Should we be considering a low carbohydrate diet? Can this help us lose weight? Is it good or bad for our health?  

Should we be cutting out carbs?

Some well known diets, such as Atkins, Dukan and South Beach, aim to limit carbohydrates in particular. That means significantly cutting back on food like potatoes, bread, rice and pasta. For example, the Atkins diet suggests that we should consume significantly less carbohydrates (ideally eating low carb vegtables instead) and replace them with proteins and fats.

This is based on the theory that if the body does not utilise its intake of carbohydrates (glucose) effectively or if we have too much carbohydrate, then in trying to be efficient, the body will turn these into fats which are stored in the body.   

However, the Association of British Dietitians argues that carbohydrates provide the main supply of energy for our body and its organs - a view supported by the NHS in the UK and the NIH (National Institutes of Health) in the USA. 

Good Carbs and Bad Carbs? 

Not all carbs are the same. For example some are digested and converted into dietary sugar (glucose) more quickly than others. This can cause a blood sugar spike and, over time, through the release of insulin, increase the risk of diabetes. In the short term also, the dip after a blood sugar spike can cause us to feel hungry again and crave sweet food, which isn't good for our health or our weight.

The Glycemic Index (GI) measures how quickly foods release sugar into the bloodstream; and the Glycemic Load measures how much carbohydrate there is in a portion of food. These measures suggest that brown rice, wholemeal bread, wholemeal pasta and sweet potatoes have a lower glycemic load and are therefore healthier than white rice, white bread and pasta and ordinary potatoes – and healthier than cakes, biscuits and sugary drinks which have a higher glycemic rating. 

We also need to consider the other ingredients in the food we're eating. For example baked potatoes have a higher GI than potato crisps but are healthier because they contain less fat and less salt.

So it seems that what type of carbohydrate we eat and what else they contain can make a difference.

Should we cool pasta then reheat it?

That was the intriguing suggestion from the TV programme Trust me I'm a Doctor in 2014. Apparently, when pasta cools down this changes its structure. It begins to behave more like a fibre, resulting in a shorter glucose peak (thereby reducing the risk of type 2 Diabetes) and helping feed the good bacteria in our gut (which may help control weight). As cold pasta may not be everyone's favourite the TV programme researched what would happen if it were reheated. Their research with a small group of volunteers suggested the reheated pasta was even healthier, producing an even smaller spike in blood glucose. However, because this was a very small study, more research is needed into this.

Low carb, low fat or balanced weight loss diet?

When it comes to weight loss there doesn’t seem to be a significant difference between the three types of diet.

A 2014 study which compared low carb and balanced diets (i.e. diets with a variety of types of food) reported that both produced short term weight loss. It also concluded there was probably little or no difference in weight loss and changes in cardiovascular risk factors in up to two years of follow-up. 

Similarly, a 2013 review reported that diets with varying degrees of carbohydrate restriction perform as well as or better than comparable low fat diets with regard to weight loss.

Which type of diet is healthier?

We’d like to give a clear cut answer. Unfortunately different studies seem to produce different results.

For instance a large, long term study in the US, published in 2008, concluded that diets lower in carbohydrate and higher in fat and protein do not increase the risk of type 2 diabetes in women. In fact, diets rich in vegetable sources of fat and protein may modestly reduce the risk of diabetes. For those who already have type 2 Diabetes, a low carbohydrate diet appears to have health benefits, according to a review of the evidence published in 2017. 

However, a large, long term study in Sweden, published in 2012, concluded that low carbohydrate-high protein diets, used on a regular basis and without consideration of the nature of carbohydrates or the source of proteins, are associated with increased risk of cardiovascular disease. While a review of published studies, in 2013, found that low carbohydrate diets appeared to be associated with an increased risk of death (all cause mortality).

What these studies usually have in common though is a recognition that the type of carbohydrate (and the type of fat and protein) matters. The Swedish study, for instance, noted that low carbohydrate-high protein diets may be nutritionally acceptable if the protein is mainly of plant origin and if you eat less simple and refined carbohydrates (like the white rice, bread and pasta explained earlier). Lentils, beans, nuts, seeds and tofu are examples of plant based proteins - as well as some vegetables, like peas, sprouts and broccoli. And a 12 month study from 2010 found a low carbohydrate Mediterranean Diet (with a mix of healthy ingredients like fruit, vegetables, fish and olive oil) most effective for controlling cardiovascular risk factors (and so reducing the risk of heart attack and stroke) and also for controlling Type 2 diabetes. 

Conclusion

• If you want to lose weight and stay healthy, choose a balanced diet. It is important to choose ‘good’ carbs, with a low glycemic load, like brown rice, wholemeal bread and wholemeal pasta – and include at least 5 portions of fruit and vegetables each day. 
• Avoid ‘bad’ carbs, with a high glycemic load, like white bread and pasta, white rice, cakes and biscuits – they’ll pile on the pounds and increase your risk of obesity, diabetes, heart attack and stroke. 

Reviewed and updated by Viktoria Semanov, October 2017. Next Review Date September 2021.