Effects of Daily Intake of Almonds on Cardiac Autonomic Functions Measured by Heart Rate Variability in Response to Acute Stress: A Randomized Controlled Trial

Stress is inversely associated with heart rate variability (HRV), an indicator of cardiac autonomic function and a predictor of risk of sudden cardiac death. At times of stress, people tend to favor high sugar and fatty foods, often as snacks, with potential adverse effects on cardiometabolic health. Dietary recommendations for cardiovascular disease (CVD) prevention emphasize fruits, vegetables, wholegrains and nuts. There is evidence that consumption of nuts can reduce LDL cholesterol and blood pressure and help with weight management, however the impact of nuts on HRV in response to stress is unknown. The ATTIS dietary intervention study investigated the HRV response to acute stress following 6-week substitution of almonds for typical snacks high in refined starch, free sugars and saturated fats, and low in fibre. The study population comprised adults aged 30–70 y, who were habitual snack consumers, and at moderate risk of developing CVD. It was hypothesized that snacking on almonds would increase HRV during stress tasks, when HRV is expected to be reduced due to increased sympathetic activity. A 6-week randomized controlled parallel trial was conducted. Participants were randomized to 1) control snacks (mini-muffins formulated to follow the average UK snack nutrient profile), or 2) dry-roasted whole almonds, both providing 20% estimated energy requirement. Supine HRV was measured (Mega Electronics Emotion Faros 180°, 2-leads wearable ECG-HRV monitor) during resting (5 min), physical stress (blood pressure monitor cuff inflation 200 mmHg, 5 min) and mental stress (Stroop colour-word test, 5 min) tasks pre- and post-intervention. A total of 105 participants (73 females and 32 males; mean age 56.2 y, SD 10.4) completed the trial. Almonds significantly increased the beat-to-beat HRV parameter, high-frequency power, during the mental stress test (mean difference 124 ms2; 95% CI 11, 237; P = 0.031) relative to control, indicating increased parasympathetic regulation. There were no treatment effects during resting and the physical stress task. Snacking on whole almonds as a replacement for typical snacks increases HRV during mental stress, indicating an increased resilience in cardiac autonomic function and a novel mechanism whereby nuts may be cardioprotective. Almond Board of California.