Personalized nutrition: Blood sugar monitoring is accurate, ZOE study shows

Measuring blood sugar responses is one of the key pillars of personalized nutrition. But this technology is still in its infancy when not used for managing diabetes. A new ZOE study shows that continuous glucose monitors are a valid tool for precision nutrition, particularly when used along with other measurements. 

In the world of personalized nutrition, the days of one-size-fits-all dietary guidelines are in the past. Food should be personal and support each individual’s current health and long-term goals. 

But does the technology that underpins this way of eating live up to expectations? 

ZOE runs the largest scientific study of nutrition and personalized responses to food, with over 20,000 participants so far. 

By combining blood sugar analysis with blood fat measurements and the latest technology to uncover the bacteria in the gut, ZOE provides personalized nutrition advice to thousands of customers.

As part of ZOE’s at-home test kit, users who opt to take part in our research program wear a continuous glucose monitor (CGM), which measures blood sugar levels every few minutes.

CGMs are designed for people living with diabetes to allow them to monitor their blood sugar levels without having to use finger prick testing. However, their use in individuals without diabetes is increasing. 

Using a CGM gives the wearer real-time insights into how their blood sugar levels change when they eat, sleep, and exercise, empowering them to make any necessary changes if their blood sugar responses are too high or low. 

Other scientists have called into question this technology, raising doubts as to whether CGMs are accurate enough at the moment for personalized nutrition, specifically to rank one type of food or meal as being better for blood sugar control than other foods.

Writing in The American Journal of Clinical Nutrition, ZOE scientists and their international collaborators recently demonstrated that CGMs are valid for personalized nutrition and can be used to rank foods.

Raising ‘a really important question’

In 2020, Dr. Kevin Hall from the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), part of the National Institutes of Health (NIH), published a study that highlighted potential problems with using CGMs.

His team found that when 16 study volunteers wore two different brands of CGM at the same time, there were significant discrepancies between the blood sugar readings and how well meals scored to minimize big blood sugar spikes. 

Dr. Sarah Berry, an associate professor in nutritional sciences at King's College London and Lead Nutritional Scientist at ZOE, explained why the team decided to dig into ZOE’s own data.

Dr. Berry and her colleagues looked at the data from 394 study participants who had taken part in ZOE’s PREDICT 1 clinical trial to see how the data would stack up when the volunteers wore two CGMs at the same time. 

“In our analysis, we looked at how well two of the same brand of CGM as well as different brands of CGM agreed in measuring blood sugar responses to different foods. So we have intra- (or within) brand measures and we have inter- (or different brand) measures,” Dr. Berry explained.

In total, the team looked at blood sugar readings across nearly 2 weeks, during which the participants ate nearly 4,500 standardized meals and over 5,500 of their usual meals. 

Consistency is key

As the scientists compared the measurements, they saw high levels of consistency. 

When the volunteers wore two CGMs from the same brand (Abbott Freestyle Libre Pro), the intra-brand blood sugar readings matched up very well, and there was little variation between them, particularly in meals with a high carbohydrate content. 

With two sensors from different companies (Abbott Freestyle Libre Pro and Dexcom G6), the inter-brand numbers didn’t match up quite as well, but there were still high levels of agreement between the readings. 

The team also analyzed how well the different CGMs agreed when ranking foods.

“This is really relevant for us at ZOE, as we need to ensure we are using precise tools to deliver precise nutrition advice,” Dr. Berry explained. “So it’s really important to see if the sensors rank in a similar way. And the ranking was in close agreement.” 

As the team concludes in the paper: “Taken together, our findings highlight the potential application of CGMs for monitoring glycemic responses to foods and meals and their potential application for personalized nutrition recommendations in healthy populations.”

While blood sugar responses are a mainstay of the budding science of personalized nutrition, they are not the only measure. 

Only one piece of the health puzzle

As part of the ZOE at-home test kit, participants who opt to take part in our research program wear a CGM and eat a range of standardized meals in the form of muffins plus their regular diet. 

But they also do a finger prick blood test called a dried blood spot (DBS) test, which is used to measure their blood fat levels. They also provide a poop sample, which is used to analyze the bacteria that currently live in their guts.

Combined together, these data allow ZOE to provide personalized nutrition advice based on multiple measurements, all of which are important players in our health. 

But these are far from off-the-shelf tests. ZOE scientists and their international academic collaborators have optimized the use of each to provide accurate and precise results.

“We’ve [optimized these tests] for a number of our outcomes. We’ve done this for the development of the metagenomics platform for our gut microbiome testing,” Dr. Berry concluded. “We’ve done this for our DBS [for blood fat responses]. And now we’ve published this huge study on the use of CGM.”

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