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A conference abstract being presented at the American Heart Association’s Epidemiology and Prevention, Lifestyle and Cardiometabolic Scientific Sessions looks at time-restricted eating and cardiovascular death.
Dr Baptiste Leurent, Associate Professor in Medical Statistics, UCL, said:
“The results provided in this conference abstract are quite striking and suggest that those following ‘time-restricted eating’ could have twice the risk of cardio-vascular death. This would challenge the commonly perceived health benefit of this popular diet.
“The study is based on a large sample of American adults, and – judging on the limited abstract presented – appear appropriately conducted.
“However, the information available is very limited. The full research has not yet been published, and these results are too brief to draw any robust conclusion. For example, it is unclear if the results reported are taking into account of the underlying difference between the groups compared. If the people following this diet tend to be older, or at higher cardio-vascular risk, then the association may not be so surprising. Conversely, if those following this diet tend to follow a healthier lifestyle, such as more physical exercise, the risk of this diet could be even higher than the observed difference in mortality.
“We look forward to seeing the full publication of these important findings.”
Prof Sir David Spiegelhalter, Emeritus Professor of Statistics, University of Cambridge, said:
“So much is unclear about this study. In particular, why were the particular two days chosen to measure times of eating? How do they know whether food was eaten outside the 8-hour window and just not entered in the questionnaire? This abstract should not have been graced with a press release.”
Prof Kevin McConway, Emeritus Professor of Applied Statistics, Open University, said:
“This is a conference presentation. It’s unlikely to have been through the full peer review process yet, and anyway it’s impossible to assess the quality of the research without seeing the full research paper. So it’s a bit of a waste of time trying to do so. I don’t blame journalists or the SMC for asking scientists to comment – but I do wish that conference organisers wouldn’t put out press releases under these circumstances.
“In this case, though, there’s just about enough in the conference abstract to throw huge doubts on whether the study can show what it purports to show. That’s an even stronger reason why there shouldn’t have been a press release, in my view. The researchers classified people into different dietary patterns on the basis of what and when they reported they ate in just two days, over a study period averaging 8 years. We don’t know whether their eating times over those two 24-hour periods was typical of the times they usually ate. So to relate those patterns to a deliberate long-term time-restricted eating intervention seems to be going far beyond the data.
“This is an observational study, so it’s in any case impossible to be sure what causes what. There will be differences in other factors between people with different eating patterns, apart from the eating patterns. Any differences in mortality could be due to those factors. The researchers made some statistical adjustments that could have allowed for some other factors, but the available information doesn’t tell us what factors they adjusted for, and it always remains possible that they missed something relevant. It could even be that there’s some sort of reverse causation. People who were already worried about their cardiovascular health, perhaps for some good reason such as signs of illness or previous unhealthy activity, might be more likely to decide to restrict their eating times. Increases in cardiovascular deaths in people who restricted their eating times, might be explained by whatever was causing the previous worries, rather than the diet restriction. We just can’t tell.
“If and when we see the full research report behind this study, it might turn out that it in fact does relate more obviously to deliberate choices to restrict eating times than it appears from the press release and abstract. But that doesn’t get round the issue that the study is observational and can’t determine cause, as the researchers themselves make clear.”
Prof Keith Frayn, Emeritus Professor of Human Metabolism, University of Oxford, said:
“Time-restricted eating is popular as a means of reducing calorie intake, although its proponents claim other benefits such as ‘ramping up metabolism’. This work is very important in showing that we need long-term studies on the effects of this practice. But this abstract leaves many questions unanswered, and further research will be needed. We don’t know the body weights of the participants: maybe the time-restricted eaters were making themselves too thin. We need to know more about their medical state, for instance, blood cholesterol and blood pressure. Finally we don’t know whether those who follow time-restricted eating might have done so because a physician has told them they need to lose weight because they are at high risk of cardiovascular disease. In general, we should be cautious about widespread adoption of eating strategies that have not been properly evaluated for longer-term effects.”
Prof Tom Sanders, Professor emeritus of Nutrition and Dietetics, King’s College London, said:
“This is an interesting study which finds an unexpectedly large increase in risk of cardiovascular disease associated with reporting time restricted eating at baseline. The strengths of the study are that there was a relatively long follow up period (8 years) and the 20,000 participants were part of national nutritional survey which is representative of the American population. What is not clear is whether those who reported restricted time eating at baseline continued with this practice throughout the study. It is also unclear whether the individual reporting time restricted eating made a voluntary choice to adopt this pattern. It is likely that individuals reporting time restricted eating may be working antisocial hours (e.g. truck drivers, security personnel, health professionals, night workers). This is important because there is evidence that this type of working practice is associated with increased risk of type 2 diabetes and CVD. It is not clear whether statistical adjustment have been made for confounding factors (smoking, physical activity, alcohol intake, social class). It will be necessary to carefully look at the study in more detail when it is published in full.
“Although time restricted eating has become popular in the media, there is lack of evidence to show it has any benefit in terms of weight loss or weight maintenance. Regarding cardiovascular risk factors, we know from previous existing evidence that it is probably better to spread food intake out throughout the day (small but often) rather than consume large meals over a shorter period. This is because large increases in blood fats and glucose result after big meals. These postprandial increase in blood fats and glucose can impair endothelial function and increase the level of blood clotting factors particularly factor VII. Prolonged fasting can contribute to raised blood cholesterol because it promotes the release of fatty acids from adipose tissue that stimulate the synthesis of very low density lipoproteins in the liver that give rise to low density lipoproteins in blood.”
Dr Duane Mellor, Registered Dietitian and Senior Lecturer, Aston Medical School, Aston University, said:
“This report is a conference presentation and lacks the detail of a full paper to be able to assess the quality of the research. It appears to show the risk of death over a range of 1-13 years, median of 8 years, looking at how people ate on two days, which were linked to risk of cardiovascular disease and death. Although a model was used to assess risk, it is unclear if it included how healthy diet pattern was or even what people ate. As the information is limited it is not clear from the available information if smoking, physical activity and alcohol were considered as variables.
“It is impossible to say if how a person restricts the time that they eat is linked to risk of health outcome as this abstract is suggesting – as it is unclear, as the data is so limited based on two days of diet recall, why they might have been restricting the time over which they ate. Some people might be doing this for health reasons, whilst others due to stressful work environments or poverty, which are both risk factors for cardiovascular death.
“We need to be very careful not to generate concerning headlines and stories based on such limited information. It is perhaps what you eat and your overall lifestyle that is more important than if you ate all your food in less than 8 hours on two days in the last decade.”
Conference abstract title: ‘Association Between Time-Restricted Eating and All-Cause and Cause-Specific Mortality’ by Meng Chen et al. This was under embargo until 20:00 UK time on Monday 18 March 2024. There is no full paper and the conference abstract is not peer reviewed.
Declared interests
Dr Baptiste Leurent: “No conflict of interest.”
Prof Sir David Spiegelhalter: “No COI.”
Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee. My quote above is in my capacity as an independent professional statistician.”
Prof Keith Frayn: “I have no conflict of interest to declare other than as an author of books on metabolism and body weight.
Author of:
Lipids: Biochemistry, Biotechnology and Health 6th edn (Wiley) published 2016– with Mike Gurr and others
Human Metabolism: a Regulatory Perspective 4th edition (Wiley) published 2019 with Rhys Evans
Understanding Human Metabolism (CUP) published 2022
Forthcoming:: A Calorie is a Calorie (Piatkus) 2025.”
Prof Tom Sanders: “Honorary Nutrtional Director Heart UK, member of science committee British Nutrition Foundation.”
Dr Duane Mellor: “No conflict of interests.”