Will I Gain Weight If I Eat Late? Food Timing and Weight Gain
Can eating late make you gain weight? Could eating a heavy meal after a certain time of night make you fat? If you are eating within the constraints of your energy requirements, for years I would have said absolutely not and that eating late at night in and of itself can’t make you gain weight. However, given my experience helping people lose weight over the past three decades, my answer has changed since then as you might indeed gain weight from eating late depending on several factors. Earlier in my career, I often advised my clients that eating late at night was not a factor in weight gain as long they stuck to their diet and didn’t overeat. Given the laws of thermodynamics, if you consume more calories that your body needs, you will gain weight. Take in less calories than your body uses for the day and you will lose weight. A simple concept, and with this in mind, the timing of your meals shouldn’t make a difference in whether you gain or lose weight. Unfortunately, in the real world, things are never so simple and this was not always my experience. Clients who worked late night shifts, such as doctors, nurses, businessmen and women who needed to be in constant communication with others in different time zones and those who simply kept odd waking hours all had a harder time losing weight compared to those who kept regular hours, even when they ate consistently less than their daily energy requirements. Another curious group were my clients who ate relatively little, (and often slightly less than their daily energy requirements), and never lost weight in the same predictable pattern as everyone else. People in that group tended to have one or sometimes two meals a day and almost always skipped breakfast. And yet when all of them started having breakfast at a regular hour and eating more food (and calories) overall but spread out over the course of the day, they lost weight just as effectively as my clients who ate on a regular schedule. Even though they were consuming more calories than they were before! The math didn’t make sense and it did seem to suggest that eating meals later in the day might have some effect on weight loss and weight gain. In this article we will look at the recent scientific findings that suggest that food timing does indeed play a role in weight loss and weight gain. As always thank you for reading and do be sure to share this article with anyone who you think it will benefit.
Before we go any further it is important to note that overeating high calorie processed foods will ALWAYS lead to weight gain if you overeat and consume more calories that your body needs. The low satiety levels of highly processed foods and the effects of sugars, fats and salt in stimulating our desire to keep on eating can makes it very easy to overshoot your daily energy needs. A fact that food manufacturers bank on as the entire processed food industry is based on the idea of doing whatever it takes to make you eat more than you should. (See my article on The Economics of Obesity). Combine this with the all too common practice of rewarding yourself with “comfort food” after a hard and stressful day as a coping mechanism, and you unfortunately have the perfect environment for gaining weight. This isn’t anything new, as night time binge eating has always been identified as a clear causative factor in weight gain, but what is new is the findings that consuming a lot of calories later in the day will make you gain MORE weight if you didn’t eat that much during the day. And that this eating pattern can predispose you to a higher risk of developing diabetes, hypertension and heart disease. [1,2]
TAKE AWAY POINT: Higher calorie intakes later in the day can make you gain weight if you didn’t eat regular meals spaced out during the day and predispose you to metabolic related diseases. Which is somewhat ironic, as having regularly spaced out meals makes it LESS likely that you will have higher calorie intakes later in the day!
How The Longer Hours Of Modern Living Can Make Us Fatter
Like every organism on Earth, we are products of our natural environment, with systems intimately tied to the diurnal rhythms of the Earth’s rotation around that giant ball of hot plasma that we call the Sun. For the past billion years, the biochemistry of every creature on Earth has been selected in some form in accordance to the rising and setting of the Sun, ours included.[4,5,6] As our behavior, physiology and biochemistry are all adaptations to the daily cycle of our planet’s movement around the sun. Yet, most of us in developed countries live in a somewhat unnatural environment as our lives no longer revolve around the apparent passage of the sun across the sky, as we do not keep the same hours as populations living in non industrialized settings that are more in tune with our ancestral heritage. Thanks largely in part to Thomas Edison’s inventions and improvements in housing we are no longer huddled over a flame for light after sunset. The advent of electricity meant that we were no longer bound to the rotation of our planet for cues on when to sleep or to be active as we now have light everywhere on demand. Free of these constraints, people in industrialized countries are awake later, eat later and sleep later than ever before in human history. Our artificial extension of the day allows us to work longer and spend more time doing what we want to do without being obliged to go to bed shortly after dark. Unfortunately, like all of our technological advancements, there is a price, and perhaps a hefty one that we pay as a result. Our world has rapidly changed while our bodies are still the same, and adapted for the most part to move during the day and sleep during the night. Modern life is proving to us over and over that our self imposed changes to long established biological patterns can wreak havoc on our health. Studies conclusively show that cardiovascular disease, diabetes, gastrointestinal disorders, depression and other ailments are far more common among those who do not have regular sleeping habits.[8,9,10] Given these findings it stand to reason that research would show that irregular timing of our meals has a significant impact in weight regulation.
How Eating Late Can Mess Up Your Internal Clocks And Make You Gain Weight
All Earth-bound organisms, plants, including insects, birds reptiles and mammals have built in circadian ‘clocks’ that operate in anticipation of changes in the environment brought on by the rising and setting of the sun. Initially it was thought that time of day regulation was the role of the suprachiasmatic nucleus (SCN)- an area of the brain populated by a large number of ‘mini clocks’ called circadian oscillator cells. [12,13,14] Cells that act kind of like a centralized timekeeper and they oversee our body’s 24 hour based rhythms. [12,13,14] However, scientists have since discovered that circadian oscillator cells also exist in other regions of the brain and in most, if not all peripheral organs and tissues. That includes the liver, kidneys, pancreas, gut, muscle tissue and interestingly enough- fat cells! [1,3,15,16,17,18] Now the SCN plays a special role within this system of oscillator cells as it determines the time of day by measuring the amount of light entering special cells in your retina. These cues are called zeitgebers and circadian oscillator cells in other parts of the body rely on other zeitgebers to determine time such as meal timing and food availability. [19,20,21] It used to be that these cues were all the same, as humans on average will eat more during day and less at night in our natural environments, but this is no longer the case. So when we consume high calorie meals later in the day, our brains are receiving a signal from one zeitgeber (light) saying it is dark outside and thus time to prepare for and sleep whereas another zeitgeber (food intake) is saying it is time to be active and awake.[2,12] Those conflicting signals appear to deregulate metabolism and may be one of the reasons why shift workers and individuals with later schedules have higher rates of metabolic related disease and obesity.
TAKE AWAY POINT: Every cell and every process in our bodies are linked to our ancestral habits of being active during the day and inactive during the night and any change to that pattern can have about negative health impact.
Food Timing And Weight Loss- How Eating At The Wrong Time Makes You Gain Weight
Adipose (fat) tissue also have circadian oscillator cells with their own time sensitive rhythm of accumulation (storing fat) and mobilization (burning fat) called temporal compartmentalization. When you are sleeping, your body tends to burn fat and while you are awake your body tends to store fat. Thanks in part to time based oscillators in the liver that controls whether your body is going to use glucose or fat as an energy source. [22,23,24] Genes responsible for using sugars as the body’s primary fuel source (PFKFB3, FUK, MPI and PFKM) have high expression levels in the morning and drop in the afternoon through the evening. On the other hand, what are referred to as ‘fuel accumulation’ genes (HMGCR, HMGSC1), that store fat have low levels in the morning and increase as the day goes on. (See also my article When Is The Best Time To Workout AM vs PM)
TAKE AWAY POINT: Your body burns fat when sleeping as an energy source and glucose when you are awake. Disrupt the natural sleep/wake time based on daylight hours and you can end up storing fat when you should be burning it.
The time you eat also affects whether you will lose weight or gain weight, even when you are ingesting less or just enough calories for your body to remain in energy balance. A groundbreaking Spanish study set out to determine whether the timing of food intake influences the success of a weight loss focused diet and researchers were also able to examine genetic, physiological and behavioral factors that may have affected the results. 420 overweight men and women following a clinically supervised weight loss diet were monitored for 20 weeks, and the results were quite surprising. Those who ate their meals later in the day lost significantly LESS weight than those who ate their main meals earlier in the day, even though they all ate followed the same diet with the same proportions of protein, fats and carbohydrates based on their individual calculated energy expenditures.
This was the first human study to observe this occurrence after many animal studies had similar findings. Research with mice, who are nocturnal by nature and have a time system that is the exact reverse of ours as they are active mainly at night and sleep during the day, show that when two groups of mice with identical activity levels are fed exactly the same amount of calories at different times there are significant differences in weight gain. Mice fed during the day when they would ordinarily be asleep gained weight and increased their body fat, while those fed at night in keeping with their normal biorhythms did not gain any weight. [2,25,26,27] An indication that the time food is consumed is a factor responsible for weight gain independent of calorie intake.
TAKE AWAY POINT: It’s not just what you eat and how much you eat, but it’s also when you eat that determines whether you might lose or gain weight.
Food Timing And Weight Gain: The Effects of Eating Mostly At Night
The much higher incidence of obesity among shift workers compared to day workers with the same energy intakes and activity levels has always been clear evidence that food timing is also important for humans. Along with the many studies that find increased obesity levels among non-breakfast eaters compared to those who regularly eat breakfast and also among and those diagnosed with night eating syndrome.[28,29] It was initially thought that weight gain associated with night time eating was due to a tendency to gravitate towards more high calorie processed foods, which are exceptionally easy to overeat and so increase the likelihood of eating more than you should and consequently gaining weight.[30,31,32] However, we now know that overeating may not necessarily be the problem as these studies demonstrate that weight gain can occur independent of energy intake if meals are predominantly eaten later in the day.
Eating Late & Weight Gain- Underlying Mechanisms In Our Genes
There many other theories as to why there is link between weight gain and meal timing. It was thought that changes in levels of hormones responsible for making you feel full or satisfied after a meal, (leptin and ghrelin), may have been responsible, possibly as a result of a decoupling from the body’s light based inner clock. [33,34] But in the Spanish study, blood tests showed no differences in satiety-related hormone levels between the early eaters and the late eaters. Lack of sleep has also been assumed to be a possible causative factor as many studies show associations between short sleep duration and risk of obesity and impaired weight loss.[35,36,37] However, in the Spanish study even though the late eaters went to bed later than early eaters there were no real differences in sleep duration or reported quality between the two groups.  Other animal and human studies have also failed to find associations with decreased sleep and weight gain[2,38] but what researchers did find were differences in a very time sensitive gene called CLOCK.
CLOCK stands for Circadian Locomotor Output Cycles Kaput (who ever said scientists don’t have a sense of humor) and it’s one of the genes found in mammals that are responsible for the persistence and duration of our body’s daily rhythms along with another transcription factor called BMAL1. You can think of these genes as the driving forces behind the circadian oscillator cells found in the SCN and peripheral organ tissues that we mentioned earlier. In the Spanish study, there was a higher occurrence of a variation in the CLOCK gene (called rs4580704) among those who ate later in the day- a variation that seems to manifest as a result of irregular food timing. Interestingly enough, other studies have associated this particular genetic mutation with increased susceptibility to obesity and metabolic disease.[39,40] Other variations (called polymorphisms) in the CLOCK gene have also been linked with increased insomnia, difficulty losing weight and increased depressive episodes among those with bipolar disorders.[41,42,43] however this study was the first to report an association between CLOCK gene variations and the timing of food intake.
Practical Meal Timing Tips For Preventing Weight Gain
The most significant take away from this study was that those who had lunch as their largest meal of the day (in the Mediterranean breakfast is usually small and lunch is the main meal) were the ones with the greatest amount of weight loss. Eating a large lunch- which represented for the participants in this study, as much as 40% of their daily energy intake appears to reset the mini clocks in our organs either indirectly or through changes in timing relative to other meals during the day. Weight loss differences in this study did not hinge on what time dinner or breakfast was eaten- just lunch, however that doesn’t necessarily mean that eating an early lunch is the only way to optimize weight loss. Researchers observed that the late lunch eaters also had a far higher tendency to have skipped breakfast or to have had a smaller than usual breakfast. Such a long time lapse between the first meal of the day and lunch seems to create a prolonged semi-fasted state and lowers blood sugar levels- which can have a negative effect on glucose metabolism and could have contributed to the difference in weight loss. Thus underlining the wisdom of having regular meals starting with a good breakfast to maintain adequate glucose metabolism. For while the study did not look at a population where eating a large breakfast is a common practice, the fact that most of the late eaters did not eat breakfast and the many studies that do verify a link between the consumption of a high protein, high fiber, carbohydrate breakfast with increased success in weight loss and lower incidence of obesity leaves little room for doubt that eating breakfast is an important part of the equation.
So what weight loss and weight gain preventative recommendations can we glean from these new studies and advances in molecular biology? There are several:
Recommendations for Not Gaining Weight From Eating Late:
- Eat the majority of your calories earlier in the day.
- Don’t skip breakfast.
- Eat meals at regularly spaced intervals the same time everyday instead of erratically.
- Avoid high calorie meals later in the day.
- Try to keep a schedule that makes it less likely that you will be eating later in the day.
In spite of our desire to extend our days there is in fact a genetically hardwired ‘wrong time’ to eat as we are unquestionably maladapted to eating at night. Taking this into consideration anyone attempting to lose weight or prevent weight gain and or achieve optimal health would do well to ensure that they ate most of their calories earlier in the day. My own experience with my clients undergoing extreme weight loss (50lbs-110lbs) is observational at best but they all consumed most of their calories earlier in the day following my recommendation to ‘breakfast like a king, lunch like a prince and dine like a pauper’ with an additional directive to turn in early and not to eat too late at night. I hope this article helped highlight the importance of meal timing with regards to weight loss and maintaining a healthy body weight and while some of the lessons may not be convenient for many of us- they are important nonetheless as we are very much still creatures intimately tied to the rotation of the Earth. Thanks as always for reading.
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