Poor old carbs – they are demonised on many a weight loss diet, and then there are the keto devotees who ban them entirely.

How can it be that so many plant-based foods – fruit, veggies, whole grains and legumes are so bad for us? And even worse, are they to blame for that dreaded belly fat?

Carbohydrates are the building blocks of plant foods and include foods such as fruit, starchy veggies, cereals, legumes as well as simple sugars including table sugar and honey.

While some carbohydrates have complex structures of many, many individual sugars or glucose molecules, others are made of simple sugars such as fructose, sucrose or glucose itself. This is where the terms ‘simple sugars’ and ‘complex carbohydrates’ came from.

In years past, when food was a lot less complicated and the extent of our sugar intake was an occasional biscuit or spoon of sugar in our tea, carbs did not pose that much of an issue, especially as we were also a lot more active and could burn them off. In the past 10-20 years, this has changed dramatically as our carbs have become a lot more processed and concentrated, and we no longer move as much to burn them off.

Carbs do not directly cause belly fat – it is not as if you eat a muffin and your body stores it around your belly. Metabolism and weight gain are a lot more complex than that.

When we eat carbs, processed carbs in particular, that contain a lot of added sugar and are made using refined flour, our fat storage hormones tend to kick into gear.

Carbohydrates rich foods such as white bread, rice, cakes and biscuits as well as sugary foods such as soft drink, juice, lollies and chocolate result in high amounts of glucose being released into the bloodstream after eating.

In order to get this heavy load of glucose out of the bloodstream as quickly as possible, the hormone insulin is secreted by the pancreas. This is the direct link between carbs and belly fat.

Insulin is the number one regulator of glucose and fat metabolism in the body. High levels of insulin over time result in fat storage, specifically fat storage around the abdomen. This means that if you consistently eat a high carb, high sugar diet then over time your insulin levels will gradually increase and there’s a higher chance you’ll store belly fat.

While this is not the case for everyone – it largely depends on age, exercise, genetics and cultural background – there’s a greater chance of fat deposition around the abdominal area when your diet is high in carbohydrates.

Carbohydrate load takes into account not just the glycaemic index or how quickly glucose is released into the bloodstream after we consume carbs, but also the total amount of carbs we eat at any one time. For example, a cup of white rice may have be low GI but as the rice contains a lot of carbohydrates overall – a cup is the equivalent of three to four slices of bread – the carbohydrate load is high.

If your goal is fat loss, and in particular belly fat loss, a diet that with a low glycaemic or carbohydrate load is the way to go.

This means that you can eat some carbs, but stick to controlled portions of just ½ – ¾ cup serves of wholegrain, low GI carbs such as legumes, vegetables or fruits. It’s the key to avoiding extra belly fat build-up.

It also means that the fewer high GI, sugary carbs we consume- think via white rice, Turkish bread, lollies, rice noodles and crackers, juices and sweet drinks – the better it is for our insulin levels and ultimately belly fat.

High insulin levels develop over time, which means that the carbs we choose to include in our day to day diets are ultimately what will influence our belly fat stores long term.

An occasional high carb treat is no cause for concern, rather it’s keeping an eye on the portions of cereal, rice and pasta we eat on a regular basis that will help keep belly fat at bay.

Susie Burrell is a dietitian and nutritionist. Continue the conversation on Twitter @SusieBDiet.