*2.2. Nut Consumption and Blood Lipids*

The effects of tree nut and peanut consumption on lipid profiles from intervention studies published in the last ten years [31–43] are summarized in Table 2. The results of these clinical trials in a middle-aged population indicate a causal association between higher nut intake and lower levels of total cholesterol (T-C), low density lipoprotein-cholesterol (LDL-C), non-high density lipoprotein-cholesterol (non-HDL-C), triglycerides (TG), and apolipoprotein B (apoB), all markers of CV morbidity and mortality.




M—men;

RCT—randomized

 controlled trial;

SD—standard

 deviation; T2DM—type

 2 diabetes mellitus; T-C—total cholesterol;

TG—triglycerides;

 W—walnuts.

After a 12 week trial and daily intake of 56 g almonds, compared with a no-nut control diet, plasma apoB, apoB/apoA-1 ratio, T-C, LDL-C, and LDL-C/HDL-C ratio decreased significantly by 15.6%, 17.4%, 6.0%, 11.6%, and 9.7%, respectively, in patients with T2DM [31]. Similarly, the inclusion of almonds in the diet of patients on chronic statin therapy revealed a 4.9% reduction in non–HDL-C compared with the no-nut group, and non-statistical significance decreases in LDL-C and TG [34]. Consumed before breakfast, 10 g almonds proved to increase serum HDL-C by 15% after 12 weeks in CAD patients with low initial HDL-C [35]. A new trial, comparing almond snacks with isocaloric carbohydrate snacks, demonstrated that almond snacks can improve the serum T-C/HDL-C ratio in women but not in men, with no change in body weight (BW) or inflammatory biomarkers in overweight and obese adults with high T2DM risk [43]. The short 8 weeks trial might be the cause for the differential gender results.

Our findings are aligned with data from a meta-analysis conducted by Musa-Veloso et al. [44] in which almond consumption was confirmed to significantly decrease T-C (*p* < 0.001), LDL-C (*p* = 0.001), and TG (*p* = 0.042), with no modification in HDL-C (*p* = 0.207). Also, Nishi et al. [45] showed that the daily consumption of almonds by middle-aged adults can improve the blood lipid profile, and a 3.5% decrease in the 10-year CHD risk was noticed for every 30 g increase in almond intake.

Consistent with the effects of other nuts, Brazil nuts and cashews can also improve lipid profiles. In a group of hypertensive and dyslipidemic subjects, the intake of partially defatted Brazil nuts significantly increased plasma selenium and the antioxidant activity of the glutathione peroxidase enzyme, and reduced oxidation in LDL-C compared to the baseline [37]. Mah et al. [39] demonstrated that adding cashews into the diet of a population with high LDL-C risk could lower the T-C, LDL-C, and LDL-C/HDL-C ratio. In agreement with these results, a very recent trial showed a significant decrease for the LDL-C/HDL-C ratio in a cashew diet group compared with a no-cashew control group [46].

Pistachio, a biochemically-rich tree nut, proved to have a lowering effect on CV risk factors. Daily pistachio intake significantly decreased the T-C and T-C/HDL-C ratio (*p* < 0.05), and TG levels (*p* = 0.003) compared to the control in T2DM adults [38]. Also, after 4 months of 57 g pistachio daily, small LDL particles and non-HDL particles significantly decreased compared to the nut-free diet [33]. This change of lipoprotein particle size may explain the decrease of CVD risk. Kay et al. [47] showed that the consumption of a pistachio-enriched diet, when compared to the control, significantly increased serum concentration of antioxidants, including beta-carotene, gamma-tocopherol, and lutein, and significantly decreased serum oxidized-LDL, an important factor in CVD.

Walnut, one of the most versatile tree nuts with its higher content of polyunsaturated fatty acids (PUFAs) including α-linolenic acid, and high antioxidant activity, may influence CVD risks via its lipid-lowering impact. Compared with a control diet without walnuts, a walnut-included diet for 6 months significantly decreased T-C and LDL-C and improved diet quality [36]. In a shorter cross-over trial, a walnut-enriched diet significantly reduced non-HDL-C (*p* = 0.025) and apoB (*p* = 0.009) compared with a control diet, while T-C displayed a tendency toward reduction (*p* = 0.073) [32]. Bamberger et al. [40] indicated that a walnut-enriched diet versus a control diet caused a significant decrease in fasting cholesterol (*p* = 0.002), LDL-C (*p* = 0.029), non-HDL-C (*p* ≤ 0.001), TG (*p* = 0.015), and apoB (*p* ≤ 0.001) in healthy mature adults. Also, 15 mL walnut oil daily (corresponding to ~28 g walnuts) added for 90 days to the diet of hyperlipidemic T2DM patients significantly decreased the T-C, LDL-C, T-C/HDL-C ratio (*p* < 0.001 for all), and TG level (*p* = 0.021), compared with the control group, while the HDL level showed an increased trend (*p* = 0.06) [48]. Similarly, Austel et al. [49] noticed beneficial changes in blood lipids after replacing saturated fats with walnut oil.

A meta-analysis of 26 trials confirmed that walnut-enriched diets compared with control groups significantly reduced T-C (*p* < 0.001), LDL-C (*p* < 0.001), TG (*p* = 0.03), and apoB (*p* = 0.008), with no significant modifications in BW or blood pressure [50].

Integrated into a typical Western diet, pecans, another tree nut with higher contents of PUFAs, showed a borderline significant lowering of T-C and LDL-C as compared to a nut-free control diet in overweight or obese adults with central adiposity [41].

A new trial confirmed that, compared to a carbohydrate control diet, adding 75 g per day of mixed nuts (tree nuts and peanuts) to healthy diets could significantly lower small LDL-C (*p* = 0.018), with a trend towards reduction for T-C (*p* = 0.066) and non-HDL-C (*p* = 0.067) in T2DM elderly patients [42].

These outcomes are validated by a meta-analysis of 61 trials which concluded that nut intake significantly lowered the levels of T-C, LDL-C, apoB, and TG, with the key factor of changing lipid profile appearing to be nut dose rather than nut type [51].

As many strategies for reducing T-C and LDL-C levels could lower HDL-C levels, all the dietary plans for lowering LDL-C levels should aim to maintain or even increase HDL-C. In their 2017 guidelines, the American Association of Clinical Endocrinologists and American College of Endocrinology recommend a minimum blood HDL-C level of 40 mg/dL in CVD risk individuals [52]. However, data [53] showed that small HDL particles present only a weak defense, the strong protection against CVD risks coming from large HDL units. Equally, small LDL particles, due to their proneness to oxidation compared with larger ones, are responsible for atherosclerosis progress and CVD, while large LDL components are only weakly linked with CVD [53]. Based on these many results, nut consumption can evidently aid in the management of a healthy lipid profile in mature adults.
