Enriched flour, the GI diet, and what to put on your sandwiches

On a forum that I belong to, one of the members recently posted a question asking why enriched flour wasn’t good for you. I put my science hat on and got a bit carried away with the explanation. Here is my answer, slightly modified in parts, and oversimplified in others, but I hope this clears up any questions you might have on the issue :

The issue with enriched flour is to do with the GI – glycemic index. To really appreciate what is going on here, I am afraid I am going to give you a chemistry lesson.

A ’saccharide’ is a sugar. A monosaccharide is a molecule made up of only one type of sugar. Examples of monosaccharides are glucose, fructose and galactose. A disaccharide has two sugar molecules linked together with a chemical bond. They can be two the same, like a glucose plus another glucose, which gives maltose. Or they can be made up of two different monosaccharides. Sucrose (table sugar) is a disachharide made up of one glucose bound to one fructose; and lactose (milk sugar) is a glucose plus a galactose. Anything with more than two sugar molecules bound together is a polysaccharide. All starches are polysachharides, and can contain hundreds, or even thousands of glucose monosacs joined together with chemical bonds.

Why this is important is that when you eat carbs, they need to be broken down by enzymes in your digestive system into their component monosaccharides before being absorbed. Only monosaccharides can be absorbed and thus released into your blood stream. The other stuff is too big to get in, to put it a little simplistically.

Obviously, if you were to eat pure glucose (or fructose) which are already monosaccharides, they do not need to be broken down further before being absorbed. Thus they are absorbed very quickly resulting in a rapid spike in your blood sugar levels. Your pancreas senses this sudden large surge in blood glucose and responds with a massive release of insulin which floods the blood stream and starts mopping up the glucose.

Glucose is absorbed into your liver and muscles, where it is converted to and stored as glycogen (lots of glucose molecules joined together). This is why if you are going to eat simple sugars, the time to do it is post exercise or first thing in the morning when your glycogen stores have been depleted. However your glycogen storage capacity is limited. Any excess above what you need to replenish these stores is converted to fat. Also, the big insulin release reduces fat oxidation (using fat as fuel, ie. fat burning) and increases fat storage.

Plus, because of the spike, and the overresponse of insulin, you tend to go too far in the opposite direction, causing too big a drop in blood glucose. This results in tiredness (mid-afternoon crash after a big carb lunch, for example), hunger and cravings, moodiness, etc. And do it too often, and the pancreas gets fed up, stops responding and/or your target organs become insensitive to the insulin in your system, failing to take up the glucose in your system and you develop type 2 diabetes.

SO, large surges in blood glucose are BAD. Right?

OK, the glycemic index is a measure of how quickly food is released into the blood stream, basically. It was originally developed for diabetics to help them keep their blood sugar on a more even keel and avoid peaks and troughs. Generally speaking, simple sugars (monosaccharides) have a high GI, ie. they are absorbed and released into your bloodstream very quickly. The more complex a carbohydrate, the more chemical bonds it has and the longer it takes to break down into component glucose molecules for absorption, and thus you get a slower, steady stream of glucose released into the blood over a longer period. This results in a more sustained energy release, without the peak and crash you get after eating simple sugars, and also insulin is released in a more appropriate, steady stream to deal with it. Therefore low GI is better than high GI. With me so far?

However, one thing to note about GI, is that it is measured for foods in isolation. Adding fibre to a carb slows down the digestion and absorption process, as does adding fat. This gives some odd results, like ice cream having a relatively low GI, so GI alone is not the whole story, from a health point of view. This is also the reason some diets tell you to avoid fruit – because the fructose is a simple carb (monosaccharide) and thus easily absorbed. Personally, I would avoid any diet that tells you to avoid fruit, unless there is a medical reason for it. There are so many good things in fruit – loads of vitamins, phytonutrients, fibre etc. Although this is one reason that whole fruit is better than fruit juice – losing all the pulp removes much of the insoluble fibre.

Obviously, a banana is better than an icecream, put add some (unsweetened natural) peanut butter, or a handful of almonds to slow down the glucose release and provide more sustained energy and prevent blood sugar swings and cravings.

Getting back to wholegrains, these contain, unsurprisingly, the whole grain – including the germ and bran. Processing of whole grains takes off the outer coating with all the fibre and most of the vitamins and begins the process of breaking down the carbs that would otherwise have had to be done in your gut. Thus, refined flour/white pasta/white rice etc, are more like simple sugars than complex ones – they result in a much more rapid release of glucose into the bloodstream (not to mention the reduced health benefits from the loss of fibre and vitamins). Enriched flour has had (some of) the vitamins put back. But other than that, it is still a processed carb and will react just like unenriched flour in terms of blood glucose. Thus enriched versions of refined carbs do not provide a better GI profile, although they do provide a few more vitamins and in that sense are better than the unenriched version.

Ideally, you should go for all wholegrains, preferably organic where possible, for maximum health benefits and best GI profile. I find that in many cases, the wholegrain tastes nicer and has a better texture than the refined version. But in situations where you simply cannot stomach the wholegrain version of the food (for example, I simply prefer white bread to wholemeal no matter how hard I try to eat the good stuff), improve (slow down) its transit time in your gut by getting one enriched with added back fibre and eating it with a healthy fat.

And then there was a follow up question:

Is a whole grain bread better for fat burning than the benefits of a low calorie bread?

And here is my answer:

To be honest, the difference in calories between a regular and a low-cal bread is not likely to be huge, and unless you eat a lot of bread, which I probably wouldn’t recommend anyway, is not likely to make a big difference in the long run. A whole grain bread, particularly if you get a seeded one (good for essential fats and additional protein) is likely to be a little higher in cals but provide slower release energy (i.e. keep you full for longer). Generally speaking, the calories you really need to worry about are the ones you put ON the bread.

So to answer your question, yes, whole grain is better. The slower release prevents the insulin surge which inhibits fat burning. It also is less likely to cause you to have a hypoglycemic binge on chocolate bars. Plus, the fibre is good for bowel health, heart health etc. Whole grains rule. However, if you can’t stomach the stuff, don’t force yourself to eat it. I usually go for a ‘best of both’ product which is a white bread with added fibre. I just prefer the taste. But I wouldn’t just put a sugar on it (like jam or honey). I use it for sandwiches with good quality protein as the filling. And I don’t eat much anyway. If I have one sandwich a week… On the other hand, I much prefer brown rice to white and only eat wholegrain pasta.

At the end of the day, once you understand the science and what different foods are doing to your body, then the choice is up to you but you can weigh up the pros and cons.