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The In's and Out's of Carbohydrates

Carbohydrates have been stigmatized in the last decade or so as being contributory to health issues, however there is often a lack of knowledge (of both food and carbohydrates) that coincides with these negative connotations. Common claims that saturate nutrition related conversations include:

"Carbohydrates turn into sugar in the body...leading to fat gain, neurological issues, cancer, etc"

"High carbohydrate diets are unhealthy/ low carbohydrate diets are healthy"

"The food pyramid (which uses carbohydrates as a base/majority of intake) is wrong and only benefits the food industry with subsidized crops being emphasized in the diet"

Before tackling these controversial topics, let's go through a review of what carbohydrates actually are:

In plants, solar energy is converted into a stored energy form via photosynthesis. (Nix, 2013) This stored energy form, known as carbohydrate (as in carbon+hydrogen+oxygen) is also classified as a saccharide (which means sugar). (Nix, 2013) These saccharides can be categorized as monosaccharides (one sugar), disaccharides (two sugars), or polysaccharides (multiple sugars). **These can also be referred to as simple sugars (mono- and disaccharides) and complex carbohydrates (polysaccharides).

Monosaccharides are the basic units of carbohydrates and they include:

  • glucose

  • fructose

  • galactose

while disaccharides include combinations of monosaccharides like:

  • lactose (glucose+galactose; found in milk)

  • sucrose (glucose+fructose; commonly known as table sugar)

  • maltose (glucose+glucose; often used as a sweetener)

Polysaccharides like starch and glycogen are highly branched chains of monosaccharides (glucose) that provide a high concentration of carbohydrate.

Dietary carbohydrates from all sources are broken down into their basic units (monosaccharides) for use in the body. Dietary carbohydrates come in the form of plant foods like vegetables, fruits, grains (and grain products), legumes (beans), tubers (potatoes), and sweeteners (honey, sugar, etc) and where lactose from milk is the only animal derived carbohydrate. The primary difference between these dietary sources is in the concentration of carbohydrates whereby starch is the densely packed storage form of carbohydrate in plants (think grains, tubers, legumes), and thus holds a higher concentration of carbohydrate than a non-starchy plant (like leafy greens). (Nix, 2013) Humans and animals store carbohydrate as glycogen in our liver (which is released into the blood for cellular energy) and skeletal muscles (for energy during physical activity).

**To satisfy your inner hippie, it's nice to emphasize the relationship between the environment, food and the human body where we require energy from plants (in the form of carbohydrates), and where that energy in plants originally came from the sun. You could argue that we are 'people of the sun'.

Similar to the amino acids being the building blocks for proteins, monosaccharides are the basic units of carbohydrates, and thus when carbohydrates are digested, they are broken down into these monosaccharides (sugars). So you could argue that yes, carbohydrates are broken down into sugars in the body; but note that there is a distinct difference between monosaccharides (glucose, fructose, galactose) compared to what we commonly think of when we hear sugar (table sugar/sucrose). I would bet that imaginations run wild with thoughts of carbohydrates turning into (table sugar) in the body like a caramel sauce flowing through the blood and saturating adipose (fat) cells, smothering neurons, and otherwise wreaking havoc. Obviously, this is not the case!

It is an unfortunate coincidence that sucrose (table sugar) and saccharides are both called 'sugar' as there are large differences between them, namely one is essential to life (saccharides; glucose specifically) whereas the other bears the brunt of negative press in the health world.

When I say that saccharides are essential to life, this is because glucose specifically is the primary fuel source for the cells of the body. As a fuel source, glucose is oxidized both anaerobically and aerobically to lead to ATP formation (cellular energy), of which is required for normal cellular functioning. (Gropper, et al. 2013) Glucose is so essential to cellular functioning, that there are metabolic processes devoted to forming glucose from other non-carbohydrate sources in cases where dietary or stored glucose (and subsequent blood glucose) is inadequate. Gluconeogenesis, or the formation of glucose from other non-carbohydrate intermediates, is essentially what maintains functioning when blood glucose is low (during sleep, periods of fasting/starvation, etc). Cells like the red blood cells, parts of the brain, and glycoproteins like the hormones thyroid stimulating hormone, follicle stimulating hormone, and luteinizing hormone require glucose and if there is an absence of adequate glucose in the blood, gluconeogenic processes will take over to convert other intermediates (amino acids, glycerol from triglycerides, and lactate) into glucose to be oxidized for energy or for glucose-specific work. (Gropper, et al. 2013) This is an adaptive mechanism for survival and maintaining adequate functioning during ebbs and flows of food intake (periods of feast and famine). **Whether or not taking advantage of these processes improves health and body composition will be a topic for another post in the near future.

What about the argument that too much 'sugar/carbohydrates' in the diet can lead to health problems?

First, let's define what is considered 'too much':

The current RDA guidelines suggest 45-65% of total daily caloric intake to come from carbohydrates. (Nix, 2013) If we were to use a standard 2,000 calorie diet, that would equate to 225g-325g carbohydrates every day. As a reference, there are roughly 15g carbohydrates in a standard slice of bread, or 45g in 1 cup of cooked rice. This guideline however proposes a wide range within which to fall, and where individual needs are going to vary largely based on activity level (energy expenditure), body composition and health status. In my opinion, most of the population would likely fall into the range of 40-55% of calories from carbohydrates (based on a 2,000 calorie/day diet, this would equate to 200g-275g carbohydrates per day) as being sufficient to meet their needs, with those who are more physically active near the higher end of the range compared to those who are less active near the lower end of the range. **These estimates of total carbohydrate intake would include all carbohydrates, not just starches, which means that yes, you would count vegetables and fruits into this total [Highly trained athletes, particularly those that are undergoing hours of exercise daily, are going to require greater amounts of carbohydrates (55-65% of calories) than the average population in order to restore their muscle glycogen, but this will all depend on the individual and their needs.] Again in my opinion, this carbohydrate intake (40-55% of total calories) would likely be best if comprised of mostly high-fiber whole food sources like vegetables, fruits, whole grains and legumes. However, high fiber whole food sources of carbohydrates are not always an easily digestible option, particularly for those who require higher amounts of carbohydrates to meet their increased needs (those with high amounts of physical activity like in multiple training sessions or multiple hours of training per day). Those that require greater total amounts of carbohydrates to meet their needs (like athletes) would have trouble physically eating and digesting such a large amount of fiber and could therefore benefit from including other low fiber carbohydrate sources in addition to their recommended fiber intake. Think of this as supplementary food.

So what happens if you consume more total carbohydrates than your needs?

After digestion, glucose is either oxidized for energy, or stored as glycogen in the liver and skeletal muscle. An excess of carbohydrates beyond storage capacity will then be converted into a glycerol backbone that can combine with fatty acids to form triglycerides that are stored in adipose cells. (Gropper, et al. 2013) I want to emphasize this last point: an excess that is beyond storage capacity; as in, the more storage capacity you have, theoretically the less likely you will end up with an excess that would then require conversion to glycerol for triglyceride formation. As with any of the macronutrients, too many total calories will result in net weight gain, regardless of whether those calories came from carbohydrates or not. (This is a survival adaptation where in times of feast, storage is preferred for excess nutrients as there could be a subsequent famine that would require this stored fuel.) But this also means that a low carbohydrate diet that is instead high in fat could also lead to weight gain if the total calories are above your needs. Hence: the carbohydrates are not specific to weight gain, but rather an excess of carbohydrates beyond storage capacity could be associated with increased triglyceride storage in adipose cells. (Gropper, et al. 2013) However, in regards to that glycogen storage capacity, those who USE a greater amount of skeletal muscle (as in physical activity like endurance training that depletes muscle glycogen stores) can in turn double their storage capacity for muscle glycogen and will preferentially store muscle glycogen as a training adaptation. (Jensen, et al. 2011) This change in storage capacity is exclusive to exercise (depleting muscle glycogen stores) whereas simply eating more carbohydrates (in the absence of glycogen-depleting exercise) does not increase this storage capacity and could instead lead to increased triglyceride formation. (Jensen, et al. 2011) This means that those who regularly utilize their muscles in exercise (and thus use the stored muscle glycogen) will then store more glycogen in those highly used muscle cells, which again could infer that they are less likely to convert any excess (if there is any) glucose into glycerol for triglycerides.

And why do the muscles prefer to use glycogen for energy during exercise?

As stated above, glucose (stored in the muscle as glycogen) can be oxidized both anaerobically and aerobically. However, regardless of the exercise being performed, there is a sequence of events in energy substrate utilization where the cell MUST go through anaerobic respiration (energy production in the absence of oxygen) before it can undergo aerobic respiration (energy production utilizing oxygen). To this point, even if you wanted to utilize aerobic respiration (like oxidizing fatty acids for long endurance events) you would still require that glucose-driven anaerobic respiration before the oxygen was even present in the cell for aerobic respiration. [Hence the phrase that 'fat burns in a carbohydrate fire']

But I hear that low carbohydrate diets are healthier? What if you consume less than the 40-50% range?

If the aim of 'eating healthier' is weight loss, then the overall goal should be a negative calorie balance. Interestingly, a recent study suggested that there was no significant difference in weight loss between a high fat/low carb diet compared to a high carb/low fat diet. (Veum, et al. 2017) In this study, a group of overweight and obese subjects were randomized to follow either a very low carb/high fat diet (10% of calories from carbohydrate, 73% of calories from fat) or a high carb/low fat diet (53% of calories from carbohydrate and 30% from fat). (Veum, et al. 2017) The diets were equal in total calories and protein and both emphasized less processed food intake and lower glycemic index foods. (Veum, et al. 2017) The results showed that the diets were both SIMILAR in reducing waist circumference, abdominal subcutaneous and visceral fat mass, total body weight and SIMILAR in improving blood lipids with reduced plasma triglycerides. (Veum, et al. 2017) What is notable however is that there were significant differences with the low fat/high carb group significantly decreasing LDL cholesterol, while the high fat/low carb group significantly increased HDL cholesterol, but the ratios of total cholesterol: HDL and total triglycerides: HDL did not change. (Veum, et al. 2017) What is the big takeaway from this? The groups both showed improvements because the previously overweight and obese subjects were now following a calorie-controlled diet that limited processed foods, regardless of whether the majority of calories came from fat or carbohydrate.

**When coming across the question of following a low carbohydrate diet for weight loss, my thoughts on the matter are based on the source of a caloric deficit. If you are increasing your physical activity with the goal of weight loss, then you will need to foster your new activity level with enough carbohydrates to actually fuel you for said activity. However if your goal is to lose weight without increasing (or starting) physical activity, then a caloric deficit in your diet will be sufficient, regardless of where the primary source of calories are coming from (high carb/low fat vs. high fat/low carb). You cannot cheat the system by forcing a caloric deficit from both increasing physical activity and decreasing caloric intake as too much of a negative calorie balance will trigger your innate survival mechanisms where your body will try to store everything it can (as an adaptation to avoid starvation in periods of famine). In my opinion, choose one or the other; increase your activity level, or decrease the amount of food you are eating. Personally, I love to eat. *

What about neurological functioning?

It has been well documented that very low carbohydrate diets (ketogenic diets) can reduce seizure frequency and therefore be therapeutic for epilepsy (possibly associated with a hyperexcitability of the hippocampus). (Gano, et al. 2014) But there are inconclusive findings regarding this efficacy for several other neurologic disorders including depression, schizophrenia, bipolar, ADHD and Alzheimer's disease as most of the current research in this area has been conducted on animals and can therefore not be extrapolated to the population. (Gano, et al. 2014)

I heard that cancer cells thrive on sugar. What about cancer and carbohydrates?

To be fair, all cells use glucose, both cancerous and non-cancerous. Most of the arguments behind sugar promoting cancer cell growth is typically associated with sucrose (table sugar) and fructose consumption. There are theories that increased fructose (as in the high concentrations present in high fructose corn syrup) may have an indirect role in propagating tumor cell growth, but fructose is also metabolized differently than glucose, and thus comparing the two as being synonymous would be shortsighted. (Das, 2015) *More on fructose metabolism in a future post

It is worth noting that a lot of the evidence of this relationship (between sugar intake and cancer) is based on observational studies where associations are drawn based on lifestyle trends, and not necessarily sugar intake directly. In one such study, sugar intake alone showed no association with an increased risk of colorectal cancer overall, however the combination of sugar intake in smokers showed a positive association with cancer risk, whereas the consumption of sugar in those who never smoked had an inverse relationship with cancer risk. (Wang, et al. 2014) Another study found associations with patterns of eating where adolescent and early adulthood eating patterns high in sugar-sweetened beverages, diet sodas, refined grains, red and processed meats and margarine but with LOW INTAKE of leafy vegetables, cruciferous vegetables, and coffee showed increased incidence of breast cancer up to 22 years later. (Harris, et al. 2017) Even more, those who were considered the most pro-inflammatory based on their adolescent lifestyles, were also noted to have been more physically inactive than the others, gained more weight than the other subjects over the years, and were more likely to use oral contraceptives than the others. (Harris, et al. 2017)

So what is the best amount of carbohydrate to have in the diet?

This will depend on the individual's needs (body composition, health status, activity level*) and on the concentration of carbohydrates in the diet (vs. the actual caloric intake). For instance, if we take a non-active person with an overweight BMI but who is otherwise metabolically healthy (non-diabetic, etc), they would likely benefit most from a carbohydrate intake that meets their energy needs (enough for normal daily functioning) coming from primarily high-fiber foods. Compare this to a person that is extremely active and with a high proportion of lean muscle to body fat, and this active person would need more carbohydrates to meet their daily needs (increased needs due to high energy expenditure) and where much of their carbohydrate is going to be stored as skeletal muscle glycogen to foster their physical activity. Due to the higher need for carbohydrates and the preferential storage largely in their skeletal muscle, this individual could theoretically include some refined carbohydrates in their diet in order to meet their needs without necessarily risking their metabolic health.

When it comes to the idea that high carbohydrate diets are unhealthy and specifically with finger-pointing to the food pyramid as being incorrect, we start to turn the corner towards a lot of conspiracy theories. The most common argument of the conspiracy theorists being that the government is to blame for today's most common health issues because they designed a food pyramid that emphasizes carbohydrates, and where diets that are high in carbohydrates lead to weight gain and metabolic issues, etc. Let's break this theory down:

The food pyramid that we all remember growing up with emphasized a base of plant-based carbohydrates like 6-11 servings of grains (called the bread, cereal, rice, pasta group), 3-5 servings of vegetables, 2-4 servings of fruit and then 2-3 servings from dairy (milk, cheese, yogurt), 2-3 servings of protein (meat, poultry, fish, beans, eggs, nuts) and sparse amounts of fats, oils and sweets. Now the primary concern from the conspiracy theorists is that the emphasis is placed on carbohydrates (and unfortunately, what constitutes a 'serving' is not made clear) but if we look at what we know about the body and it's primary fuel source, doesn't it sound logical to include a base of glucose-rich foods as that will be your primary fuel source? The one blatant flaw that stands out is the lack of guidance with regards to physical activity level and appropriate portion/serving requirements. Obviously, this type of recommendation is going to change from person to person based on what their needs are, but a generic recommendation of 6-11 servings offers way too much room for interpretation that an otherwise uninformed audience may misconstrue. (Technically, 'one serving' of carbohydrates is ~15g or 1/3 cup of cooked rice. If you have ever eaten at a Japanese steakhouse for example, the rice that comes with the meal is served in a bowl, roughly 1-2 cups worth. If we were to actually measure out a typically eaten portion of rice like 1-2 cups, that would actually equal 3-6 servings) Adding to that, there is a lack of properly defining foods where for instance most people do not know that there is a difference between cereal grains (oats, barley, rye, millet) and breakfast cereals (frosted flakes, cocoa puffs, etc) and so following the guidelines with their own interpretation is most likely to lead to less than nutritionally dense choices, and in amounts that may not be favorable for their body composition and activity level.

And for those who believe so strongly that the fat content is too low based on the food pyramid recommendations, consider this:

If you are eating regular diary products and protein sources, you are getting in adequate amounts of fat with your foods to the point that being sparse with your added fats and oils is totally acceptable. Think about the caloric (and fat) density of oils (1 tablespoon oil= ~14g fat, 120 calories) and then relate that to a portion size. All of sudden, being sparse with your added fats and oils sounds reasonable when you take into account the fat content of other foods you are already eating.

And if you think the protein suggestions are too low, consider this:

The recommendations include 2-3 servings of animal proteins in the form of meats (or plant proteins from dried beans and nuts) AND 2-3 servings of animal proteins in the form of dairy (think whey and casein proteins). Now it seems like you really are getting enough protein, as well as a solid base of glucose-rich carbohydrates to foster cellular energy production and a healthy amount of fats present in whole foods with some additional fats and oils used sparingly. Doesn't sound so disastrous to our health now, right?

Take from this what you will, but never stop learning.


Das U. Sucrose, fructose, glucose, and their link to metabolic syndrome and cancer. Nutrition. 2015; 31(1):249- 257.

Gano L, Patel M, Rho J. Ketogenic diets, mitochondria and neurological diseases. Journal of Lipid Research. 2014; 55(11):2211-2228.

Gropper S, Smith J. Advanced Nutrition and Human Metabolism. 6th edition. Wadsworth-Cengage Learning. 2013.

Harris H, Willett W, Vaidya R, et al. An Adolescent and Early Adulthood Dietary Pattern Associated with Inflammation and the Incidence of Breast Cancer. Cancer Research. 2017; 77(5):

Jensen J, Rustad P, Kolnes A, et al. The Role of Skeletal Muscle Glycogen Breakdown for Regulation of Insulin Sensitivity by Exercise. Frontiers in Physiology. 2011; 2:112.

Nix S. Williams' Basic Nutrition and Diet Therapy. 14th edition. Elsevier Mosby. St. Louis, MO. 2013.

Veum V, Laupsa-Borge J, Eng O, et al. Visceral adiposity and metabolic syndrome after very high-fat and low-fat isocaloric diets: a randomized controlled trial. The American Journal of Clinical Nutrition. 2017; 105(1):85-99.

Wang Z, Uchida K, Ohnaka K, et al. Sugars, sucrose and colorectal cancer risk: the Fukuoka colorectal cancer study. Scandinavian Journal of Gastroenterology. 2014; 49(5):581-588.

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