Does sugar really make kids hyperactive? Is fresh fruit and veg better than frozen? And does coffee actually make you dehydrated? The answer to all of the questions I just posed is 'no'. Welcome to the world of nutrition myths and in this podcast, I’ll go over some of the more popular myths I’ve come across and explain where the truth really lies. 

The field of nutrition can be fertile ground for myths and poor advice to propagate. That doesn’t mean that scientist don’t ever get it wrong too. They do. But as research and evidence changes, so too should advice. But some advice that was accepted as fact and later was shown to be not-so-factual does stick around for some time. So, today, here is a new instalment of some popular myths I’ve come across over the years.

Myth 1: Sugar makes kids hyperactive

And my first myth is to do with sugar making kids hyperactive. The connection between sugar and hyperactivity is one of the most popular food-behaviour myths going around. Where there’s sugar, there must be hyperactive kids – or so says conventional wisdom. Science says otherwise.

There have been a whole bunch of published randomised controlled trials done in this area and they have been unable to find any difference in behaviour between children who ate sugar (from lollies, chocolate or natural sources) and those who did not. In fact, a meta-analysis of this very topic and included 16 trials and I’ll link to this study in the show notes. And the clear conclusion was that sugar didn’t affect kids’ behaviour. https://jamanetwork.com/journals/jama/article-abstract/391812

Even studies that included children with ADHD could not detect any meaningful difference between the behaviour of children who ate sugar compared with those who did not.

Now, this review was done way back in 1995 so you may be thinking that it is horribly out of date. No. Scientists have better things to do with their time than to keep repeating the same type of experiments over and over again, only to find no effect so it was time to move on once the answer was pretty clear. 

The most important aspect of all these myth-busting studies is they used a study design where the researchers or parents and the children were unaware of whether they were consuming a product containing sugar or a non-sugar substitute.

It is only when you introduce an intentional bias into the experiments – and allow the parents to know what food their child was given – that the real culprit behind the myth emerges. When parents believe their child has been given a drink containing sugar, they consistently rate their child’s behaviour as more hyperactive, even if the drink did not contain any sugar.

Why do kids seem so hyperactive when they eat a lot of sugar? It all comes down to context. When kids are having fun at birthday parties, on holidays, and at family celebrations, sugar-laden food is often served. The fun, freedom and contact with other kids makes kids hyperactive, not the food they eat.

But that doesn’t mean hyperactivity should be ignored. ADHD is a serious behavioural and developmental disorder that can impact on the child’s academic performance and family life. As such, extreme hyperactivity should be investigated by an appropriate health professional. Simply removing sugar from the child’s diet isn’t going to reduce their hyperactivity.

Having too much sugar, especially if it is coming from drinks, has been linked to excess weight gain and dental problems in kids. So even with the sugar equals hyperactivity myth busted, there are valid reasons to restrict how much kids consume.

Myth 2: Fresh is better than frozen

For good health, is it always a case of ‘fresh is best’? Not at all. Nutritionally, there isn’t a big difference between fresh and frozen produce. And by fresh here I mean what you purchase from the supermarket or greengrocer that has spent some time in transport and storage. Not everyone has the time or access to get produce through a farmers market or even grow it themselves.

Frozen produce is normally blanched and frozen shortly after harvest. The blanching does degrade some of the vitamins such as vitamin C but is on par with what happens with fresh produce when cooked. After this, freezing ‘locks in’ most of the nutrients. To keep that nutrition locked in, it is best to use cooking methods like steaming and microwaving to minimise heat and water losses.

The limited shelf-life of fresh produce means it isn’t always possible to have plenty of fresh produce on hand. The situation can be even more difficult for people living in remote areas. Considering we eat so few vegetables, then having convenient options like frozen on hand can only help address this. 

So, do people who have plenty of frozen produce on hand eat more fruit and vegetables? Using food and nutrient intake data from two large dietary surveys conducted in the United States, researchers looked at fresh and frozen fruit and vegetable consumption at the household level. And I’ll link to this study in the show notes https://www.sciencedirect.com/science/article/pii/S0899900717301958 

People who were regular consumers of frozen fruit and vegetables together with fresh ate significantly more compared to people who only ate fresh produce. The flow on from this was that eating more frozen fruit and vegetables meant that a person’s diet was healthier. More fibre, potassium, calcium, and vitamin D, and less salt was a feature of the diets for those who had frozen produce as part of their diet.

Frozen fruit and vegetables should be a backup option in the freezers of most people. Such foods are a nutritious, cost-effective and convenient way to get more fruit and vegetables in the diet each day.

Myth 3: Coffee makes you dehydrated

We often hear that coffee and other caffeine-containing drinks will make you dehydrated. But how much truth is there to this claim?

If water consumption from foods and beverages matches water losses (mostly from the urine) then that is the happy place of fluid balance. A diuretic is something that can upset this delicate balance by causing more water to be lost. Caffeine for many years has been considered a diuretic, but this view has been changing as more research comes to light showing its effect on fluid balance is minor at best.

There is a small kernel of truth to claims that caffeine acts as a diuretic, but the key is the amount you have. Early research studies did find that caffeine causes water loss, but the amount of caffeine required is over 500 milligrams. That’s equivalent to about 5 to 6 cups of coffee or an even greater number of cups of tea.

In the more recent research looking at how coffee can affect hydration, 50 regular coffee drinkers had a range of tests to measure their hydration over 3 days. The hydration tests were repeated after they swapped their coffee for water for 3 days. Their food, fluid and exercise habits stayed constant. And I’ll link to this study in the show notes http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0084154 

And after all that drinking and testing, the research team found no differences between the effect of caffeine or plain water on any measure of hydration. The participants were regular coffee drinkers so the result may have been different in people who consume little caffeine. But if someone drinks coffee rarely, then any effect on hydration will be fleeting. And what is already known is that we habituate to the effects of coffee so this latest study agrees with that.

With much interest in how different drinks can affect fluid balance, scientists have developed a ‘beverage hydration index’. The index ranks fluids by the balance between how much the body retains or loses fluid when compared against water over 4 hours. Using the beverage hydration index, there is little to separate coffee and plain water. And the same goes for cola, diet cola, tea, iced tea, orange juice and even sports drinks – they all can keep a person hydrated just as well as water.

Before you switch your drinking habits from ‘8 glasses of water’ to ‘8 cups of coffee’ a day to meet your likely fluid needs, a word of caution. Too much caffeine is not good for your health. Poor sleep patterns and insomnia, agitation, anxiety, and heart palpitations are well-described effects of too much caffeine. Keeping your daily caffeine habit below around 400 milligrams (about 4-5 cups of coffee) is best to aim for.

For regular drinkers of coffee and tea, the good news is that there is little need to worry about it dehydrating you. Another bit of good news is that coffee and tea have many health benefits linked to them including decreased risk of some cancers, heart disease and even type 2 diabetes so check out two of my earlier podcasts on both coffee and tea to get the good news.

So that’s it for today’s show. You can find the show notes either in the app you’re listening to this podcast on if it supports it, or else head over to my webpage www.thinkingnutrition.com.au and click on the podcast section to find this episode to read the show notes.

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I’m Tim Crowe and you’ve been listening to Thinking Nutrition.