Circadian Rhythm: How Meal Timing Affects Fat Loss

Rudy Mawer
Written By: Rudy Mawer
September 12th, 2016
Updated: June 13th, 2020
Categories: Articles Nutrition
37.4K Reads
Circadian Rhythm: How Meal Timing Affects Fat Loss
A lot of debate surrounds the effectiveness of meal timing & it's ability to boost your metabolism. Find out what the science behind your circadian rhythm.

It is likely you have heard the common saying “eat like a king in the morning, a prince at noon, and a peasant at dinner.” This idea was proposed almost 1,000 years ago1 and still remains today.

In recent years, the topic of meal timing has come to the forefront, with some believing the time of day, or your ‘Circadian Rhythm’, should dictate when to eat certain foods.

This is supported by evidence, with research now suggesting that meal timing can influence a wide variety of physiological processes, including your sleep/wake cycle, core body temperature, performance and alertness1.

It has also been theorized that your schedule of food intake can have a dramatic effect on your health, fat loss and possibly the likelihood of developing chronic diseases1.

In this article, we will cover how your circadian rhythm affects your weight status, including the odds of maintaining a healthy body weight, and the influence on weight loss and on health.

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What is your Circadian Rhythm?

Your body’s circadian rhythm is essentially your body’s own clock. It is controlled by a number of “internal clocks”, with the main orchestrator or controller being a paired structure in the brain called the suprachiasmatic nucleus (SCN)1.

The SCN controls a host of gene expressing factors such as CLOCK and BMAL1, which influence a wide array of physiological processes e.g. sleep-wake cycles, feeding behavior, body temperature and hormonal levels.2,3,4,5

Related: Hacking Your Sleep 101: Nine Tips For Better Gains

Disruption of the circadian clock can alter these biochemical, physiological, and behavioral circadian effects6,7. In modern day life, this may be a result of environmental factors such as jet lag, shift work, late night exposure to blue light or light pollution along with overnight recreational activities, such as hitting the clubs or bars6,8.

Along with this, increasingly more evidence is emerging which suggests that the time we eat can have a big influence on our circadian rhythms and metabolism. This has promoted an eating style or pattern known as “chrono-nutrition”, which refers to food consumption in coordination with the body’s daily rhythms or timing1.

Despite this making sense in theory, does it provide any additional benefit to your physique?

How Your Circadian Rhythm Influences Your Weight and Metabolism?

Initial studies found a strong link between the circadian clock and metabolism. In other words, differing times of eating may elicit a different effect on digestion and utilization of the food and nutrients9,10,11,12.

Circadian Rhythm, girl looking for protein scooper

Importantly, unusual or irregular eating times may cause disruption in our circadian system thus carrying implications for staying lean and optimizing our metabolic health13,14. Initial research began in animals, like mice, as it’s much easier to control and feed them at specific times! Here’s a breakdown:

Animal Studies

Studies using mice highlight that timing of food intake can carry clear metabolic implications. As expected for nocturnal animals such as mice, they consume most of the daily food intake during the night, or dark phase, which equates to the daytime for humans15.

In these studies, when the mice were given food exclusively during the day, their actual circadian rhythm and therefore metabolism started to change16. Further studies have shown that these alterations in normal feeding patterns resulted in greater food or calorie intakes and in the long term, elevated body weight and unhealthy metabolic parameters.

For example, when mice were housed in constant bright light, they consumed more food and calories. However, when switched back to their natural light/dark rhythm, their calorie intake reduced.

Interestingly, despite returning to a lower caloric intake and increased activity levels, these mice still displayed significantly increased body mass and impaired blood sugar (carbohydrate) tolerance compared with mice who had been housed solely under their natural light/dark cycles17.

Finally, in mouse research where they genetically modified their normal circadian rhythm, these mice exhibited significantly altered eating patterns and developed obesity and metabolic syndrome, a condition linked to impaired carbohydrate tolerance and several diseases such as diabetes and heart disease20.

These studies have laid down the foundation research, showing a significant impact on health and physique when food intake is not in alignment with the normal sleep/wake cycle. But, does this also apply to humans?

Circadian rhythm and meal frequencies effect on humans

Human Studies

In addition to the animal research above, there is emerging evidence in humans that eating late at night is linked to a higher risk of developing obesity and/or difficulties in losing weight.

Several other studies have demonstrated significantly higher risk for developing obesity and diabetes with short sleep duration (<5 hours) or late sleeping patterns (midpoint of sleep > 5:30 AM)22,23. These studies have also found that individuals tended to eat later dinners and consumed more calories late in the evening.

In other reviews and studies, delayed eating patterns are also positively associated with elevated body mass index (BMI), which, while it may not be accurate for a bodybuilder, is in fact a good measure for the general public who have normal amounts of lean mass or muscle24.

In a 2013 study, eating late led to a decrease in effectiveness and success of a weight-loss intervention. Most interesting of all, both groups of subjects had similar characteristics: age, appetite hormones values, energy intake, sleep duration and macronutrients distribution.

As shown below, although they were identical, the group who had their main meal of the day after 3 pm lost significantly less weight than those who had their main meal before 3 pm25.

Circadian Rhythm Early vs Late eaters Line graph

More recently, in a study using obese subjects who had gastric or bariatric surgery, it was found that individuals who did not eat late at night had greater weight loss compared to those that ate late at night.

Again, these findings were found despite similar obesity-related variables, including biochemical parameters, pre-surgical total energy expenditure, sleep duration, energy intake and macronutrient distribution between groups6,26.

Finally, in a controlled study using 32 young lean women, researchers found that after 1 week of eating late (lunch at 4:30pm), the women suffered from metabolic alterations that play a role in obesity, such as blunted variations in cortisol and body temperature, decreased blood sugar tolerance, decreased resting energy expenditure and decreased carbohydrate utilization27.

These findings were in comparison to a similar week where lunch was provided at 1pm.

Here is a visual showing the researchers proposed mechanisms behind altered eating times and negative issues on metabolism and weight:

Circadian Rhythm Clock

Along with these issues, another potential negative of eating late at night is its effects on your body’s natural release of the key hormone called Growth Hormone (GH). Growth Hormone is known as a key bodybuilding or physique based hormone, which has an effect on fat loss and nutrient metabolism.

Related: How To Plan Your Muscle Building Diet

In normal conditions, GH is released later in the evening as you go to sleep and peaks around midnight. However, another issue with eating later at night is it may alter this release, and therefore cause lower GH levels if late night eating is a regular part of your routine.

The current evidence suggests that delayed eating patterns, or eating later in the day, can alter the body’s metabolism of food and increase the likelihood of gaining weight, even when we consume exactly the same amount of calories or food!

How to Optimize Eating Times

While control of total daily calorie intake and other fundamental factors such as protein and exercise remain key, if you are trying to optimize every factor of your diet, consuming food in line with your natural circadian rhythm may be something you wish to consider.

While the odd meal later in the day will likely make no difference, if you start to eat later in the day or late at night on a regular basis, it may negatively impact your metabolism, hormones and possibly lead to weight gain.

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This may be supported with some of the supportive research in eating breakfast, which shows that eating earlier in the day is more beneficial for weight loss.

Rather than breakfast being magical, it may in fact simply be that people who eat breakfast are just eating earlier in the day and therefore avoiding the negative issues associated with eating later at night.

Once you’ve mastered the basics, reducing your food intake late at night may be a very simple, yet effective method to take your physique one step further!

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1 Comment
Joe C
Posted on: Sun, 09/18/2016 - 12:38

Does this also apply to those who train later in the evening. Sometimes I don't get to the gym until 6 or 7 which means I'm not home to eat until 8 or 9. Even when I prep food in advance, that's still a late meal, or is it OK since I just came out of training and my metabolism should be high enough to handle?