MODESTO, Calif., Aug. 4, 2020 /PRNewswire/ -- Mental stress is among the psychosocial factors thought to contribute to cardiovascular disease (CVD) risk. Heart rate variability (HRV), a measure of the fluctuation in time intervals between consecutive heartbeats, is an important indicator of the cardiovascular system's response to stress and it is thought that lifestyle factors including physical activity and diet might impact HRV. Higher HRV represents greater adaptability of the heart in response to environmental and psychological challenges, while low HRV is linked to cardiovascular disease and sudden cardiac death. As part of a recent clinical trial, researchers at King's College London measured HRV in participants undergoing a laboratory mental stress challenge and saw improvement in some measures of HRV in participants who had been replacing typical snacks with almonds over a six-week period. The study1 was funded by the Almond Board of California.
This new research finding was a secondary outcome measure of the ATTIS study, a 6-week randomized control, parallel-arm trial, where participants with above average cardiovascular disease risk consumed a daily snack of almonds or a calorie-matched control snack providing 20% of each participants' estimated daily energy needs.
Participants in this study were British men and women, aged 30 to 70 years. Researchers measured their real-time heart rate (HR) and heart rate variability (HRV) at rest (lying down for 5-minute periods) and during a Stroop test (in which participants were asked to read colored words i.e. say "red" in a green font) to simulate a short period of mental stress.
During acute mental stress, participants in the almond group showed greater cardiac resilience. This was demonstrated by better heart rate regulation compared to the control group, indicated by statistically significant differences in high frequency power, which specifically evaluates beat-to-beat intervals (a measure of HRV).
"This study shows that the simple dietary strategy of swapping almonds for typical snacks may bolster resilience to the adverse cardiovascular effects of mental stress by improving regulation of heart rate. We found that the stress-induced reduction in heart rate variability was lessened in the almond group compared to control following the dietary intervention, which indicates a cardiovascular health benefit. It is useful to think of having a higher HRV as the heart being able to switch gears faster in response to demands on the body, which means more cardiac resilience and flexibility during periods of stress. In the long term, this is beneficial for cardiovascular health," said Dr. Wendy Hall, PhD, co-principal investigator and Reader in Nutritional Sciences at King's College London. The researchers acknowledge that the mechanisms underlying this effect are still unknown and long-term studies are needed to understand this as well as the effects of almonds on HRV in at-risk populations.
"These results support our growing knowledge about almonds and heart health. And, they're particularly timely given the heightened levels of stress many of us are experiencing right now, alongside increased snacking, from working at home," said Dr Sarah Berry, PhD, co-principal investigator.
Years of heart health research – including a systematic review and meta-analysis2 – support the inclusion of almonds in heart healthy eating plans.* Both ATTIS studies included measures that had never before been evaluated in clinical research trials investigating the impact of almonds. Although additional studies are needed to confirm these findings, the improvements in certain measures of HRV suggest that almonds may provide unexpected heart health benefits. Almonds provide 6 grams of plant protein, 4 grams of filling fiber and 15 essential nutrients - including 20% of the Daily Value for magnesium and 50% of daily needs for vitamin E - in every healthy handful.
Study at a Glance:
- This randomized, controlled parallel dietary intervention study investigated the effects of almond consumption on cardiometabolic risk factors in adults with above average risk of CVD. The study looked at the impact of almonds vs. a control food designed to provide the same number of calories and carbohydrate/fat/protein composition to match average snack intakes in an adult UK population.
- Adults 30-70 years old (n=51 in almond group, n=56 in control group) consumed 20% of their calorie requirements as whole roasted almonds or a control food for 6 weeks. Cardiometabolic risk factors were measured, including endothelial function (flow-mediated dilation), heart rate variability, liver fat, insulin resistance, blood cholesterol and triglycerides, and body composition.
- Prior to beginning the study, a separate 3-week trial was conducted to ensure that the control food had a neutral effect on lipids, blood pressure and body weight/composition.
- Participants had their heart rate (HR) and heart rate variability (HRV) measured in 5-minute periods at resting and during mental stress.
- Real-time HRV was measured before (resting) and during a Stroop test (mental stress) while participants were in a supine position by using an ambulatory/ECG monitor. The 5-min stress test was performed 15 minutes after recording resting HRV values.
- The HRV parameters including high frequency (HF) and low frequency (LF) power and the LF/HF ratio were measured using a chest-worn heart rate monitor and specialized analytical software.
- There were no changes in body weight, and total energy intakes of both the almond group and the control group did not differ, but the almond group had improved diet quality (higher fiber, favorable ratio of unsaturated fats to saturated fats, increased magnesium, potassium, vitamin E and riboflavin; and decreased total carbohydrate, starch, free sugars and sodium).
- During mental stress (Stroop test), HF power was higher following almond treatment by 124 ms2 (95% CI 11, 237), relative to control. The LF/HF ratio was lower by -1.0 (95% CI -1.9, -0.1) relative to control. No differences were found in other indices during mental stress.
- In the resting state, there were no significant differences between treatment groups in the change in HRV indices following intervention.
Limitations of the study were the fact that there were some differences between groups in cardiometabolic disease risk factors at baseline. Also, the participants were free-living, and although almond compliance was confirmed, it is possible there is potential for some inaccuracies in their reported food intake. Finally, more research is required because the mechanisms for the increase in HRV are unknown and further research is needed to understand the effects of almonds on HRV in at-risk populations.
Snacking on whole almonds in place of typical snacks can increase HRV parameters in response to mental stress, indicating improved cardiac autonomic function. Incorporating almonds in daily snacking is encouraged as a positive lifestyle change and enhances cardiovascular health, not only by lowering cholesterol, but also potentially by increasing resilience to mental stress.
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California almonds make life better by what we grow and how we grow. The Almond Board of California promotes natural, wholesome and quality almonds through leadership in strategic market development, innovative research, and accelerated adoption of industry best practices on behalf of the more than 7,600 almond farmers and processors in California, most of whom are multi-generational family operations. Established in 1950 and based in Modesto, California, the Almond Board of California is a non-profit organization that administers a grower-enacted Federal Marketing Order under the supervision of the United States Department of Agriculture. For more information on the Almond Board of California or almonds, visit Almonds.com or check out California Almonds on Facebook, Twitter, Pinterest, Instagram and the California Almonds blog.
1 Vita Dikariyanto, Leanne Smith, Philip J Chowienczyk, Sarah E Berry, Wendy L Hall. Snacking on whole almonds for six weeks increases heart rate variability during mental stress in healthy adults: a randomized controlled trial. Nutrients 2020, 12(6), 1828; https://doi.org/10.3390/nu12061828.
2 Musa-Veloso K, Paulionis L, Poon T, Lee HL. The effects of almond consumption on fasting blood lipid levels: a systematic review and meta-analysis of randomised controlled trials. Journal of Nutritional Science 2016; 5(e34):1-15.
*Good news about almonds and heart health. Scientific evidence suggests, but does not prove, that eating 1.5 ounces per day of most nuts, such as almonds, as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease. One serving of almonds (28g) has 13g of unsaturated fat and only 1g of saturated fat.
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SOURCE Almond Board of California