When it comes to nutrition, many people have loud opinions. And while some theories may sound plausible, they are not always backed by science.

Maybe it is an opinionated co-worker who takes great delight in informing you the skim milk in your coffee is not good for you. Or that your mid-morning banana is not a great option because fruit is high in sugar.

Perhaps you tell yourself it’s not a good idea to skip afternoon tea even though you are not hungry because you want to avoid slowing your metabolism.

If you find yourself surrounded by nutritional tall tales, here are some of the most commonly espoused food myths, and what the nutritional science actually shows.

Potatoes are fattening

A dietary staple for thousands of years, a small, whole potato contains roughly 100 calories, 20 grams of total carbohydrate along with a couple of grams of dietary fibre and protein.

While the carbohydrate in potato has a higher glycemic index (the ranking of carbohydrates based on their effect on blood sugar levels) than some other high-carbohydrate foods, potatoes are ranked as one of the most filling and satisfying foods you can eat.

There is also no scientific evidence to show that the regular consumption of potatoes is associated with weight gain. One study, published in the Journal of the American College of Nutrition, followed participants who were instructed to consume five to seven serves of potato each week. It found regular potato consumption had no adverse effect on weight loss.

Rather, the primary issue with potato consumption is that more than half the potatoes consumed in Australia are processed – made into potato chips or deep-fried to make fries and hot chips, which not only adds much extra fat and calories, but also means you lose the natural nutrient profile and satiating effects of eating a potato whole.

This explains why it is difficult to overconsume a whole potato, but you can down hundreds of calories worth of French fries in minutes. The issue with potatoes is not the humble spud itself; rather, it is with how we choose to eat it.

Skim milk has added sugar

Whether it is the natural sweetness of skim milk that has propagated this myth, or the commonly held belief that skim milk is the unduly processed form of full-cream milk, the reality is that the only difference between regular milk and low- and reduced-fat milk is the latter two have had the fat removed.

There is nothing else added, no flavours, colours, additives or sugars, as clearly evident on nutrition labels. In fact, full-cream milk actually contains slightly more of the naturally occurring sugar lactose than skim milk.

There is also no evidence to show that regular consumption of the naturally occurring sugar lactose, found in dairy products, is associated with a negative effect on weight. Rather, the evidence available suggests that dairy consumption helps to increase lean body mass and reduce body fat.

This effect is thought to be largely a result of the benefits of consuming whole, nutritionally dense foods, which includes both regular and reduced-fat dairy.

You need to limit the eggs you eat if you have high cholesterol

Another whole food that had been frequently demonised is the egg, largely due to the fact that eggs, like all animal foods, contain cholesterol. It has long been believed that cholesterol in food increases blood cholesterol levels.

We now understand that this is not how things work. Rather, it is a combination of fat intake overall, saturated fat in particular, along with liver function, that determines how much cholesterol is produced.

Dietary studies, including one study conducted in Australia by the CSIRO, found that in the diets of more than 80,000 Australians, those who consumed more eggs tended to have a better diet overall, with more vegetables and less processed food, which ultimately helped to keep cholesterol levels controlled.

While it is still recommended that those with high blood cholesterol levels stick to just one egg a day, for those who do not have high blood cholesterol, enjoying a couple of eggs each day is not associated with a negative effect on blood cholesterol levels.

Fruit contains too much sugar

It was the low-carb movements of the early 2000s that largely fuelled the global belief that sugar in all forms, especially fructose, was the key reason so many adults worldwide are overweight and obese.

Indeed, the data available does show a close association between the consumption of high fructose corn syrup, which is rampant in the US food supply, and weight gain.

This form of refined carbohydrate is fundamentally different from the naturally occurring sugar found in fruit, fructose. When we consume whole pieces of fruit, even more energy-dense types such as bananas, we are also getting a load of other key nutrients, including dietary fibre.

There is no scientific evidence to show that there is an association between fruit intake and weight gain. In fact, there is a proven inverse relationship, with individuals who consume fresh fruit regularly having lower body weights overall.

Unlike most vegetables, which are largely water, fruit does contain carbohydrates so cannot be consumed in limitless quantities (and dried fruit and fruit juice cannot be considered the same as fresh fruit). But a couple of pieces of fresh fruit can be enjoyed as part of a healthy diet. It will not play any role in making you fat.

Gluten-free means healthy

With loads of gluten-free foods including crackers, snacks, bars, chips and meal bases sold in the health food section at supermarkets, it is not surprising that gluten-free alternatives have become synonymous with health and wellbeing.

A closer look at the ingredient lists of gluten-free alternatives will generally reveal a long list of highly processed additives and ingredients that attempt to make food that doesn’t contain wheat flour taste and look like it does.

While it may be imperative for the one in 100 Aussies with coeliac disease to actively avoid gluten, and may also be beneficial for those with IBS, it does not mean that these processed alternatives are “healthy” – a cake is a cake, whether it is gluten-free or not.

For those of us who may choose a gluten-free diet with the belief that it is healthier, there is evidence to show that these diets may actually do more harm to our nutrient intake long term.

A 2018 review published in the journal Gastroenterology and Hepatology found that women who followed a gluten-free diet by choice consumed less carbohydrate, dietary fibre, folate, iron and calcium, and more fat in their diet overall. The review concluded that gluten-free is only the best option if you actually need to be gluten-free.

You should not skip meals

For anyone who likes to eat – most of us – the belief that skipping a meal will be detrimental for metabolism is enough to justify a tasty toast and coffee on the run, or a serving of dinner whether we are hungry or not.

While extremely long periods without food, or literally days without eating, will eventually result in the breakdown of muscle mass and reductions in metabolic rate, this is not what happens when you skip a meal or snack occasionally.

Many of us live in perpetual fear of feeling hungry, which ultimately results in daily overeating and gradual weight gain. In fact, with so many large, indulgent meals now a part of our weekly routine, many of us would benefit from not eating when we don’t need to, without any fear of detrimental effects on metabolism.

There is research available to show that habitual meal skipping, of breakfast in particular, is associated with an increase in inflammation in the body. But, in general, the extended overnight fast has beneficial effects metabolically, so if you get home late, it is no issue to skip dinner, or push back the first meal of the day and wait until you are genuinely hungry to eat.

You should not cook with olive oil

Contrary to popular belief, extra virgin olive oil is not chemically altered when heated to high cooking temperatures, largely because its high natural antioxidant content helps to protect the oil from molecular changes when it is heated to typical household cooking temperatures.

Specifically, good quality Australian extra virgin olive oil will only start to smoke at temperatures above 210C, which is higher than the heat needed for deep-frying.

This means that extra virgin olive oil is the healthiest oil to cook with at home, with the highest proportions of monounsaturated fat and lowest proportion of saturated fat of all cooking oils available.

Also, remember that while the standard of Australian oil is high, imported olive oils are often “blends” of oil, and do not offer the antioxidant benefits that fresh, local extra virgin olive oil does, and will not be as good a choice for cooking.

Fresh food is healthier than frozen

We have heard that “fresh is always best” for most of our lives, and while this holds true if you grow your own produce and consume it immediately after harvest, this is not how the majority of us consume our fresh produce.

Rather, the fresh produce we buy may have been stored for weeks, if not months before it gets to us, which does impact its nutritional profile.

While both canned and frozen foods are “processed”, advances in food technology means that much of the fresh food, like peas we buy frozen and even canned, has been harvested at peak ripeness and snap frozen and processed within hours, preserving much of the nutrition. This is unlike techniques of old in which the process would take a lot longer.

Studies have shown that frozen foods are higher in nutrients than fresh foods that have not been stored in the most ideal of conditions after harvest.

For example, spinach stored at room temperature can lose up to 100 per cent of its vitamin C content within seven days, as its leaves are thin and vulnerable to oxidative damage. On the other hand, frozen spinach that has been snap frozen immediately after harvest will retain its vitamin content until it is cooked.

As for canned produce, while it may have some salts and at times sugars added, nutritionally it is certainly not an inferior product. The take-home message is, when it comes to fruits and vegetables, it doesn’t really matter which variety you opt for, just eat more of it, and don’t overcook it, as this will also harm the nutritional profile.