If we can work out how much energy we are giving the body, then we can get a handle on how much we should have before we start over-feeding ourselves. So the basic premise is, if the amount of energy in the diet is less than the output of energy from a person, then there is a deficit and the person must lose weight. But the way the body extracts energy from food is far more sophisticated and complex than this. If we were to find the way the body absorbs energy down to its lowest common denominator, we could isolate it to the action of a single hormone and that hormone would be insulin.
Insulin and carbohydrates
When we eat a meal, almost without exception, we will include carbohydrates - whether it is the bread roll that's wrapped around the salad you had for lunch, potatoes on the side of your plate while having your main course, or even the sugar that someone has added to your food to make it taste better. When we eat something that has carbohydrates, the body happily breaks it down to glucose to get what it needs. The average person has about 5 grams of glucose in their blood at any one time, and what is left over gets converted into glycogen, which is stored in the liver and muscle for later use. The body can convert glycogen back into glucose and re-release it if glucose levels fall, but there is only a limited amount that can be put away - when it has enough it then does a very peculiar thing of converting the remaining glycogen into fat. What this effectively means is you can eat carbohydrates that contain no fat, but a certain percentage of what you are eating will be turned into fat by the body. But before you start throwing out all the so-called healthy food in your kitchen, there's the other bit about fats contained in the diet.
Dietary fat and carbohydrate
When you eat something that contains fat, fat on its own does not raise your blood sugar levels. For your body to store it, blood sugar levels have to be raised and insulin released, i.e. fast releasing carbohydrates have to be consumed because without the carbohydrates, there will be no insulin, and without insulin the fat does not get pushed into the adipose tissue. So, essentially it's about insulin and blood sugar levels, and if there is a way of controlling blood sugar levels then we have a way to control insulin and, as a result, control what our body does with all the surplus energy we throw at it. Imagine if there was a way we could still eat yummy food but cleverly avoid any of it becoming storage or, even better, what if we could eat yummy food and actually make our bodies give up the fat that it had in storage and lose weight at the same time! Enter the world of glycemic index.
The glycemic index
When insulin is released and blood sugar levels start to fall, what is actually happening is the body has started converting excess sugars into glycogen and, eventually, fat. That has been the way the body has dealt with excess blood sugar levels since the time of creation. So what the GI tells, is that some carbohydrates were just like glucose and caused insulin to be released, some were just on the border line and some were so low it didn't matter how much one ate, it would never be enough to raise blood sugar levels. If we think of carbohydrates in terms of nourishment, then all carbohydrates are good, but if we are trying to control our weight, lower cholesterol, prevent diabetes, and prevent heart disease, then there are many carbohydrates that can be considered bad.
To continue next week...
Monika Seth/Nutritionist and diet consultant specialising in weight loss at Al Raffah Hospital