August 8, 2022

expert reaction to study looking at early time-restricted eating and weight loss in obese adults

A study published in JAMA Internal Medicine looks at the effectiveness of time-restricted eating (TRE) for weight loss, fat loss, and cardiometabolic health in adults with obesity.

Dr Simon Steenson, Nutrition Scientist, British Nutrition Foundation, said:

“Intermittent fasting has gained widespread popularity in recent years as a weight loss approach, and many different diets have been touted in the media as being potentially beneficial for weight and cardiometabolic health, including the 16/8 diet, Warrior diet, and others.

“This latest study by Jamshed et al. randomised 90 participants (aged 25 to 75 years) living with obesity (BMI 30 to 60 kg/2), who were receiving weight loss treatment, and were instructed to only eat during a set 8-hour window (7am to 3pm, ‘eTRE’ group) or to eat throughout the day (‘CON’ group).  Both groups received weight loss counselling to follow a hypocaloric diet (500 kcal/d below their resting energy expenditure) and to exercise 75 to 150 minutes per week, depending on their baseline physical activity.  After 14 weeks, those who only ate during a set 8-hour window (eTRE group) had lost an additional 2.3 kg compared to those who ate throughout the day (CON group), which was estimated to equate to a 214 kcal/day reduction in energy intake.  The authors also reported that the eTRE intervention improved diastolic blood pressure by an additional 4mmHg and mood disturbances, including fatigue-inertia, vigor-activity, and depression-dejection.

“One of the strengths of this new study is the trial design and the number of people who were recruited, compared to many of the previous trials to date.  However, another trial published in April of this year that recruited 139 people in China found that there was no significant difference between those following a TRE or continuous energy restriction diet after a longer period of 12 months.  The inconsistency between this larger study and the newly published trial by Jamshed et al. is similar to the lack of consistency across earlier trials of time-restricted feeding, and highlights the need for larger scale studies to provide more robust evidence of the potential clinical benefits for weight loss and cardiometabolic health for those with overweight and obesity.

“While this study adds to the current evidence base, it remains difficult to say with any certainty if time-restricted feeding is a superior approach to weight loss than eating fewer calories throughout the day.  However, for individuals who may find that this pattern of eating fits better with their lifestyle and preferences, time-restricted feeding is one option for reducing overall calorie intake that might be a suitable approach for some.  Ultimately, it is about finding the best approach to moderate calorie intake that works for each person, as successful and sustained weight loss is about ensuring the diet is feasible to follow in the long-term.”

Prof Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“This is small trial but it does suggest eating only between 7am and 3pm helps people lose weight (through being able to eat less calories, one imagines) and linked to this improve their blood pressure and some aspects linked to weight such as mood and vitality.  This is interesting and encouraging but it is a very small trial with short follow-up (around 14 weeks is when most lifestyle treatments tend to show maximum benefit) so longer term trials over a year or longer are needed to see if people can keep up this behaviour and maintain all reported short term benefits as only such evidence will eventually alter guidelines.”

Prof Peter Hajek, Lead of the Health and Lifestyle Research Unit, Wolfson Institute of Population Health, Queen Mary University of London, said:

“This small trial provides additional evidence that time-restricted eating (TRE) can contribute to weight loss over short term (14 weeks) if combined with caloric restriction.  21 previous small and mostly also short-term trials of TRE provided mixed but overall also mostly encouraging results.  However, a number of interventions can generate short-term weight loss.  The challenge is invariably whether the benefits can be sustained.  TRE is an exceptionally simple and practicable intervention that may have a better potential for being manageable over long-term than most alternative methods.  A proper large trial of TRE on its own with long-term follow-up is now needed.”

‘Effectiveness of early time-restricted eating for weight loss, fat loss, and cardiometabolic health in adults with obesity: a randomized clinical trial’ by Humaira Jamshed et al. was published in JAMA Internal Medicine at 16:00 UK time on Monday 8 August 2022.

DOI: 10.1001/jamainternmed.2022.3050

Declared interests

Dr Simon Steenson: “Funding to support the British Nutrition Foundation’s charitable aims and objectives comes from a range of sources including membership, donations and project grants from food producers and manufacturers, retailers and food service companies, contracts with government departments; conferences, publications and training; overseas projects; funding from grant providing bodies, trusts and other charities. Further information about the British Nutrition Foundation’s activities and funding can be found at http://www.nutrition.org.uk/aboutbnf/.”

Prof Naveed Sattar: “I have consulted for Astrazeneca, Boehringer Ingelheim, Eli Lilly, Novo Nordisk, Pfizer and Sanofi in areas linked to weight loss.”

Prof Peter Hajek: “No conflicts to declare.”