HEART RATE VARIABILITY/BLOOD GLUCOSE INDEX: WHAT IS IT?

Posted by Simone do Carmo

Last Saturday, I attended the Integrative Healthcare and Applied Nutrition (IHCAN) Conference in London where the theme was Functional Sports Nutrition. It was a full day of learning with some of the best experts in the field.

One expert whose work really peaked my interest was Alessandro Ferretti, a nutritional therapist, educator and researcher who focuses on the ketogenic diet and its applications in health and sport, nutrigenomics, heart rate variability (HRV) and environmental influences on physiology and performance. Alessandro’s excellent presentation on “Why metabolic preferences cannot be standardised in athletes” shared some of his own research and explained the importance of individuality and why nutritional practitioners should not rely on generalised research findings when treating patients and athletes.

He also explained the concept of the heart rate variability (HRV)/blood glucose index, which I will discuss after explaining the relevance of these two variables first. Measuring HRV is an easy, useful and an accurate marker of sympathetic activation (stress load) and/or inflammation status in the body (although it does not distinguish well between the two). A healthy and well-rested body produces lower heart rates with a greater variability (high HRV), while a stressed and overtrained body, produces higher heart rates with a lower variability (low HRV). Athletes’ HRV measurements are commonly used to obtain objective data and then manipulate their training intensity and recovery by identifying changes between the sympathetic (‘fight or flight’ response) and parasympathetic (rest or recovery) nervous systems. These measurements can also help us understand individual environmental stressors.

Although inflammation is a necessary part of the body’s response for muscles to get bigger and stronger, this can eventually become counterproductive. The same applies to sympathetic activation. An overactive sympathetic system results in the classic sign of an increased resting heart rate and can also lead to: (i) hormonal dysfunction, most commonly high cortisol levels that have a catabolic effect, (ii) lower the testosterone and DHEA levels that are essential for recovery, and (iii) possibly increase the insulin levels that further raise the sympathetic activation. Blood glucose monitoring is the main tool used by type II diabetic patients to manage their condition. Blood glucose is known to be affected by many different factors, including food choices, timing of food intake, exercise habits, lifestyle, hormonal balance etc. Blood glucose levels can also be affected by sympathetic activation and/or inflammation. Generally, higher and irregular blood glucose levels relate to sympathetic activation and/or inflammation, while stable levels of blood glucose levels relate to parasympathetic activation. Monitoring an athlete’s blood glucose levels is an under-appreciated biomarker, but it can reveal a lot about what is going on in their body.

Alessandro showed us some data of an Olympian’s blood glucose levels over the course of a month and it was alarming that his blood glucose behaviour was similar to that of a pre-diabetic! The most interesting part of the presentation was the concept of developing a metabolic signature for athletes by considering variations in both their HRV and blood glucose levels. Alessandro did this by putting together the simple formula: rMSSD/BG2 (rMSSD = a measure of HRV; BG = blood glucose level), known as the HRV/blood glucose index, which should be used by looking at long-term trends. He argues that the formula could provide insight into a wider range of inflammatory responses. By this, he means that while we know there might be inflammation from sympathetic activation, this could also be caused by the presence of elevated glucose levels which are known to trigger a different side of the inflammatory response, for example by damaging blood vessels. Alessandro also argued that the formula can explain an athlete’s “metabolic flexibility”, i.e. the capacity for the body to adapt fuel oxidation to fuel availability. This would provide a useful tool to evaluate whether an athlete is eating the right food to support their health and performance, and to individualise their nutrition accordingly.

If you would like to find out more about Alessandro’s work, you can visit his website at http://www.alessandroferretti.co.uk.