Wearable blood sugar monitors hailed by celebrities such as Davina McCall as a tool to control appetite are effectively useless for people without diabetes and are unlikely to help with weight loss, experts have warned.
The devices, worn as a small circular sticker on the arm, provide detailed information about blood sugar levels after eating food through a small probe in the skin that transmits information to the paired smartphone.
While they have been used by diabetics for years, the devices are now increasingly sold to healthy people as a way to track foods that may cause a worrying rise in their blood.
Health brands like Professor Tim Spector’s ZOE, which sells its own monitor, say avoiding these spikes can help reduce cravings, limiting excessive calorie intake.
Therefore, identifying foods that have this effect and avoiding them is said to reduce the risk of obesity and related diseases.
But a new study, in which experts tested the devices on 30 non-diabetic volunteers, has called into question the accuracy of such monitors for people with healthy blood sugar control.
Analysis of their results suggests that a healthy person using the devices would need to eat the same food up to 67 times to get an accurate picture of its effect on blood sugar.
In the new experiment, participants were given a carefully crafted menu for two weeks in a row. The meals of the first week were identical to those of the second.
Experts have warned that the wearable blood sugar monitors loved by celebrities such as Davina McCall are essentially “useless” for non-diabetics.
The devices, which are no larger than a £2 coin, transmit updates on blood sugar levels to the user’s phone.
This allowed scientists at the US National Institute of Diabetes and Digestive and Kidney Diseases to compare the accuracy of blood sugar monitors for the exact same food and for the same person, but at two different times.
The results showed that the readings were “highly variable” between weeks and were also very different from the results of standard blood tests.
Results, published in The American Journal of Clinical NutritionThey were so inconsistent that the authors determined that the monitors, also called continuous glucose monitors (CGMs), were essentially ineffective for personalized nutrition.
“To be useful, CGM responses must be reliable,” they wrote.
They added: “Our study found that the reliability of postprandial CGM responses after eating many duplicate multi-component meals was poor.”
The researchers said their results came during a growing trend of healthy adults using the devices as part of receiving “personalized dietary advice.”
Nicola Guess, an academic dietitian and researcher at the University of Oxford who was not involved in the study, said the research showed the devices were “absolutely useless” for healthy people.
‘Proponents of CGMs claim that they help people identify which foods they cannot tolerate; That is, if they eat a banana and it gives them “a kick” and their partner doesn’t, it means that they can’t tolerate the banana but their partner can.
Several companies, including the ZOE program, founded by diet guru Professor Tim Spector, offer high-tech devices, called continuous glucose monitors (CGMs), that track a client’s blood sugar levels through an adhesive patch on the arm.
“But what this study shows is that you and your partner may need to eat that food 67 times each in order to know if you really respond differently.”
He added that there is limited evidence to support the idea that identifying foods that “raise” blood sugar has any health benefits.
“It’s silly that people are asked to ‘monitor’ their glucose with CGM because as far as we know, as long as it’s within the normal range, it’s not a problem,” he said.
Blood sugar levels vary from person to person, but typically range between 4 and 6 mmol before meals and up to 8 mmol up to two hours after eating.
This is not the first time that the use of CGM in healthy people has been questioned.
Earlier this year, experts warned that the devices could cause people to develop anxiety and eating disorders.
Furthermore, while experts say the evidence for the benefits of CGMs in diabetics was clear, the evidence for its usefulness for healthy people was much more limited.
ZOE has stated on its website that blood sugar spikes can, over time, lead to an increased risk of heart disease and offers a diet to help minimize them.
Davina has appeared in several promotional videos using ZOE’s CGM.
In a post on her Instagram, she described the device as a “trick up my sleeve to help smooth out my sugar spikes and the foods I know trigger me.”
However, several experts have questioned the research evidence behind ZOE’s claims, as well as other similar programs.