Twenty-three studies (577 participants) were included in the review: 2 parallel randomised controlled trials (RCTs; 64 participants), 15 crossover RCTs (381 participants), 1 parallel controlled trial (25 participants), 2 crossover controlled trials (34 participants) and 3 uncontrolled trials (73 participants).
Almonds: in 3 of the 4 highly rated studies, 50 to 100 g of almonds per day reduced TC and LDL in people with normal and raised cholesterol, compared with the control, muffins-control or Step I diet: the TC reduction was 4 to 16% and the LDL reduction was 7 to 19%. Diets with less than 50 g of almonds per day had no effect on LDL. There was no significant difference in lipids with almonds in comparison with an olive oil-based diet. There was no effect on triacyglycerols.
Macadamia nuts: in one highly rated study, macadamia nuts statistically significantly reduced TC (5%), LDL (5%), triacyglycerols (9%) and HDL (4%) in comparison with the average American diet. However, a second trial found no difference in lipid reductions for macadamia nuts compared with a low-fat high-complex carbohydrate diet.
Peanuts: in one highly rated study, peanuts statistically significantly reduced TC (7%) and LDL (9%) in comparison with a low-fat diet; in a second trial, TC was reduced by 11% and LDL by 14% compared with the average American diet and TC reduced by 2% compared with a Step II diet. Peanuts had no effect on lipids in comparison with an olive oil-based diet.
Pecans (72 g per day): one highly rated study showed pecans statistically significantly lowered lipids compared with a Step I diet (TC 7%, LDL 10%, triacyglycerols 11%); HDL was increased by 6%.
Walnuts (7 highly rated studies): in 4 studies (40 to 84 g per day) there was a statistically significant decrease in TC (4 to 12%) and LDL (6 to 16%) compared with Step I, Mediterranean and Japanese diets. Three studies of walnuts (41 to 78 g per day) showed no significant changes in comparison with low-fat, Mediterranean or Step 1 diets. In most studies HDL was not significantly affected.
No studies scoring 1 or 2 for quality assessed the effects of hazelnuts or pistachio nuts.