Many of us start the day with a small breakfast as we run out the door, followed by a medium sized lunch and a large dinner. We also tend to snack throughout the day and even grab a bite before bed. However, while what we eat is important, a growing body of research suggests when we eat matters too.
The digestive system's circadian rhythm
While you have likely heard of the circadian rhythm, the master "clock" in the brain that governs our sleep-wake cycle, we actually have a variety of circadian clocks that govern the daily cycle of activity for every organ.
These rhythms exist because every organ needs downtime for repair and regeneration.
The digestive system is no exception. During the day, the pancreas increases production of insulin, which controls blood sugar levels, and then ramps it down at night.
Circadian clocks optimize our health by aligning our biological functions with regular and predictable environmental patterns. Disrupting our circadian clocks — such as by skipping breakfast or eating at midnight — can result in health issues such as weight gain, metabolic syndrome, cancer, cardiovascular disease, and more.
Eat breakfast daily
About 20 to 30 percent of American adults skip breakfast. Some do it to save time, many do it in an effort to lose weight. However, studies show that people who eat breakfast daily are less likely to be obese, malnourished, suffer from impaired blood sugar metabolism, or be diagnosed with diabetes.
They are also less likely to have the heart disease risk factors of high blood pressure and high cholesterol. Even the American Heart Association recently endorsed biologically appropriate meal timing to reduce the risk of heart disease.
Just eating breakfast isn't the only important thing however. It's critical to start the day with a breakfast that provides plenty of protein and healthy fats, and a minimum of sugars. This helps support blood sugar balance and proper brain function throughout the day.
Make breakfast the largest meal for weight control and fat loss
The timing in relation to the size of our meals is also important.
Research shows having the largest meal in the morning appears to help with weight control compared to having a large meal in the evening.
In fact, a person eating the identical meal at different times of day might deposit more fat after an evening meal than a morning meal.
This is partially because insulin, a hormone that helps with blood sugar control, appears to be most efficient in the morning. In addition, we burn more calories and digest food more efficiently in the morning than later in the day when most of us eat our largest meal.
In one study, a group of overweight women with metabolic problems were put on a 1400 calorie-per-day diet. Half consumed 700 calories at breakfast, 500 calories at lunch, and 200 calories at supper, and the other half reversed that pattern.
Women in both groups lost weight and experienced reduction in fasting glucose, insulin, and ghrelin (a hunger hormone), but in the same time frame the large-breakfast group experienced added benefits:
- They lost 2.5 times the weight compared to those who ate the largest meal at dinner.
- They had significantly greater decrease in fasting glucose, insulin, and triglyceride levels.
- Their satiety (sense of fullness) scores were significantly higher.
- They also lost more body fat, especially in the belly.
According to the researchers, a high‐calorie breakfast and a reduced calorie dinner is beneficial and might be a useful alternative for managing obesity and metabolic syndrome.
The body needs fasting periods for optimum health
Fasting signals to the body to start burning stores of fat for fuel. Most of us eat meals and snack from the time we wake up until shortly before bed — or even in the middle of the night. In fact, studies show the average person eats over a 15-hour period during the day. This short fasting time period may interfere with optimal metabolism and increase weight gain.
Researchers put a group of prediabetic men through two eating cycles. In one phase, they ate meals within a 12-hour window for five weeks.
Then in another phase, they ate the same meals in a time-restricted six-hour window starting in the morning.
They ate enough to maintain their weight, so they could assess whether the time-restricted regimen had benefits unrelated to weight loss.
The six-hour meal schedule improved insulin sensitivity, insulin beta cell responsiveness, reduced oxidative stress, increased appetite, and significantly lowered blood pressure.
In addition, the men who ate only one or two meals per day fared better than those who ate three meals.
A recent review of the dietary patterns of 50,000 adults over seven years provides added evidence that we should ingest most of our calories early in the day, including a plentiful breakfast, a smaller lunch, and a light supper.
The researchers said that eating breakfast and lunch five to six hours apart and making the overnight fast last 18 to 19 hours may be an effective method for preventing long-term weight gain.
Another recent study found that subjects who added snacks to their daily meals tended to gain weight over time, while those who had no snacks tended to lose weight.
Light exposure is key for proper metabolism
Sufficient exposure to natural light and darkness also play an important role in how we metabolize food for either energy production or fat gain.
At night, the lack of sunlight signals our brain to release melatonin, the hormone that prepares us for sleep. In the morning, the light stops melatonin production and we wake up.
When we change that signaling — whether from a late-night meal, artificial lighting at night (especially blue screen light), shift work, flying and travel, or changing our eating patterns — it confuses our bodies' circadian clocks. Eating at the wrong time of day strains the digestive organs, forcing them to work when they are supposed to rest.
Shift workers, who account for about 20 percent of the country’s work force, have a particular problem with disturbed circadian clocks. Many frequently work overnight shifts, forcing them to eat and sleep at odd times. Nighttime shift work has been linked to increased risk of obesity, diabetes, heart disease, and breast cancer.
Studies have linked poor melatonin activity and disrupted sleep-wake cycles with increased risk of dementia and Alzheimer's, cancer, autoimmune flare-ups, obesity, and more.
Low blood sugar may require a before-bed snack
One important exception to the "don't eat right before bed" rule is for those who have chronic low blood sugar. For these people, keeping blood sugar stable throughout the day — and night — is critical for brain health, energy level, and more.
If you suffer from the following chronic low blood sugar symptoms, it may be best to take a small, high-protein low sugar snack just before bed:
- Constant sugar cravings
- Nausea or lack of appetite in the morning
- Irritability, light-headedness, dizziness, or brain fog if meals are missed
- Craving caffeine for energy
- Eating to relieve fatigue
- Afternoon energy crashes
- Waking around 3 a.m.
Daily habits to maximize your dietary rhythm
To help maximize your meal timing and metabolism, incorporate the following habits into your day:
Make breakfast your largest meal and make dinner your smallest. While this may prove difficult for those with a busy social life or family that sits down to a big dinner every evening, make the evening meal smaller whenever possible.
Prioritize protein and healthy fats with breakfast, and minimize sugar and caffeine intake especially before lunch, to stabilize blood sugar and regulate metabolism.
Avoid between-meal snacks and bedtime goodies. The exception is for those who have chronic low blood sugar as mentioned above.
Try time-restricted eating pattern, or intermittent fasting, to maximize weight management.
Manage exposure to blue light at night:
- Avoid screen light in the evening
- Install the f.lux app on your phone and computer
- Read a book
- Wear blue-blocker glasses at night
- Install amber or red light bulbs for evening use
If you have chronic low blood sugar, a small before-bed snack with plenty of protein may be a good idea to keep your blood sugar stable all night and prevent that 3 a.m. wake-up.
While studies suggest that prioritizing larger meals early in the day helps support metabolic health, it does not necessarily mean that you should skip dinner. Instead, have your dinners earlier and make them relatively light.
The take-home message here is like the old proverb, "Eat breakfast like a king, lunch like a prince and dinner like a pauper."