Maybe it's the end of a terrible day, or perhaps you are fighting off the latest flu bug that's been doing the rounds. Whatever the reason, reaching for your favourite comfort food can provide the bolstering lift you need.

Whether it's a huge portion of mashed potatoes, a big bowl of pasta or an enormous slice of chocolate cake, we all have a preferred comfort food. But what is it about comfort food that makes it comforting?

A recent study investigating comfort food may provide the answer. Researchers at Buffalo University in the US have linked comfort food with positive memories we have of the person who first prepared the food for us.

"Comfort foods are often the foods that our caregivers gave us when we were children. As long as we have positive association with the person who made that food, then there's a good chance that you will be drawn to that food during times of rejection or isolation.

"It can be understood as straight-up classical conditioning," psychologist Shira Gabriel told the journal Appetite.

Kate Gudorf, an accredited practising dietitian and spokeswoman for the Dietitians Association of Australia, says that while comfort food can be associated with fond memories of the people who prepared it, comfort eating can also be defined more broadly.

"Comfort eating may be a form of emotional eating, for example, eating as a reward or to celebrate, out of boredom, depression, loneliness, out of a need for security or out of habit," she said.

Gudorf notes that comfort eating can become problematic because comfort foods are typically high in kilojoules, saturated fat, salt or sugar.

"Unfortunately, these foods provide very little nutrition and should be considered occasional treats and not everyday foods."

According to Gudorf, comfort food could cause some serious health concerns.

"Long term, overindulging in comfort foods may lead to weight gain. Excess weight may increase your risk of developing health problems, like joint problems, high blood pressure or type 2 diabetes."

Gudorf's advice is to be conscious of portion size and to balance comfort foods with a broad range of healthy food. For example, she notes that a small amount of dark chocolate (20 grams), two to three times a week, with regular exercise and an otherwise balanced diet is unlikely to have much impact on your health.

However, eating two rows (about 50 grams) of chocolate four or five times a week could add more than 6000 kilojoules and 50 grams of saturated fat to your diet, making it much easier to gain weight and impact on your health.

"A balanced diet includes both healthy and unhealthy foods, in the right proportion," Gudorf said.

"For quality of life, it is important to eat foods that you love, like comfort foods."