So how exactly does the human body digest carbohydrates, and why exactly are large amounts of carbohydrates unhealthy for humans? A great guide, if you are interested in more in-depth information, is Robb Wolf’s book The Paleo Solution. But in a nutshell, carbohydrates can be roughly divided up into three categories: monosaccharides, disaccharides, and polysaccahrides. Monosaccharides (mono meaning one, and saccharide meaning sugar, so literally ‘one sugar’) are the simplest carbohydrates, and can enter the blood stream directly and immediately. Disaccharides (literally ‘two sugars’) must be split into their two constituent parts at the top of the intestine. Table sugar, or sucrose, is perhaps the most common example of a disaccharide, which is split into glucose and fructose by the body. Finally we have the polysaccharides, or the ‘complex carbohydrates,’ as many health gurus have touted them. But polysaccharides, if you translate their name literally, are many sugars. That is exactly how they enter the human bloodstream. All carbohydrates are reduced to a single molecule, absorbed through the intestinal wall, and absorbed into the bloodstream. Once broken into its constituent parts, polysaccharides enter the system like any other simple carbohydrate: as lots and lots of glucose and fructose, in other words, sugar. The only benefit to these complex carbohydrates is that they are absorbed at a slightly slower rate, so they will produce a less dramatic sugar ‘high,’ followed by a less dramatic sugar ‘crash.’ The insulin response may not be as sharp, but it is still there.
So what are the effects of sugar on the human body, whether derived from mono-, di-, or polysaccharides? Sugar stimulates a stress reaction that causes adrenaline and cortisol release, thickens the blood, decreases the body’s production of the satiety hormone leptin (so you feel hungry even though you just ate), induces significant oxidative stress in the body, promotes inflammation (which is linked to a host of ailments, including heart disease, stroke, and dementia), disrupts the effective transfer of amino acids to muscle tissues, and promotes fat storage and weight gain.
Over time, high sugar intake spurs insulin resistance, subsequent Type II diabetes, and an entire host of related health issues like nerve damage and cardiovascular disease. When you eat sugar, your blood sugar levels rise. Then your pancreas releases insulin to help move sugar from your blood into your cells. As blood sugar levels go down, your insulin levels return to normal. However, over time, it takes more and more insulin to get the job done. Eventually the pancreas wears out and may become less effective at lowering blood sugars.
The worst offenders are, of course, refined or white sugars. Even in moderation these substances spike insulin levels, and they provide no nutrients whatsoever to the body. White bread, white flour, white pasta, white rice, and potatoes all release their sugars very rapidly in the body. These foods raise blood sugar more quickly even than putting table sugar directly on your tongue. Processed, high-glycemic carbs are a greatest problem. Sugar is an addictive drug, and when we eat high-glycemic meals on a regular basis our bodies begin to demand them.
Does this mean that we ought to avoid carbohydrates altogether? I do not believe it does. If you look at my day of eating in harmony with evolution, you will notice that I consumed a fair bit of carbs. You will also notice that all of the carbs I consumed came from fruits and vegetables (yes, ten servings in one day), which contain vitamins, minerals, phytonutrients, and antioxidants, and digest more slowly (thus provoking less of an insulin response) than processed or refined carbs.
I believe that an excellent, down-to-earth suggestion of how many carbs we should be eating for optimal health is Mark Sisson’s Primal Carbohydrate Curve. In my day of primal eating I consumed 109g of carbs (26g of which were fiber, so 83g net carbs). I was able to get a full ten servings of fruits and vegetables and still remain comfortably in what he terms the “Primal Sweet Spot” for healthy functioning of the human body. The USDA food pyramid, on the other hand, recommends 150-300g of carbohydrates every day, coming mainly from bread, pasta, and rice products, which produce a much more dramatic insulin spike and contain much poorer nutrition – and the nutrients they do contain are more often than not present only because these products have been fortified at some point during their (heavy) processing.
And how does this all relate to nutrition during pregnancy? Most obviously, a generally healthy and fit woman is going to be a healthy and fit mother, and provide a healthy, nourishing environment for her baby during the nine months of gestation. It is also worthy of note, however, that women have an increased insulin response during pregnancy (to create fat stores for the baby and to divert nutrients to him or her to encourage growth). This increased insulin response means that excess carbohydrate intake will have an even more dramatically negative impact on a woman when she is pregnant, and on her baby as well. Following the high-carbohydrate, bread-based diet advocated by the USDA does not encourage maternal or fetal health, but rather puts a baby on the road to sugar addiction and insulin resistance.