesterol
NS dec
NS dec
NS inc
Zibaeenezhad [10]
60
45 days
3g oil
baseline
NS
NS
NSC
Ros [1]
21
4 weeks
40-65g
baseline
-7
-9
NSC
-5
        Meditteranean diet
-4
-6
-5
NSC=no significant change, NS=non-significant, dec=decrease, inc=increase

The trials [1, 3-10] are small (16-67 participants), of short duration (3-6 weeks on a diet) carried out under free-living or metabolic ward conditions, and have methodological limitations (eg blinding, monitoring of diet). Participants were mainly Caucasian, young or middle-aged, with either normal lipid profiles or mild-to-moderate hyperlipidemia and few cases of established coronary heart disease.

In the three trials that compared walnut-rich diet to baseline, the weighted mean reduction in total cholesterol was 7% and in LDL-cholesterol was 10%. In seven comparisons between walnut-rich diet and a reference diet, the weighted mean reduction in total cholesterol was 3% and in LDL-cholesterol was 5%. Where measured, the LDL:HDL ratio showed reductions of 0-9%. There are suggestions that walnut-rich diets may have beneficial effects beyond changes in plasma lipid levels, but there is too little evidence to draw any conclusions.

Comment

Ultimately we want to know whether including walnuts in the diet can reduce cardiovascular disease. These trials use established markers of cardiovascular risk as surrogate endpoints, but evidence from clinical trials for a sustained effect or clinical benefit in terms of disease reduction is lacking. A number of observational studies support a role for a diet rich in walnuts for the reduction of coronary heart disease [11]. The trials reviewed here use 40 to 84 g walnuts/day, equivalent to approximately 8 to 16 walnuts, and it is debatable whether this intake is sustainable long-term in real life. Cholesterol reductions are equivalent to those seen with oatmeal and oatbran, and soy protein [2], but clinical trials using more realistic levels of around 30 g/day are needed to establish their relevance in disease prevention. While it is likely that there are benefits from including walnuts in the diet as part of a cardiovascular risk-reduction strategy, they are clearly not in the same league as statins.

References

  1. Ros E, Nunez I, Perez-Heras A, Serra M, Gilabert R, Casals E, Deulofeu R. A walnut diet improves endothelial function in hypercholesterolemic subjects: a randomized crossover trial. Circulation 2004 109: 1609-1614.
  2. Feldman EB. The scientific evidence for a beneficial health relationship between walnuts and coronary heart disease. J Nutr 2002 132: 1062S-1101S.
  3. Sabate J, Fraser GE, Burke K, Knutsen SF, Bennett H, Lindsted KD. Effects of walnuts on serum lipid levels and blood pressure in normal men. N Engl J Med 1993 328: 603-607.
  4. Abbey M, Noakes M, Belling GB, Nestel PJ. Partial replacement of saturated fatty acids with almonds or walnuts lowers total plasma cholesterol and low-density-lipoprotein cholesterol. Am J Clin Nutr 1994 59: 995-999.
  5. Chisholm A, Mann J, Skeaff M, Frampton C, Sutherland W, Duncan A, Tiszavari S. A diet rich in walnuts favourably influences plasma fatty acid profile in moderately hyperlipidaemic subjects. Eur J Clin Nutr 1998 52: 12-16.
  6. Zambon D, Sabate J, Munoz S, Campero B, Casals E, Merlos M, Laguna JC, Ros E. Substituting walnuts for monounsaturated fat improves the serum lipid profile of hypercholesterolemic men and women. A randomized crossover trial. Ann Intern Med 2000 132: 538-546.
  7. Almario RU, Vonghavaravat V, Wong R, Kasim-Karakas SE. Effects of walnut consumption on plasma fatty acids and lipoproteins in combined hyperlipidemia. Am J Clin Nutr 2001 74: 72-79.
  8. Iwamoto M, Sato M, Kono M, Hirooka Y, Sakai K, Takeshita A, Imaizumi K. Walnuts lower serum cholesterol in Japanese men and women. J Nutr 2000 130:171-176.
  9. Morgan JM, Horton K, Reese D, Carey C, Walker K, Capuzzi DM. Effects of walnut consumption as part of a low-fat, low-cholesterol diet on serum cardiovascular risk factors. Int J Vitam Nutr Res 2002 72: 341-347.
  10. Zibaeenezhad MJ, Rezaiezadeh M, Mowla A, Ayatollahi SM, Panjehshahin MR. Antihypertriglyceridemic effect of walnut oil. Angiology 2003 54: 411-414.
  11. Lavedrine F, Zmirou D, Ravel A, Balducci F, Alary J. Blood cholesterol and walnut consumption: a cross-sectional survey in France. Prev Med 1999 28: 333-339.