This article was written by Enhad Chowdhury and James Betts from the University of Bath, and was originally published by The Conversation.
In the middle of the last century, popular nutrition author Adelle Davis advised people to eat breakfast like a king, lunch like a prince, and dinner like a pauper. Her advice stuck. Recent examination of the merits of adults eating breakfast has raised the question of whether we should indeed eat like kings at breakfast or just skip it all together.
First of all, the "most important meal of the day" is not a title anybody should give to any meal whether it's breakfast, lunch or dinner. To attempt to arbitrarily define a specific meal as the most important is not sensible, but there are a few commonly held truths that may have contributed to breakfast receiving this rather lofty title. When considering these ideas, it becomes clear that some don't have the weight of evidence you might expect.
Here are some of the commonly asked questions about breakfast and some of the evidence. As you will see, it's not a cut and dry issue.
Does skipping breakfast make you eat more?
We know that skipping breakfast causes the brain to be more responsive to highly palatable foods and that people often eat more at lunchtime if they skip breakfast. But in laboratory situations and in more realistic investigations conducted with people going about their normal routines, most studies show that skipping breakfast results in lower total energy intake over the course of a day than eating breakfast. So, despite greater hunger during the morning and some compensation during lunch, the effect of skipping breakfast doesn't seem great enough to make people overshoot the calorie deficit created by missing the morning meal.
Does breakfast 'kick start' your metabolism?
Eating sets a variety of biological processes associated with digesting and storing food into action, which result in increased energy expenditure known as diet induced thermogenesis (DIT). So, yes, breakfast does kick start your metabolism.
A recent study has even shown that this increase in expenditure is more pronounced in the morning than the evening. But there is a major problem with pinning your hopes on this 'jump start' to offset the energy in your breakfast.
DIT accounts for a proportion of the food you eat. For a normal diet it's only about 10 percent of energy intake. Higher proportions of protein can push this figure up, but even at its greatest, DIT might only account for about 15 percent of what you eat.
But there might be more to this than just the increased metabolism due to digestion. New evidence from our group, published in the American Journal of Clinical Nutrition, found that those assigned to eat breakfast used more energy through physical activity (in particular during the morning) than those fasting. So it might be that skipping breakfast makes people feel less energetic so they reduce their levels of physical activity, without consciously realising it.
Does skipping breakfast make you gain weight?
Skipping breakfast is associated with greater weight and increased fatness over time. But this doesn't necessarily mean that skipping breakfast causes the weight gain. It could be that eating breakfast is simply a marker of a healthy lifestyle and, in itself, doesn't protect against obesity.
Several randomised trials (where people are randomly assigned to a certain behaviour, such as eating breakfast or skipping breakfast) have not found any evidence to suggest that skipping breakfast causes weight gain. Despite the association between skipping breakfast and weight gain, experiments specifically designed to try and establish cause and effect haven't provided evidence that skipping breakfast causes you to put on weight.
Thinking beyond weight
Having covered the common perceptions relating to breakfast and weight, it's important to recognise that there are other dimensions to the debate on breakfast:
The term 'breakfast' covers a vast array of foods from sugary cereals to fry ups. Research examining how different breakfast types affect the body is still ongoing.
It's possible that consuming breakfast (depending on the type) may make you more likely to consume recommended amounts of certain nutrients.
There is evidence that eating breakfast can improve endurance exercise performance.
Eating breakfast might help the body regulate blood glucose concentrations. Skipping breakfast has been shown to increase postprandial hyperglycaemia (high blood sugar following a meal) in people with type 2 diabetes.
So, should you eat breakfast?
The prevailing public wisdom suggests that, yes, you should eat breakfast. But the current state of scientific evidence means that, unfortunately, the simple answer is: I don't know. It depends.
Whether you are a religious breakfast consumer or a staunch skipper, keep in mind that both sides might have some merit and the answer is probably not as simple as you've been led to believe.