Food and diet

Breakfast 'not the most important meal of the day'

"Breakfast might not be the most important meal of the day after all,” the Mail Online reports.

The concept that breakfast is the most important meal of the day is up there in the pantheon of received wisdom with “never swim after eating” or “getting wet will give you a cold”. But is there any hard evidence to back the claim?

A new study in 38 lean people found that six weeks of regularly eating breakfast had no significant effect on metabolism or eating patterns for the rest of the day compared to total fasting before midday.

It also found no difference between the groups at the end of the study in body mass, fat mass, or indicators of cardiovascular health (such as cholesterol or inflammatory markers).

There are various important limitations to this trial though such as the short follow-up time. For example, people who fasted had much more variable blood sugar levels in the afternoon and evening, and we do not know what the longer-term effects of this could be.

Overall, based on this study alone, we would not recommend completely starving your body of all nutrition before 12pm each day, not least because not eating something in the morning may not make you feel very happy or energetic, if nothing else. 

Where did the story come from?

The study was carried out by researchers from the University of Bath and published in the peer-reviewed American Journal of Clinical Nutrition. The study has been published on an open-access basis, so is available for free online. The work was funded by a grant from the Biotechnology and Biological Sciences Research Council. The authors declare no conflicts of interest.

In concluding that breakfast is not the most important meal of the day, the Mail does not consider the various limitations of this very small study.

What kind of research was this?

This was a randomised controlled trial looking at how breakfast habits were associated with energy balance in the rest of the day in people living their normal daily life.

As the researchers say, it is the popular belief that “breakfast is the most important meal of the day”. But this assumption is only grounded in cross-sectional studies observing that eating breakfast is associated with reduced risk of weight gain and certain chronic diseases (such as diabetes and cardiovascular disease). However, this does not prove cause and effect. The researchers also note that such observational studies do not take into account the fact that people who eat breakfast also tend to be more physically active, eat less fat, be non-smokers and moderate drinkers, opening up the possibility of confounding factors.

So it could be the case that rather than regularly eating breakfast making you healthy, healthy people are more likely to eat breakfast.

The researchers say that though breakfast is said to influence metabolism, studies have lacked measurement tools capable of accurately measuring this during normal daily activities. This study aimed to get a better indication of this by measuring all aspects of energy balance, including the heat generated during physical activity, and in-depth laboratory tests (including blood tests and DEXA scan of bone mineral density).

Ultimately, they wanted to find out whether eating breakfast was a cause of good health or whether it was simply a sign of an already healthy lifestyle.

What did the research involve?

The research was given the title the “Bath Breakfast Project”. Adults between the ages of 21 and 60 were eligible for the trial if they were either normal weight (20 to 25kg/m²) or overweight (25 to 30kg/m²). People were randomised to eat a daily breakfast or to extended morning fasting for six weeks. Each of the two randomised groups was intended to include an even balance of normal and overweight participants, and of people who frequently and infrequently ate breakfast. This was done to allow a stratified (representative) analysis based on these two factors.

The total sample size was around 60-70. This publication reports the findings for the 38 "lean" people in the study – omen with a DEXA fat mass index of 11kg/m² or less, and men with a fat mass index of 7.5kg/m² or less (DEXA fat mass index is assessed using X-rays to give a very precise measurement of body fat).

Before the trial, participants came to the laboratory to have baseline measurements taken. This included blood tests to look at hormones, metabolites and blood fats, assessments of metabolic rate, and body mass and fat mass measurements. A small tissue sample was also taken to look at key genes related to appetite and physical activity. 

The breakfast group were told to eat 3,000kJ (around 720 calories – or around two bacon sandwiches) of energy prior to 11am, with half of this provided within two hours of waking. The breakfasts were self-selected by the participants, though they were said to be provided with detailed examples of the foods that would give the appropriate energy intake. The extended morning fasting group could drink only water before 12pm each day.

During the first and last weeks of the six-week trial, participants kept detailed records of their food and fluid intakes for later analysis of daily energy and macronutrient intake. During these two weeks, they were also fitted with a combined heart rate/accelerometer to accurately record energy expenditure/physical activity habits for the entire duration of each of these seven-day periods. A glucose monitor was also fitted under the skin.

They were told when these devices were fitted: “Your lifestyle choices during this free-living monitoring period are central to this study. We are interested in any natural changes in your diet and/or physical activity habits, which you may or may not make in response to the intervention. This monitoring period has been carefully scheduled to avoid any pre-planned changes in these habits, such as a holiday or diet/exercise plan. You should inform us immediately if unforeseen factors external to the study may influence your lifestyle.”

After the six weeks of the trial, the participants returned to the laboratory for repeat body measurements.

What were the basic results?

The study reports data for the 33 people who completed the trial, 16 in the breakfast group and 17 in the fasting group. These people were of average age 36, 64% were female and 79% of them regularly ate breakfast.

The researchers found that compared to the fasting group those in the breakfast group generated significantly more heat energy during physical activity before 12pm, and also engaged in more physical activity, in particular more “light” physical activity. Resting metabolic rate was stable between the groups, and there was no subsequent suppression of appetite in the breakfast group (energy intake remained 539 kcal/d greater than the fasting group throughout the day).

There was no difference in waking or sleeping times, and at the end of the study there were no differences between groups in body mass or fat mass, body hormones, cholesterol or inflammatory markers. There was no difference between groups in fasting blood sugar or insulin at six weeks, but during continuous sugar monitoring in the last week of the trial the fasting group demonstrated more variability in their afternoon and evening sugar measures.

How did the researchers interpret the results?

The researchers conclude that: “Daily breakfast is causally linked to higher physical activity thermogenesis [heat generation] in lean adults, with greater overall dietary energy intake, but no change in resting metabolism. Cardiovascular health indexes were unaffected by either of the treatments, but breakfast maintained more stable afternoon and evening glycemia [glucose control] than did fasting.”


This trial aimed to measure the direct effect that eating breakfast or fasting before 12pm has on energy balance and indicators of cardiovascular health in people living their normal daily lives. The trial has been carefully designed study and has taken extensive body measurements to try and measure the direct effects of breakfast or fasting upon the body. However, there are limitations to bear in mind:

  • This study reports the findings for the 33 lean people in the study. The researchers randomised between 60 and 70 people, including a balanced mix of normal weight and obese people. A later publication will report the findings in the remaining obese cohort.
  • The intervention was intended to apply “under free-living conditions” where all lifestyle choices were allowed to vary naturally. However, it is difficult to gauge how accurately people did comply with their allocated interventions. Compliance was said to be confirmed via self-report and verified via continuous glucose monitoring; however, this only apparently happened during the first and sixth weeks of the trial. It is unclear whether compliance would have been accurately measured during the intervening weeks.
  • The study only measures the effect of a very specific intervention of eating 3,000kJ for breakfast, or eating absolutely nothing at all, except for water before 12pm. This total fasting example is quite extreme, and its effects have only been measured over six weeks. We don’t know what the longer-term effects upon health would be. For example, the study did find that people who fasted had much more variable blood glucose control in the afternoon, and we don’t know what the longer-term effects of this pattern would be.
  • The study has also not measured the wider effects upon general feelings of wellbeing, emotions, concentration, lethargy, etc, that fasting may have. Participants in the fasting group were observed to do less physical activity in the morning, and this may have been an indicator of them feeling that they had less energy.
  • Study of different timings of breakfast, or different compositions (e.g. of carbohydrate, protein or fat) or different total calories, may be more beneficial for future study than the comparison of this 3,000kJ breakfast or total fast before 12pm studied here.

Overall, this study does not settle the debate on whether breakfast is the most important meal of the day, because it was quite narrow in its scope. Dr Betts, a senior lecturer in nutrition, metabolism and statistics, told the Mail Online that “It is certainly true that people who regularly eat breakfast tend to be slimmer and healthier, but these individuals also typically follow most other recommendations for a healthy lifestyle, so have more balanced diets and take more physical exercise." 

In normal life situations, breakfast does therefore seem to be linked to health in some way, though direct cause and effect is difficult to apply, due to the influence of other health and lifestyle factors in relationship. However, this study does not provide many more answers of whether we should eat breakfast, or what type of breakfast we should eat.

However, based on this study alone we would not recommend missing breakfast, not least because it may have a negative impact on your mood; you could spend all morning feeling “hangry”.

If you have slipped into the habit of skipping breakfast, then it is never too late to break the habit.

NHS Attribution