Diet myths: True or false?

1) An apple a day keeps the doctor away | This well-known statement is based on an 1860s Welsh proverb that eating apples will diminish doctor visits. And it has actually been put to the test — in a 2015 April Fools’ Day issue of JAMA Internal Medicine (while the topics were zany, the studies were real). Researchers investigated whether people who reported eating apples daily actually had fewer annual doctor visits or were in better overall health. Of the 8,399 study participants, 753 ate at least one small apple daily. The results showed that 39 percent of apple eaters avoided physician visits compared to 34 percent of non-apple-eaters, which was not a statistically significant difference. Researchers did find that apple eaters were a bit less likely to require prescription medications compared to non-apple-eaters, leading the researcher to joke that “an apple a day keeps the pharmacist away”. Of course, the doctor proverb shouldn’t be taken literally, but the overall sentiment is true: Eating vegetables and fruits daily does have health benefits. That’s because the combination of fiber, vitamins, minerals and phytonutrients may help reduce inflammation and combat cardiovascular disease and some types of cancer.

2) Carrots are good for your eyes | This narrative traces back to the Second World War. In 1940, British Royal Air Force pilots began using radar to shoot down enemy planes in the dark. To keep this new technology a secret, the Ministry of Information’s propaganda was that the pilots had great visual accuracy because they ate carrots, which improved their night vision. It seemed plausible, too, because carrots are rich in the antioxidant beta carotene, the precursor to vitamin A. Once absorbed by the body, vitamin A helps make rhodopsin, a pigment that helps eyes work better in low light. Carrots can help if you have vitamin A deficiency that causes poor night vision, but of course they can’t really help you (or air force pilots) see in complete darkness. So, yes, carrots are good for eyesight, but other foods rich in beta carotene, such as sweet potatoes, squash and leafy green vegetables, have the same benefits.

3) Turkey makes you tired | Many people say this after a Thanksgiving dinner: “The turkey made you fall asleep!” Turkey contains an amino acid (a building block of protein) known as tryptophan, which the body uses to generate serotonin, which helps promote sleep. So then there must be something to this whole turkey-sleep connection, right? Not so fast. Turkey contains no more tryptophan than beef, egg, fish or chicken and tryptophan has a hard time getting past the blood-brain barrier, so it’s not an effective sleep inducer on its own. But the effect of tryptophan increases when insulin levels are high, as happens after you eat a carb-rich meal — such as a Thanksgiving dinner with stuffing, potatoes and apple pie. So it’s actually carbs that increase serotonin levels and help with the production of the hormone melatonin, which makes you sleepy. Eating a large meal can have a similar effect because there’s increased blood flow to the stomach for digestion, and decreased blood flow to the brain. So it’s definitely not just turkey that makes you sleepy.

4) Ginger relieves nausea | This remedy has strong roots. More than 5,000 years ago, people from India and China used ginger as a tonic to treat many ailments. The most common and well-established historical use is to alleviate nausea and vomiting. Today, many clinical studies support the use of ginger for exactly this purpose. Research shows that ginger helps relieve nausea and vomiting caused by motion sickness, morning sickness in pregnancy, during chemotherapy treatments and post-surgically after anaesthetic. It’s thought that the constituents in ginger — including gingerols and shogaols — help speed gastric emptying, which relieves nausea. Some people sip ginger tea for relief, while others prefer to take a ginger capsule, and studies show that both options can work. My mum used to open a can of ginger ale when I was queasy. While she was on the right track, it turns out many soda brands use artificial flavouring rather than real ginger, so those are of little benefit.

5) Fish is good for your brain | In his 1930 short-story collection Very Good Jeeves, British author and humorist P.G. Wodehouse wrote: “They say fish are good for the brain. Have a go at the sardines and come back and report.” Wodehouse was on to something! In 2016, researchers found that weekly consumption of fish was associated with high volume of gray matter, the dark tissue of the brain that’s in charge of processing information and controlling vision and memory. Many people have postulated that the value of fish comes largely from omega-3 fats, which play many important roles in brain health. Yet, interestingly, this study showed that any fish — not just those high in omega-3 fat — had this positive effect. Another review study found that fish intake may help delay cognitive impairment and Alzheimer’s disease, but cast doubt as to whether the omega-3 fats are the reason. That means taking omega-3 fish oil supplements (or drinking cod liver oil) for brain health may not cut it — there’s something about eating a whole fish fillet that’s more beneficial.

6) Mustard helps with leg cramps | Have you ever been jolted from sleep with a leg cramp, or felt your calf seize after a run? Maybe you were told to take a shot of pickle juice or a teaspoon of yellow mustard. For years, people assumed this worked because the pickles and mustard contain fluids and sodium, which may help ease leg cramps caused by dehydration or an electrolyte imbalance. But research doesn’t confirm this reasoning. In one study, researchers induced leg cramps in male subjects, then gave them pickle juice or water. The pickle juice made the cramps go away faster, but effect was not due to restoring body fluids, or the water would have worked just as well. Now researchers believe the problem is not actually with the muscle itself, but with the motor neurons that send signals to it, which become hyperactive. The researchers hypothesise that strong flavours (as in mustard or pickle juice) stimulate neurons in the mouth and upper GI tract, which in turn restores the normal activity of the motor neurons involved in muscle cramping — sort of like a distraction. There are no rigorous studies to prove this interesting theory, so drinking pickle juice remains mostly unsubstantiated. But if it works for you, drink up.

7) You can’t drink water while eating | The theory behind this persistent claim is that drinking water shortly before or while you eat dilutes digestive juices. This, in turn, allegedly interferes with the proper breakdown of food, impairing nutrient absorption. It also supposedly slows the emptying of the stomach, leaving you uncomfortably bloated. It is “totally false,” says registered dietitian Tamara Duker Freuman, author of The Bloated Belly Whisperer. The bottom line is that you should feel free to drink as much water as you’d like before and during your meal, knowing there are no digestive downsides - as long as you take it slowly.