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 per cent of energy intake. Higher proportions of protein can push this figure up, but even at its greatest, DIT might only account for about 15 per cent 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 may 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 have found no evidence to suggest skipping breakfast causes weight gain.
Thinking beyond 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 eating 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 hyperglycemia (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 a religious breakfast consumer or a staunch skipper, remember both sides might have some merit and the answer is probably not as simple as you've been led to believe.
Enhad Chowdhury is a Postdoctoral Research Associate and James Betts is a Senior Lecturer in Nutrition, Metabolism and Statistics - both at the University of Bath.
