"There's some validity to some of them, but many of them are just old wives' tales or myths that have trickled down over the years," said Annette Frain, a registered dietitian in North Carolina, on the topic of why many food-related myths still persist.

Here we revisit some familiar food myths to see if the evidence backs it up.

1. Chocolate causes acne

Calories aside, chocolate is widely believed to mar good complexion. Is this just a pre-teen myth?

"Chocolate has been studied, and there's no hard evidence it has anything to do with acne,” said Sarah Taylor, a dermatologist at Wake Forest Baptist Medical Centre.

Echoing this view, Los Angeles dermatologist Ava Shamban said, “There is little evidence that chocolate or any specific fatty foods will cause acne, but we do know that a high-sugar/high-fat diet can increase sebum production and promote inflammatory responses in the body — which can lead to acne.”

What actually triggers acne? Researchers have pointed to hormonal changes and heredity as likely factors. Dr. Shamban says, “One reason is that some women like to indulge in sweets, particularly chocolate, during the premenstrual part of their cycle (PMS). Acne-prone women may notice breakouts coincide with this time in their cycle. Therefore it may be your menstrual cycle itself, not the chocolate you crave during it, which causes you to break out.”

2. Fish makes you brainy

Many Asian mothers are convinced that fish is “brain food” for their children, but is this true? Dietitian Annette Frain says, "This isn't a speedy fix - you're not going to get a higher score on your test or do a better job on your project at work because you ate fish last night. It's rather the build-up over time. So the sooner you start, the better off you'll be in the long run."

"Many long-term studies have found a correlation between improved cognition and the consumption of fish that are high in omega-3 fatty acids such as DHA," she added.

A new study by Martha Clare Morris and colleagues at Rush Medical Centre in Chicago suggested that despite the increased mercury levels through fish consumption, fish is beneficial for the brain and associated with a reduced risk of Alzheimer's disease.

Interestingly, the authors found no statistically significant correlation between fish oil supplements and any neuropathologic marker. So we may be better off just eating fish.

3. Spicy foods bring on ulcers

We were once told to stay away from chilli to keep ulcers away.

"Some legends just live on," said Joel Bruggen, a gastroenterologist at Wake Forest Baptist Medical Centre.

"About 75% of all ulcers are caused by bacteria called Helicobacter pylori," added Bruggen. "Most of the others are caused by the use of aspirin and other non-steroidal anti-inflammatory medications."

In a recent study when participants were given a meal of ground jalapeños, researchers found no damage to their stomach linings.

The mistaken link happens when people who felt a burning sensation in their stomachs after eating spicy food assumed that they had ulcer when they could be irritating an existing ulcer which they had no knowledge of.

4. Eating carrots gives good eyesight

"Carrots are a good source of vitamin A, which is one of the nutrients necessary for good ocular health," said Craig Greven, chair of ophthalmology at Wake Forest Baptist. "But they won't improve your eyesight."

However, under certain conditions, eating carrots may help improve eyesight. Emily Chew, deputy clinical director at the National Eye Institute in Maryland, noted that an estimated 250,000 to 500,000 American children become blind every year, as a result of vitamin A deficiency, and in impoverished settings like Nepal or India, vitamin A supplements have helped to improve night vision. Most studies, however, have focused on the benefits of beta-carotene or vitamin A instead of carrots alone.

“I don’t have any numbers to give you about how many carrots you should eat per day, but everything should be balanced in moderation,” she said.

5. Gluten-free food swaps for weight loss

Going gluten-free is becoming a lifestyle fad as many think it is healthier, without realising they could be exposed to twice as much arsenic and mercury, researchers warned. Except for those suffering from celiac disease, the ordinary person has no need of such products.

Gluten-free versions of bread, spaghetti and cereals often contain rice flour as a substitute for wheat, and brown rice has higher levels because the arsenic is found in the outer coating, which is removed in the milling process to produce white rice.

“Gluten does not make you fat,” said dietician Kristen Kirkpatrick, who manages wellness and nutrition services at the Cleveland Clinic. “Calories make you fat regardless of where those calories are coming from, whether they’re coming from brown rice, which gluten free or wheat bagel.” MIMS

Read more:
11 healthy diet habits debunked
Nurses, see these myths busted: 7 foods that aren’t as healthy as expected
Science debunks common “unhealthy” food perceptions

Sources:
https://www.sciencedaily.com/releases/2017/02/170214095827.htm
http://www.forbes.com/sites/stevensalzberg/2016/02/08/new-study-shows-that-fish-really-is-brain-food/#7bf6533f30e7
http://www.huffingtonpost.com/2012/06/05/does-chocolate-cause-acne_n_1566076.html
https://www.scientificamerican.com/article/fact-or-fiction-carrots-improve-your-vision/
http://www.realsimple.com/health/first-aid-health-basics/health-facts-fiction/eating-spicy-foods-ulcer
http://abcnews.go.com/Health/gluten-myths-embarrassed/story?id=23645211
http://www.dailymail.co.uk/health/article-4223422/Gluten-free-diets-higher-levels-arsenic.html