Whether or not you should eat breakfast for weight loss has got to be up there with some of the most debated topics in the nutrition world.
One camp argues that breakfast consumption can boost your metabolism, while the other contends that intermittent fasting helps maintain lower insulin levels, potentially facilitating fat loss.
In between those two points, you could also hear a statement like “eating breakfast simply makes it easier to make healthier choices later in the day, which in turn reduces calorie intake.” And similarly, “while there is nothing magical about fasting, it does make it easier to reduce your calorie intake.”
In this post, all these points will be covered. More importantly, the research-looking outcomes will also be explored. Then it will all be summarised at the end so that you can make a choice based on what will work best for you.
How Breakfast Consumption or Skipping Can Theoretically Play a Role in Weight Loss
It is important to understand the principles involved in weight loss.
For a comprehensive overview, checking out this post would put you in a good position to understand how breakfast might play a role.
If you do not read that post though, a brief summary is:
- Calories in vs calories out has the biggest influence over what we weigh.
- This is because the body is made up of calories. One kilogram of body fat is made up of ~7,700kcal. One kilogram of muscle is made up of ~1,200kcal (although it is energetically expensive to create).
- Eating fewer calories than you burn leads to weight loss over time.
- Although people can criticise calories in vs calories out, all criticisms have a logical counterargument.
- For example, if somebody was to say “CICO is oversimplified and doesn’t account for hormones” a simple counterargument could be to point to examples of how specific hormones affect either the calories in, or the calories out portion of the equation. Hormones are involved in both sides of the equation. The formula is simple, but the variables that determine the numbers are complex.
Based on that brief overview, for breakfast to help with weight loss it would either need to help reduce energy intake or increase energy expenditure.
Assessing the Claim That Breakfast Helps Speed Up Your Metabolism
This claim can be looked at from two perspectives.
One angle could be to take it literally and take it to mean “breakfast speeds up your resting metabolic rate.” The other could be that “breakfast increases total daily energy expenditure.”
Resting metabolic rate is one component of total daily energy expenditure. It is the number of calories your body burns while performing basic life-sustaining functions, without any form of movement or anything else.
In the absence of any confounding factors, such as differences in total calorie intake, there is no scientific evidence to support the claim that consuming breakfast raises basal metabolic rate.
What if Breakfast Makes You Move More Throughout the Day Though?
A theoretical way that eating breakfast could increase total daily energy expenditure is by facilitating more physical activity throughout the day. This could be in the form of formal exercise, or just incidental movement in general.
We have a fair bit of observational evidence indicating that people who eat breakfast do more physical activity on average.
This is an individual topic though, because while we see that on average, it is also a case-by-case situation.
Research Directly Looking at Total Daily Energy Expenditure
If eating breakfast speeds up your metabolism, we should be able to identify that in the research on the topic. So, what does the research show?
The most tightly controlled study that has been done on the topic found no difference in 24hr energy expenditure.
Looking at 24hr energy expenditure is important here. It can be easy to come to a different conclusion if you looked at more acute research.
If you looked at energy expenditure in a 4-hour window after eating breakfast, energy expenditure would be higher in comparison to not eating breakfast, due to components such as the thermic effect of food.
It is also important for total calories to be matched in research specifically looking at this topic.
Research involving a higher energy intake would also likely involve higher energy expenditure due to how the body responds to this intake.
Under circumstances where the total calorie intake is going to be the same regardless, eating breakfast does not speed up your metabolism.
The main exception to this could be individuals who literally feel a large difference in their desires to do physical activity, depending on whether they consume breakfast.
Does Eating Breakfast Reduce Energy Intake Elsewhere?
The theory here is that if you eat breakfast, you might be less hungry later in the day. This could lead to fewer calories consumed.
You can see how this can work well for certain people.
If somebody finds themselves absolutely starving at lunchtime, for example, they might not be looking for the most nutritious option. They might also have a larger portion size than they want.
From another perspective, the opposite could happen.
If you skipped breakfast and did not change the rest of your intake, it could lead to a reduction in calories.
Alternatively, if you normally skipped breakfast and then added it in, but did not change the rest of your intake, it could increase your calorie intake.
What Does the Research Show on This Topic?
A 2019 meta-analysis of all the randomized controlled trials on the topic found that people who consumed breakfast ate 260kcal MORE than those who skipped breakfast.
There are a few things to unpack there.
Firstly, this indicates a combination of both of those points mentioned above.
Since the breakfasts consumed were larger than 260kcal, it means that these participants ate fewer calories for the rest of the day than they otherwise would have. The reduction in calories was not as significant as the addition of the breakfast calories though.
A systematic review of randomized controlled trials is the gold standard form of research. There are three clear flaws left though if we only looked at this research:
- The sample sizes of all these studies were small. Only two had more than 50 people.
- We are limited by study design. Although there are 13 studies, many different approaches have been missed.
- We could miss individual preferences and situations by over-focusing on this. Somebody could notice clear differences in their own life that are significantly different from these results.
While not necessarily a flaw, it is important to remember that the 260kcal number is an average. Some people ate more, some ate less.
Intermittent Fasting
Technically, research on skipping breakfast does not directly overlap with research on intermittent fasting.
One reason for this is that “skipping breakfast” does not also have a defined timeframe of when to stop eating at the end of the day, in comparison to something like 16:8 fasting which has a defined end time point.
Although we have 13 RCTs looking at eating breakfast vs skipping breakfast, we have a lot more looking at intermittent fasting.
The majority of the research on intermittent fasting finds that if people adhere to it, on average, their calorie intake decreases, and their body weight reduces.
A 2020 systematic review found that ALL 27 randomised controlled trials on intermittent fasting resulted in weight loss on average.
This is simply due to the reductions in calorie intake. A reduced window to eat food in typically translates to fewer calories consumed, on average.
Often, but not always, intermittent fasting will involve skipping breakfast.
Although all 27 RCTs found reduced calories on average, there are two key points to focus on:
- These are averages. You might try it and have a different experience. For example, you might find that you are so hungry that you eat more calories during your eating window.
- It still requires adherence. These people were participants in a study and had pressure to stick with it. In your own life, there could be factors that might make it less appealing.
What Does the Research Show on Weight?
Now that we have covered a lot of the individual components, it is worth putting it together and looking at what the research on weight directly shows.
That 2019 systematic review of all the RCTs looking at this topic found minimal difference. They found a difference of an additional 0.44kg in the direction of those who were eating breakfast. This lined up with the slightly higher calorie intake found among people consuming breakfast.
Based on that RCT data, it would be inaccurate to claim that breakfast helps with weight loss.
If the controlled research is so clear – why would anybody claim the opposite?
We have already touched on some theoretical reasons. And anecdotal experiences can be varied. But one area that adds a bit of strength to the argument is the observational evidence.
Most of the observational evidence finds that on average, people who eat breakfast have lower body weights on average.
To be clear though, this research shows that people who eat breakfast have lower body weights on average but does not prove that breakfast itself caused it.
Research also often finds that those who eat breakfast tend to eat healthier diets in general.
Other Pros and Cons of Breakfast
Stating the obvious, not everything is about weight. Other things matter.
Breakfast can be a good opportunity to get in certain micronutrients and forms of fibre that would be less likely to be consumed at other times of the day.
We also have evidence that protein distribution throughout the day could help optimise muscle growth.
Having a decent amount of protein at breakfast could help with this.
Having protein at breakfast has also been linked with improved satiety, in comparison to having a low-protein breakfast.
This also brings us to another important topic: The quality of the breakfast matters.
A high protein, high fibre and micronutrient-rich breakfast is likely going to be a better choice than a breakfast that is the opposite of that.
It is another example of why it is relevant to focus on your individual situation.
Summary
Breakfast does not speed up your metabolism. The research is also mixed as to whether it does much on average for calorie intake and weight loss.
Although the research is mixed there are trends showing:
- People who consume breakfast, on average, consume slightly more calories than those who do not, in controlled studies.
- People who consume breakfast, on average, do a bit more physical activity than those who do not.
- People who consume breakfast, on average, have healthier diets than those who do not, in uncontrolled studies.
- In controlled studies, when breakfast consumption vs breakfast skipping is compared, there is minimal change in weight on average. But the trend is favouring slightly higher weights in those eating breakfast.
- Research on intermittent fasting (instead of breakfast skipping specifically) finds larger reductions in body weight. But this has other pros and cons too.
The good thing about understanding this from a theoretical perspective AND seeing that average trends do not massively favour either side is that it allows you to choose based on personal preference.
If you do not want to eat breakfast, you do not have to. Ideally, you still cover any positive nutritional gaps that might exist due to missing breakfast, at another time, but you do not need to eat breakfast.
If you like to eat breakfast, you can still eat breakfast. There is nothing magical about intermittent fasting for weight loss beyond the reduction in calories. If you create a calorie deficit regardless, you will still achieve weight loss.
