Are carbohydrates necessary for a balanced diet?

Carby goodness: Jill Dupleix's quinoa porridge.
Carby goodness: Jill Dupleix's quinoa porridge. Photo: Edwina Pickles

With low-carb diets dominating the headlines when it comes to losing weight, it makes you wonder what the deal with carbohydrates is – are they no good for our health or or perfectly fine to eat in moderation? 

A study published in The Lancet Public Health journal last year provides inside into the carb debate, suggesting that neither a low-carb diet nor a high-carb diet are ideal long-term if you're going to live a long and healthy life. Rather, moderate carb consumption - accounting for 50 to 55 per cent of energy intake - will give you the lowest risk of mortality.

The Harvard researchers also examined the source of proteins and fats consumed in low-carb diets. They found that replacing carbohydrates with protein and fat from animal sources was associated with a higher risk of mortality than moderate carbohydrate intake. In contrast, replacing carbohydrates with plant-based foods was linked to a lower risk of mortality.

"These findings bring together several strands that have been controversial," says Dr Walter Willett, a professor of epidemiology and nutrition at Harvard T. H. Chan School of Public Health and a co-author of the study. 

"Too much and too little carbohydrate can be harmful but what counts most is the type of fat, protein, and carbohydrate." 

Carbs are our body's primary source of energy, especially for the brain, which relies almost completely on glucose to function optimally.

Dietitian Rachel Hawkins

Another review published in the journal BMJ similarly concludes it's the quality of carbohydrate-rich foods rather than quantity that has the strongest effect on major health outcomes.

Accredited practising dietitian Rachel Hawkins, who blogs at thenakedtruthaustralia.com, agrees that carbohydrates are essential for a balanced mind and body and that quality matters over quantity.

"Carbs are our body's primary source of energy, especially for the brain, which relies almost completely on glucose to function optimally," Hawkins says.

Advertisement

"Therefore, restricting your brain glucose from carbs can leave you feeling tired, fatigued, and foggy headed."

While the body will draw on fats and proteins as sources of energy, limiting carbohydrate consumption in the long-term can have detrimental health outcomes, she says. This is because whole plant foods - including vegetables, fruits, legumes, and whole grains - contain unique essential nutrients, such as dietary fibre, phytonutrients and antioxidants as well as plant protein and healthy fats.

"The research emphasising the importance of dietary fibre on the microbiome is evolving but there's definitely a link between fibre that comes from eating a colourful variety of whole plant foods and healthy gut bacteria, but also on immunity, digestive, heart and brain health," Hawkins says. 

Victorian naturopath Erin Keane adds that restricting carbs for too long can mess with female hormones. "It can compromise proper thyroid and adrenal gland function and even lead to amenorrhea [absence of menstruation]."

Hawkins also highlights how eating a lot of meat on low-carb diets as the main source of protein, equals an increase in saturated fats which have been proven to have negative consequences on cardiac health.

Why do carbs get a bad rap?

To understand the dietary grey area around carbohydrates, it's important to know the difference between two types of carbs - as not all carbs are created equal.     

"Simple carbs are your sugary foods like biscuits, sweets and syrups, which the body essentially breaks down very quickly, causing blood-sugar spikes," Hawkins says.

"But whole foods such as nuts, grains, vegetables and fruits, including starches, have complex carbs, which takes the body longer to break down and absorb, and in effect provide us with longer-lasting energy throughout the day."

In other words, when we hear about carbs being bad for our health, it's mainly related to simple carbs.

Health research suggests that excessive consumption of simple carbs, predominantly found as added sugars in highly processed foods, tends to drive metabolic disorders such as type 2 diabetes, cardiovascular disease and stroke. They are also principal factors behind high obesity levels and even hypertension.

"For people who are diabetic or pre-diabetic consuming low-glycemic foods, closely related to complex carbs, can help regulate their blood-sugar levels," Hawkins says.

But before you dismiss simple carbs completely, Hawkins points out that simple carbs can be useful in terms of providing us with quick bouts of energy as a pre-workout snack or enjoyment. 

"A few pieces of chocolate a couple of nights a week will not be detrimental to your health," she says.

"In the same way, excluding simple carbs all together will not necessarily make your diet healthier."  

How about weight loss?

Many studies suggest that low-carb diets help weight loss, including one BMJ study that put 234 overweight adults on a 10-week weight-loss diet. It found that people on low-carb diets burned more than 200 extra calories per day compared to those on high-carb diets.

"As with any weight loss plan the most important to focus on is diet quality, so the health impact of any diet for weight loss and its success depends on its nutrient density," says accredited practising dietitian Kate Save, founder of meal-delivery service Be Fit Food. 

"Reducing your intake of calorie-dense simple carbs automatically forces your body to burn fat stored around your midsection for energy, suggesting that with the right carbs we lose weight not pile it on," she says.

"Therefore, if your carb intake consists mostly of non-starchy vegetables, leafy greens, and whole grains, together with the right quality fats and protein, you can achieve your weight-loss goals easier."

To maintain a healthy weight, quantity control is also required, Keane adds. "If you're not eating more calories than you need, then you aren't going to put on weight - even if the majority of your calories come from carbs," she says.  

Carbohydrate health benefits

Grains: Whole grains, such as quinoa, brown rice, buckwheat and millet have been scientifically proven to reduce the risk of cancer while stabilising blood sugar, cholesterol and triglyceride levels, plus optimising digestive function. Wholegrain varieties found in oats and rye specifically lower the risk of cardiovascular disease.

Legumes: Beans and legumes in the form of kidney beans, lentils, fava, black-eyed peas and chickpeas are naturally low in fat, and practically free of saturated fat, and cholesterol.  As a result, they lower the risk of developing type 2 diabetes, and help improve both unhealthy cholesterol and triglyceride levels while regulating blood pressure. Fibre, protein, and slowly digested carbohydrate content aid in satiety, helping with weight loss and weight control.    

Potatoes: Resistant starch from potatoes is mostly converted into the short-chain fatty acid butyrate - the preferred food source for gut bacteria. Studies have shown that butyrate can reduce inflammation in the colon, strengthen the colon's defenses and reduce the risk of colorectal cancer.

Whole fruits: While the effects of fructose on metabolism can be harmful, this is only true when consumed in concentrated form such as fruit juice. When eaten as a whole fruit with the skin on, fruit adds the positive benefits of fibre, water and "chewing resistance", which means it takes a while to eat and digest, so fructose hits the liver slower and doesn't cause harm.  

So what's the answer?

"Don't vilify carbs but increase awareness of the various roles different types play in your diet," Hawkins says.

"And as long as you're making smart choices - a moderate carb consumption which prioritises quality over quantity - there's no reason to limit or exclude carbs from a healthy diet plan."