Flavour of the Week

Weight-loss by the Clock?

On and on we struggle… trying to find successful and sustainable ways for people to lose weight and keep the weight off. Diets, flavour-of-the-week-logodrugs, natural health products, probiotics, functional foods, etc. They can all play a role but the honest truth is that we don’t yet have a tried, tested and true method that is pleasing to the population. In the never-ending search for new possibilities, some have opted to focus on the timing of our meals to see if that can play a role.

Can time-restricted feeding help people lose weight?

What Is Time-Restricted Feeding?

Time restricted feeding – not surprisingly- focuses on limiting the time during which one can consume foods; not the amount of food that can be eaten during that time. The way it works, is that there would be a time range during the day, usually 3-12 hours long, where you can eat ad libitum (as much as you are comfortable and not restricted in any way – it does not imply excessive binge eating). The result is that the remaining 12-21 hours are fasted.

Time-restricted feeding is similar to the intermittent fasting weight-loss technique; check out our previous post Intermittent Fasting: Skip Meals, Lose Weight? for more information. However, intermittent fasting requires that people severely restrict their caloric intake for 1-3 days; which can be very challenging and uncomfortable, causing problems with adherence. Conversely, time-restricted feeding “only” requires restriction of food intake for part of the day.

Can Time-Restricted Feeding Help People Lose Weight?

The idea of skipping meals or restricting the time of food intake is controversial. Nay sayers claim that skipping meals will simply cause people to overeat later on in order to compensate. On the other hand, there is some emerging evidence that restricting eating times may have benefits.

weight lossAccording to a recent review (1), 11 trials have been conducted to evaluate the effect of time-restricted feeding on body weight. The results are messy as the time varies from 4 to 12  hours of allowed eating time.

Overweight and normal weight males restricted to eating for a four hour window every second day for two weeks did not show any weight-loss; however, in both of these studies they were instructed to eat as much as they needed to maintain their body weight in those four hours so no surprise there (1)!

Three studies used a 7-8 hour feeding range and two found no effect; however, the third found a 5% weight-loss after 4 weeks. Five percent may not sound like much but it is the threshold for a weight-loss drug to be considered effective. Shockingly, however, two of these studies did not measure caloric intake so the interpretation of the results is limited. The one study that did measure caloric intake, found a reduction of 10%; however, since the same study did not find a corresponding weight-loss, the accuracy of the food records is questioned (1).

This is where it gets interesting! Six trials looked at the effects of  10-12 hour feeding window and fairly consistently found 1-3% reductions in body weight. Importantly, however, many of the studies occurred during Ramadan, thus much of the eating time would have been at night when, presumably, people were sleeping (1).

Can Time-Restricted Feeding Improve Health?

There are many health concerns associated with obesity including increased risk for heart disease and type 2 diabetes. Studies looking at the impact of time-restricted feeding on indicators of these diseases find mixed results.

Cholesterol and blood lipids improved in one trial with 8 hours of feeding for 4 weeks. Notably, this was also the only study where weight loss occurred; so the effects could have been due to the weight-loss more so than the timing of food intakes. Lipids also improved in most of the 10-12 hour studies but accurate food records make it impossible to determine if the changes were due to the timing of the food or the actual foods eaten (1).blood sugar testing

Blood sugar control is an indicator of risk for diabetes. Unsurprisingly, the effects of time-restricted feeding on blood sugar control are controversial with some studies showing improvements and others no effect. Again, however, if there is any improvement it seems to be in the 10-12 hour feeding groups (1).

No Baloney’s Advice? Time-restricted feeding does not appear to have a noticeable effect on body weight or health. The marginal weight-loss shown in only a few studies hardly make it worth the effort. You would be better off to stick with positive dietary changes and increased physical activity. Plebeian though they may seem, adhering to these methods has consistently shown weight loss and health improvements to boot. If you are still keen to try time-restricted feeding, it looks like the more moderate 10-12 hour time restriction is a better choice than the more extreme, shorter eating times.



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