Australasian Science: Australia's authority on science since 1938

The Importance of Meal Times on Weight Loss

Credit: showcake/Adobe

Credit: showcake/Adobe

By Amanda Page

Our modern 24/7 appetite is disrupting natural gastric signalling oscillations to the brain. Restricting meal times could help weight loss and maintenance, particularly among shiftworkers.

Obesity is a huge global issue, with levels nearly tripling since 1975. In 2016, more than 1.9 billion adults were overweight, of which 650 million were obese.

According to the Australian Bureau of Statistics, 62.8% of Australian adults were overweight or obese in 2011–12. This has increased from 56.3% in 1995 and 61.2% in 2007–08.

Being overweight or obese increases an individual’s risk of developing chronic health conditions, including cardiovascular disease, high blood pressure, type 2 diabetes and certain cancers (e.g. breast, ovarian, prostate and colon cancer). However, the successful treatment of obesity is limited. For example, while lifestyle interventions such as exercise and changes in diet result in weight loss, it is difficult to maintain and requires a degree of vigilance that most busy people cannot maintain.

As a result there is a low probability that people who achieve weight loss actually maintain it in the long term. The literature in this area is quite diverse with success rates for weight loss maintenance ranging from 2% to 20%.

At present, the most effective treatment for obesity is bariatric surgery. However, this option is not practical considering the large percentage of people who are overweight or obese and the economical burden this places on society. Bariatric surgery is limited to individuals with a body mass index above 35 and a weight- related health problem, such as type 2 diabetes. The simple fact that bariatric surgery targets the gastrointestinal tract indicates that this region should be an area of research to establish other strategies or pharmacotherapies for the treatment of obesity.

The gastrointestinal tract senses the arrival, amount and nutrient composition of a meal. For example, as food enters the stomach it stretches it. This activates stretch-sensitive sensory nerves in the stomach wall that send signals that inform the brain about the arrival and amount of food consumed. The greater the degree of fullness of the stomach, the higher the degree of stretch of the stomach wall and the greater the intensity of the signal to the brain. The brain processes this information and eventually this leads to feelings of satiety and fullness. Therefore, these sensory signals initiate the termination of a meal.

These sensory nerve signals are not static, and the intensity of the signal in response to a specific stretch stimuli will depend on the time of day. It is thought that these sensory signals finally regulate food intake to match energy demand.

Mice are nocturnal animals whose food intake patterns are the opposite of humans. Therefore, mice eat the majority of their food during the night when they are active.

We have shown that the response of sensory nerves to stretching of the stomach wall is high during the day when the mice are resting and energy demands are low. Therefore, if they eat during this period they will feel fuller quicker, and consequently the meal will be terminated earlier, limiting the amount of food consumed during the day. But at night, when energy demands are high, the responses of these sensory nerves to stretch are dampened, allowing the intake of more food before the termination of a meal. As a consequence, mice exhibit daily rhythms in food intake.

In high-fat diet-induced obese mice, these oscillations in the intensity of the signals from the stomach in response to food intake are lost. As a consequence, high-fat diet-induced obese mice tend to graze over a 24-hour period.

We recently reported in the Journal of Neuroscience (https://goo.gl/r4xLPW) that the loss of oscillations in gastric sensory nerve signalling is prevented when feeding times are restricted. In our study, mice fed a standard mouse chow or a high-fat diet were split into three groups (Fig. 1). One group had free access to food; another group only had access to food for 12 hours during the night, when they normally eat; and one group only had access to food during the day.

We found that the time-restricted fed mice on the standard mouse diet were able to fully compensate food intake in the period when food was available, and there was no difference in weight gain between the three groups of mice. However, in mice fed a high-fat diet, the time-restricted feeding groups were unable to fully compensate food intake and gained less weight than the mice that had free access to a high-fat diet.

Further, if high-fat diet-induced obese mice are fed just during the night period, when they normally eat and in line with their energy requirements, then the oscillations in gastric sensory nerve signalling are maintained. Conversely, if high-fat diet-induced obese mice were fed just during the day period, the oscillations in sensory nerve signals were maintained but inverted.

Therefore these sensory signals from the stomach can be entrained by food intake. This is quite important when we consider shift workers, who are at significantly greater risk of developing obesity than individuals who work during a normal day. If we can standardise the timing of food intake in shift workers then maybe we can reduce some of the detrimental metabolic effects associated with shift work. This is an important area requiring further research.

With the development of new technologies and the extension of normal working hours, the range of time that people eat has greatly expanded so that now many people eat late at night and then again first thing in the morning; basically there is no fasting period (Fig. 2). Research in humans is at the very early stages but some studies indicate that overweight individuals who are not asked to change their diet but simply restrict eating to within 10–11 hours each day lose on average about 3.5% of their body weight in 16 weeks. Another study has found that eating for a short period early in the day can actually reduce hunger swings.

It is possible that the maintenance of oscillations in sensory signalling from the stomach in time-restricted feeding conditions can put people back in control of their appetite cues. Our report may also explain why, in a study by Dr Satchidananda Panda of the Salk Institute (https://goo.gl/ekNArN), mice that were only exposed to time-restricted feeding during weekdays had similar results to those that were time-restricted for the whole week: the maintenance of the oscillations in gastric sensory signalling would enable control of food intake during the periods when food was unrestricted.

In conclusion, the data from our study supports the idea that time-restricted feeding can have beneficial effects on weight loss and weight loss maintenance.


Prof Amanda Page is Head of the Vagal Afferent Research Group at the University of Adelaide’s Centre for Nutrition and Gastrointestinal Diseases.