Study under review: Effect of breakfast on weight and energy intake: systematic review and meta-analysis of randomised controlled trials

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Breakfast, defined as the first meal in the morning after an overnight fast, has a healthy reputation in the popular opinion. Claims about its importance for a healthy lifestyle, ranging from weight control to chronic disease risk reduction, are widespread and come from several sources, including official authorities from different countries, including the U.K.^[1], the U.S.^[2] and Australia^[3]. Recommendations from the aforementioned organizations highlight the importance of breakfast consumption for weight loss. In some, skipping breakfast is explicitly discouraged^[4]. Breakfast skipping has also been proposed to be a risk factor for developing heart disease^[5], type 2 diabetes^[6], and even increasing all-cause mortality^[7].

However, most claims about the positive effects of breakfast consumption on weight loss have been derived from observational evidence^[8] that has found a correlation between breakfast eating and lower weight gain or risk of obesity. Conversely, recent randomized controlled trials (RCTs) have found no effect^[9] of consuming breakfast on weight loss, arguing against an effect of this meal on weight control.

Because of the discordance between individual RCTs and observational evidence, the current systematic review and meta-analysis sought to examine data from available RCTs that evaluated the impact of breakfast eating on bodyweight and daily energy intake.

Breakfast consumption has been advocated as an important strategy for weight loss. However, this idea has been supported primarily by observational evidence, with discordant findings among RCTs. The current meta-analysis examined results from RCTs that tested the effects of breakfast consumption on bodyweight and energy intake.

Who and what was studied?

The current systematic review and meta-analysis was conducted according to the PRISMA^[10] statement and registered with PROSPERO^[11].

The authors searched for RCTs comparing the effects of consuming breakfast with that of skipping breakfast on energy intake (measured or self-reported) and/or bodyweight. These were the two primary outcomes. Studies involving children or adolescents, populations with conditions other than obesity (e.g., type 2 diabetes), or populations in low-income countries were excluded.

Ultimately, 13 RCTs were included in the systematic review, of which seven examined the relationship between breakfast and bodyweight (n = 486), and 10 analyzed the effect of breakfast consumption on 24-hour energy intake (n = 930). Six studies each were conducted in the U.S. and U.K., with the remaining study contributed by Japanese researchers. Five trials involved only overweight and obese participants, while the remainder included people with any BMI.

Studies evaluating bodyweight lasted two to 16 weeks (average of seven weeks), and those reporting on energy intake ranged from eight hours to six weeks (average of two weeks). Weight and energy intake were measured objectively in most studies (n=11), but only six studies directly monitored breakfast consumption in a research lab—the remainder used food logs and recall methods with participants eating at home.

Every study was deemed at high risk of bias, with the main issues being a lack of participant, researcher, and outcome assessor blinding, as well as unclear risks for random sequence generation and allocation concealment.

This meta-analysis investigated how breakfast consumption affected bodyweight (seven studies) and daily energy intake (10 studies) when compared to breakfast skipping (13 studies total). Studies involved mostly overweight and obese participants living in high-income countries.

What were the findings?

Overall, breakfast skipping resulted in a significantly lower bodyweight (-0.44 kilograms, or -0.97 pounds) compared to breakfast eating over an average of about seven weeks. These results weren’t affected by the duration of trials or BMI.

Consistent with the results on weight loss, breakfast consumption resulted in a statistically significant increase in total daily energy intake (+260 kcal) compared to skipping breakfast. Excluding the single study with only obese participants did not meaningfully affect the outcome.

The main results are depicted in Figure 1.

Breakfast skipping led to lower daily energy intake and lower bodyweight compared to eating breakfast.

What does the study really tell us?

The current meta-analysis suggests that breakfast consumption increases total daily energy intake and bodyweight compared with breakfast omission. The extra calories consumed at breakfast do not appear to be fully compensated for later in the day.

These results go against what has been regularly promoted by many official nutritional guidelines, which encourage eating breakfast as one of the key strategies to maintaining a healthy weight. This recommendation is based primarily on observational data showing an association between breakfast consumption and lower weight and fat mass.

However, this association is confounded^[12] greatly by other habits of people who regularly eat breakfast, such as being more physically active, drinking less alcohol, and not smoking as much. Data from successful long-term weight loss maintainers, depicted in Figure 2, has shown^[13] that 78% eat breakfast daily, and that 90% eat breakfast at least four times per week. Yet, there were no differences between breakfast eaters and skippers for the degree of weight loss or duration of weight loss maintenance.

Overall, it is likely that breakfast is commonly part of a healthy lifestyle that promotes weight loss or the maintenance of a normal BMI, but it isn’t the cause of either. When the effect of breakfast is directly tested (as in this meta-analysis), no positive effect on weight loss is seen.

One of the main arguments in favor of consuming breakfast for maintaining a healthy body weight has been the suggestion that it would reduce^[3] subsequent food intake during the day, and therefore prevent the consumption of excessive calories later in the day. As this meta-analysis shows, breakfast consumption does not lead to lower food intake later in the day and hence adds more energy to the daily diet. This effect seems to be consistent, as it was observed in six of the nine trials included that assessed this metric. Accordingly, other authors have observed that the absolute amount of calories consumed for breakfast are strongly and positively correlated^[14] with total daily calorie intake. Because of this, eating breakfast per se does not constitute a necessary intervention for promoting a caloric deficit conductive to weight loss.

On the contrary, it could even promote weight gain, given that it adds more energy to the daily diet, compared to skipping breakfast. This has important implications for obesity recommendations, as people associate eating breakfast with healthy eating patterns and start eating breakfast in attempts to adopt a healthy lifestyle.

In some cases, this strategy could backfire and promote weight gain. This has been shown in an RCT included^[9] in the meta-analysis, which found that breakfast consumption in women who regularly skipped breakfast led to an increase in daily energy intake (+266 kcal) and gained 0.7 kilograms (1.5 pounds) over four weeks, compared to the group who kept skipping breakfast.

A major strength of this meta-analysis is that it included only trials from high income countries, which reduces heterogeneity due to food availability under different economic or geographic situations. On the other hand, the analyzed RCTs only included adults without any disease besides being overweight or obese (such as diabetes, metabolic syndrome, etc.), so extrapolation to other populations such as children, adolescents, older people, those with chronic diseases or highly active people is not possible. In addition, the effects of different breakfast compositions were not assessed. Finally, the included studies only followed participants for a very short time (less than four months) and overall were of low quality. Also, it is conceivable that adaptations to breakfast in the long term include a reduction on calorie intake later in the day, and therefore, the weight-promoting effect is only observed in the short term.

In view of the overall high risk of bias, mediocre quality of the available research as a whole, and lack of assessment of breakfast composition or habits, higher quality evidence and adjustment for breakfast habits in future research could overturn these results in either direction down the road. So, while the evidence points toward breakfast helping with weight loss, it does so quite weakly. Higher quality evidence is needed to come to firm conclusions.

In contrast to what observational studies have suggested, this meta-analysis found that skipping breakfast does not increase bodyweight nor total daily energy intake. On the contrary, breakfast skipping reduces daily energy intake and bodyweight. This discrepancy might be explained by the fact that breakfast eaters also have other healthy habits that promote weight maintenance. However, the data that went into this meta-analysis is generally short-term and of low quality — longer and higher quality studies are needed.

The big picture

Much of the focus on the topic of breakfast and health has been on the consumption of the meal per se instead of its composition. Typical breakfast items include energy-dense foods rich in refined flour, sugar, and fat—a combination that is not just nutrient-poor but also hyperpalatable and thus prone to trigger overeating. Conversely, consumption of a breakfast rich in protein might promote longer satiety and therefore lead to fewer calories eaten later in the day. For instance, consumption of eggs for breakfast during an energy-restricted diet promotes more weight loss^[15] than consumption of an energy-matched breakfast consisting of bagels. This agrees with other research^[16] showing higher satiety and lower daily energy intake after consumption of a breakfast higher in protein and fat, and lower in carbohydrates (eggs and toast), compared to an isocaloric breakfast higher in carbohydrates. Therefore, the consumption of a high protein breakfast might be advisable for weight loss.

Besides weight loss, breakfast consumption might influence other metabolic parameters that are important for overall health, like insulin sensitivity. Some data suggests that in participants with type 2 diabetes, skipping breakfast worsens glycemic control^[17]. Similarly, one study showed that, in healthy women, skipping breakfast increased^[18] total daily energy intake and decreased post-meal insulin sensitivity. In addition, emerging research on the timing of food intake and its relationship with health parameters has suggested that breakfast consumption might be of importance^[19] for maintenance of a healthy circadian rhythm (the oscillatory patterns observed in distinct physiological metrics that occur during 24 hours)—with all its potential downstream effects on human cardio-metabolic health^[20].

In sedentary conditions, insulin sensitivity follows a circadian pattern^[21], in that it is higher in the morning and declines nearer to night. Hence, some authors have suggested^[22] that skipping breakfast might negatively affect the circadian rhythm and therefore health. However, most of these studies have assessed the effects of breakfast omission acutely on one test day, without taking into account the breakfast habits of the participants. Indeed, it has been observed^[23] that the metabolic issues seen after skipping breakfast occur only in habitual breakfast eaters. Therefore, research must take into account the breakfast eating habits of participants when assessing the effects of skipping breakfast. Over time, the body appears to adapt to different eating patterns, such as one which regularly skips breakfast.

The putative healthy effect of breakfast may be an example of over-reliance on observational data (that can determine associations but is generally insufficient for establishing causation) for making nutritional guidelines and recommendations. As such, some authors have suggested^[24] that the “proposed effect of breakfast on obesity” is not supported strongly by scientific evidence and constitutes a “belief beyond the evidence.” As observational data can only be hypothesis-generating, it is important that observational associations are tested under controlled conditions.

Although much of the research has focused on the influence of breakfast eating per se, an important parameter that has to be taken into account is the composition of the meal. Specifically, it appears that a breakfast rich in protein and fat, and lower in carbohydrate, increases satiety and reduces subsequent calorie intake. Moreover, most evidence showing negative effects of breakfast skipping have been performed acutely, and it appears that these effects are observed only in habitual breakfast eaters.

Frequently asked questions

Q. Is there any evidence regarding the effects of breakfast on cognition or mental tasks?

Evidence in this regard is equivocal and methodologically heterogenous. In healthy adults, some studies^[25] suggest a small benefit of consuming breakfast for memory (particularly delayed recall, which involves reproducing information learned about 15-45 minutes before), but overall, no differences after skipping breakfast are observed.

However, as with other research on breakfast consumption, these studies are acute and do not differentiate between people who habitually eat breakfast or not. Thus, it’s possible that the memory effects are simply due to the fact that people who habitually eat breakfast are not physiologically adapted to skipping it. Nevertheless, it is worth pointing out that there is no strong evidence favoring breakfast for cognition, as it is commonly believed.

What should I know?

Breakfast consumption has been considered an important part of a healthy lifestyle that promotes weight loss. However, this idea has been derived mainly from observational evidence and there is a discordance with RCTs on the subject. Therefore, the authors of this study performed a systematic review and meta-analysis of RCTs examining the effects of breakfast on weight loss and energy intake in overweight and obese participants from high-income countries.

The results show that breakfast consumption increases total daily energy intake and bodyweight relative to skipping breakfast. Thus, contrary to current suggestions, consumption of breakfast could promote weight gain over time. However, personal breakfast habits and the nutritional composition of breakfast might influence the effects of breakfast on weight and energy intake. As the available studies are short-term and of low quality, longer term experiments with higher quality are needed to determine if the observed effects are maintained.