Is Intermittent Fasting Going to Kill Me?

Is Intermittent Fasting Going to Kill Me?

Dr Sean Wheatley, MSc, PhD. Science and Research Lead.

A number of recent news reports (which I’m not going to link to as they don’t deserve the clicks) have reported that time restricted eating significantly increases the risk of dying from cardiovascular disease (which includes things such as heart disease, heart attacks and strokes). In fact, the claim is that the risk is almost doubled. This blog takes a look at whether this is true.

Spoiler alert: it isn’t!

This is by no means the only blog/article debunking the claims made, but as the news reports seem to be lingering we felt it would be valuable to add to the dissenting voices, and to hopefully help a few more people feel more comfortable with making informed dietary choices that are right for them.

What is time-restricted eating?

Time-restricted eating is a type of intermittent fasting where people eat all their meals within a specific window. This window is usually between four hours (such as from 2pm to 6pm) and eight hours (such as between 11am and 7pm) long. This creates an extended period of fasting during the rest of the day, helping the body to be able to better access its fat stores, amongst other potential benefits. Short-term evidence suggests that this can have a number of health benefits, such as helping to improve weight management and blood glucose control.

Where did the headlines come from?

The news stories were based on an abstract and poster presentation from an American Heart Association (AHA) conference. You can see the abstract here. Importantly, this means the full study has NOT been published in an academic journal, and that it has NOT been peer reviewed. It also means that it is more difficult for other researchers to be able fully appraise the claims being made, because they are not able to access all of the relevant information that can help them to do this.

The fact that this information is only available as an abstract and poster should be enough in itself to prevent it from being widely reported and publicised, but here we are!

What can we tell from the abstract?

As mentioned above, because the reports are based on an abstract a number of the details of the methods and the results we would normally look to when appraising research are not available. But even with the limited details presented, we can immediately tell there are some significant limitations. These include:

– It is an observational study, which has a number of innate limitations. These include, but are not limited to, that:

*The data collection methods are often flawed – for example, methods for assessing people’s diet are often severely limited, so we cannot be confident that the data used is a fair reflection of what/when people are eating at all.

*There are generally a number of factors that can affect the outcomes that are not adequately controlled for (or are not controlled for at all). This often includes things like the general health of the individuals included and other areas of their lifestyle that are likely to impact on their health.

*We cannot judge cause and affect. That is to say, just because there is a relationship between two things, it doesn’t mean one causes the other. This is demonstrated beautifully here.

– The participants were asked about their diet on just two occasions. This information was then used to judge the impact of their diet over the course of eight years. The questionnaires used to assess diet are known to be limited anyway (as noted above), but even if the dietary assessments did provide an accurate representation of the days they were logged for, the assumption that the information collected is a fair reflection of the participants diet for the entire duration of the study is highly problematic.

– There is no information presented on other elements of people’s diets, such as the quality of the foods they were eating, or, in fact, what they were eating at all. Person A might be eating exclusively homemade meals prepared using minimally processed, nutrient dense ingredients. Person B’s meals might all be ultra-processed ready meals with little to no nutritional value. But if they were eating their meals at similar times this study would consider them to be equal.  Making judgements on the healthfulness of people’s diets without considering what they eat is somewhere between questionable and laughable.

– There is no information on the reasons people were eating more/less often. This is important, as it means we do not know if any of the people in the study were consciously following a time-restricted eating plan specifically to try and improve their health, or whether they were only eating within a short window for other reasons (for example they could be very busy, rushing around all day, then just grabbing a takeaway on the way home). It is therefore unfair to claim this is a study about time-restricted eating at all, as we have no evidence that it is!

– We cannot, based on the abstract, tell what other factors the researchers have or have not tried to control for (or whether the methods they have used for trying to control for these things are appropriate). We also don’t know much about differences in the general health of the people within the groups they are comparing, including things such as their age, rates of obesity, blood pressure, alcohol intake, or how many people were smokers. It is entirely possible (if not probable) that differences in factors other than when people were eating may explain some (or all) of the differences seen.

Anything else worth knowing?

As well as the significant limitations and gaps in information outlined above, it is also worth noting that

– There was no difference in all-cause mortality (i.e., the number of people who died from any cause). This is ultimately the most important outcome. It is also less subject to bias than some of the other analyses (including the number of people who died from cardiovascular disease), as there is no ambiguity in the definition. That is to say, whether someone has died or not is pretty clear cut, but categorising the cause of death is not always as straightforward.

That there was no difference in overall mortality rates has largely been ignored in the media, and where it is reported it has been reported as “time-restricted eating does not lead to decreased all-cause mortality”. It would be more appropriate to report it as “time-restricted eating does not lead to increased all-cause mortality”, seeing as the headlines have all been about increased risk.

– The reported increase in the risk of dying from cardiovascular diabetes was 91%. This is a substantial increase. It is also implausible, especially when you consider that the vast majority of studies assessing the shorter-term effects of time-restricted eating have shown a range of benefits. It is hard to see how a reduction in key risk factors in these shorter, better controlled studies, can translate to such a large long-term negative effect.

– If there was a true link, reverse causality seems more likely to be at play. Reverse causality is where the direction of cause and effect is opposite to what is being tested or implied. In this case, reverse causality would mean that people were eating less often because they were unwell, rather than people becoming unwell because they were eating less often. This is plausible, as it is common for people to have a reduced appetite when they are seriously ill, or to make dietary changes to try to address health problems.

So, what’s the bottom line?

The bottom line is that these reports can be ignored. The media have latched on to a sensationalist headline on a popular contemporary topic, even though the quality of the information used to make such claims is very limited. Although it is always important for further research to be carried out to help us understand the likely effects of different choices and behaviours on health and wellbeing, there is currently no good quality evidence that time-restricted eating, or other forms of intermittent fasting, are likely to increase the risk of adverse outcomes. In fact, the available evidence suggests that it can be a good option for people who are trying to improve their health.

So, if you think intermittent fasting could work for you, then there is nothing in this study which should put you off trying it. The same is true if you are already trying it – if it fits in with your lifestyle, you feel better for doing it, and it is helping you make progress towards your health goals, then there is no reason for you to stop

IF YOU ARE TAKING ANY MEDICATION AND ARE PLANNING ON TRYING INTERMITTENT FASTING YOU SHOULD DISCUSS THIS WITH YOUR HEALTHCARE TEAM BEFORE MAKING THESE CHANGES. THIS IS BECAUSE EATING LESS OFTEN CAN AFFECT YOUR MEDICATION NEEDS, WHICH CAN LEAD TO UNWANTED SIDE EFFECTS IF APPROPRIATE ADJUSTMENTS ARE NOT MADE. THE SAME APPLIES TO OTHER BIG DIETARY CHANGES.