Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Digital interventions, or mHealth or eHealth interventions, are increasingly common in health care and it's important to evaluate their effects. With this in mind, a new Cochrane Review from February 2024 examines the evidence for smartphone interventions for adolescents and adults with overweight or obesity. In this podcast, Eva Madrid, from the University of Valparaíso in Chile, talks with lead author Maria-Inti Metzendorf, from the University of Düsseldorf, Germany, both of whom are currently on fellowships at the Iberoamerican Cochrane Center in Barcelona, Spain.

Eva: Hello Maria-Inti, first of all, please tell us why smartphone apps are thought to help people with overweight or obesity?

Maria-Inti: Hello Eva, sure. Many people use smartphone apps daily and some are designed specifically for health purposes, to try to help people to stay on track with healthy habits. In the case of our review, the apps we examined were intended to help people with overweight and obesity to make good health choices. This means that teenagers and adults who use them might become more physically active, change how they eat, or think more positively about themselves.

Eva: So why is it important to have research, and a systematic review, of the effectiveness of these apps?

Maria-Inti: For some time, people living with obesity have been offered multi-component programmes, such as a combination of diet, physical activity and behaviour change techniques, but more and more people are now using smartphones and other mobile devices, usually worn close to the body, to try to support healthy behaviours, in a low-threshold manner. This makes it important to know if the apps really do what is intended.

Eva: And, what do these apps aim to do?

Maria-Inti: They are thought to promote people´s self-efficacy and adherence, for example by monitoring physical activity and dietary behaviours or sending reminders. They might also provide actionable feedback or guidance on self-management. However, even though there are good theories about how the apps might work, it's essential to know if they work in the real world, which is why we did this Cochrane review.

Eva: For your review, I understand that you included studies testing interventions that need to be delivered primarily through a smartphone app, with, at most, one in-person contact with a health professional each month. The app also needed to include at least two 'behaviour change techniques', for instance, tracking weight, food or activity while also providing motivational messages or information about healthy habits, right?

Maria-Inti: Yes, that was the broad scope but because the studies were so different we had to break things down into several comparisons and I'll mention a couple.
The main comparison was smartphone app versus no app which had 13 studies with adult participants. This found that apps probably result in little to no change in total activity time at 12 months and in leisure time physical activity at 24 months. We also saw that an app may reduce body mass index in the medium-term, but the evidence is very uncertain, and there is probably little to no change in body weight after two years. Regarding quality of life and well-being, apps probably result in little to no difference after one year and there was little to no difference in dietary habits after one or two years.
We also compared a smartphone app to a personal coaching intervention, but there was only one study in teenagers, and the app resulted in little to no difference in body mass index after six months.

Eva: How certain are you about the results?

Maria-Inti: That is a good question. In general, we are moderately to very uncertain about the effects. The effects varied widely across the studies and the comparisons, and none of the results clearly favoured the apps.

Eva: Interesting. Were these studies based on apps that are currently available in app stores? 

Maria-Inti: Actually, only two were commercially available smartphone apps, 'Lose It!' and 'WW' (formerly Weight Watchers). But there are several other widely used apps for overweight or obesity, such as 'MyFitnessPal', 'Noom', 'Fitbit', and many more. However, these have not yet been evaluated in studies that would be eligible for our review and we cannot say if they are effective or not. This is probably related to the fact that, unlike drugs, apps do not usually require a study backing their claims. Interestingly, we could include one app ('zanadio') recently approved by the German Federal Institute for Drugs and Medical Devices for people living with obesity that is available upon prescription by physicians and psychotherapists. But generally, most of the apps are available to the general public without a prescription.

Eva: What is the most critical challenge you encountered when doing the review?

Maria-Inti: This is very relevant, Eva, because we faced some methodological challenges common to systematic reviews of mobile health interventions. For example, there wasn't enough information about the features, specific components or behaviour change techniques in the apps or the intensity of the intervention. We were also unable to assess the effect of automated versus human feedback, which are key to user engagement and adherence and could impact the apps´ effectiveness. We also couldn't investigate whether personalised apps are more effective than one-size-fits-all approaches because the apps in the review used quite different personalisation options. Lastly, there were no studies from low-income countries, so we don't know how well they might perform in such settings. 

Eva: Looking to the future, do you think that some of these gaps will be filled?

Maria-Inti: We hope so. We identified 34 ongoing studies and we'll extend our evaluation as more studies become available. Also, the current trend goes towards greater tailoring and personalisation of apps with so called 'just-in-time adaptive interventions' (JITAIs). They will be worth investigating in a future update of the review.

Eva: Let's end with a take-home message for listeners. There seem to be lots of uncertainties about effectiveness, but at the same time there is almost no information about harms. Would it be wrong if people gave these apps a try?

Maria-Inti: I'd say that because the evidence is limited and does not demonstrate a clear benefit of smartphone apps, people living with obesity should carefully consider the potential benefits, harms and uncertainties when deciding whether or not to use one. I wouldn't rule out smartphone apps, but the current evidence is too uncertain to say that they work, so expectations should be moderated. I'd encourage people to discuss this with their doctor or primary care provider, in case there are more effective alternatives that might help them.

Eva: Thanks for talking with me today Maria-Inti. People can read the review by going to Cochrane Library dot com and searching using the three words: 'smartphone overweight obesity'. They can also find the link next to this podcast on the Cochrane website.