In terms of diet trends, fat was banished back in the 1990s while in more recent years, carbs have become the new bad guy courtesy of growing public interest in keto and no-sugar diet regimes.

Packaged and processed foods are now often labelled as “low sugar” or “zero carbs”, and it is not uncommon for dieters to sign up to low-carb diets.

While global statements regarding the healthiness of carbs are routinely made, the reality is that the human body runs on the building block of all carbs – glucose.

When considering whether carbs are necessary or good for us, the most important thing to look at is the type of carbs we routinely choose and how they affect health and longevity.

What are carbs?

Carbohydrates are the base of plant-based foods including cereals, fruit, starchy vegies and grains. They include the simple sugars glucose, fructose and lactose. All carbohydrates are built from the single sugar glucose, which is the primary fuel for the muscles and the brain.

The average person’s diet consists largely of carbohydrates, with white bread, rice and fruits, along with processed snack foods and sugars, forming the base of the average diet. More refined, processed carbs result in higher blood glucose levels over time, which in turn is associated with weight gain and an increased risk of developing type 2 diabetes.

Carbohydrates that are naturally found in whole foods – fruit, dairy, whole grains – have a significantly different effect on the body metabolically compared to processed forms of carbohydrates that are made from refined grains. The latter are digested more quickly, and offer far less nutritionally than naturally occurring carbs consumed in whole foods.

Why do carbs get a bad rap?

While carbs are often clumped together as “bad”, the scientific reality is that the brain and the liver are programmed to run on carbs. The issue is not carbs generally but rather the ones we tend to reach for – the white breads, wraps, rice, muffins, cakes and biscuits, which are based on refined, processed carbohydrates that negatively impact blood glucose control.

Carbs and blood glucose control

Different types of carbohydrate are digested at different rates, with more processed carbs releasing glucose into the blood stream more quickly than less processed types of carbohydrate such as whole grains, dairy and fruit. These foods are referred to as high glycaemic index carbohydrates or high GI carbs.

Relatively high amounts of glucose being released at one time results in higher amounts of the hormone insulin being released, and high insulin levels over time are associated with weight gain, and an increased risk of developing type 2 diabetes for individuals who are predisposed.

Glycaemic load

While the glycaemic index of any individual carbohydrate food is important, the factor that’s even more important when it comes to blood glucose and weight control is glycaemic load.

The glycaemic load of a carbohydrate-rich food takes into account the overall carbohydrate content of the food. For example, while a lower GI rice such as basmati may rank more highly than regular white rice in terms of GI, its overall glycaemic load is still high as it contains relatively large amounts of carbohydrate.

This means that limiting portion sizes of carbohydrate-rich foods such as rice and large slices of bread is important, especially if the goal is glucose and weight control.

The F word

When it comes to switching to a low-carb diet, perhaps the most important dietary factor that is missed is dietary fibre. As nutrition research grows, the more we come to understand the powerful role that dietary fibre plays in disease prevention as we age.

Ideally adults need at least 30g of dietary fibre each day, and a mix of different plant foods will tick the box on an optimal intake of soluble fibre, found in fruits, oats and legumes. This aids satiety, as well as insoluble fibre found in whole grains, which aids digestive health. Then there is also the nutritional wonder that is resistant starch, which can be found in a number of carbohydrate-based foods.

The power of resistant starch

Acting in a similar way to dietary fibre, resistant starch is a molecule that is undigested as it moves through the small intestine, before then fermenting in the large intestine, producing good bacteria that supports gut health. It is found in only a handful of foods including lightly cooked pasta, unripened bananas, raw oats and potato or rice that has been cooked and then cooled in the fridge before eating.

Including some resistant starch in your diet has a number of health-related benefits including improved glucose control and lower blood cholesterol levels. As such, enjoying some potato or rice that has been cooked then cooled, or including uncooked oats in the diet via overnight oats, is a smart way to increase the natural resistant starch content in your diet.

Carbs to avoid

While there are plenty of nutritious carbohydrates, there are a handful of carbohydrates that offer little to no nutritive value other than calories, and as such are commonly used “empty calories” or simple sugars. This includes white sugar, jam and ultra-processed foods such as lollies and soft drink. More scientific evidence is building to show that the less of these processed carbs we consume, the better thanks to the dramatic increases in blood glucose that result after consumption.

The take-home message

Before you completely ditch the potato, the key thing to remember is that it’s not the potato per se that is causing issues in your diet. If you regularly eat your potato as French fries with aioli, however, that could be the issue. Certainly, as we get older, most of us need less carbohydrate simply as we are a lot less active, and carbohydrates are primarily a source of fuel.

This means that seeking out the more nutrient-dense, calorie-controlled carbohydrates found in legumes, dairy, fruits, vegetables and controlled portions of whole grains is the best way to strike a balance between carbs, health and weight control. These will give you all the dietary fibre you need for digestive health and wellbeing, minus the white, refined carbs that cause havoc with blood glucose levels, energy and weight control.