Reduced saturated fat intake is associated with a decreased risk of cardiovascular disease (CVD) events, but this dietary change may also cause lower levels of “good” high-density lipoprotein (HDL) cholesterol. A previous study, the 2005 OmniHeart Trial, found that a diet with higher unsaturated fat intake prevented decreases in HDL cholesterol compared to diets with higher carbohydrate or protein intake levels even though all diets reduced LDL cholesterol.
The authors previously conducted a randomized, cross-over, controlled-feeding study and found that a cholesterol-lowering diet with 43 g/d almonds (Prunus dulcis, Rosaceae) slightly, but significantly prevented the reduction in HDL cholesterol compared with a similar diet containing an isocaloric high-carbohydrate snack.1 The almond diet also resulted in better HDL subfractions of HDL2 and HDL3 compared to the control. There is some evidence that HDL’s cardioprotective effects may be more dependent on subpopulation distribution and function (cholesterol efflux to apoB-depleted serum) than on absolute HDL-cholesterol concentrations. Therefore, the authors conducted an analysis of blood samples from their previous study to evaluate HDL function and subspecies and their effects in normal and overweight participants.
In summary, men and women aged 30-65 years with a body mass index (BMI) of 20-35 kg/m2 and hyperlipidemia (LDL cholesterol levels of 121-190 mg/dL for women and 128-194 mg/dL for men) were included in the randomized, crossover, two period (six weeks/period) controlled-feeding study. Exclusion criteria were tobacco (Nicotiana tabacum, Solanaceae) leaf use, alcohol consumption of >14 drinks/week, chronic illness, use of prescription cholesterol-lowering medications or supplements, vegetarian diet, weight gain or loss of >10% within the previous six months, and pregnancy or lactation. Forty-eight subjects were randomized to consume either the almond or the control diet for six weeks before crossing over to the alternate diet. The almond and control diets were identical except for the snack which consisted of 42.5 g (1.5 ounces) unsalted, whole, natural almonds with skins (253 kcal/day) or 106 g banana (Musa × paradisiaca, Musaceae) fruit muffin + 2.7 g butter (273 kcal/d). The nutritional composition of the almond diet was 51% carbohydrate, 16% protein, and 32% total and 8% saturated fat. The control diet consisted of 58% carbohydrate, 15% protein, and 26% total and 8% saturated fat. Serum lipids, lipoproteins, apolipoproteins, plasma HDL subpopulations, cholesterol efflux to serum, and body-composition distribution were assessed at baseline and at the end of each 6-week diet period.
The sub-group analyses showed that in normal-weight subjects (BMI 22-25; n=14), the almond diet improved HDL cholesterol and α-1 HDL levels, the ratio of the antiatherogenic α-1 HDL to the pro-atherogenic pre-β-1 HDL, and cholesterol efflux via non-ABCA1 transporters compared to the control diet. In normal-weight subjects, the almond diet also decreased pre-β-2 and α-3 HDL compared with the control diet. In overweight and obese subjects (BMI 25-33; n=34), the almond diet did not result in any significant changes compared to the control.
According to the authors, this is the first study to evaluate the effects of almond consumption on HDL subspecies and HDL function. The authors conclude that including almonds in a traditional low-fat diet to reduce blood cholesterol levels produced fewer decreases in the treatment normal-weight group, but not overweight or obese subjects, compared to the controls. There is previous clinical evidence that α-1 HDL is a better predictor of ischemic heart disease than total HDL cholesterol. Furthermore, high concentrations of α-1 HDL and low concentrations of pre-β-HDL have been shown to decrease the risk of CVD.2 This sub-group analysis showed that in normal-weight subjects, almond consumption improves HDL subpopulation distribution and non-ABCA1–mediated cholesterol efflux, compared to the control diet. The authors point to the need to standardize HDL subclasses in order to adequately study HDL biology and function, and the subsequent effects of dietary interventions. The study was funded by the Almond Board of California. For further reading, see the recent review by Kalita and associates, entitled, “Almonds and cardiovascular health: A review” (Nutrients. April 2018;10(4):pii: E468. doi: 10.3390/nu10040468.).
Berryman CE, West SG, Fleming JA, Bordi PL, Kris-Etherton PM. Effects of daily almond consumption on cardiometabolic risk and abdominal adiposity in healthy adults with elevated LDL-cholesterol: a randomized controlled trial. J Am Heart Assoc. January 2015;4:e000993. doi: 10.1161/JAHA.114.000993.
2Asztalos BF, Cupples LA, Demissie S, et al. High-density lipoprotein subpopulation profile and coronary heart disease prevalence in male participants of the Framingham Offspring Study. Arterioscler Thromb Vasc Biol. November 2004;24(11):2181-2187. doi: 10.1161/01.ATV.0000146325.93749.a8.
Berryman CE, Fleming JA, Kris-Etherton PM. The inclusion of almonds in a cholesterol-lowering diet improves plasma HDL subspecies and cholesterol efflux to serum in normal-weight individuals with elevated LDL cholesterol. J Nutr. August 2017;147(8):1517-1523.