New research on time-restricted eating

New research on time-restricted eating

New research on Time-Restricted Eating

You’re familiar with the 5:2 diet which has been around for a while now. It’s a form of Intermittent Fasting (IF) where you fast for two days a week to regulate your overall food intake. Intermittent Fasting can take any form – so 6:1 (fasting on just one day every week) is equally a form of IF – but 5:2 is the version that seems to have caught on.

Being able to eat normally for 5 days of every week and stick to 800 calories a day for the other two has its appeal, and I know people who have adopted this as a way of life, which means they have kept the weight off after they lost it. But I’ve also met many people who liked the idea but found they couldn’t stick with it. For those people the search continues – to find a way of eating which will mean they can lose weight and keep it off.

In recent years, an interest in fasting for just part of the day, but doing that every day, has developed into the approach known as “Time-Restricted Eating”. I’ve noticed that an increasing number of clients who contact me have experimented with using TRE, whilst others haven’t heard of it at all. For some, it offers a simple and practical strategy to help to lose weight and keep it off.

What is Time-Restricted Eating (TRE)?

Time-restricted eating means choosing a particular window of time during which you eat during the day, and then not eating (fasting) for the rest of the 24-hour cycle. The time window that has been publicised most is 8 hours, and this approach has been dubbed 16:8 because you fast for 16 hours and eat all your meals and snacks during one 8-hour stretch of time.

There are no specific recommendations about what you eat – you just need to keep to the window consistently. For example, if you choose an eating window of 10am to 6pm, you stick to that every day, and don’t eat outside those times.

Strengths of Time-Restricted Eating

  • Simplicity – your client doesn’t have to count calories or syns or points and doesn’t have to stick to particular food groups. They can eat the same food as the rest of their household and can use their own recipes.
  • Choice – your client chooses the 8-hour window that will suit them best
  • Control – your client chooses the length of their eating window – it doesn’t have to be 8 hours, though this appears to be the most popular, and most studied duration.

I recently attended an excellent webinar organised by the Association for the Study of Obesity* on the question of whether meal timing influences weight loss, where TRE was discussed.  It was a great event and I wanted to share with you some of the key take-home points made by the speakers in the webinar, so that if you have clients who want to use TRE, you can advise them about how to do this based on up-to-date research…

How long does it take to get used to a time-window for eating?

It takes people on average 10 days to get used to time-restricted eating, so you can explain this to clients and reassure them that even if they find it hard in the first few days, it’s likely to get a lot easier within a fortnight or so.

Is there a best time of day for your window for eating?

According to Professor Krista Varady of the University of Illinois, an expert in the field, it is healthier for us to have the eating window in the morning, because our bodies can process sugar more effectively in the mornings. This may be particularly motivating for clients who wouldn’t miss evening eating too much. But Professor Varady has found that people tend to drop out of TRE studies if they have to miss their evening meal, so as with everything, your client will need to weigh up what may give them the greatest health benefits against what is easiest to stick to. Which in turn will depend on what matters most to them.

Is a shorter window always better?

In a study of 23 TRE volunteers, the average was a loss of 2.6% of their body weight in 12 weeks. People who shortened the window to 6 or 4 hours both showed weight loss of 3.2% of body weight, which suggests that 6-hour window has about the same weight loss effect as 4-hour window. This means that a shorter window doesn’t mean greater weight loss, and it’s important to keep an eye on what is sustainable – around 3% of body weight lost may not sound much, but if you can stick to that TRE pattern, that weight is likely to stay off. And TRE can be just one of a number of changes that your client can use towards achieving their overall goal.

Don’t clients simply compensate for eating in fewer hours by having larger meals?

Professor Varady’s research found that following an 8-hour eating window led to people unintentionally reducing their intake by 350 calories a day, and the unintentional calorie reduction with a 6-hour window was 550 calories per day! This is quite something – unintentional calorie reduction will be very appealing to clients who have found calorie-counting diets a real battle.

This finding means that even if people are compensating to some extent, overall this one habit change is significant in terms of daily calorie reduction. As ever, if the TRE pattern works with your lifestyle and you can stick to it, the weight you lose is likely to stay off.

Could TRE trigger disordered eating?

Professor Varady’s study found that if you don’t have a history of eating disorders, TRE does not increase the risk of you developing an eating disorder. So for people who have not struggled with disordered eating in the past, TRE may be a helpful strategy to think about.

It was not clear from the study whether if you have experienced disordered eating in the past, whether TRE would increase your risk of relapsing, because the study had screened out people who had a history of disordered eating.

In my opinion, if you have a client with an eating disorder or a history of disordered eating, they should be encouraged to focus on developing regular, spaced meal times and not encouraged to narrow the window of eating.

An interesting and useful extra point

Professor Varady said that research found that post-menopausal women lose approximately twice the amount of weight as pre-menopausal women. This is striking, because women tend to feel pessimistic about the prospect of losing weight post-menopause. So if you have a client who is post-menopausal and does not have a history of eating disorders, TRE may be a fruitful avenue to explore.

Downsides of TRE

  • Your client may have to choose between what’s healthiest for their body (an earlier eating window) and what will be do-able for their lifestyle. Professor Varady reported that people tend to drop out of TRE if they have to miss their evening meal. Perhaps that’s because it’s the one with the greatest social contact, or because it’s the one where they enjoy the tastiest food. Like everything else, TRE will only help your client lose weight and keep it off if it is achievable and sustainable for them as an individual, with their unique lifestyle demands.
  • Your client’s eating window may mean that they aren’t eating at the same time as others in their household, and for some people this just won’t work.
  • Andrew Healing who gave a patient perspective on the challenges and opportunities to modulate meal timing in the webinar made the point that whether someone is able to deploy TRE as a pattern for eating will partly depend on their work pattern, particularly if they work variable shifts. This underlines again the point that how your client approaches weight loss will depend on their unique lifestyle.

Training for you on The Psychology of Weight Loss

I run regular two-day workshops for professionals of all disciplines whose work involves helping people change how they eat. These workshops, which are approved by the British Psychological Society, are held twice a year and in 2021 they will be March 4th/5th and September 23rd/24th. You’ll learn how to incorporate up-to-date research from experimental, clinical and health psychology into your work with clients who want to lose weight or simply change their unhelpful eating habits. To find out more about Appetite Retraining, have a look at my website and my self-help book “How to Retrain Your Appetite”.


* The Association for the Study of Obesity is a network for obesity researchers,
clinicians, HCPs and academics in the UK and membership is open to anyone working or studying in the field of obesity. They host really useful events such as the webinar I attended. As a professional working in the field you could check out the benefits of joining.


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