Controversial carbohydrates! How can some carbohydrates—fruits, sweet potatoes, whole grains, and beans— be considered “good” and other carbohydrates—flour, sugar, and corn syrup—be considered “bad?” Doesn’t our brain need daily carbohydrate for energy? If so, how do people eating low-carb diets get by?
Let's start with the basics . . .
What are carbohydrates?
Carbohydrates are sugars and starches. They are very simple molecules made out of carbon, hydrogen, and oxygen. All plants and animals can use carbohydrates for energy (and for building body parts and body chemicals).
What is the difference between sugars and starches?
“Sugars” are by definition very small. Glucose is a single-molecule sugar, or “monosaccharide.” Sucrose (table sugar) is a “disaccharide”, made of two molecules: one molecule of glucose plus one molecule of fructose (fruit sugar) linked together. Lactose (milk sugar) is also a disaccharide, made of one molecule of glucose plus one molecule of galactose linked together. These small sugars are sometimes referred to as “simple sugars.” Fruits are high in simple sugars.
“Starches” are big—they are made up of lots of simple sugars stuck together. Potato starch and corn starch are good examples. Starches are often referred to as “complex carbohydrates.” Most people are aware that grains, beans, nuts, seeds, and root vegetables are high in starches. However, animals also contain a small amount of starch that most people are less familiar with, called glycogen. This is a special starch designed especially for animals; plants do not contain any glycogen.
Storing sugar as starch
Humans store glycogen as an emergency source of carbohydrate. Glycogen is made of lots of glucose molecules linked together in short branches. If your blood sugar drops, or if you’re in an emergency situation and need fast energy, glycogen from the liver can be rapidly broken down into glucose and released immediately into the bloodstream.
The liver can only store somewhere between 250 and 400 calories worth of glycogen. (Glycogen is also stored in the muscles, but this glycogen is reserved exclusively for the muscles to use while exercising; it cannot be used to maintain blood sugar levels.) So, what does your liver do to make blood sugar if it runs out of glycogen between meals? It will turn to the protein in your muscles. The liver can turn muscle protein into glucose via a process called gluconeogenesis, which essentially means “making glucose from scratch.”
Why we store energy as fat
Starches are very dense and heavy. This is why we don’t store very much energy as glycogen—it would take up too much room and weigh too much. We store less than a day’s worth of energy as glycogen; the rest we store as fat.
Plants store their energy as starch, in thick, heavy roots and tubers and bulbs. That’s ok for them, because they don’t have to move, but imagine if we had to store all of our energy as starch—we’d have to carry around enormous lumps of carbohydrate—like gigantic potatoes growing underneath our skin—everywhere we went. And, if we overate and gained weight, the lumps would get so big and heavy that it would be impossible for us to move.
This is why animals like us, who need to move around, store energy as fat. Fat is much lighter and it is flexible, so it moves with us (ever try to bend a potato?). Plus, we can store lots and lots of it. There is a very low limit to the amount of glycogen we can store, but the amount of fat we can store is practically unlimited. (Just another clue that humans are designed to burn fat, not carbohydrate . . .)
Blood sugar regulation
All animals, including humans, have a simple sugar in their blood called glucose, which is also known as “blood sugar.” Glucose is used for fast energy by our cells. Because glucose is a monosaccharide (it exists as single molecules), it doesn’t have to be broken down—it is ready to burn.
It is critical that our blood sugar be kept in a very tight range for us to feel well and function properly. If blood sugar goes too high, we feel logey and foggy. Over long periods of time, high blood sugar (such as in untreated type 2 diabetes) can cause a variety of serious chronic health problems. However, if blood sugar drops too low, we are in immediate danger of serious consequences, such as seizure, coma, and death, because under normal circumstances, the brain requires some glucose to function.
Because tight blood sugar control is so important, we have a very sophisticated system for regulating it. If you eat a low-carbohydrate diet, your blood sugar levels tend to stay fairly even, but if you are like most people and eat carbohydrate throughout the day, your blood sugar will rise after you eat. It will rise even faster and higher if you eat refined or high glycemic index carbohydrates, such as sugar, flour, or fruit juice, because these types of carbohydrates are digested and absorbed very rapidly. How does the body manage these blood sugar surges?
How carbohydrates can make us fat
Let’s say you eat a popsicle. The simple sugars in the sweet popsicle are rapidly absorbed into your bloodstream, and your blood sugar quickly starts to rise. Since the body wants to harness that energy and prevent high blood sugar, your pancreas releases the hormone insulin into your bloodstream. Insulin lowers your blood sugar putting the body into sugar-burning, fat-storing mode. It literally turns off your body’s ability to burn fat so that excess sugar will be burned instead of fat. If your body has enough energy already and your cells don’t need to burn any more sugar, insulin tells the liver to turn the extra sugar into fat (lipogenesis), and then squirrels that fat away in your fat cells. That’s how sugar can make you fat.
Now, if you are not particularly carbohydrate sensitive, that may be the end of the story. You ate the popsicle, your blood sugar rose briefly, but insulin quickly took care of it, and now you’re fine. But what if you are carbohydrate sensitive? [To find out how carbohydrate-sensitive you are, take my free carbohydrate sensitivity quiz.]
Hypoglycemia and the invisible hormonal roller coaster
If you are carbohydrate sensitive (or have insulin resistance), you may have an exaggerated response to eating that popsicle. Not only does this mean that your blood sugar will rise more than usual, and stay higher for longer, it also means that your insulin level will rise more than usual, and stay higher for longer, causing your blood sugar to then drop too low or too fast. The body perceives this as a crisis, because it is very dangerous for blood sugar to drop too low.
So, there are other hormones that rush in to work against insulin and raise blood sugar. One of these is epinephrine, better known as adrenaline. Epinephrine raises your blood sugar by turning off insulin release and telling your liver to break down some of its emergency glycogen supply into glucose and release it into the bloodstream. Epinephrine is an ancient “fight or flight” hormone—it’s produced when we are in danger, such as when a saber-toothed tiger wanders into our cave. It is designed to give our bodies a surge of energy to help prepare us to fight or run away, but if we don’t use that energy to fight or flee, it just tends to make us feel panicky, shaky, agitated, and irritable.
The epinephrine reaction is responsible for most symptoms of “hypoglycemia”, which can occur within a couple of hours of eating sweet or starchy foods. Other hormones that are released to counteract insulin include glucagon (which may cause hunger sensations, headaches, and stomach upset), cortisol (our “stress hormone”), and growth hormone. These hormones work together to turn off your insulin response and return your blood sugar to normal.
For some people, this unstable pattern of rising and falling blood sugar is happening to some degree several times per day. Because most people eat refined and high glycemic index carbohydrates every day, they may not be aware that their daily cycles of moodiness, hunger, and physical discomfort are tied to this invisible hormonal roller coaster.
Why do carbohydrates make some people sleepy?
Many people feel sleepy after they eat or drink carbohydrates. It is not unusual to look around the dinner table and find people nodding off after dessert, or wanting to take a nap after a big starchy holiday meal. Why would that be if sugar carbohydrates are supposed to give us energy?
Relatively new research (conducted in mice) suggests that this effect may be due to a specialized group of brain cells called “orexin/hypocretin” neurons. These cells are responsible for alertness, and they appear to be turned on by proteins and turned off by carbohydrates.
How much carbohydrate do we need to eat?
Once we are weaned from breast milk, we can live a whole lifetime without eating a single molecule of carbohydrate:
"The lower limit of dietary carbohydrate compatible with life apparently is ZERO [my emphasis], provided that adequate amounts of protein and fat are consumed.”
“There are traditional populations that ingested a high fat, high protein diet containing only a minimal amount of carbohydrate for extended periods of time (Masai), and in some cases for a lifetime after infancy (Alaska and Greenland Natives, Inuits, and Pampas indigenous people). There was no apparent effect on health or longevity. Caucasians eating an essentially carbohydrate-free diet, resembling that of Greenland natives, for a year tolerated the diet quite well. However, a detailed modern comparison with populations ingesting the majority of food energy as carbohydrate has never been done.”
—Institute of Medicine and the Food and Nutrition Board 2005. Dietary Reference Intakes for Macronutrients. National Academics Press
Doesn’t the brain require glucose to function?
Well, yes . . . but:
- The brain doesn’t need very much glucose. Depending on circumstances, the brain needs between 30 and 130 grams (1/8 cup to 1/2 cup) per 24 hours.
- The brain can burn other fuels besides glucose—it can burn ketones (which are made from fat) and lactate (which is created by working muscles).
- Your liver can make all the glucose your brain needs out of protein. This process is called “gluconeogenesis,” which means “making sugar from scratch.” You don’t have to eat sugar to make blood sugar.
How might carbohydrates cause common diseases?
There is growing interest in and scientific momentum behind what is called “the carbohydrate hypothesis of disease.” This is the idea that most diseases of civilization are caused by our so-called “Western” diet, and that the ingredient in the Western diet that is most dangerous is refined carbohydrate. The diseases on this list include:
- Type 2 diabetes
- Coronary artery disease
- Cancer of certain kinds
- Hypertension (high blood pressure)
- Alzheimer’s disease
- Peripheral vascular disease
As a psychiatrist, I strongly suspect that the modern diet is a major culprit in many common mental health disorders, as well. I encourage you to read my blog posts about low-carbohydrate diets and bipolar disorder and the role of sugar in ADHD.
There have been numerous traditional human societies, which have eaten diets high in carbohydrate and have been healthy; however the types of carbohydrates in these diets were unrefined and tended to be low in glycemic index. Therefore, we will focus on the role of refined and high glycemic index carbohydrates in disease. For the sake of efficiency, let’s refer to them as “fast carbs.” I will be writing more about the potential dangers of fast carbs in the future, but for now, here are just a few important ways that they could raise our risk for serious diseases.
Advanced glycation end products (AGE’s)
Fast carbs raise blood sugar levels, and excess blood sugar can bind to vital proteins, DNA, RNA, and fats in the body and damage them, sometimes beyond repair. This process is called “glycation”. Think of it this way: sugars make proteins sticky. Proteins are supposed to be able to fold and move in special ways to perform their various special functions, but they can’t do that if sugar is gumming up the works. When sugars bind permanently to proteins, they turn the proteins into nuisance compounds called “Advanced Glycation End Products” or AGE’s. AGE’s have been linked to a wide variety of chronic diseases, including heart disease, kidney failure, diabetic retinopathy, Alzheimer’s disease, and aging.
Carbohydrates and oxidative damage
Fast carbs are “pro-oxidants.” This means that they have the power to damage important body molecules, such as DNA, by stealing their electrons away from them. Pro-oxidants are the opposite of anti-oxidants; they fight against each other. In a healthy body, pro-oxidants and the antioxidants are in balance. However, most of us are out of balance, most likely due to our Western diet, which is very high in pro-oxidants, such as refined carbohydrates. We are told all the time that we need to eat foods high in antioxidants but we are never told that we are supposed to avoid foods that are high in pro-oxidants! Perhaps if we weren’t eating so many pro-oxidants, scientists wouldn’t think we needed to add anti-oxidants to our bodies. [Read my post on Psychology Today, "The Antioxidant Myth" to learn more about this.]
Oxidative damage caused by pro-oxidants such as sugars can be the first step towards serious problems, such as cancer (by damaging DNA) and heart disease (by oxidizing cholesterol).
Carbohydrates and inflammation
Both glycation and oxidation trigger inflammation in the body. Physicians and scientists have come to understand that most common chronic diseases are rooted in inflammation. This is not necessarily the kind of inflammation we can see or feel—it is usually on a much smaller scale that we may not be aware of. For example, the cholesterol plaques that block arteries to the heart and cause heart attacks are found to contain all the mini-markers of inflammation when you look at them under a microscope. Even diseases such as depression are associated with mini-markers of inflammation. [You can learn more about inflammation and mental illness in my Psychology Today post]
Bottom line about carbohydrates
It is completely unnecessary to eat any carbohydrate once you are old enough to eat solid food.
Rapidly digested carbohydrates such as sugar and flour have the potential to disrupt our hormonal rhythms, our appetite regulation mechanism, and our internal pro-oxidant/anti-oxidant balance. They put us at risk for chronic inflammatory diseases, mood instability, and obesity.
Because carbohydrates are completely unnecessary, it would be wise to consider substantially reducing the amount of carbohydrate in your diet, especially refined and high glycemic index carbohydrate.
I’ve given you a lot of information about carbohydrates to digest guilt-free, but don’t want to leave you hanging. The following suggestions include both further reading and practical help to implement changes in your diet if you choose to reduce your carbohydrate intake.
I recently wrote a series about fructose and glucose metabolism and insulin resistance that further explores some of the information mentioned above.
- "Has Fructose Been Framed" takes a more detailed look at how the liver processes glucose and fructose.
- "Why Sugar Is Bad for You: A Summary of the Research" more closely examines how insulin resistance contributes to major chronic illnesses such as diabetes type 2, cancer, high cholesterol, heart disease, fatty liver disease, gout, and obesity.
- "How to Diagnose, Prevent, and Treat Insulin Resistance" provides valuable tips on how to determine if you are insulin resistant (including a downloadable pdf with medical tests that you can discuss with your health care provider), guidelines for how many carbs are safe to eat based on your health status, and an infographic with tips for increasing insulin sensitivity.
- I wrote an entire post about carbohydrates and the hormonal roller coaster for Psychology Today: "Stabilize Your Mood with Food."
You may also want to take the carbohydrate sensitivity quiz to get a sense of your personal level of carb sensitivity and if you are considering trying a low-carb or ketogenic diet, my "Ketogenic Diet 101" post is full of practical tips and resources that you may find helpful.
If you have questions or stories about your personal journey, please share them in the comments section. And if you know others who would benefit from this information, please share this page on your favorite social media site. Hope to see you in the comments!