Thanks to nutritional labelling and education, most of us know or have a rough idea of how much junk food makes an acceptable portion.
When it comes to healthy foods, however, your portion sizes can become a bit more relaxed and this just might be undoing all your good nutritional work.
In fact, Accredited Practising Dietitian and director of Food & Nutrition Australia Sharon Natoli says most people don't know what a proper serving size for healthy food is.
''This means we often don’t have the same sense of control that we may exercise with foods we know are ‘treat foods,' '' Ms Natoli says.
Not only that, she also says it's a common misconception that you can't overeat healthy foods.
She says she often has exasperated clients who can't understand why they are overweight or have high cholesterol, even though they have a healthy diet.
''Frequently the answer lies in the amount of food they are eating,'' Ms Natoli says. ''While they are eating healthy foods they are just eating too much.''
Ms Natoli says that along with a sedentary job, overeating even healthy foods can lead to weight gain.
Are there any healthy foods you cannot overeat? ''I think it’s possible to overeat on anything,'' Ms Natoli says.
Before you chuck out the broccoli, however, Ms Natoli says overeating food such as celery probably won't make you gain weight. What it might do, however, is make you too full to eat the variety of foods you need to meet your nutritional requirements.
Ms Natoli says there are a handful of healthy foods that almost everyone is guilty of overeating. She suggests ways people can moderate their intake and still enjoy a truly healthy diet.
Sometimes called ''nature's butter'', these delicious green fruit are full of vitamins, minerals and omega-6. They are also full of good fats, and despite the fact that overall it's a great food, thanks to that fat content it's easy to eat too much.
Slices of avocado on toast is certainly a popular dish, but Ms Natoli says a better way to prepare it is to mash the avocado up first. ''Mash it and use it to spread on your bread, so a little goes a long way.''
Definitely healthier for you than Nutri-Grain or Fruit Loops, but we probably all free-pour our muesli the same way we would serve ourselves corn flakes.
The problem with that, Ms Natoli says, is that muesli is much denser, so if you pour the same amount into your bowl, you will end up eating much more that you should.
To combat the problem, Ms Natoli suggests serving your muesli in a smaller bowl so you aren't tempted to serve yourself too much.
''A serving of muesli should be about half the volume you would normally eat for flaky-style cereals,'' she says.
A bowl of nuts can be a tempting snack, and unroasted nuts are certainly healthy. But it is easy to keep going back for more.
Ms Natoli says you should limit yourself to a handful at a time.
''Use them to sprinkle on salads or in stir fries, so you get the benefits of nuts without the risk of overeating them.''
Juice can be good for you, and while fruit (with all its natural fibre still intact) is much better, a juice on the go can be a great pick-me-up.
Unfortunately they often come in large sizes, which Ms Natoli says is a big no-no.
''Aim for a serving size of about 200 millilitres of a 100 per cent juice – a small glass – and avoid the super-sized takeaway types you often find when you are out,'' she says.
She also says drinking water before you have a juice will quench your thirst, so you don't feel like drinking so much fruit juice.
Cheese is made from milk, which we know is healthy. It has calcium and other vitamins and minerals, it is high in protein and it has good fat.
But cheese is easy to overeat, especially when there is a large selection of cheese and crackers on offer. When added to sandwiches or salads in combination with something like avocado, you end up seriously boosting the fat content of your meal as well.
Ms Natoli says cut it as thin as possible, so you still get the taste but without too much extra fat.
''When using on crackers, sandwiches or in salads, use a peeler to peel slices rather than cutting the cheese into thicker slices or cubes.''