Do time-restricted eating habits reduce obesity?
“Want to lose weight? Eat all your food in an eight-hour time frame – and never snack at night,” reports the Mail Online. However, these tips are based on a mouse study – no humans were involved.
Nearly 400 mice were studied in a series of experiments for up to 26 weeks. Sets of mice were given unrestricted 24-hour access to high-fat food, high-fat and high-sugar food or low-fat, high-fruit sugar foods. Their weight gain was compared to mice given the same types of food, but restricted to 9, 12, or 15 hours per day.
Mice ate the same number of calories per day irrespective of the number of hours they had access. All mice on high-fat or high-fat and high-sugar diets gained a large amount of weight regardless of access timescales. However, those with time-restricted access gained less weight.
The current stage of this research has limited application for people. We already know that high-fat and high-sugar diets cause weight gain, as was found here. It may be that future randomised controlled trials in humans will show that the amount of weight gain is more if the calories are consumed at times which do not make the most of our natural metabolic rhythm. However, despite the continued quest to “have your cake and eat it”, at present the best advice to combat obesity is to eat a balanced diet and to take regular exercise.
Where did the story come from?
The study was carried out by researchers from the Salk Institute for Biological Studies in La Jolla and the University of California. It was funded by the US National Institutes for Health, grants from the American Federation for Aging Research, Leona M and Harry B Helmsley Charitable Trust, the Glenn Center for Aging, the American Diabetes Association, the Philippe Foundation and the American Association for the Study of Liver Diseases.
The study was published in the peer-reviewed medical journal Cell Metabolism.
BBC News reported the story accurately; however, the Mail Online’s report was misleading. Its headline implies this study was conducted on humans, when it was only on mice. It also says that people should stop “eating after 4pm”. The restricted feeding times used in this study were for mice with nocturnal eating habits. There is no evidence from this study that weight gain would be avoided in people if we stopped eating at 4pm.
What kind of research was this?
This was a piece of animal research that aimed to look at whether restricting the timing of feeding could prevent weight gain or cause weight reduction in obese mice.
Obesity rates are increasing at an alarming rate and traditional methods of weight control – such as calorie restriction, change in diet and increase in exercise – are hard for many people to adhere to.
A person’s metabolic rhythm changes over the course of the day. Previous research has shown that this rhythm is heavily dependent on eating at the same time each day. Therefore, the researchers wanted to see if sticking to the optimal time of eating within this rhythm would prevent weight gain. They called this time-restricted feeding (TRF). As this study was conducted on mice, the optimal nine-hour feeding time was chosen to be during the night.
Research such as this is a good starting point for understanding the biological processes within an animal’s body, and seeing what can influence this, but we don’t know that the results will be directly applicable to people.
As the researchers conclude, a randomised controlled trial in people would be required.
What did the research involve?
The researchers used 392 male wild-type mice aged 12 weeks for a series of experiments lasting up to 26 weeks.
The mice were given free access to food 24 hours a day or TRF for either 9, 12 or 15 hours overnight. Some mice were switched from one type of access to the other.
The mice were given one of the following types of diets:
- high-fat (32%), high-sucrose (25% table sugar) diet
- high-fat (62%) diet
- low-fat (13%) and fructose (60% fruit sugar) diet
- normal chow diet
The weights of the mice on each regime and diet were compared. Further studies looked at the effect of obese mice switching to TRF regimes.
What were the basic results?
Mice fed a high-fat, high-sucrose diet for 12 weeks gained at least a fifth of their body weight. Weight gain doubled if they could eat at any time, despite eating the same number of calories:
- 9 hours of access caused 21% weight gain
- 24-hour access caused 42% weight gain
Mice fed a high-fat diet had higher weight gain with longer periods of food accessibility, despite consuming the same number of calories:
- 9-hour access caused 26% weight gain
- 15-hour access caused 43% weight gain
- 24-hour access caused 65% weight gain
To measure whether a “lapse” in TRF had any effect, mice were fed a high-fat diet for five days using TRF and two days of unrestricted feeding (to mimic the two-day weekend). They gained 29% body weight over 12 weeks, similar to the weight gain without the lapse.
Mice fed a low-fat, high-fructose diet had a 6% weight gain in both feeding situations over 12 weeks, which was similar to control mice fed a normal chow diet.
Mice fed a high-fat diet for 13 weeks using TRF and then given 24-hour access for 12 weeks, rapidly gained weight after switching so that they gained the same amount of weight as mice with unrestricted access for the whole 15 weeks (111% to 112% body weight). A control set who had TRF for the 25 weeks gained 51% body weight.
In mice with pre-existing dietary-induced obesity from having 24-hour access to a high-fat diet, switching to TRF caused them to consume the same number of calories within a few days. However, they lost weight:
- switching from 13 weeks of unrestricted access to 12 weeks TRF caused a drop in weight from 40g to 38g (5% body weight loss)
- switching from 26 weeks of unrestricted access to 12 weeks TRF caused a drop in weight from 53.7g to 47.5g (12% body weight loss)
MRI images showed that the difference in body weight for all of these experiments was due to fat mass rather than lean body mass. There were also inflammatory markers in the fatty tissue of mice with round the clock access compared to no inflammatory markers in TRF mice.
How did the researchers interpret the results?
The researchers concluded that these “results highlight the great potential for TRF (time-restricted feeding) in counteracting human obesity and its associated metabolic disorders”. They believe “it is worth investigating whether the physiological observations found in mice apply to humans” and say that “a large-scale randomised control trial investigating the role of TRF would show whether it is applicable to humans”.
Conclusion
Time-restricted feeding caused less weight gain than all-hour access for mice eating a high-fat, high-sugar diet over 12 to 26 weeks. It also led to weight loss of up to 12% when applied to mice that were already obese. TRF does not appear to have an influence on weight gain for mice eating a healthy or normal diet.
The current stage of this research means it has limited application for humans. We already know that high-fat and high-sugar diets cause weight gain, as was found here. It may be that future randomised controlled trials in humans will show that the amount of weight gain is more if the calories are consumed at times that do not make the most of our natural metabolic rhythm.
Even if the timing of eating patterns do have an effect on weight gain, we suspect that any beneficial effects would be modest. If you regularly consume high-fat and high-sugar foods, and do not exercise, you will put on weight regardless of any time-restricted eating habits. Sadly, there is no quick fix to weight loss.
