Arguably the most misunderstood macronutrient, carbohydrates can be classified as either simple or complex. What leads me to label them misunderstood? Simple. There has been a lot of confusion in the past and still to this day, about what a carbohydrate is and the effect it has on one's weight. Lets take a look at how public perception about carbohydrates has changed over the years:
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| International Food Information Council (IFIC) Food and Health Survey (2006-2013) |
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| 2018 Food and Health Survey |
The information in the graphs' was collected as part of the International Food Information Councils annual health and food survey. The top graph shows that in 2011, only 9% of participants believed carbohydrates led to weight gain, as opposed to 25% in 2018.
So what's the deal; are carbohydrates the main reason why America is land of the free and home of the obese? First lets make sure we have a good understanding of just what a carbohydrate is.
The carbohydrate group contains sugar, starch, glycogen and fiber. Simple carbohydrates (sugar) include monosaccharides and disaccharides; Complex carbohydrates (starch, glycogen and fiber) include oligosaccharides and polysaccharides.
Common carbohydrates include grains (such as grits and rice), fruit, vegetables, bread and milk products.
Are All Carbs Created Equal?
The short answer is no. Different carbohydrates affect our bodies blood glucose levels differently. Hyperglycemia is defined by a fasting blood glucose (BG) rate of 125 mg/dl ( milligrams per deciliter). The glycemic index (GI) is a resource that ranks the extent to which blood glucose spikes post-cibum (after food), compared with a reference item such as pure glucose. Carbs such as: bread (white or wheat) cookies, white potatoes and bananas, are considered high glycemic-index foods. High glycemic-index foods have a score of 70 or higher on a scale from 0-100. (Note: glucose represents 100.) Low glycemic index foods include: sweet potatoes, pasta, beans and ice cream; these have a score of 55 or less. You can find many different GI tables on the internet but the most complete is the International table of glycemic index and glycemic load values. Here you can find two tables with over 2000 different foods, composed of research from over 200 studies.
The glycemic load is another tool that can be used to estimate carbohydrates effects on blood glucose. It is equal to the glycemic index times the grams of carbohydrate in a usual serving of the food. Many consider the glycemic load to be more useful because it takes into account both the quantity and quality of carbohydrates. With that being said, it is important to keep in mind that many health professionals shy away from recommending the use of either the glycemic index or load. The reason is due to variations between glycemic values and lab values for common foods. Some factors influencing these differences include: temperature, meal composition, and glucose tolerance of the person.
Simple Carbohydrates:
Monosaccharides
- Glucose- The most plentiful simple carbohydrate that exists, glucose molecules combine to form disaccharides and polysaccharides. Also referred to as dextrose or blood sugar, glucose plays a key role in energy metabolism in the body.
- Fructose (also known as levulose, sweetest of all sugars)
- Galactose (forms lactose)
Disaccharides
- Maltose (Contains two glucose molecules)
- Sucrose ( Glucose + Fructose)
- Lactose ( Glucose + Galactose)
Note: saccharide is another term for sugar. Thus, monosaccharide means one sugar molecule and disaccharide means two sugar molecules. Glucose is the most abundant carbohydrate or simple sugar that we consume. In the body, glucose is used for energy and excess amounts can be stored for future use. The sugars talked about so far are naturally occurring and are not the same as added sugars which will be covered later.
Complex Carbohydrates:
Two oligosaccharides of note are raffinose and stachyose. Both are indigestible carbohydrates commonly found in beans, cabbage, broccoli, and whole wheat. Because they are indigestible, after finding their way into the large intestine they are metabolized by bacteria and eventually lead to flatulence.
Why are some carbohydrates digestible and others not? Lets compare polysaccharides of differing digestibility: starch, glycogen, and fiber.
Digestible
Starch is the number one digestible polysaccharide that we consume. Two types of starch-- amylose and amylopectin, are made up of glucose units linked by alpha bonds. Amylopectin causes blood sugar levels to rise swifter than amylose due to the former's branched chain molecular structure. Common starchy foods include: beans, pasta, bread, rice and potatoes.
Glycogen is another form of digestible carbohydrate. Due to its highly branched nature, glycogen has the ability to be broken down by enzymes and stored in cells. Around 90 grams (360 calories) of glycogen can be stored in the liver, while 300 grams (1200 calories) can be stored in muscles. Similar to starch, glycogen contains numerous glucose pieces combined with alpha bonds. This connection with alpha bonds is what makes these two polysaccharides digestible.
An important distinction between the two is that starch is the storage form of carbohydrates for plants while glycogen holds that same role for humans and animals. To put simply, excess glucose is stored as glycogen in our bodies and stored as starch in plants.
Indigestible
The primary indigestible carbohydrate that we consume is fiber, which we get strictly through plant foods. Recommendations for fiber intake vary based on gender and age. The most current include roughly 34 grams per day for men ages 19-30, and 28 grams for women in that same age range. The amount needed for both genders decreases by about 6 grams per day once 51 years of age is reached.
Glycosidic bonds are the bonds that connect glucose molecules in complex carbohydrates. The reason why fiber can not be completely digested is because its molecules are linked by beta bonds. Surprisingly, beta bonds are much stronger than the alpha bonds that link glycogen and starch glucose molecules.
People who are lactose intolerant do not have enough lactase enzymes to break the beta bonds that link the glucose and galactose molecules. This inability to completely digest lactose leads to stomach aches and gas.
Health Benefits of Fiber
Table 1
| Disease | No. of subjects (no. of studies) | Relative risk† | 95% CI | Reference |
|---|---|---|---|---|
| Coronary heart disease | 158,327 (7) | 0.71 | 0.47–0.95 | 24 |
| Stroke‡ | 134,787 (4) | 0.74 | 0.63–0.86 | 1,2,27,28 |
| Diabetes | 239,485 (5) | 0.81 | 0.70–0.93 | 23 |
| Obesity | 115,789 (4) | 0.70 | 0.62–0.78 | 64 |
This table taken from the Nutrition Review, "Health benefits of dietary fiber", shows the relative risk for four diseases associated with one's diet (specifically fiber). Relative risk is defined as, "the risk of an event in an experimental group relative to that in a control group." A relative risk (RR) value equal to 1.00 shows that risk is comparable in each group. A value higher than 1.00 highlights increased risk, while a value lower than 1.00 presents decreased risk. The RR values in the above table were calculated by variance weighting and have also been modified for demographic, dietary, and non dietary circumstances.
The CI column is showing us the confidence interval which lets us know that 95% of the average population tested falls within these amounts. The CI values for each of these four diseases show the quintile range of participants. A quintile represents 20% of a population divided into 5 equal parts. The higher CI value is the experimental group (those with high fiber intakes) while the lower value serves as the control group (those with lower fiber intakes). Experimenters were looking to see if consuming more dietary fiber improved one's odds of developing a disease. In regards to coronary heart disease, participants in the fifth quintile (0.95) were compared with participants in the third quintile (0.47). So know that we have a basic understanding of what this table show us, lets dive into the numbers.
In the first row, we can see that for coronary heart disease 158,327 subjects were involved across 7 cohort studies. The RR value was computed at 0.71 and as we learned earlier, this means that the risk is lower in the experiment group. Now, we can take that RR value of 0.71 and subtract it from 1.00 (which is equal to 100 mathematically) and obtain the percent differential between the experimental and control group.
Remember, the purpose of these studies was to see if there was any link between the amount of dietary fiber consumed and susceptibility of one of the four diseases listed. We can thus conclude that the risk of coronary heart disease is 29% (0.71 - 1.00) less prevalent in participants with the highest intake of fiber compared to those with the lowest intake. From table 1 we can similarly see that the risk prevalence for the remaining diseases drops significantly as fiber intake increases. The risk of having a stroke drops 26% when comparing the highest intake of fiber (0.86) and lowest (0.63).
Table 2
Effects of soluble fiber intake on serum LDL-cholesterol values in randomized, controlled clinical trials with weighted mean changes based on number of subjects
As we've all heard countless times by now; LDL is bad, HDL is good. This table shows the results that certain types of fiber have on low density lipoprotein (LDL) cholesterol levels. While short term trials (4-8 weeks), the studies of psyllium and Oat B-glucan are considered high quality due to the amount of participants and number of trials. LDL levels decreased with each type of fiber introduced to one's diet.
In addition to the health benefits already mentioned, fiber helps promote satiety and adds bulk to our feces, which translates to less straining in the bathroom. High fiber diets (50-60 g/day) should be avoided for several reasons including:
- Causing individuals to fill up too quickly at the expense of consuming other necessary nutrients.
- Dry, hard stool if adequate fluid intake is not maintained.
Effect on Weight
We have looked at public perception of carbohydrates and discussed benefits as well as different types. Now lets examine if carbohydrates have a higher impact on weight gain/loss than other food sources.
Current dietary guideline recommendations for carbohydrates are set at 130 g a day or 45-65 % of total calories. Carbohydrates provide 4 kcal per gram which makes it a less dense source of energy than fat (9 kcal per gram). Based on that knowledge alone we can surmise that eating a high fat diet would put you at a higher risk of weight gain than a similar carbohydrate focused diet.
Several studies have disputed the idea that one weight loss diet is better than another, including this one which noted minimal difference in weight loss for balanced vs low carb diets.
A meta analysis of several cohort studies, comprising over 400,000 participants found that both low carb (< 40%) and high carb (> 70%) diets led to a higher mortality rate than a moderate intake. That suggests to me that the food scientists who developed the dietary recommendations seem to know what they are talking about.
There is no denying that low carb diets can be effective at weight loss. Concern arises due to a lack of data surrounding the long term effects of low carb diets that replace those lost carbs with fat or protein. A study that included over 20,000 Greek adults followed over a 10 year period concluded that, "prolonged consumption of diets low in carbohydrates and high in protein is associated with an increased mortality rate."
Carbohydrates are an important part of a healthy, balanced diet. Effort should be take to choose whole over refined grains and limit added sugars.
Added Sugars
The FDA has recently taken action to improve consumer awareness about added sugars. Per the FDA website, "manufacturers with $10 million or more in annual food sales have until 2020 before the new label is required, and manufacturers with less than $10 million in annual food sales will have until 2021."
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| https://www.healthline.com/health-news/see-how-nutrition-labels-highlight-added-sugar |
Sugar has been and still is, a hot topic in the nutrition community. The role of sugar in regards to weight gain and cavities is well documented. High fructose corn syrup has been shown to increase triglyceride, LDL, and uric acid levels. As a way to help slow down the deleterious effects of sugar, some areas have implemented a soda tax and there is much debate about adopting a nationwide policy. Despite the risks, I am a firm believer in freedom of choice in regards to dietary practices.
What do you think, should the government try to dissuade the purchase of soft drinks or just leave it alone?
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