Glycaemic Index

The Truth About Carbohydrates and Low-Carb Diets

There has been a lot of controversy regarding carbohydrates of late when it comes to healthy eating habits. The World Health Organisation advocates the consumption of a low-fat and relative higher percentage of carbohydrate based diet - about 60% of the diet comprising this component. Indeed, traditionally, the diets of most cultures are carbohydrate-based, with the consumption of rice in the East and potatoes, pasta and bread in the West.

Low-Carbohydrate Diets

However, low-carb diets(diets low in carbohydrates) have received a lot of media attention of late, with many celebrities showing dramatic weight loss after switching over to high-protein, high-fat, low-carb diets. This has confounded doctors and nutritionists, who, on the whole, remain wary. The concern ultimately centres over whether such diets are safe, both in the short term and long term.

If that wasn't confusing enough, the old theory of complex carbohydrates being healthier than simple carbohydrates,brown bread/ rice being healthier than white bread/rice have all been disputed of late! This is due to inconsistencies between this theory and the actual breakdown and absorption of carbohydrates in our body.

The Glycaemic Index and Blood Sugar Level

The Glycaemic Index(GI) is a way of comparing the effect different types of food have on the blood sugar (glucose) level. It is a ranking from 0 to 100 which rates the increase in blood sugar levels after eating a portion of food providing 50 grams of carbohydrate. A 50-gram portion of pure glucose is used as the basis of comparison.

Foods that break down quickly during digestion, for example bread, have the highest glycaemic indices. They raise blood sugar levels higher and more quickly than foods with low GI's Low GI foods, such as baked beans, break down more slowly, releasing sugar gradually into the bloodstream.

Increasing our intake of low GI foods results in a reduction in the rate of digestion and absorption, thus producing the feeling of being full for a longer period after a meal. This should lengthen the interval between meals and reduce the total amount of food eaten over a given period of time.

Low GI foods have the added advantage of helping reduce the risk of heart disease and improve the control of diabetes mellitus.

Low GI (<60) foods include:

  • Apples, apricots, peaches, plums
  • Yoghurt, ice cream

Moderate GI (60-85) foods include:

  • Grapes, oranges, yam, sweet potatoes
  • Oatmeal biscuits, All Bran
  • Sponge cake, crisps
  • Porridge, Oats
  • White pasta, wholemeal pasta, noodles

High GI (>85) foods include:

  • Potatoes, bananas, broad beans, sweetcorn
  • Plain crackers, Mars bars, chocolate biscuits
  • Cornflakes, Weetabix, muesli, shredded wheat
  • Glucose, honey, soft drinks
  • Raisins
  • White rice, white bread, wholemeal bread

If you study the list carefully, you will find a number of surprises. For example, white bread and brown bread are both classed as high GI food. And my favorite ice cream is in the low GI group!

These "quirks" in the Glycaemic Index classification are explained by the index being a function of the components of each food type. The presence of protein, fat and fibre will reduce the rate of digestion and absorption of the 50g of carbohydrate.Hence we must not interpret the GI in isolation. Eating a low GI diet could result in the consumption of excessive amounts of fat. The total amount of carbohydrate, the amount and type of fat, the fibre and the salt content of a food are all important considerations in one's diet.

Interestingly, different rice strains have markedly different GIs. Basmati rice, which has a high amylose (a type of starch) content, has a low GI. If rice is sticky and the grains clump together, it is likely to have a high GI factor because there is less amylose present. Rice that is drier with separate grains generally has a lower GI.

If people are eating a low fat diet and are physically active, the GI content of their diet is not such a critical factor. However, the GI becomes more important when dietary habits and physical activity levels decline. Insulin resistance worsens as people age and put on weight.

So when should high GI foods be consumed? Evidence shows that eating high GI carbohydrates (1g/kg body weight) within two hours of exercise speeds up the replenishment of glycogen stores and speeds up recovery time.

The avoidance of highly processed foods with high Glycaemic Index should be avoided as a general rule.

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