There has been a lot of buzz around timing of meals recently, especially after two studies were published in October. One suggesting that eating late may be directly related to weight gain and another suggesting that eating late may change hunger and appetite but does not impact weight. While caution should always be used with new study findings, these results of course gave the media plenty of materials to scare consumers from enjoying dinner past 6 PM, reminding us of some very antiquated health advice. If you are a client or follow me for a while, you know that I encourage eating at any time of the day, as long as it works for you. Was I wrong?

The circadian rhythm

To better understand the relationship between timing of meals and health, we need to first talk about the circadian rhythm. Known as the body's "internal clock" the circadian rhythm is a system that regulates most of our physiology. We are eager to teach our children about the importance of routines - bed times, meal times, wake times etc. but quickly forget how important they are when we grow older. That's a shame because having a rhythm is essential for our system, no matter how old we are. A disruption to the circadian rhythm can have massive consequences, with some research indicating that shift workers are more likely to develop metabolic syndrome or depression due to disruption of this "internal clock" system.

People are likely to experience negative health effects when they carry out tasks (or consume food) during the "biological night". Our internal clock is regulated by environmental light, melatonin production, or activities like food consumption. A misalignment in circadian rhythm is defined as having to be awake at night or sleeping during the day. In most studies, looking at the link between disease and circadian rhythm, negative health consequences were attributed to such a misalignment or simply short sleep duration, which is known to be a cause for many health problems.

Chronotypes

We aren't all the same, and our chronotypes - a natural tendency to be a morning or evening person - vary as well. Some people are early risers (morning chronotype) and others prefer to sleep in and go to bed later (evening chronotype). Some evidence suggests that those with evening chronotypes are more at risk for developing certain diseases but more research is needed to determine a definitive link between chronotype and disease risk. No matter your chronotype, as mentioned above, having a routine is essential for your body. Even waking up later on weekends as opposed to work days could throw your body's internal clock off. Known as social jet lag, changing your sleep habits on weekends is suggested to result in increased metabolic disease risk over time.

Should you eat at night?

I don't know anyone who would recommend eating at night - there is a difference between eating a little later and midnight snacking. So, why not eat at night? Simply because our bodies want to rest too. Many functions are down-regulated during the biological night. For example, we know that insulin sensitivity decreases at night.  But does that mean you can't eat dinner?

According to one study, it's not so much about not eating dinner at all (a bad idea!) but about energy distribution throughout the day. You are not prohibited from eating after dark - this would be extremely challenging in places like New York. It is now late October. The next sunset after 6 PM will be in March. It's simply not feasible to consume all your meals when it is light out. Not to mention that you would have to keep adjusting meal times to the length of day, which is not in line with the recommendation of having a solid routine to support your circadian rhythm.

It may be more beneficial to simply focus on consuming lighter evening meals. People whose biggest meal is dinner could be more at risk for being overweight, elevated blood sugar or dyslipidemia. According to researchers, it may be a good idea to make your evening meal no more than about 40% of your total energy, as eating the majority of your calories earlier during the day is linked to better health outcomes. Additionally, it could help to make your evening meal slightly higher in protein, since it will have less of an effect on insulin.

What do the new findings suggest?

Now back to the recent studies mentioned before. Let's look at the study that found a link between lat eating and weight gain first. While it confirms some of the mechanisms discussed before, some important limitations need to be considered. The data is based on a protocol that lasted just 6 days. Only 16 participants completed the protocol, of which just 5 were women. People also stayed in a closely controlled environment, including temperature, light, and humidity, which hardly resembles real-life conditions. The study is an interesting experiment of what happens when you change your diet for 6 days but tells us little about how our bodies adapt to long-term changes in eating patterns.

The second study that was recently published followed 30 overweight people (16 male, 14 female) for two 4-week cycles of weight loss diets. The calories were either "morning loaded" or "evening loaded", to observe if a difference in weight loss would occur with a higher distribution of calories in the morning versus evening. In this study, weight loss results were "near-identical" in morning loaded and evening loaded weight loss diets. However, the diet that provided most calories earlier in the day resulted in lower perceived hunger and appetite. This suggests that while the timing of meals may not directly impact weight, it could increase appetite and hunger, leading to more weight gain in uncontrolled (real-life) conditions.

Both studies were not long enough to make conclusions about long-term metabolic adaptations to diet and only give clues for further research. They also only studied a small sample size, and never assessed the participant's chronotypes, giving little actionable data. What they do suggest is that eating most of your calories earlier in the day could be beneficial - something we already knew. However, what time exactly people eat and go to sleep may not be as important as having a routine and sticking to it, especially keeping in mind that day length varies in many geographic locations.

What does all this mean for you?

First and foremost - don't skip dinner! Going to bed hungry has no health benefits and is likely to keep you up at night, resulting in a disturbance to your circadian rhythm. Additionally, don't beat yourself up over special occasions. If you eat a later dinner every once in a while, your circadian rhythm will not suddenly blow up.

People survive jet-lag without gaining 20 lbs, so you can survive a birthday or anniversary dinner. And this is the problem with over-interpreting mechanisms and preliminary research. We forget that our social lives are an essential part of health. Sure, you can sit at home and eat timed meals every day but would that be beneficial for your mental health? Would you really be healthier if you never went out, slept in, or traveled to a different time zone? Maybe there's more to life than religiously following health rituals?

The bottom line:

From a public health standpoint, the timing of meals is one of the smaller problems we have when it comes to nutrition. Sensationalizing small trials with findings that cannot be applied to the general public is not helpful. Any "expert" who scares you from nourishing your body because it's past 6 PM has no idea what they are talking about. I would much rather have you eat a late dinner than skipping meals and putting yourself at risk for nutritional deficiencies.

We simply don't know enough about the direct impact of meal timing on health to make any solid recommendations. If you want to be healthy, you should emphasize eating a balanced diet that's rich in fruits, vegetables, whole grains, lean protein and healthy fats, no matter what time you are able to sit down and have a meal mindfully. It could also be a good idea to eat most calories earlier in the day and avoid heavy evening meals.

Remember that there is a big difference between eating at 8 PM and eating at midnight. What research has not shown yet is what exactly is late and how late is too late for which chronotype. Until we know more, we just can't use this theory for solid recommendations.

Sources

1. Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity
2. Timing of daily calorie loading affects appetite and hunger responses without changes in energy metabolism in healthy subjects with obesity
3. The genetics of circadian rhythms, sleep and health
4. Identifying shift worker chronotype: implications for health
5. Morning Circadian Misalignment during Short Sleep Duration Impacts Insulin Sensitivity
6. Chrono-nutrition: From molecular and neuronal mechanisms to human epidemiology and timed feeding patterns
7. The Connection Prescription: Using the Power of Social Interactions and the Deep Desire for Connectedness to Empower Health and Wellness