Rapid Response: Do We Recommend Time-Restricted Feeding (TRF)?

Over the last few years, the world of wellness and weight loss saw a sharp pivot in its focus from what and how much you eat to when you eat. Intermittent fasting (IF)–now a household terminology–is an eating pattern in which individuals go for extended periods with little to no energy intake with intervening periods of normal food intake. For instance, while following IF you may fast for 16 hours, or 48 hours, or fast on alternate days on a recurring basis. Time restricted feeding (TRF) on the other hand involves the compression of caloric intake for the day to a certain time period, so food intake is restricted to a time window of 8 or less hours every day - although not necessarily with caloric restriction.  With the recent NYT article, ‘Scientists Find No Benefit to Time-Restricted Eating’ creating a bit of a stir, we find ourselves revisiting the debate on the efficacy of time-restricted eating. 

First and foremost, we believe that the title of the NYT article is veering slightly on the side of sensationalism as it does not accurately represent the findings of the main study that it is based on. In this new study, published in the New England Journal of Medicine, researchers put 139 obese patients through a randomized trial of daily calorie restriction - one group with time restrictive eating pattern, and the other without. The study concluded that there was no additional benefit in terms of reduction of body weight, fat, and metabolic risk factors amongst those that followed the TRF pattern of eating, versus those that only followed daily caloric restriction. 

The study was extremely well done in that there was a high participation rate and good adherence to protocol in terms of monitoring of food intake with pictures, scales etc. The randomization and control were also appropriate for the scale of this study. However, despite the excellent study design, the study simply set out by asking the wrong questions. 

The primary question of the research it seems is as follows: does a time-restricted feeding pattern provide additional benefits to those trying to lose weight on a restricted calorie diet? To answer this question the study compares patients that are eating an isocaloric (similar caloric values) and hypocaloric (eating fewer calories than what is needed to lose weight) diets over a 1 year period. However, in the real world setting those following the TRF diet pattern would eat as normal, but focus on restricting the window of their food intake. As such, the study design does little to test the actual benefits of TRF as a lifestyle choice, and instead the main finding seems to testify more to the efficacy of calorie restriction for weight loss. In essence, when calories are accounted for, with any hypocaloric diet, results tend to be similar in terms of weight loss, and a plateau is eventually reached, with or without the addition of time-restrictive eating - a finding already agreed upon in several studies.

The study misses the key benefit that TRF provides in lieu of a general hypocaloric diet: convenience and sustainability. TRF is a behavior based adjustment and does not require a complete overhaul of eating or physical activities. People opt for time restriction simply as a tool to achieve the goal of overall calorie reduction in their day, and usually not to further supplement calorie-counting. It is an accountability tool to some, and simply a matter of lifestyle adjustment to reduce calorie intake sustainably for others. In any case, the right question to ask would be: at weight maintenance, which diet is more convenient and sustainable to stick to in a way that fits your lifestyle?

Further, the trial patients in the study go from eating across a 10-hour window to an 8-hour window - the change being marginal to come to a conclusion on the efficacy of TRF. The results may be vastly different for people living in the US where the average eating window tends to be 14-hours, thus meriting a bigger difference in the narrowing down of the eating window using TRF.  

The study also does not measure the total energy expenditure of the trial patients, meaning there is no way to tell if there is a metabolic benefit of calorie restriction at weight maintenance, for eg., is it better for long term adherence if you can maintain a 17lb weight loss while eating about 1800 kcal a day in an 8 hour window, versus only eating 1500 calories across a larger time window? Almost universally, prolonged calorie restriction beyond 3-4 months at a stretch results in the body reaching a plateau, and anything that mitigates the accompanying metabolic slowdown would be an essential tool for weight loss maintenance.

So would we, in our practice, recommend TRF? Well, we would have to evaluate the answer differently for each patient, but in general as a lifestyle switch for someone trying to lose weight we would say: yes!  If a patient is striving to lose weight sustainably and achieve metabolic improvements and molecular effects associated with longevity,  TRF certainly has added benefits when overlapped with mild calorie restriction. TRF is known to improve insulin sensitivity overall - something the study does not measure in real world conditions, hence not accounting for a major additional benefit that TRF can provide in addition to aiding weight loss. When we spend less time in the fasted state and more in the fed state, our cells spend less time mobilizing and burning stored body fat and thus the body continuously uses glucose-burning pathways, which in turns leads to a spike in insulin levels, and greater reliance on glucose. Thus, if improvement in insulin sensitivity was found to be better amongst patients following the TRF pattern of eating - that alone would override the lack of additional weight loss benefits. 

Finally, we would recommend TRF to appropriate patients because it reduces decision fatigue around making food choices and lowers the effort required in policing one’s diet on a daily basis. It’s a low-to-no cost intervention without convoluted rules that need to be followed. Overall, TRF is found to maintain metabolic homeostasis by sustaining daily rhythms in feeding and fasting and by maintaining the balance between nutrient and cellular stress response. For most people, it also eliminates breakfast - which is a meal usually loaded with processed carbohydrates. Shortening one’s eating window also allows more time for liver glycogen (sugar) depletion (essentially, emptying the storage tank before adding more fuel with your first meal), and improves prolonged satiety/feeling of fullness. The best diet is one that feels less like a chore, and more like a healthful, long-term lifestyle adjustment, and in that category the benefits of TRF are almost always worth exploring if coming from the typical all-day eating patterns!