Eating nuts improves cholesterol and other blood lipid levels, which may help stave off heart disease, researchers found.
In a pooled analysis of 25 intervention trials, eating an average of 67 grams of nuts a day (2.4 ounces) reduced total cholesterol by 5.9 percent and LDL, or bad, cholesterol by 7.4 percent, according to Dr. Joan Sabaté of Loma Linda University in California and colleagues.
The ratios of total to HDL (good) cholesterol and of LDL to HDL cholesterol also were reduced, they reported in the May 10 Archives of Internal Medicine.
Epidemiological studies have linked nut consumption with a reduced risk of coronary heart disease, and many dietary intervention trials have studied the effects of nut consumption on blood lipid levels.
"This study gives evidence that the cholesterol-lowering mechanism is one of the driving forces in the previously discovered relationship that nuts prevents heart attack," Sabaté said in an interview
In 2003, the U.S. Food and Drug Administration okayed a qualified health claim that evidence suggests -- but does not prove -- that eating 1.5 ounces (43 grams) of nuts per day as part of a diet low in saturated fat and cholesterol reduces coronary heart disease risk.
The government allows the claim on dietary labeling for specific nuts, including almonds, hazelnuts, pecans, pistachios, walnuts, peanuts, and some pine nuts.
Although the decrease in LDL cholesterol in the current analysis is modest compared with that seen with statins, "the value of regular nut consumption for coronary heart disease prevention is unlikely due to the blood cholesterol-lowering effect alone," Sabaté and his colleagues wrote.
Indeed, they wrote, "nut consumption exerts beneficial effects by improving endothelial function, lowering oxidative stress, and reducing lipoprotein(a) level."
To assess the effects of nut consumption, the researchers performed a pooled analysis of raw data from 25 intervention trials conducted in seven countries that included 583 men and women with various blood lipid problems. None of the participants was taking lipid-lowering medications. Sample size ranged from 10 to 49.
All of the dietary interventions were exclusively nuts -- mostly almonds and walnuts -- and ranged in duration from three to eight weeks.
Quantities ranged from 23 to 132 grams per day, with a mean of 67 grams.
The interventions resulted in the following average reductions (with percentage changes), regardless of the type of nut used:
Total cholesterol: 10.9 mg/dL (5.1 percent)
LDL cholesterol: 10.2 mg/dL (7.4 percent)
Ratio of LDL to HDL cholesterol: 0.22 (8.3 percent)
Ratio of total to HDL cholesterol: 0.24 (5.6 percent)
Triglycerides were reduced only for individuals with hypertriglyceridemia (baseline level of at least 150 mg/dL). The mean reduction in this group was 20.6 mg/dL (10.2 percent).
HDL cholesterol concentration was not affected.
Nut consumption improved blood lipid levels in a dose-dependent fashion. For example, if 20 percent of dietary energy came from nuts, there were 4.5 percent and 6.5 percent reductions in total and LDL cholesterol, respectively.
If 10 percent of dietary energy came from nuts, the reductions were 2.8 percent and 4.2 percent, respectively.
At the amount included in the FDA-approved claim statement -- about 43 grams per day -- the reductions were 3.2 percent for total and 4.9 percent for LDL cholesterol.
The lipid-lowering effects of nuts were magnified among individuals with higher baseline LDL levels, those with a lower body mass index, and those consuming a Western diet high in total and saturated fat (versus a Mediterranean diet high in total fat but low in saturated fat).
"Greater cholesterol lowering effect is found when nuts replace saturated fat than when olive oil or carbohydrates are replaced," Sabaté and his colleagues wrote. "This finding has important clinical and public health applications."