You’ve probably heard it all of your life – breakfast is the most important meal of the day.
And research shows eating something before you bolt out the door in the morning – be it porridge, poached eggs or peanut butter on toast – can help to boost your concentration, energy levels and set you up for better eating throughout the day.
You’ve probably also been told eating breakfast will help kickstart your metabolism – helping you burn energy efficiently and avoid weight gain.
But is eating breakfast really necessary to get your metabolism going? (And what does this mean anyway?)
There is no clear evidence breakfast can significantly affect your metabolism, says Dr Therese O’Sullivan, senior lecturer in nutrition and dietetics at Edith Cowan University.
But what is clear is breakfast has other benefits.
“From observational studies what we see is people who eat breakfast also tend to eat a healthier overall diet, one that is more nutritious and higher in fibre. People who skip breakfast are more likely to miss out on important nutrients,” O’Sullivan says.
What is your metabolism?
Your metabolism involves all the chemical processes going on inside your body that keep you alive and functioning. These processes include breaking down the food you eat into nutrients as well as those necessary for the building and repairing your body.
The food you eat provides your metabolism with the energey it requires to carry out these processes, take in more than you need and your body stores it. But your metabolism also affects the amount of energy your body needs at any given point.
Your metabolism can be divided into three components:
- basal metabolic rate (BMR), which is the amount of kilojoules your body burns to maintain functioning at rest. This accounts for 50 to 80 per cent of your overall energy requirements.
- the energy you use when physically active, this accounts for 20 per cent of your daily energy use, and contributes to your metabolism in terms of the amount of energy the body needs to burn.
- thermic effect of food, which is the energy you need in order to eat, digest and metabolise your food.
Starvation diets slow metabolism
One possible explanation for why so many of us believe breakfast affects our metabolism is due to the way our metabolism responds when we go long periods without food.
O’Sullivan says randomised controlled trials have shown the metabolisms of people on starvation or crash diets slow down to conserve energy, which means their BMR can drop by up to about 15 per cent.
As well, when people lose weight quickly during long periods without food they also lose lean muscle tissue or muscle mass, which can also contribute to a reduced metabolism. Most of your basal metabolic rate is determined by the amount of muscle you have, so the more muscle you have the faster your metabolism is.
However, O’Sullivan says, studies looking at the effects of reduced food consumption on your metabolism were conducted over a period of 10 days to a month. So while it is possible a shorter fast – such as that we do every night when we sleep – may have a similar impact, there is no solid evidence at the moment to support this, she says.
What affects your basal metabolic rate?
As well as the amount of muscle mass you have, there are a range of other factors that will affect your metabolism.
Age – As you get older your metabolism generally slows, this is thought to be because of a loss of muscle tissue, and also hormonal and neurological changes. When babies and children go through periods of growth, their metabolism speeds up.
Gender – As men are usually larger than women, they generally have faster metabolisms.
Body size – People with bigger bodies tend to have a larger BMR.
Genetics – This can also play a role in whether you have a slower or faster metabolism, and some genetic metabolic disorders can also affect your metabolism.
Physical activity – Regular exercise increases muscle mass and encourages your body to burn kilojoules at a faster rate, even when at rest.
Hormonal factors – Hormonal imbalances caused by certain conditions, including hypo- and hyperthyroidism, can affect your metabolism.
Environmental factors – The weather can also have an effect on your metabolism – if it is very cold or very hot, your body has to work harder to maintain its normal temperature and that increases the metabolic rate.
Drugs – Caffeine and nicotine can increase your metabolic rate, while medications including some antidepressants and anabolic steroids can contribute to weight-gain regardless of what you eat.
Diet – Certain aspects of your diet can also affect the metabolism, for instance if you don’t have enough iodine for optimal thyroid function it can slow down your metabolism.
Reasons to eat breakfast
While none of the factors known to affect your metabolism appear to be strongly linked to breakfast, it doesn’t mean you should skip it.
People who don’t eat breakfast may miss important nutrients needed for the day, and are less likely to make up for it later on, says O’Sullivan.
“If you don’t have any breakfast you may be hungrier than usual around mid-morning, and the hungrier people are, the more likely they are to go for energy dense snacks,” she says.
“When you’re really hungry you’re more likely to make choices that are more energy dense, and that may be foods that are less nutritious,” O’Sullivan says. “It’s important to keep a range of healthy snack options on hand like nuts, fruit and yoghurt.”
Dr Therese O’Sullivan is a senior lecturer in nutrition and dietetics at Edith Cowan University, she spoke to Jenny Pogson.