Is When You Eat Just as Important as What You Eat?

food clock


Wouldn’t it be great if there was a simple way to lose weight? Instead of counting calories or cutting carbs, what if you could just avoid eating during certain times? A study in 2012 showed that mice who were restricted to only eating at regular times throughout an eight hour period weighed 28% less than mice who consumed the same number of calories but ate frequently throughout the entire day.[1] But the study didn’t define these “regular times” or explain which 8 out of the 24 hours matter most. And of course, we’re people—not mice!

Is there any evidence from studies of humans that when we eat or don’t eat matters?

Our Changing Habits and Circadian Rhythms

Skipping meals, snacking instead of eating breakfast, lunch, and dinner, and late night food-runs have become the norm, especially among teens and college students.[2] Due to differences in culture, work/school/family schedules, and individual preference, the times that people are eating their meals vary.[3] Changes in our circadian rhythms and daily sleep patterns also alter our meal times and affect when we feel hungry.[4]

Timing of Eating and Weight Gain in a Normal Sleep-Wake Cycle

First, let’s de-bunk the breakfast myth that you will lose weight if you eat breakfast. It’s not so much that eating breakfast leads to weight loss, but more that those that eat breakfast tend to eat more regular meals and/or begin and end their eating earlier in the day. Breakfast is typically one’s smallest meal of the day, usually accounting for 16-18% of one’s daily calories Many people skip breakfast altogether which leads to eating later on in the day, eating larger meals, and snacking throughout the day.[5] Non-breakfast eaters who tend to eat later in the day or those with night-eating syndrome may be at risk for an increased Body Mass Index (BMI).[6]

But What If You are a Night-Owl or Work a Night Shift and Do Not Follow a Normal Sleep-Wake Cycle?

In one of our previous articles on sleep apnea, found here, we discussed a similar problem—is it one’s weight that causes poor sleep, or poor sleep that causes weight gain? It’s a vicious cycle. When one’s sleeping and eating habits are being simultaneously affected, this may lead to night eating syndrome, which is when a person wakes up during the night and cannot fall back to sleep unless they eat something.[7]

Night-owls and late-night shift workers are found to be most vulnerable to consuming most of their calories late at night, due to having to stay awake during the times of day when appetite and cravings for sweet, salty, and starchy food are at their highest.[8] If night workers limited their eating to 8 hours, regardless of the time of day, would having to work during the night not be quite so bad for their health?

What have the Studies Shown?

A study conducted in 2010 showed that night snacking syndrome is associated with poor dietary quality and that skipping main meals and snacking instead has led to significant changes in the eating patterns and life style of older adolescents.[9]

In 2013, a study evaluated the role of food-timing in weight-loss effectiveness among 252 women and 258 men with BMI’s above 31.4, who followed a 20-week weight loss treatment. The participants were categorized into two groups: early-lunch eaters and late-lunch eaters. Early-eaters were defined as those who ate lunch before 3:00 PM, while late-eaters were those who ate lunch after 3:00 PM. They found that late-lunch eaters lost less weight and lost it at a slower rate, even though calories, type of diet, physical activity, and amount of sleep were similar among both groups. These results indicate that understanding the role of circadian rhythms in weight regulation could help reduce obesity.[10]

Another 2013 study compared two 12-week weight loss diets among overweight and obese women with BMI’s above 32.4. One group was randomly assigned to have a high calorie breakfast (700 calories) and small dinner (200 calories), and the other had the same number of calories per day, but 700 calories at dinner and 200 at breakfast instead.  Calories at lunch were the same (500) for both groups. These women were also randomly asked to eat their meals at different times to allow for variation, with breakfast being from between 6:00-9:00 am, lunch between 12:00-3:00 pm, and dinner from 6:00-9:00 pm. The researchers found that a high-calorie breakfast and low calorie dinner improved weight loss, insulin sensitivity, and hunger suppression, regardless of when the women ate their meals.[11]

Conclusion—The Bottom Line

If you are regularly consuming high calorie foods and do not exercise, you will gain weight regardless of when you eat. Unfortunately, there is no magic bullet for weight loss, but working to change your habits and ensure that most, if not all, of your calories are consumed earlier in the day (between 6 am and 7 pm) may help.

Since many of these studies have only been conducted on small sample sizes, future research evaluating more people studied over a longer period of time are needed to determine the long-term benefits of a particular eating schedule for weight loss success.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff. 

  1. Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JA, Ellisman MH, Panda S. Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Cell Metab. 2012 Jun 6; 15(6): 848–860.
  2. Suri S, Pradhan, R. Assessment of Night Eating Syndrome Among Late Adolescents. Indian J Psychol Med. 2010 Jan-Jun; 32(1): 71–72.
  3. Scheer FA, Morris CJ, Shea SA. The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors. Obesity (Silver Spring) 2013 Mar; 21(3): 421-423.
  4. Bienertova-Vasku J, Bienert P, Forejt M, Tom and1 J, Brazdova Z, Vasku A. Genotype x nutrient association of common polymorphisms in obesity-related genes with food preferences and time structure of energy intake. Br J Nutr. 2010; 193(3): 352-9.
  5. US Department of Agriculture ARS, Beltsville Human Nutrition Research Center, Food Surveys Research Group & US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Health Statistics. What We Eat in America, NHANES 2009-2010. Available at: www.ars.usda.gov/ba/bhnrc/fsrg, 2014. Accessed on 1 June 2015.
  6. Arble DM, Bass J, Laposky AD, Vitaterna MH, Turek FW. Circadian timing of food intake contributes to weight gain. Obesity (Silver Spring). 2009 Nov; 17(11): 2100–2102.
  7. Suri S, Pradhan, R. Assessment of Night Eating Syndrome Among Late Adolescents. Indian J Psychol Med. 2010 Jan-Jun; 32(1): 71–72.
  8. Scheer FA, Morris CJ, Shea SA. The internal circadian clock increases hunger and appetite in the evening independent of food intake and other behaviors. Obesity (Silver Spring) 2013 Mar; 21(3): 421-423.
  9. Suri S, Pradhan, R. Assessment of Night Eating Syndrome Among Late Adolescents. Indian J Psychol Med. 2010 Jan-Jun; 32(1): 71–72.
  10. Garaulet M, Gómez-Abellán P, Alburquerque-Béjar JJ, Lee YC, Ordovás JM, Scheer FA. Timing of food intake predicts weight loss effectiveness. Int J Obes (Lond). 2013 Apr; 37(4): 604–611.
  11. Jakubowicz D, Barnea M, Wainstein J, Froy O. High Caloric Intake at Breakfast vs. Dinner Differentially Influences Weight Loss of Overweight and Obese Women. Obesity, 21: 2504–2512.