Is There Such a Thing as a Good Carb?

By Joanne R. Lupton, PhD

A good answer to this question requires an understanding of what carbs are and the difference between a carbohydrate and a carbohydrate-containing food, so let’s first get the nomenclature out of the way.

What is a carbohydrate? Technically, carbohydrates are specific types of molecules based on single sugar units.
The three most common single sugar units (or monosaccharides) are glucose, fructose, and galactose.  The term “sugars” is used to describe these single sugar units and also to describe units composed of two sugars linked together (technically known as disaccharides).
Disaccharides include sucrose (table sugar) and lactose (the sugar in milk).
Sucrose = glucose + fructose

Lactose = glucose + galactose

Polysaccharides are more than 10 sugar units linked together, and the most important and ubiquitous polysaccharide in food is starch – which is hundreds of glucose units linked together. Dietary fibers are also polysaccharides, but in contrast to starch, the single sugar units in dietary fibers are linked in such a way that humans cannot break the links.
Since all carbohydrates are absorbed into the body as single sugar units (i.e. glucose, fructose, or galactose) if we can’t break the links (a.k.a. “bonds”) in a polysaccharide (such as dietary fiber) then we can’t absorb the carbohydrate.  Instead it will pass intact into the large intestine, where it can be fermented by gut microbes to gases and other substances called short chain fatty acids.
Carbohydrates are neither good nor bad: the issue is the food source. If you’ve made it this far, you can see it doesn’t make a lot of sense to call a carbohydrate “good” or “bad.”  They are all absorbed into the body as single sugar units (by far and away, glucose is the primary unit absorbed because it’s half of every disaccharide and it’s the only molecule in starch – and we eat a lot of starch.)
Glucose is the primary energy source for the brain.  We’ve all experienced the fuzzy feeling resulting from a drop in our blood glucose levels when we haven’t eaten.  Glucose is also the only source of energy for the red blood cell, and every cell in the body can use glucose for energy. We need glucose to survive. But we don’t eat glucose, per se.  Instead we eat carbohydrate-containing foods.
The question then becomes “Are some carbohydrate-rich foods better than others?”  The answer to that question is a resounding “Yes.”  Here’s why.
High fiber foods are great. Since fiber is a carbohydrate, high fiber foods are high carbohydrate foods.  A strong case could be made that if one got the recommended amount of fiber every day without exceeding one’s energy requirement, it would automatically be a great diet.
High fiber foods include:
  • whole grains
  • legumes
  • fruits
  • vegetables
These foods not only contain fiber, they are also generally low in calories and contain phytochemicals which are protective against a variety of diseases.  They add “bulk” to the diet and can produce a feeling of satiety, thus decreasing overeating at the next meal.
Low fat and non fat milk are important foods. Milk contains the carbohydrate lactose.  In fact, lactose is almost exclusively found in dairy products.  Since milk is an excellent source of protein, calcium, potassium and vitamins, that means getting some carbohydrates from milk is a good choice.

The issue with added sugars. The issue with other sources of carbohydrates (that is everything except fruits, vegetables, whole grains and low fat dairy) is not that the carbohydrates are bad.  Rather, these sources of carbohydrates contain calories and not a lot of nutrients such as vitamins and minerals.

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