By Laura Mack
March 16, 2016
There’s a lot in the news lately about sugar and it’s various substitutes. Boy, oh, boy, is it confusing! I’m a non-expert layperson, but I’ve done quite a bit of research in order to choose an approach that feels best for me. My goal in this post is to briefly summarize the information that I’ve found useful.
The human body does not need dietary sources of sugar to survive. That said, we seem to be genetically programmed to be drawn to the taste of sweet things. That programming undoubtedly served a useful purpose in the evolution of man. In the modern world, however, it appears that we would be perfectly healthy if we never consumed anything sweet.
Sugar is the sweet siren we hate to love, as well as the villain we love to hate. Sweet foods, whether in the form of natural fruits and vegetables or from confections with added sugar, have been part of the human experience for a very long time. Do we need to give up sweet things entirely? Probably not. Consider the old saying, “The dose makes the poison.” With regard to sweet foods, a safe dose is going to vary from person to person and appears to be largely a matter of opinion.
When we hear the term “sugar,” we tend to think of table sugar. Table sugar is sucrose derived from sugar cane, sugar beets, and sugar maple. Fruits and vegetables also contain sucrose. So, if fruits and vegetables are healthy, how could the sucrose from them be harmful to us? Whether it’s harmful or harmless seems to depend on a number of factors in addition to the dose.
Sucrose = Glucose + Fructose
Sucrose is essentially comprised of two linked simple sugar molecules, glucose, and fructose. Our bodies convert most of the carbohydrates we eat into blood glucose, also called blood sugar.
Glucose from the foods we eat is used for energy (either immediately or stored as fat for later). Insulin is a hormone we secrete largely in response to rises in blood glucose and helps the glucose enter our cells to be used for energy.
What about fructose? Is it better than dietary glucose? Not necessarily. Our bodies use fructose differently than glucose. Glucose is used first by our bodies over fructose as an energy source for our muscles and brain. “Unlike glucose, [fructose] does not cause insulin to be released or stimulate the production of leptin, a key hormone for regulating energy intake and expenditure.” While this could be viewed as beneficial because excess blood glucose and insulin are the underlying basis of diabetes, “…the body will use glucose as its main energy source and the excess energy from fructose, if not needed, will be poured into fat synthesis, which is stimulated by the insulin released in response to glucose.” [1]
To put it succinctly, dietary glucose will increase our insulin and blood glucose levels, and any excess (more than we need for immediate energy) will be stored as fat. However, excess fructose is even more lipogenic (fat-producing) than glucose, especially in the liver, which can lead to fatty liver disease. It also causes more fat in the blood (triglycerides), which can contribute to heart disease.
The sucrose in fruits, vegetables, and added sugars (all forms, including table sugar, honey, maple syrup, agave, molasses, coconut sugar, fruit juice, high fructose corn syrup, etc.) have differing proportions of glucose and fructose. The glucose to fructose ratio, along with any accompanying fiber, influences the “glycemic index” (GI) value. (The Glycemic Index is a tool that was developed to measure how quickly blood glucose levels respond to a particular food.) Added sugars, as well as natural sugars (including plant foods), that have a greater proportion of fructose to glucose tend to have a lower GI than those with more glucose to fructose.
Lactose = Glucose + Galactose
Lactose, a sugar found primarily in milk and milk products, is made up of glucose and another simple sugar molecule known as galactose. Galactose and glucose are metabolized in much the same way, so lactose does have an effect on insulin and blood glucose. Galactose is less sweet than glucose and fructose, however, so the GI of milk products is generally lower than foods containing sucrose.
Limited Usefulness of the Glycemic Index
A slower blood glucose response as a result of consuming foods with a low GI value is beneficial to reduce spikes. It’s important to note, however, that the glucose in the blood must eventually be processed by the body, either used immediately for energy or stored for later as fat. That is, there is still a blood glucose response — it is simply more spread out over time. Reducing the blood glucose response altogether (by limiting the intake of foods that raise blood glucose, even low GI foods) is important, especially for those with diabetes, pre-diabetes, or any degree of insulin resistance and blood glucose impairment. If a food contains carbohydrates, there will an increase to insulin and blood glucose.
Furthermore, what is often missing in the discussion of the Glycemic Index is the recognition that a low GI value doesn’t necessarily mean that a food isn’t delivering excess fructose. Consuming more fructose than we should, as we now know, leads to unhealthy fat storage and contributes to abnormal triglycerides (blood fat) and fatty liver.
Natural Sugars vs. Processed Sugars
Similarly, fruits and vegetables are natural sources of sucrose. Consuming them will raise insulin and blood glucose. That doesn’t mean that most people cannot consume them as part of a healthy diet. However, as with added sugar, the type and the dose influence the outcome, as does the individual’s tolerance and health goals.
Two people can eat the same amount of the same food — carrots, for instance — and have different insulin and blood glucose response. One person may find that they can eat an average portion (1/2 cup) of carrots without any noticeable effect. The other may find that it raises their blood glucose, kicks off cravings, slows their weight loss, or interferes with their weight maintenance. They may need to eat a smaller amount of carrots less frequently in order to reach their blood glucose or weight goals. That’s why it’s not unusual for low carb or ketogenic diet plans to suggest that people limit the quantities of certain vegetables and fruits, or avoid certain ones altogether.
For instance, starchy vegetables (below the ground) and legumes are typically discouraged on low carb/ketogenic diets. So are most fruits, with perhaps the exception of small quantities of berries occasionally. While there are useful vitamins, minerals, and fiber in those foods, the metabolic consequence for some people is prohibitive. Plus, there are usually other available food sources with similar nutritional benefits, but without the negative metabolic response. The same can be said of starchy grains, such as wheat, corn, rice, and oats. Whole grains don’t contain sucrose, their starches are converted to glucose in the body and have a similar effect on insulin and blood sugar.
What’s the Right Dose for You?
It can be a challenge to determine what level of sugar (carbohydrates) works for you, given the state of your metabolic health and your health goals. For instance, I found that I needed to consume a lower number of carbs when I was still in weight-loss mode compared with now that I am in maintenance. Deb and I have discovered that certain foods can kick off cravings for us, despite the fact that the carbs aren’t any higher than some other food that doesn’t cause a problem. Because there’s no one-size-fits-all solution, it requires experimentation to find your sweet spot (OK, pun intended!). Whatever the reason, Deb and I don’t seem to have a very high threshold for carbs. For example, to lose weight, 20 net carbs or under is where I need to be. For maintenance, I seem to do okay at 20-30 net carbs. (We substract dietary fiber from our carb counts to determine “net” carbs; some people count total carbs. Expert opinions vary, but net carbs works for us.)
So, what’s left for those of us who need to severely limit the sources of natural and added sugars, as well as starches, in our diet? Some people will find that they can manage quite well with virtually eliminating sweet and starchy foods. Others, like myself and Deb, have found that there are natural low carb sweeteners that can help stave off feelings of deprivation while still moderating blood sugar responses. As with regular sugars, there are pros and cons to each type of sweetener and individual results may vary.
Next week, I’ll talk about some of the low carb natural sweeteners available, what’s worked for us, and how they might fit into your healthy low carb/ketogenic way of eating.
[1] http://healthyeating.sfgate.com/difference-between-sucrose-glucose-fructose-8704.html
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