- Click here for explanation of classification scheme.

1.  To review the epidemiologic and clinical studies that have demonstrated the effects of nuts on cardiovascular health

2.  To address the question of whether the reduction in CHD risk can be explained solely by the fatty acid profile of nuts or if other compounds in nuts contribute to risk reduction. 

Must be:

1. a large epidemiological study showing a decreased risk in CHD due to nut consumption or
2. a clinical study evaluating the effects of diets containing nuts on lipid and lipoprotein endpoints.

Criteria for inclusion of articles:  "studies to date"; no other specific criteria given

1. studies not epidemiologically or clinically designed.
2. study conducted before 1991.

Narrative Review: Protocol for review not described.  Reports of epidemilogic and clinical studies summarized and synthesized in tables and narrative.

Epidemiologic studies:

• Large cohort studies examined the association of nut consumption with CHD.
• Nut consumption assessed using FFQ

 Clinical Studies:

Test blood lowering effect of average American diet or low fat diet compared to same diet with nuts.  Many examined the effect of nuts on fatty acid profile of the diet. 

Meta-analysis:

Diet composition data from 8 clinical studies were used in the cholesterol predictive equations from Mensink and Katan, and Hegsted to predict changes in total and LDL cholesterol. These values were then compared with the observed changes from the clinical studies.

 

Epidemiologic studies:

Frequency of nut consumption (1 ounce serving per week), endpoints:

• total CHD mortality
• definite fatal CHD
• nonfatal MI
• total cardiac death or sudden death.

Clinical studies:

Diet compositin, baseline and endpoints lipids/lipoproteins

Meta-analysis:

Predicted change in total and LDL cholesterol.

Estimated percent changes in CHD risk with isocaloric substitution of fat from nuts for carbohydrate in the diet

Actual Sample:

Reports from:

• 5 large epidemiologic studies involving over 200,000 men and women
• 3 controlled feeding trials with total of 42 male and 28 female subjects
• 8 free-living subject studies with total of 90 male and 109 female subjects

Epidemiological Studies and Results:

• California Seventh-Day Adventist Health Study (Fraser, 1995)
• Adventist Health Study (Fraser, 1992; Fraser, 1997a; Fraser, 1997b)
• Iowa Women's Health Study (Prineas, 1993; Kushi, 1996)
• Nurses' Health Study (Hu, 1998)
• Cholesterol and Recurrent Events (CARE) Study (Brown, 1999)
• Physicians Health Study (Albert, 1999) 11 clinical studies

Results from Epidemiological Studies:

An inverse dose-response existed between frequency of consumption of nuts and RR of CHD in men and women.

Consuming nuts (1 oz. serving) more than 1 time/wk significantly decreased the relative risk of CHD.

RR for nut consumption >4 or 5 time/wk compared to <1 time/wk
Total CHD           .45 to .65
Fatal CHD           .52 to .61
Nonfatal CHD      .49 to .68

Clinical Studies and Lipid Change Results:

Controlled Feeding Studies

Curb, 2000--RCT (crossover)
Macademia nuts fed for 30 d 15 M, 15 F
•  Baseline LDL-Chol 3.47 mmol/L vs. 30 days on nuts: 3.22 mmol/L (P<0.01)

Kris-Etherton, 1999 RCT (double-blind crossover) 
Peanuts/peanut butter fed for 5 wk 9 M, 13 F w hypercholesterolemia
• Baseline LDL-chol: 3.05 mmol/L vs. 3.03 mmol/L after 5 weeks (P<0.05).

Sabate, 1993 RCT (crossover)
84 g/d of walnuts for 4 wk 18M
•  LDL-chol 2.43 mmol/L compared to 2.90 mmol/L for those on diet without walnuts (P<0.001)

Free-Living Subjects Studies

Abbey, 1994 Consecutive supplemental trial for 3 wk
84 g almonds/d or 68 g walnuts/d 16 M
•  LDL-chol 3.21 mmol/L on almonds, 3.26 mmol/L on walnuts and 3.58 mmol/L for control dieet (P<0.001)

Chisholm, 1998 RCT (crossover)
78 g/d of walnuts for 4 wk 21M w hypercholesterolemia
•  LDL-chol 3.94 mmol/L vs 4.10 mmol/L low fat diet (P<0.001)

Colquhoun, 1996 RCT (crossover)
50 to 100 g macademia nuts/d for 4 wk 7 M, 7 F w hypercholesterolemia
•  Baseline LDL-chol: 4.13 mmol/L compared with 4 wk: 3.68 mmol/L (P<0.01)

Edwards, 1999 RCT (crossover)
Pistachio uts for 3 wk 4 M, 6 F w hypercholesterolemia
•  No significant effect on LDL-chol (baseline: 4.65 mmol/L vs. 3 wk: 4.08 mmol/L

Morgan et al. RCT (parallel artm)
68 g pecans/d for 8 wk 4 M, 15 F
•  LDL-chol at baseline: 2.61 mmol/L vs 2.46 mmol/L at 8wk (P<0.005)

O'Bryne, 1997 Parallel arm
35-68 g peanuts/d for 6 mo 25 F w hypercholesterolemia
•  LDL-chol at baseline: 4.71 mmol/L vs. 4.16 mmol/L (P<0.01).

Spiller, 1998 RCT (parallel arm)
Almonds 100g/d for 4 wk
•  LDL-chol: baseline 4.29 mmol/L compared to 4.16 mmol/L after 4 wk (P<0.01)

Zambon, 2000 RCT (crossover)
Walnuts 41-56 g/d for 6 wk 26 M, 23F w hypercholesterolemia
•  LDL-chol at baseline: 5.50 mmol/L vs 4.48 mmol/L after 6 wk (P<0.001).

Collectively, the clinical studies indicate that inclusion of nuts in a blood cholesterol-lowering diet has favorable effects on lipid and lipoprotein profiles (as would be expected based on the fatty acid and cholesterol profile of the diet).

Six of 7 studies with a hyperlipidemic subjects found significant cholesterol lowering.

Meta-analysis:

4 of 8 studies had greater cholesterol-lowering than predicted from change in fatty acid composition of diet.

Using data from the Hu study, the predicted percent change in CHD risk attributable to the changes in the fatty acid profile after consuming nuts was compared to that reported.  CHD risk was lower in most instances when nuts were consumed.

 

Author's Conclusions:

There is consistent evidence, especially from epidemiologic studies, that nuts have a strong protective effect against CHD morbidity, and mortality in different population groups.

Clinical studies have reported total and low-density lipoprotein cholesterol-lowering effects of health-healthy diets that contain various nuts or legume peanuts.

Evidence from a growing database of clinical studies with nuts indicates that part of the cardioprotective effect is due to their favorable effects on plasma lipids and lipoproteins due to the fatty acid composition of the diet when nuts replace dietary SFA and/or carbohydrate.

It is appropriate to recommend inclusion of nuts in a healthy diet that meets energy needs to reduce CHD and there s a need to provide dietary guidance necessary for the public to understand how to plan heart healthy diets that include nuts.

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0 Foundation associated with industry:

The authors did what they set out to do, and provide an excellent summary of studies that show the benefits of nuts on serum lipids and the prevention of CHD. The information is organized in table format for easy review. A limitation is the authors' failure to describe how articles were selected.  Thus the reader is unable to determine if other studies have been done with negative findings.