To breakfast, or not to breakfast? That’s the million-dollar question… one that no one seems to have a definitive answer to! On one hand, we’ve long been inundated with the message that breakfast is the most important meal of the day and that eating a protein-rich breakfast increases metabolism and makes healthy choices easier for the rest of the day. But on the other hand, the rise in popularity of intermittent fasting (which has plenty of legitimate health and longevity perks—see, “The Benefits of Intermittent Fasting”) has encouraged many of us to say sayonara to our morning meal. There seems to be evidence backing up both approaches. So, what should we believe?!
Skipping Breakfast Pros…
A recent study published in the American Journal of Clinical Nutrition sheds some light on the contradictory claims surrounding breakfast (or lack thereof)! Using a randomized crossover design (where every participant undergoes each treatment at a different time, instead of having only a control group and an experimental group), researchers took 17 participants and assigned them to three different one-day diet interventions. One involved skipping breakfast, one involved skipping dinner, and one involved eating the standard three square meals (all of the diets contained the same number of calories and had the same macronutrient ratios: 55% carbohydrate, 30% fat, and 15% protein). For each of the interventions, the researchers measured the participants’ post-meal blood glucose, insulin, and inflammatory responses, and also measured their blood sugar and insulin secretion over the course of the full 24-hour day.
As proponents of intermittent fasting might expect, the meal-skipping days had some definite benefits: ditching either breakfast or dinner resulted in slightly higher energy expenditure for the day, and skipping breakfast (but not skipping dinner) increased fat oxidation (AKA fat burning). On the surface, that might lead us to conclude that fasting until lunch would be helpful for weight loss.
…and Skipping Breakfast Cons!
But, the researchers also found some less favorable outcomes from skipping breakfast! During the no-breakfast intervention, participants had higher inflammasome activity (inflammasomes are innate immune system receptors that play a role in inducing inflammation) and greater inflammatory responses of peripheral blood cells later in the day—suggesting higher inflammatory potential associated with breakfast skipping. Likewise, compared to skipping dinner, skipping breakfast led to a 54% increase in the postprandial homeostasis model assessment (HOMA) index (which helps measure insulin resistance) and higher blood sugar and insulin levels after lunch, indicating a decrease in metabolic flexibility (with the implication that a long-term dietary pattern of skipping breakfast could lead to insulin resistance! Yikes!). Skipping dinner, on the other hand, resulted in far fewer unfavorable changes (while still being associated with greater energy expenditure for the day).
What’s going on here?! Ultimately, the study suggests that despite some immediate benefits for total energy expenditure, skipping breakfast on a regular basis could lead to low-grade inflammation and impaired glucose homeostasis. Scary, right?
This study does have some important limitations we need to consider. For one, the number of participants was relatively small (17 men and women), and it’s possible that a larger sample size would have yielded different results. Two, the interventions only lasted one day each, so it’s impossible to tell what the long-term effects would be for habitually skipping breakfast or dinner (effects could compound or the body could adapt in a favorable way). Three, because calorie intake was controlled, we can’t tell how skipping breakfast or dinner would have effected total energy intake in a real-world setting (for example, even though meal skipping increased total energy expenditure for the day, would participants have over-compensated by eating more if they had unlimited access to food?). Four, the participants in this study were free from metabolic diseases, and most were at a healthy weight based on BMI (only four were overweight or obese, and one participant was underweight). That makes it hard to extrapolate the results to a specific population like diabetics or people who are trying to lose weight. And five, since the meals in this study were skewed towards higher carbohydrate and lower protein content (see Plants vs Animals: Macronutrients are Overrated but also Carbs Vs. Protein Vs. Fat: Insight from Hunter-Gatherers and New Scientific Study: Calories Matter), we don’t know whether a different macronutrient composition would have changed the results. (Likewise, since the energy intake for each intervention was designed to match what the participants needed for weight maintenance, we also don’t know from this study how skipping breakfast in the context of a reduced-calorie diet would have affected the outcome.)
All that said, there’s good reason to seriously consider the results of this trial instead of dismissing them based on design limitations (which all studies have!). Other research has shown similar problems associated with skipping (or skimping on) breakfast, including a longer trial in which healthy lean women experienced unfavorable fasting lipids, impaired post-meal insulin sensitivity, and higher energy intake when they skipped breakfast for two weeks straight (compared to a breakfast-eating control group). For overweight and obese participants, eating a high-calorie breakfast versus a high-calorie dinner for 12 weeks was associated with greater weight loss, lower fasting glucose, lower triglycerides, reduced insulin, and lower HOMA-IR (suggesting a metabolic advantage to skewing food intake more towards the morning than towards the night–particularly interesting because not eating for several hours before bed increases sleep quality and there is a strong Link Between Sleep and Your Weight). In people with type 2 diabetes, skipping breakfast (and eating the first meal of the day at noon) resulted in higher postprandial hyperglycemia and impaired insulin response, compared to eating breakfast. In women with PCOS, eating a high-calorie breakfast and sparse dinner (compared to the reverse) caused a significant decrease in glucose AUC and insulin AUC, as well as a reduction in free testosterone (50% reduction), an increase in sex-hormone binding globulin (105% increase!), and even an increased ovulation rate. All of this evidence supports the idea that for a variety of populations, eating food in the morning is 1) more beneficial than eating the same quantity of food at night, and 2) is probably superior to not eating anything at all!
Although researchers are still trying to pinpoint the mechanisms behind the unfavorable effects of skipping breakfast, one likely possibility is the daily variations in energy expenditure and metabolism associated with our circadian rhythm. Previous studies have shown that diet-induced thermogenesis is lower in the evening than in the morning (44% lower, in one study!), and we can take advantage of this fact by increasing our food intake in the first half of the day (where it will result in the greatest thermogenesis and the most favorable metabolic effects) and reducing our intake in the evening hours. Likewise, when we skip breakfast, our bodies compensate by increasing cortisol in order to stimulate gluconeogenesis or glycolysis in order to raise our blood sugar. For people who already have dysregulated cortisol levels or impaired insulin or leptin sensitivity, this can lead to either elevated cortisol levels throughout the day, or abnormal cortisol swings (neither of which are a good thing!). See also Demystifying Adrenal Fatigue, Pt. 1: What Is Adrenal Fatigue?
The Verdict on Breakfast
So, what should we take away from all this? From a health standpoint, the benefits of intermittent fasting might be better achieved by skipping dinner than by skipping breakfast (and for women, who are more susceptible to exaggerated cortisol responses from fasting, intermittent fasting might pose more problems in general). And, skipping breakfast is unlikely to be a helpful strategy for sustained weight loss. However, we really need more studies on the long-term consequences of skipping meals to better understand how our bodies might adjust to different eating patterns over time. And, many people report anecdotal benefits from skipping breakfast (such as better focus and concentration) that could make the risks seem worth it (again, we don’t know if these effects are transient or even placebo). As with most things, there’s a highly individual component to the effects of eating (or not eating) breakfast, and we need to balance what we learn from the scientific literature with our own body’s reactions! That being said, the current body of scientific evidence points to regularly eating breakfast being a better choice than skipping it.
Farshchi HR, et al. “Deleterious effects of omitting breakfast on insulin sensitivity and fasting lipid profiles in healthy lean women.” Am J Clin Nutr. 2005 Feb;81(2):388-96.
Jakubowicz D, et al. “Effects of caloric intake timing on insulin resistance and hyperandrogenism in lean women with polycystic ovary syndrome.” Clin Sci (Lond). 2013 Nov;125(9):423-32. doi: 10.1042/CS20130071.
Jakubowicz D, et al. “Fasting until noon triggers increased postprandial hyperglycemia and impaired insulin response after lunch and dinner in individuals with type 2 diabetes: a randomized clinical trial.” Diabetes Care. 2015 Oct;38(10):1820-6. doi: 10.2337/dc15-0761. Epub 2015 Jul 28.
Jakubowicz D, et al. “High caloric intake at breakfast vs. dinner differentially influences weight loss of overweight and obese women.” Obesity (Silver Spring). 2013 Dec;21(12):2504-12. doi: 10.1002/oby.20460. Epub 2013 Jul 2.
Nas A, et al. “Impact of breakfast skipping compared with dinner skipping on regulation of energy balance and metabolic risk.” Am J Clin Nutr. 2017 Jun;105(6):1351-1361. doi: 10.3945/ajcn.116.151332. Epub 2017 May 10.