Glycemic Index and fat differentiation sheds new light on high fat and low carbs debate

Low carb, high protein, low fat…? Sports science fundi, Prof Tim Noakes’ recent advocacy of a high protein-low carb eating regimen has put diet high on SA middle-class agendas in recent weeks. The GI Foundation of SA (GIFSA) has released this advice in reaction to the debate…

The whole high fat and low carbohydrates debate raises its head every few decades. But it is now the 21st century and since the introduction of the glycaemic index (GI) in 1981 (Jenkins et al, 1981) GI has finally become part of the debate. It brings a whole new perspective to the table.

Detailed studies have shown that a diet high in high GI (refined) carbohydrates indeed promotes many illnesses including heart diseases (Jacobsen et al, 2010 and Liu and Willett, 2000), diabetes (Salmeron et al, 1997a and b), cancer (Augustin et al, 2001) as well as overweight and obesity (Pawlak et al, 2004).

It is for this very reason that lower GI-carbohydrates should be preferred in a daily diet, many of them being staple foods in the Mediterranean diet, namely oats, whole grain bread, brown rice and legumes (Bond Brill, 2009).

Low GI-carbohydrates are well known to not raise blood glucose levels too much, to lead to less insulin being produced by the pancreas, lessens pancreatic activity and in so doing helps to prevent diabetes and other life style diseases (Craoi et akm 1977, Pawlak et al, 2004, Jacobsen et al, 2010, Liu en Willett, 2000, Salmeron et al, 1977a and b and Augustin et al, 2001). Low GI foods offer protection from heart diseases (Jacobsen et al, 2010), lead to improvement in diseases such as diabetes (Brand Miller et al, 2003 and Opperman et al, 2004) and better weight loss than any other diet (McMillan-Price et al, 2006).

The Mediterranean diet is not shy of fat, but it consists substantially of mono and poly-unsaturated fats (mainly obtained from omega-3 poly-unsaturated fatty acids). It has been conclusively proved that when saturated fats in the diet are replaced with mono and poly-unsaturated fats (omega-3 and 6) insulin sensitivity is increased which helps prevent diabetes (Riserus et al, 2009), reduces dangerous LdL-cholesterol whilst increasing advantageous HdL-cholesterol and prevents heart diseases (Kaushik et al, 2009) and drastically reduces the risk of various cancers such as colon cancer (World Cancer Research Fund, 2007).

It has been shown in many studies that a diet high in saturated fat has been coupled with high levels of LdL-cholesterol, weakened functioning of cell membranes (Haag and Dippenaar , 2005) and increased risk of heart disease and other life style diseases, including overweight (Ascherio, 2002, Hu et al, 2001 and Hu and Wukkett, 2002), as well as increased risk of cancer e.g. breast cancer (Kushi and Giovannucci, 2002).

No studies show any advantage to the use of saturated fats and in no country’s heart foundation do they recommend its increased intake.

Prof Nola Dippenaar suggests that not more than 30% of your total fat intake of 10% of your kilojule intake should be saturated fat. The rest should consist of mono-unsaturated fats (half) and poly-unsaturated fats (half). In the South African context we should aim to include omega 3 daily, because it is not generally available in our diet and has many advantages, such as protection against Alzheimer’s disease and improvements in concentration and insulin sensitivity (Haag and Dippenaar , 2005), decrease of triglycerides and blood pressure etc.

Healthy diet is a matter of balance and there is general agreement between dieticians and nutritionists that a healthy diet should consist of 50% carbohydrate, 30% fat and 15 – 20% protein. The energy intake must be balanced by the energy usage otherwise one is liable to become fat regardless of whether the diet is higher in fat or carbohydrates.

Most of us also tend to take in far too much macro-nutrients and too few micro-nutrients that are obtained from vegetables and fruit.

In my 30 years experience as dietician, I have noticed that it is almost impossible for most people to follow a diet that contains less than 50% carbohydrates. When skimping on the better foods like slower-absorbed carbohydrates, fruits, vegetables, nuts and other good fat and lower fat protein sources, they break out only to crave sweets, high fat foods, alcoholic drinks or meat, all the bad stuff.

They end up having too little energy to exercise and don’t loose any weight and definitely not fat mass. [Read Roald’s case study] Research by Harvard underscores this, that people who consistently choose the less nutritious foods on a consistent basis do indeed pick up weight and increase their risk to the major lifestyle diseases.

As soon as they begin eating GI smart, (i.e. low GI when inactive and before exercise, but higher GI during extended periods of exercise), as well as eating fat smart (i.e. lower fat with a focus on healthy fats), their cravings disappear and they have enough energy to exercise and they loose weight and mostly body fat. This type of diet is much easier to become a life style. [Read the case study of Jacques]

As the Glycaemic Index Foundation of SA (GIFSA) we have tried to capture this healthy, balanced diet pattern with the words “GI Smart – Fat Smart” eating. With food science development to date it will be irresponsible to ignore the types of carbohydrates (GI) and types of fats.

Written by: Elizabeth Delport RD (SA), R&D Manager GIFSA, MSc Dietetics

References are available on request: email [email protected]