8 Food Myths You Probably Believe

Turkey making you sleepy is one myth that gets repeated often around the festive season – and especially at Thanksgiving in the US. Turkey's supposed sleep-inducing properties were even mentioned in an episode of Seinfeld. But they don't hold up to scientific scrutiny.

Turkey contains the amino acid tryptophan, a building block for the hormones serotonin and melatonin, which help regulate sleep. And tryptophan has been shown to ease insomnia.

But the levels of tryptophan in turkey are not high enough to induce that effect, and are comparable to those in other meats. In their book Don't Swallow Your Gum (Penguin, 2009), Dr Aaron Carroll and Dr Rachel Vreeman write:

"The amount of tryptophan in a single 4-ounce serving of turkey (350 milligrams) is also lower than the amount typically used to induce sleep. The recommendations for tryptophan supplements to help you sleep are 500 to 1,000 milligrams."

After a tough day or a break-up it's often food we turn to for comfort. But according to a recent study published in the journal Health Psychology, it's time – not comfort food – that makes people feel better.

A hundred people watched a 20-minute film designed to make them sad and angry. The group who ate their specially chosen comfort food afterwards did have significant improvements in their mood, but no more than the groups who ate other foods or no food at all. From this, the study authors concluded: "You don't need comfort food to feel better; the mind will do the trick all on its own if you give it time."

However, if you do choose to cook and eat a family-size macaroni cheese in that time, it's entirely your own business.

Gastroenterologist Roger Liddle from the Duke University School of Medicine told Scientific American: "Nothing would reside that long, unless it was so large it couldn't get out of the stomach or it was trapped in the intestine."

Most of what gum is made of is indigestible. Some components, such as the sweeteners, will break down, and the rest of the gum will pass through pretty much undisturbed.

Some foods – particularly celery – are touted as having "negative calories", meaning your body supposedly uses up more calories digesting them than you get from the food itself.

So let's look at the numbers: A large stick of celery has something like 10 calories, but Dr Tim Garvey, chair of the department of nutrition sciences at the University of Alabama, Birmingham, US, told the BBC that it only takes something like two calories to digest it. "In actuality there are no negative-calorie foods," he said.

One of the first questions people ask when they find out someone is vegetarian is how they get enough protein if they don't eat meat.

According to the US Centres for Disease Control and Prevention, the average woman needs 46g of protein a day and men need 56g. Most Americans consume more than the required amount, and there are plenty of protein sources that are veggie-friendly.

You also don't need to combine plant foods in one meal to get "complete" proteins – just make sure you eat a variety of food over the day. "Research indicates that an assortment of plant foods eaten over the course of a day can provide all essential amino acids," said the Journal of the American Dietetic Association.

Read more about protein here.

Lots of people think milk is essential for healthy bones. And while it's true that you need to make sure you get enough calcium to help prevent osteoporosis, drinking milk is not the only way to get that. In fact, gram for gram, kale has slightly more calcium than whole milk, and spinach is not far behind. In general, leafy greens, tofu, and dried fruit are all great non-dairy sources of calcium.

But calcium alone won't cut it. You need vitamin D too to help your body absorb the calcium – either from your diet or from exposure to sunlight.

And to really make sure your bones are healthy, regular exercise is as important as diet. "Weight-bearing exercise and resistance exercise are particularly important for improving bone density and helping to prevent osteoporosis," the National Health Service says.

There are plenty of reasons to limit the sugar you give to your children, but it turns out one often-cited reason – that too much sugar makes kids hyperactive – has no basis in fact. There have been at least 12 double-blind, randomised control trials testing how children react to different levels of sugar in their diet. None of them found a link between eating sugar and hyperactivity: The scientists could not find any differences in behaviour between the children who had sugar and those that did not.

In another experiment, scientists found that if parents thought their child had been given a sugary drink they rated the child's behaviour as more hyperactive, even if the drink was really sugar-free.

People often don't think about the alcohol they put into food, thinking that it all burns off during the cooking process. But, according to the Journal of the American Dietetic Association, "Cooking always results in some, but not total loss of alcohol."

A study published in the journal in 1992 tested six recipes and found that they retained between 4 and 85% of the alcohol content after cooking. The recipes ranged from Brandy Alexander pie (which you'd expect to keep most of its alcohol) to a pot roast simmered for a long time.