When it comes to healthy eating, we know that what we eat matters. So does how much we eat. And research shows that when we eat is important, too.

Many studies point to health improvements from making changes to when you eat. That’s because our bodies operate on a biological clock that regulates our circadian rhythms. Circadian rhythms  are physical, mental and behavioral changes that follow a 24-hour cycle. They coordinate the timing of our daily behaviors (like sleep/wake times) and biological functions (like hormone release). And they respond to signals from our environment, like light and food.

Part of this daily biological cycle relates to food and drink intake. Your body is best at digesting food and drinks when you’re active and light is present. So eating or drinking when your body expects you to be resting or when it’s dark can disrupt your body’s biological processes. That can lead to health issues like weight gain, type 2 diabetes and heart problems.

Research into the science of circadian biology is offering new information about potential optimal timing for eating. 

Eat at Regular Times

Eating at regular times each day may have a positive impact on your health. Eating at consistent times is important for keeping your circadian rhythms in sync. Changing mealtimes from day to day may disrupt those rhythms and cause health issues. Much like how we can have mood and health problems when our sleep patterns are disturbed.

Studies show that irregular eating patterns are related to weight gain, type 2 diabetes and heart disease.

Eat During Certain Hours

The number of hours between when you first eat and when you last eat each day is called your daily eating duration. Time-restricted eating, or TRE, is only eating during the same period of time each day. The period of eating is usually 8, 10 or 12 hours each day. The important part is that it be the same period each day.

Studies show that a consistent and limited eating duration each day may improve your metabolism and heart health. That’s because it helps keep your circadian clock working at its best.

Time of Day Matters

Studies show that eating during or too close to the sleep/rest phase of our circadian clock plays a role in metabolic diseases and heart health. For example, those who eat close to bedtime are more likely to have more body fat. And studies of people trying to lose weight have found that those who ate earlier in the day lost more weight.

Because of our circadian rhythms, our bodies are more efficient at digesting, absorbing, and metabolizing food earlier in the day. There are health benefits to having most of your daily calories in the first half of day. Studies also show that people lost more weight and felt less hungry when they had large breakfasts and small dinners. Another study found that late eating was linked to increased risk for obesity. 

Some of this increased risk for obesity is due to how blood sugar levels change throughout the day. Researchers at the NYU Grossman School of Medicine  found that eating more of your daily calories earlier in the day may help you level out blood sugar fluctuations and trim the time that blood sugar is above normal levels. That helps you maintain a healthy weight.

Make a Plan

While more study is ongoing, research shows that several habits related to when you eat are good for your health.

Set a consistent daily eating duration. Limit the time you eat each day to 8, 10 or 12 hours. Make it the same hours every day. Try not to eat outside of those hours.

Start early. Start your daily eating duration early in the day. And eat most of your calories in the first half of the day.

Stop early. Make sure you stop eating for the day before your body starts winding down for sleep.

Eat a hearty, healthy breakfast. UT Southwestern Medical Center  suggests combining complex carbs, healthy fats and lean protein. Try these combinations:

• An omelet with fresh vegetables.
• Low-fat cottage cheese and fruit.
• Granola with fruit, seeds or nuts, and low-fat milk.
• Yogurt with wheat germ, fruit or nuts.
• Whole grain toast topped with almond or peanut butter.
• Low fat, whole grain muffins or waffles with a bit of low-fat ricotta cheese and a dash of cinnamon.

Talk to Your Doctor

Ready to make a change to when you eat? It’s best to check with your doctor about your plans before you start. That’s especially important for those with diabetes or other health issues. Your doctor can help you make sure the timing for your snacks and meals is best for your health concerns.

Don’t Forget the Basics

How much you eat is also important. How much food we need varies by individual. Talk to your doctor about what calorie range is best for you. And make sure you’ve got a good sense of healthy portion sizes. 

Sources: Circadian Rhythms,  National Institute of General Medical Sciences, NIH, 2023; Distribution of energy intake across the day and weight loss: A systematic review and meta-analysis,  Obesity Reviews, Wiley Online Library, 2022; When to Eat: The Importance of Eating Patterns in Health and Disease,  Journal of Biological Rhythms, National Library of Medicine, 2019; Study Finds That Eating Meals Earlier Improves Metabolic Health,  NYU Langone Health, 2023; Late isocaloric eating increases hunger, decreases energy expenditure, and modifies metabolic pathways in adults with overweight and obesity,  Cell Metabolism, 2022; Can eating earlier in the day jumpstart weight loss?,  UT Southwestern Medical Center, 2015