Nutritional Pearls: More Reasons to Eat Breakfast?
John is a 32-year-old man interested in losing weight. He tells you that recently, he has stopped eating breakfast in an attempt to cut down on the amount of calories he takes in on a normal day.
(Answer and discussion on next page)
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The breakfast controversy, such as it is, continues.
Skipping meals is a common weight loss strategy, and it seems like breakfast is the one people most often skip.
I understand why people do it: We typically eat 3 meals a day, so if you don't eat one of those meals, you must be eating fewer calories, right? And people are busy in the mornings, so breakfast seems to be the easiest to skip.
This might work if people were robots and only needed to consume 1/3 of their daily calories at each meal. Instead, appetite as well as metabolism also play a role in what we eat and how and when those calories are burned: we know from research that those who eat a breakfast higher in fiber tend to eat less at their next meal, those who have more protein at breakfast feel more full than those consuming less protein at breakfast, and when cutting calories, those who eat most of their calories in the morning tend to lose more weight than those who eat most of their calories in the evening.
One aspect of metabolism is known as "diet-induced thermogenesis." Essentially, this is the amount of heat your body produces in response to eating. This is somewhat related to the "thermic effect of food"—the fact that the body uses a certain percentage of the calories we consume for the process of digestion itself. The negative calorie diet is based on the thermic effect of food, arguing that some foods require the body to burn more calories in breaking down the food than the food itself supplies (simply not true).
While both diet-induced thermogenesis and the thermic effect of food are certainly real, they are overall still just part of the total number of calories your body burns in a day.
A team in Germany sought to find out whether diet-induced thermogenesis varied across the time of day and the amount eaten. Was there a time of day when our bodies created more heat—that is, burned more calories? Did it matter how much we ate?
The researchers recruited 16 healthy men in their 20's who were of clinically normal weight to participate in a feeding study. Each of the participants spent 3 days living in the teams' laboratory on 2 separate occasions set at least 2 weeks apart.
The participants came to the lab in the evening of the first day to consume a standardized evening meal. They then went to bed—still in the lab—at 11:30pm and were awakened at 7am, with a standardized breakfast following at 9am, lunch at 2pm, and dinner at 7pm for the following 2 days.
After breakfast and dinner, the authors performed multiple tests of how many calories the participants burned at rest, using sophisticated measures of oxygen consumption and carbon dioxide exhalation. The first test came 1/2 hour after the meal, then again 1, 2, and 3 hours later.
To make sure that the number of calories burned after a meal were not dependent on the number of calories consumed, the authors randomly assigned the participants to one of the following conditions for each 3-day period in the lab: 11% of calories at breakfast, 20% of calories at lunch, and 69% of calories at dinner; or 69% of calories at breakfast, 20% at lunch, and 11% at dinner. Percentage of calories from protein, fat, and carbohydrate were standardized for each meal, as well.
The authors were careful to maintain the participants' current body weights, tailoring the appropriate number of calories to each participant based on their weight at the initial dinnertime visit for each three-day period in the lab.
None of the participants lost or gained weight, as you might expect. But the authors found that regardless of whether the young men had a large or small breakfast, their bodies put out over twice as much heat after eating breakfast than they did after eating dinner.
What's the Take Home?
This is certainly thought-provoking: might this greater thermogenesis at breakfast be one of the reasons people lost more weight eating the majority of their calories at breakfast? More sophisticated studies will be necessary to find out if the 2 effects are related.
Until then I won't be making any specific recommendations to my patients based on this study. I'll continue to recommend that they eat a breakfast that includes high quality calories and both fiber and protein, so they feel satisfied throughout the morning.
Richter J, Herzog N, Janka S, et al. Twice as high diet-induced thermogenesis after breakfast vs dinner on high-calorie as well as low-calorie meals. J. Clin. Endocrinol. Metab. 2020;105(3):3211-e221. Doi: 10.1210/clinem/dgz311