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A study published in the Annals of Internal Medicine looks at the effect of 4:3 intermittent fasting on weight loss.
Dr Maria Chondronikola, Principal Investigator and Lead for Human Nutrition, University of Cambridge Metabolic Research Laboratories, University of Cambridge, said:
“This is an intriguing study on a topic that has attracted significant scientific and public interest. The study is of high quality and its conclusion regarding the effect of 3:4 IMF on weight loss is well-supported. The results indicate that the 3:4 IMF group achieved significantly greater weight loss after 12 months, most likely due to a greater reduction in calorie intake during the 12-month intervention. It remains unclear whether the superior improvements in marker of insulin sensitivity observed in the 3:4 IMF group were due to greater weight loss or if they resulted from a direct effect of intermittent fasting.
“The press release does not fully capture the study’s findings with complete accuracy. There were no statistically significant differences between the two groups in terms of blood pressure, total and low-density lipoprotein cholesterol levels, or fasting glucose levels. This is not surprising, as the study was not specifically designed to assess the effects of 3:4 IMF on cardiometabolic health.
“Nonetheless, it is possible that 3:4 IMF, when combined with an intensive behavioural support program led by a dietitian, may lead to superior weight loss outcomes compared to standard caloric restriction.”
Dr Adam Collins, Associate Professor of Nutrition, University of Surrey, said:
Does the press release accurately reflect the science?
“The press release is lifted from the abstract, and so is a faithful summary of the study. However, it does not provide explanations or context for these findings.
Is this good quality research? Are the conclusions backed up by solid data?
“The robustness of this study is in the administration of the two dietary approaches within a supported behavioural programme for weight loss. The authors have also used an interesting objective measure of energy (calorie) deficit achieved across the intervention using estimates of energy expenditure and changes in body composition (fat and lean tissue).
“The study’s main finding was that a 4:3 approach gives more weight loss than conventional calorie restriction, despite participants prescribed the same overall calories. Yet, this is not a magic property of the 4:3 approach per se, but because they achieved a bigger calorie deficit. The dietary intake data reveals some clues as to why this may be the case, based on what wasn’t measured, as much as what was. Those assigned the 4:3 diet were only requested to record their intake on “fast” days, but we know from early studies on intermittent energy restriction (especially alternate day fasting), that there is a tendency for some people to eat less on non fast days too, whether that’s unconscious or subconscious. Hence, measuring intake on fast days only may underestimate true intake. In contrast, adherence to continuous calorie restriction (i.e. every day) can be variable as seen from their dietary intake data. Adherence to any diet over 6-12 months is challenging at the best of times, but this may explain why the 4:3 group were closer to the calorie deficit target overall. Nevertheless, it does support the notion that, in the real world, intermittent energy restriction protocols outperform conventional everyday calorie restriction both in terms of compliance and results (i.e weight loss).
How does this work fit with the existing evidence?
“Studies on this type of intervention are not new but it is interesting to see a recent study published on this 4:3 form of intermittent fasting, or more specifically, intermittent energy restriction (IER). Especially given that interest in intermittent fasting has shifted towards time restricted eating approaches (restricting eating windows to extend the “fast” within each 24 hour period). It reaffirms the fact that IER can be an effective and sustainable weight loss intervention.
When viewed in the round, you could argue that the difference in weight loss between these groups is not that large, given this was over a 12 month intervention. But it does allude to a more interesting feature of intermittent fasting which is the independent metabolic benefits it may provide. Indeed, this has been a focus of our studies in this area. A study we conducted 10 years ago, similarly randomised participants to either continuous or intermittent energy restriction (a 5:2 protocol) of the same overall calorie prescription. Crucially, follow up measurements were taken once participants had a 5% weight loss, to control for differences in weight lost. The study was specifically powered to examine differences in markers of metabolic handling and health and suggested that the intermittent energy restricted approach gave more favourable improvements in metabolic handling of a meal.
Have the authors accounted for confounders? Are there important limitations to be aware of?
“The authors have been careful to caveat their findings within the limitations of their study, and have mainly focussed on the primary outcome of weight loss. They stress that the study was not powered for the secondary outcome measured related to cardiometabolic risk, nor that the findings can be generalised across the whole population, as outcomes may vary by gender, age, ethnicity, disease state, or underlying disorders or eating behaviours.
What are the implications in the real world? Is there any overspeculation?
“The research reaffirms that IER can be an effective and sustainable weight loss intervention, but within each group the extent of weight loss was highly variable, suggesting it may not be the best for everyone. The authors themselves acknowledge this in their conclusion: “Future studies should evaluate biological and behavioural predictors of response to both 4:3 IMF and DCR to provide insight for personalization of dietary recommendations for weight loss”
‘The Effect of 4:3 Intermittent Fasting on Weight Loss at 12 Months’ by Catenacci et al. was published in Annals of Internal Medicine at 22:00 UK time on Monday 31st March.
Declared interests
Dr Maria Chondronikola “I am currently leading a intervention study on the effects of time restricted eating in cardiometabolic health https://trestudy.org.uk/#:~:text=Dr.,in%20the%20UK%20and%20worldwide.”
Dr Adam Collins “No conflicts of interest to declare on this”