Chrononutrition: Why Timing of Eating Matters When it Comes to Weight and Health

Do you feel like you are starting the day off being “good” by having a small breakfast (or skipping it entirely), limit yourself to a “healthy salad” for lunch in order to lose weight, then find yourself famished by dinner? I am guessing after restricting like this all day it is hard not to find yourself grabbing snack after snack in the evening…..only to wake up not feeling too hungry.

As it turns out, our eating patterns are influenced by the type of lifestyle we lead which may affect our weight and health. Are you a “morning person” or a “night owl”? We all know people who get up at the crack of dawn and are running around the minute their feet hit the floor. There are also those who manage to stay up watching TV or reading or surfing the internet until the wee hours of the night. They are the ones who tend to hit the snooze button several times before dragging themselves out of bed to get to work. They don’t actually start thinking clearly until the morning person has been up for a few hours and has already made the coffee, fried the eggs and read the paper. Or, like some people, you could be a mix of the two.

Most of us have heard of “circadian rhythm”. Circadian rhythms are the natural physical, mental, and behavioral changes that a body goes through during a 24-hour cycle. It is sometimes referred to as our “body clock”. It is affected by light and darkness as well as genetics and other factors (like our habits). We typically think of sleep issues when we think of our body clock, however over recent years researchers in the field of “chronobiology” are discovering that our biological processes (such as digestion and metabolism, body temperature and even hunger) are affected by these cycles. Our “central body clock” does not just operate in one part of our brain to control only sleep. The timing of eating can “synchronize” organs and tissues that control food digestion, nutrient absorption, and metabolism (such as the stomach, liver, pancreas and fat tissue). Therefore, the time you do things every day, like eating and sleeping, matters when it comes to weight and health.

So what is the proof that it is worth it to pack that lunch? A recent study (August 2021) looking at energy intake at lunch vs dinner found that eating more at lunch instead of dinner may actually protect against weight gain and metabolic syndrome. Over 600 individuals were followed for over 5 years. Researchers looked at energy intake of all meals and snacks to come up with their conclusion that eating earlier appeared to be more protective than eating late. Apparently, eating lunch after 3 pm was most detrimental whereas eating lunch before 1 pm was best.

Another study looked at women with metabolic syndrome who were in a weight loss program. They compared those who ate their largest meal at breakfast verses those who ate their largest meal at dinner (700 calories vs 200 calories) and found those who ate the most at breakfast (both eating the same size lunch) ended up with lower triglycerides, glucose, insulin and even lower hunger levels (resulting in more weight loss).

A review article on the influence of timing on breakfast, lunch and dinner further supports the fact that when we eat affects our weight and health. The authors reviewed 23 studies from 2004 to 2019 that looked at timing of meals and weight, metabolism, glucose tolerance and other related factors. One interesting finding was the possible role of melatonin, the hormone that signals bedtime. Apparently, eating too close to when your melatonin is high may be detrimental to glucose tolerance as well as weight loss efforts. The authors suggest looking at “clock time”, or the actual time it is, is less important than an individuals natural (biological) start of night time, signaled by when they start to release melatonin (probably when you start to really feel tired and get to bed).

When researchers looked at melatonin onset, timing was different depending on your body clock (chronotype). Melatonin onset occurs approximately at 7 pm for early chronotype (“morning”) people, 1 AM for late chronotype (“night owl” ) people and about 10 pm for those in between. They also looked at what time of day a subject consumed about 50 percent (half) of their total daily calories. So, for example, if a person eats 2000 calories a day, 200 at breakfast, 400 at lunch and 1400 at dinner and after, 1000 calories (or 50 percent of 2000) would be consumed at some point in the evening. They found that subjects who ate half their calories early (about 8 hours before their biological night (melatonin onset, when you get sleepy and go to bed) were less likely to have gained excessive weight while those who ate half of their calories about 4 hours before melatonin onset or bedtime were more likely to have higher body fat, be over their normal weight, etc. When it comes to weight, the authors summarize that eating your biggest meal 2 hours or less before bedtime increases five times the chance that you will gain weight whereas eating a larger meal 2 hours after waking up doubles your chance of having a healthy weight. Bottom line message for dieters: don’t “save” your calories for dinner.

I believe the most important outcome is the health improvements and possible decreased risk of developing metabolic syndrome. You, however, may be like the majority of people today who are mostly concerned with weight. Even though we know through years of research that a person’s weight does NOT necessarily predict their health, I know I can’t wave a magic wand and shift everyone’s focus to just health. Also, if your weight has jumped up over the years due to shifts in lifestyle or eating habits that are not normal or typical for you, and less health-promoting as they used to be, then your increased weight may not be normal for you (and that could affect your health). Working on reestablishing your more normal eating and lifestyle vs restricting or dieting will eventually bring you back to your normal weight, whatever that was. Therefore, even though I am reporting on the fact that shifting energy intake to breakfast and lunch will likely promote weight loss or prevent weight gain, does not mean that is the reason I think you might consider it. The important thing is that you will likely feel better and end up healthier.

There are other really important reasons to eat more during the day and less at night. Assuming you are a typical person who is most active during the daylight hours (9-5 job, school, etc) your body needs fuel (food) to be successful and best perform during your day. What happens when you start your day out skipping breakfast and/or lunch, or eating very little all day, waiting for dinnertime, or even later when you can finally relax and eat? Or maybe eating and food plays a different role, and feels like a reward, like “I deserve this, I didn’t eat all day!”. The repercussions of that thinking may backfire if it is your weight you are caring about. For instance:

  1. When you starve your body during the day you are likely to burn more muscle than fat. The more muscle you have on your body the higher your metabolism (even if you don’t have bulging muscles, trust me, it is there) . That is why men typically burn more calories than women. When you burn up your muscle you lower your metabolism, in other words, burn less fat.
  2. You train your body to decrease digestive enzymes so you are not hungry. This is not a good thing because remember, you want to eat MORE during the day and less at night. This can’t happen if you don’t get hungry for breakfast and/or lunch.. We all know people who don’t eat all day and say they just aren’t hungry. They aren’t lying, they have probably just trained their bodies by doing this over time. It is hard to make yourself eat when you don’t feel hunger anymore. Unfortunately, these same people tend to eat more at night, training their body to be really hungry later, typically leading to overeating and weight gain.
  3. We have enzymes that burn fat and enzymes that make fat. When you starve or don’t eat much during the day you are at risk of leading your body to make more “fat storage” enzymes because your body knows it is not going to get any energy until later (and needs to store more).
  4. At some extremes of daily meal skipping and restriction, some individuals may be at risk of damaging heart muscle (since your heart is a muscle and that is what you burn when you starve).
  5. You totally slow down your metabolism and you probably don’t have as much energy to do things. Movement and physical activity or paramount to a healthy body and healthy weight (which is the weight at which you are stable, can eat enough to feel satisfied and have energy and get good nutrition). You can’t find your healthy weight on a chart. Everyone is different.
  6. When you don’t eat all day you are more at risk for becoming obsessed with thoughts about food and eating. You are more likely to binge eat in the evening. This may lead to extreme negative thinking, self-loathing and disordered eating.

What is the take-home message? First, remember we are all different genetically, and some people may be totally fine eating their largest meal at night. If you don’t have the specific genes where you may be more at risk of this behavior leading to trouble, you may be fine and can just keep doing what you are doing. One study actually showed that wanting to eat a big breakfast is half genetic (so harder to change) whereas wanting to eat a large dinner instead is more cultural and behavioral (and therefore, easier to change). It is important to pay attention to your body signals and also to what is happening with your individual health and body/weight. If you are stable and happy with your eating style, and your health is good (normal glucose tolerance, no prediabetes, stable weight, etc.) then by all means, what you are doing is working. However, if you are someone who is a night owl, who can’t fall asleep until the wee hours and who has experienced some health and/or weight changes over the years, AND you tend to eat more at dinner and after, then eating more of your calories/energy/food earlier in the day (lunch before 3 pm, dinner more than 2 hours before bedtime) might benefit you. If you find you don’t feel hungry during the day, start to increase your digestive enzymes slowly by gradually adding more food. If you skip breakfast, or can’t eat early, it is ok (and even beneficial for night owls who still may have high levels of melatonin) to wait and eat 2 hours after waking. If you still aren’t hungry start with something small (a yogurt, small bowl of cereal, etc). and go from there. Try eating your typical dinner at lunch time instead or dinner time (switch dinner and lunch).
Finally, please remember, it is your health and well-being that is important. If you find you are struggling with getting a hold on erratic eating, don’t jump on the next diet bandwagon. Instead consider a consultation with a registered dietitian who will be able to go through your diet history and eating habits and evaluate what may be contributing to any behavioral issues around eating. Although sometimes it is simply tweaking nutritional intake that does the job, often it is way more complicated and may require consultation with a therapist who specializes in eating issues (your doctor or dietitian should be able to refer you to someone in your area). Sometimes, there are medical reasons for issues so it is important to mention your concerns to your doctor.

It seems the old advice continues to apply today. All this detailed, scientific, complicated research spanning over decades appears to be providing the science to help us understand what we knew all along. Maybe Adelle Davis was right:

Eat breakfast like a king, lunch like a prince and dinner like a pauper.

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