Many of us have repeatedly heard that breakfast is the most important meal of the day. In fact, if you’re not a fan of a.m. eating, there’s a good chance your primary care doctor has given you a slap on the wrist and warned skipping breakfast is harming your health and waistline.
But new research throws that idea into question, particularly when it comes to weight loss. The study, published in April 2019 in The Journal of Nutrition, found that men who weren’t allowed to eat until well after an early exercise session consumed fewer calories over the course of a day than men who ate before physical activity. “Skipping breakfast before exercise could conceivably help with weight loss simply by reducing total food intake across the day,” says study coauthor Javier Gonzalez, PhD, associate professor at the University of Bath in the England. That of course depends on people not compensating by eating more calories later in the day or reducing their level of activity, he adds.
William Yancy, MD, director of the Duke Diet and Fitness Center in Durham, North Carolina, who wasn’t involved in this study, says the findings aren’t exactly new. “The findings fit with other research, which shows that people who skip breakfast do not fully compensate over the rest of the day, regardless of their activity level during the day,” he says.
For example, a meta-analysis published in January 2019 in The BMJ found people who skipped breakfast lost a little more weight than those who didn’t. Participants in the studies who were assigned to eat breakfast consumed more calories over the course of a day than those who did not.
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Skipping Breakfast Before Exercise Led to a Bigger Lunch but Fewer Calories Daily
Researchers set out to determine how the presence of available carbohydrates during exercise could impact overall calorie balance over 24 hours. They looked at 12 healthy and physically active young men ages 20 to 26. On three separate mornings, the scientists tested the following scenarios on the men:
- Consuming a 430-calorie bowl of oatmeal and then resting for several hours
- Eating the same amount of oatmeal and then riding a stationary bike at a moderate intensity for an hour
- Skipping the oatmeal and riding for a moderate hour and not consuming any food until lunch
The participants stayed in the lab to eat their lunch and authors instructed them to eat until they felt “comfortably full.” Each man ate by himself without the distraction of a TV or phone, and the meal they ate was warm but relatively bland (another version of oatmeal) to ensure that participants ate just until they were satisfied and not because they were distracted or because the food was so tasty.
Upon leaving, each man was given a basket of food that contained pasta, sauce, cheese, snack bars, and chocolate milk. Again, they were told to eat only until they were comfortably full, and not to eat anything that was not provided in the basket. This way the researchers could track exactly how much food and calories each subject consumed over the course of the day.
Using sophisticated mathematical models, researchers calculated energy expenditure for each man by analyzing the gas they exhaled when breathing. To measure how many calories the men were burning throughout the day, researchers used a device called Actiheart, which integrates accelerometer and heart rate signals.
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On the day when the men ate and then sat, they ended up consuming almost 500 more calories more than their body burned. When the men ate the oatmeal and then exercised, the “calories in” to “calories burned” ratio was almost exactly the same.
The day that the participants skipped breakfast, they consumed a much bigger lunch than they did the other two days, but for the rest of the day, they ate more moderately. At the end of the 24-hour period, the men who skipped breakfast and exercised burned nearly 400 more calories than they ate.
Because the study only looked at how the body reacted on three different days, it’s unclear if skipping breakfast before a workout would translate into weight loss, says Dr. Yancy. “There might be additional compensation on future days that eliminates the initial advantage that these researchers observed, or compensation may become more complete if someone exercises regularly with this schedule,” says Yancy. In other words, the body might start to conserve or use calories in a different way if skipping breakfast became the new normal for a person.
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How Does Skipping Breakfast Impact the Body?
Several mechanisms may be leading to these results, says Yancy. “The body could be hungry at certain times of the day, and if those mealtimes are missed or delayed, then the hunger diminishes again until the next mealtime, without full compensation at the next meal,” says Yancy.
Another possibility is that exercise may reduce hunger, at least in the short period afterward, so there is not full compensation after exercise, says Yancy.
The calorie deficit could also be related to the kind of fuel our body is burning, says Dr. Gonzalez. “There is evidence that people who burn through their carbohydrate stores very quickly during exercise (especially their liver glycogen stores), may be more likely to compensate with their food intake after exercise,” says Gonzalez.
Studies in mice (such as a study published in October 2016 in the journal Scientific Reports) have confirmed that liver glycogen is sensed by the brain to regulate food intake, he says. “If we skip breakfast before exercise, we burn more fat and less carbohydrate during exercise,” says Gonzalez. The reduction in carbohydrates burned during exercise on an empty stomach may have contributed to why the men ate less on that day, he says.
The way the body reacts short term after skipping breakfast may not stay the same over the course of several days, says Amy Gannon, RD, at Cleveland Clinic Wellness in Ohio, who was not involved in the current study. “We don’t give our bodies enough credit for knowing when they need fuel and when they are satisfied with what we are eating,” says Gannon.
“It may take another day or two or three — longer than was tracked in this study — for our bodies to signal stronger hunger cues because of a calorie deficit caused by skipping breakfast in this manner,” she says. Just because the calorie deficit was not compensated for this day does not mean we wouldn’t see that calorie deficit adjusted for later, Gannon adds.
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Cutting Breakfast May Impact Performance and Energy
Regardless of how skipping breakfast may influence weight loss, not eating before a sweat session could have other unwanted effects.
“There is evidence from a number of groups showing that skipping breakfast can negatively impact athletic performance,” says Gonzalez. Skipping breakfast can hurt performance even when the activity is in the evening and the person eats lunch, he says.
Whether you decide to skip breakfast may depend on your individual goals and lifestyle, he says. “For example, someone looking to maximize the health benefits of exercise may wish to perform some sessions in the overnight fasted state, whereas someone looking to compete in a race that day should probably consume breakfast,” he says.
Skipping breakfast might not be the only strategy in this study that could hurt performance, says Gannon. Nutrient-timing is also important for recovery, she says. “Ideally athletes should have some carbohydrates and protein within 30 minutes of finishing their activity — especially if they haven’t eaten before — but in this study the participants didn’t eat lunch until two hours after their activity, so I would be very concerned about performance long term with this schedule,” she says.
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Is Skipping Breakfast a Good Idea if You Want to Shed Pounds?
This study suggests that people looking to lose weight may see better results if they exercise after fasting overnight, says Gonzalez. If a totally empty stomach seems too challenging, drinking a large glass of water and a cup of black coffee can help you feel fuller and more alert without affecting your fat burning during exercise, he suggests. “Even eating a low-carbohydrate breakfast could facilitate greater fat oxidation during exercise, but there is less evidence on this,” says Gonzalez.
Consider your general activity level, preferences, and general food choices when deciding whether to try this strategy, says Gannon. “Some people prefer not to have breakfast and eat well throughout the rest of the day to manage their health goals, while others are hungry when they wake up and start each morning with a healthy breakfast,” she says. Either strategy can work, she adds. “If you wake up hungry and feel irritated and fatigued by skipping breakfast, then this plan to skip breakfast would not be for you,” she says.
There are certain groups where it’s clearly beneficial to eat a healthy breakfast, like in children, says Gannon. “For kids, having breakfast is associated with better performance in school and getting enough essential vitamins and minerals,” she says.
Although this research is not conclusive enough to make decisions on what is best for everyone, it does support recent research that skipping breakfast is an acceptable strategy for weight loss, says Yancy. It’s a myth that people need to eat breakfast to manage their weight, he says. “Try to determine objectively what is working for you,” says Yancy. “If you are trying to lose weight and it’s not happening, then something needs to be changed.”