This randomized, crossover clinical trial was designed to examine the impact of almonds incorporated to a NCEP step 1 diet on vascular reactivity and other CVD risk factors in patients with CAD, using the NCEP step 1 diet without nuts as the control phase. Neither the ALM nor CON diet affected measures of endothelial vasodilator function, including FMD, lnPAT ratio, and PWV, a measure of arterial stiffness. In addition, no significant effect of ALM compared to CON on the plasma lipid profile or selected biomarkers of inflammation, endothelial function, and oxidative stress was observed.
Endothelial dysfunction, a critical early event in the pathogenesis of atherosclerosis characterized by the reduced bioavailability of NO (a vasodilator) and the increased expression of cellular adhesion molecules, is related to perfusion abnormalities and subsequent ischemic events. However, we found no beneficial effect of chronic almond consumption on vascular reactivity reflected by FMD, NMD, lnPAT ratio, and PWV, even though the ALM diet significantly increased intake of several nutrients associated with improved endothelial function in other studies. Our results are consistent with the study by López-Uriarte et al. in which a 12-weeks intervention study with mixed nuts (15 g walnuts, 7.5 g almonds, and 7.5 g hazelnuts) did not show an effect on endothelial function assessed by PAT in patients with Metabolic Syndrome. In contrast, Choudhury et al. reported that 50 g almonds/day for 4 weeks improved FMD asymptomatic men as compared to no almonds (3.6 vs. 2.9 %). Similarly, a 4-weeks intervention where hazelnuts replaced ~20 % daily energy intake significantly improved FMD (56.6 %) from 15.2 to 21.8 % as compared to control in 21 adults with hypercholesterolemia. Further, Katz et al. found the intake of 56 g/day walnuts for 8 weeks significantly increased FMD from 8.8 to 10.2 % in overweight patients with Metabolic Syndrome, accompanied by a reduction in systolic blood pressure. Ros et al. also reported that walnuts incorporated into a cholesterol-lowering Mediterranean diet to replace 32 % MUFA energy improved endothelium-dependent FMD from 4.1 to 5.1 % in subjects with hypercholesterolemia. Differences in the study design, subject characteristics (including health status, lifestyle, and drug therapy), and nut nutrient composition may account for the discordant results obtained here. For example, all of our patients were receiving multiple risk-reduction therapies and had well-controlled lipid profiles at baseline. The discrepant results might also reflect differences in the nutrient content of the various tree nuts; e.g., walnuts contain more polyunsaturated fats, including α-linoleic acid, than MUFA compared to other tree nuts. However, the exact mechanism(s) for the discrepancy between our studies and others remain to be explored in the future studies.
The effect of chronic consumption of almonds and other tree nuts on blood biomarkers of CVD have been demonstrated, although the results are mixed with regard to individual biomarkers. Previously, we observed that almonds replacing 20 % daily caloric intake in a NCEP step 2 diet improved lipid profile in Chinese patients with type 2 diabetes. The benefits of almonds on the lipid profile of healthy adults or those who have hypercholesterolemia, dyslipidemia, and/or prediabetes have been reported in several studies. More recently, Nishi et al. found that almond consumption at 37 or 73 g/day for 4 weeks increased oleic acid and MUFA content in serum TG and non-esterified fatty acid fractions. Jenkins et al. extrapolated from their dose–response study to suggest that each 7-g portion of almonds would induce a 1 % reduction in LDL-C. In contrast, we did not find that the addition of almonds to the NCEP step 1 diet affected TC, TG, HDL-C, LDL-C or small density LDL-C. However, as the lipid profile at study baseline in our subjects were being maintained within normal ranges by statins and/or the NCEP Step 1 diet, it seems unlikely that any single food would enable a further significant improvement.
Inflammation plays a critical role in the risk for and progression of CVD such that inflammatory biomarkers like CRP and IL-6 are generally recognized as independent predictors of atherosclerosis. Cell adhesion molecules, including VCAM-1, E-selectin, and intercellular adhesion molecule-1 (ICAM-1), also contribute to the pathogenesis of this condition. Jiang et al. noted in the Multi-Ethnic Study of Atherosclerosis that inflammatory biomarkers were inversely associated with an increased frequency of nut and seed consumption. Consistent with this observational data, we previously found that almonds decreased IL-6 and CRP, and TNF-α in Chinese patients with type 2 diabetes but did not affect ICAM-1 or VCAM-1. Rajaram et al. also reported that almond intake diminished CRP in free-living healthy adults although no dose–response relationship was noted. In contrast, Damasceno et al. reported that neither almonds nor walnuts affected CRP, ICAM-1 or VCAM-1 in asymptomatic adults with moderate hypercholesterolemia. In our study of well-controlled CAD patients, neither the ALM nor the CON diet had an impact on IL-6, CRP, TNF-α or E-selectin. However, there was a trend toward reduction in VCAM-1 after the ALM phase. It is noteworthy that the concentration of CRP, IL-6 and TNF observed in this study appeared to be slightly larger than the values found in Chinese patients with type 2 diabetes or coronary heart disease and in the prospective Multi-Ethnic Study of Atherosclerosis. Thus, it is plausible that the larger starting values in inflammatory biomarkers may account for the observed null results. Also, the null effect may be attributed to the direct or indirect anti-inflammatory effects of multiple medications taken by the patients. Similar to the slight improvement in VCAM-1, urinary excretion of NO tended to increase with the ALM diet. These trends suggest a possible modest benefit of almond intake on endothelial function in CAD patients, so further research on this potential benefit is warranted.
Almonds are a good source for a number of nutrients, with 85 g providing >10 % of the daily value of many vitamins (vitamin E, riboflavin, niacin, thiamin, and folate), minerals (calcium, copper, iron, magnesium, manganese, phosphorus, potassium, zinc), and fiber as well as arginine and oleic acid. In addition, 85 g almonds contain 111 mg β-sistosterol, 9.3 mg flavonoids, and 156.5 mg proanthocyanins. Relative to the CON diet, the ALM diet had a more positive impact on nutritional quality by increasing intake of calcium, magnesium, choline, and fiber above recommended values. The intake of these nutrients were below either the EAR or RDA when the subjects were consuming CON diet. These results are consistent with Jaceldo-Siegl et al. who found the addition of 52 g/day almonds to the habitual diets of healthy men and women for 6 months significantly increased their intakes of MUFA, PUFA, fiber, vegetable protein, vitamin E, copper, and magnesium and decreased the amount of trans fatty acids, animal protein, sodium, cholesterol, and sugars. Consumption of dietary polyphenols is associated inversely with the risk of CVD and cancer. As almonds contain an array of polyphenols, particularly proanthocyanins, they can be part of recommended guidelines for healthy diets rich in plant foods.
The study participants were patients with angiographically proven CAD and were taking on average 8 medications daily. Their polypharmacy regimen remained stable and effective during the 6-weeks almond intervention, suggesting intakes at 85 g/day are absent any indication of untoward drug-food interactions. Importantly, the change in the profile of nutrient intake during the ALM phase matched well general dietary recommendations to reduce the risk of CVD. It is also noteworthy that even though the ALM diet increased the percent of total calorie intake from fat from 29.1 to 44.4 %, there was no adverse effect on the lipid profile. These results are consistent with the favorable effect of almonds on lipid profiles reported by others.
Our study had several limitations. The study duration of 6 weeks for each arm is a relatively short period to affect some biomarkers of CVD risk and progression, so a longer intervention or larger sample size may have resulted in a statistically significant reduction in plasma VCAM-1 and increase in urinary NO. Conversely, while we found no untoward impact of the ALM diet on concurrent drug therapy, we cannot exclude the development of such interactions over a longer period. It is possible the study design, including a 6-weeks run-in period on the NCEP Step 1 diet that was then continued throughout both study arms and the 4-weeks washout, may have masked an impact of the almond intervention. Similarly, efficacy of the polypharmacy regimens of the subjects may have largely achieved the maximal benefit possible in these patients on the outcome parameters of vascular reactivity, inflammation, and oxidative stress. Finally, the study might be underpowered for both the primary and secondary outcome measures since the power calculation was performed based on the improvement in FMD.