This is the first of three posts looking at the main macro nutrients we need: carbohydrates, fats and protein. I joked to a friend that one of my goals for 2012 was to make people realise that “sugar is the enemy”. So far I’ve not done much about it, but hopefully this will go some way towards rectifying that fact ;) Also, the three posts will act as a precursor to further posts looking at more specific diets – hopefully these will lay the groundwork and provide some context for those.
So, why’s it so bad?
The body has an in-built mechanism to keep blood sugar levels stable – the pancreas releases insulin which helps transport glucose into cells to be used for energy. If we are active, this glucose would go to muscle cells to provide the energy to fuel our activity, however for people with sedentary lifestyles, most of it goes to fat cells to be stored as fat.
As well as this, there is another bad effect – when we eat sweet foods (those with a high GI – glycaemic index – explained below), the sharp spike in blood sugar causes a dramatic increase in the amount of insulin released. Since the spike in blood sugar is metabolised quicker than the insulin in the blood, excess insulin remains after the blood sugar spike subsides. This excess insulin has a detrimental effect on a range of bodily functions:
- Increases LDL (“bad”) cholesterol and lowers HDL (“good”) cholesterol – excess insulin causes your cells to produce LDL cholesterol, rather than consume cholesterol present in the blood stream, thus elevating LDL cholesterol. Tests show that HDL cholesterol levels of patients with excess insulin levels are reduced. CITATION
- Increases blood pressure – high insulin levels cause the kidneys to produce angiotension, which increases blood pressure.
- Leads to higher “free-estrogen” levels in the body, which has been linked to accelerating breast cancer in women. It should be noted that this is of particular relevance to women who have hormonal problems. For example, it is interesting to note that Metformin (link), one of the main drugs prescrbed to those who have been diagnosed with Polycyctic Ovary Syndrome actually works by stabising blood sugars.
- Leads to diabetes – Over time this excessively high level of insulin can cause the “insulin-receptors” in our cells to become less sensitive to insulin, resulting in a condition called “insulin resistance”, which leads to the onset of diabetes.
- An insulin-resistant patient may not develop diabetes (because the pancreas continues to produce sufficient insulin) but, instead, acquires a condition called “hyperinsulinism” (abnormally high levels of insulin in the blood), which can cause chronic obesity as well as high blood pressure, high levels of triglycerides, low HDL (good) cholesterol, heart disease, and possibly some cancers.
- Is linked to Alzheimer’s disease – According to a study published in August 2005, moderately elevated levels of insulin increase the levels of inflammatory markers that may contribute to Alzheimer’s disease (link)
And these are only a few of the main points – a quick google will list thousands more. I did have some links to share, but they’re on my laptop which is temporarily dead, so you’ll have to look yourself if you’re interested :P
Glycaemic Index (GI)
You’ve probably heard about this concept before, but here’s a quick explanation:
GI scores are allocated to carbohydrates based on how much blood glucose rises after consuming a particular food over a two hour period. This is compared to a reference food, usually glucose (pure sugar), which is given a score of 100.
For instance, if you consumed 50 grams of glucose, you’d get a dramatic elevation in blood sugars, but it you consumed 50 grams of carbs in the form of apples, which have a score of 40, your blood glucose would rise only about 40% as high, compared to glucose.
Here are a few examples of common foods and their scores. Note the differences between different types of fruit, cereals, pulses and brown and white rice:
Instant rice 87
Baked potato 85
Corn flakes 83
White bread 70
Brown rice 55
Sourdough bread 52
Baked beans 48
All bran 42
So, why eat low GI?
When you eat a substantial quantity of high GI food, the amount of insulin released is so large that not only does it disperse the food-glucose we have just eaten, it disperses a lot more. The result? Our blood glucose falls too low. So, within a short time the brain tells us we’re hungry and we recommence eating. This rapid rise and fall in blood glucose, caused by excess production of insulin, is not good for our health or our eating habits.
Foods with a lower GI will leave you feeling fuller for longer. Oats are a much better choice for breakfast than, say, corn flakes, pulses a better choice for lunch than pasta, and steamed vegetables better for dinner than white rice. They will keep your blood glucose levels stable, thus avoiding the swings in insulin and the problems outlined above, and also avoiding the gnawing hunger that follows those afternoon chocolate biscuits you had with your cup of tea.
Protein, fat and deception
Neither protein nor fat have a GI score – they do not contain any sugars which affect insulin or any of the other metabolic processes related to carbohydrates. What they do, however, is slow the absorpion of any carbohydrate that they are eaten with. So ice cream, despite being very sweet, actually has a relatively low GI. And sweet barbecue sauce actually has a lower GI when consumed with a pork chop than it does if you were to eat it on its own off a spoon.
This has been quite a simplictic explanation, because (like everthing!) there is a lot more to it. GI isn’t perfect – it doesn’t actually look at the percentage of carbohydrate in a foodstuff, nor at portion size, but hopefully it’s given you enough information to think about.