When it comes to weight loss, there’s a great body of research that suggests when you eat may be just as important as what you eat.
Time restricted eating, avoiding large meals before you sleep and having consistent meal times have all been shown to help you lose weight. To understand why, it’s important to dive into what circadian rhythms are and how your body clock works.
Circadian rhythms are biological processes or behavioural changes that oscillate on a 24-hour scale. The sleep-wake cycle is probably the most well-known circadian rhythm, but temperature, hormone levels, heart rate, and metabolism all vary depending on what time of day it is too.
These rhythms are driven by an internal body clock, which is present in every organ in the body and driven by the master clock in the brain. This master clock is synchronised to the environment by light, exercise and food.
There is a complex relationship between environmental cues, your body clock, and every physiological process in the body. Disrupting your circadian rhythms by changing these cues, such as by changing your sleep, exercise or eating patterns has detrimental impacts on both your mental and physical health.
People who consistently disrupt their circadian rhythms are more likely to be diagnosed with mood disorders, suffer from depression or anxiety, have an increased risk of obesity, heart disease and cancer.
In contrast, maintaining a consistent schedule for eating, exercise and sleep reverses the likelihood of these ailments and underpins good health.
Eat larger meals earlier in the day
When eating, there are certain periods throughout the day where food can be more easily digested and metabolised than others, suggesting the timing of eating could be directly linked to the number you see on your bathroom scale.
This is exactly what a team of researchers from the Wolfson Medical Centre, Tel Aviv University, found when they examined the weight of two groups of participants consuming their calories at different times of the day.
The same number of calories was consumed by both groups. Group 1 consumed most of their calories in the morning (700 calories for breakfast, 500 calories for lunch and 200 calories for dinner), whereas Group 2 consumed most of their calories in the evening (200 calories for breakfast, 500 calories for lunch and 700 calories for dinner).
The results were astonishing; Group 1 showed a 2.5 fold greater reduction in weight, 5% greater reduction in BMI, and 4.7% reduction in weight size. Eating a bigger breakfast also helped reduce insulin and fasting glucose; both of which lower the risk of type 2 diabetes.
These findings were backed up by a recent study published in the International Journal of Obesity. Researchers examined the weight of 510 subjects split into either the early eaters or late eaters category. The former group lost 25% more weight than the latter, despite the same caloric intake.
So what are the reasons behind weight loss when you shift to eating more calories earlier in the day? Dr. Nada Milosavljevic, MD and Director of Integrative Health at Mass General Hospital, explains that cortisol, which supports thyroid production and metabolism, is more abundant in the morning than in the evening.
This means the food you consume earlier in the day is more likely to be turned in to fuel than stored as fat. And conversely, the food you eat late in the evening is more likely to be stored as fat as opposed to being used for fuel.
Weight gain and eating too close to bedtime
Scientists have recently discovered that food intake relative to your sleep time is also associated with weight gain.
One study analysed the weight and circadian behaviours, such as the timing of melatonin release (which is a marker of sleep onset) and eating habits, of 110 adults. They found that participants with the highest body fat percentages consumed most of their calories within an hour of their natural sleep time, when melatonin levels were high.
In contrast those with lower body fat percentages tended to eat a few hours before they went to bed, when melatonin levels were lower. Andrew McHill, Division of Sleep and Circadian Disorders lead author at BWH, explains “these findings suggest that the timing of when you consume calories, relative to your own biological timing may be more important for health than the actual time of day”.
In other words, waiting a few hours after eating before you sleep is likely to help with weight reduction.
Time restricted eating and weight loss
As well as reducing caloric intake in the evening, researches have also demonstrated that reducing your eating window could help you lose weight.
A recent study showed that subjects who limited their eating to a consistent 10-hour window showed a 3% reduction in weight, as well as reporting sleeping better and having more energy.
The bottom line
Monitoring what you eat and how much you eat is important when trying to lose weight. But recent scientific findings in this area shed light on how important the timing of your meals is too.
Eating too many calories in the evening and eating too close to bedtime may lead to weight gain, even if your diet is on point! Aligning your meals with your circadian rhythms could be the first step to a healthier, happier life.