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So far in this series, we’ve covered calories and protein.
Next up is the macronutrient that probably causes the most confusion:
Carbohydrates.
Carbs get blamed for everything from low energy to weight gain — and at the same time, athletes are told they’re “rocket fuel” and absolutely essential.
As usual, the truth is more nuanced.
What Carbohydrates Actually Are
Carbohydrates are molecules made of carbon, hydrogen, and oxygen that serve as the body’s primary and preferred source of energy — especially for higher-intensity work.
At their most basic level, carbs are made of sugar units. You’ll recognize them because they usually end in “-ose”:
- Glucose
- Fructose
- Galactose
- Lactose
- Maltose
All dietary carbohydrates are either:
- Single sugar molecules
- Or chains of sugars linked together
The Three Categories of Carbohydrates
1. Monosaccharides (single sugars)
- Glucose
- Fructose
- Galactose
2. Disaccharides (two sugars bonded together)
- Sucrose (glucose + fructose)
- Lactose (glucose + galactose)
- Maltose (glucose + glucose)
3. Polysaccharides (many sugars linked together)
- Starch (from plants)
- Glycogen (stored in animals, including humans)
- Cellulose (fiber — indigestible for humans)
Your body produces specific enzymes to break these chains down into individual sugars. If you’re missing one of those enzymes — like lactase — digestion problems show up quickly (hello, lactose intolerance).
Simple vs. Complex Carbs (Why It Matters)
Simple carbohydrates (single or double sugars) are:
- Digested quickly
- Absorbed rapidly
- More likely to spike blood sugar
Complex carbohydrates (longer chains) take longer to digest and usually come packaged with:
- Fiber
- Vitamins
- Minerals
That built-in structure slows absorption and creates more stable energy.
What About Fiber?
Fiber is technically a carbohydrate — but one your body can’t break down.
We don’t have the enzymes needed to digest fiber, so it passes through the digestive tract mostly intact. That’s a good thing.
Fiber helps:
- Slow digestion
- Improve gut health
- Regulate blood sugar
- Increase satiety
Glucose: The Body’s Go-To Fuel
All digestible carbohydrates are ultimately broken down into simple sugars and absorbed into the bloodstream. Most of them end up as glucose.
Glucose is:
- The most readily available fuel in the body
- Usable by every cell
- Absolutely required by some cells (like red blood cells and parts of the brain)
Here’s the wild part:
At any given moment, your bloodstream contains about 4 grams of glucose — roughly one teaspoon.
That level is tightly regulated.
- Too high (around 8–12 grams): damage starts occurring
- Too low (around 2 grams): performance and brain function drop fast
Your body works around the clock to keep glucose in a narrow, safe range — during workouts, between meals, and even while you sleep.
Fructose Is Different (And Context Matters)
Fructose — found naturally in fruit and heavily in added sugars — follows a different path.
Unlike glucose:
- Most cells can’t use fructose directly
- It’s processed primarily in the liver
When fructose intake is low and comes from whole foods like fruit, this isn’t a problem.
When fructose intake is high — especially from added sugars and ultra-processed foods — the liver converts much of it into fat through a process called de novo lipogenesis (“making new fat”).
Over time, this contributes to:
- Fatty liver
- Insulin resistance
- Metabolic dysfunction
Again, context matters.
Fruit ≠ soda.
Are Carbohydrates Essential?
Here’s something that surprises a lot of people:
There are no essential carbohydrates.
Unlike protein (essential amino acids) and fat (essential fatty acids), there is no deficiency disease associated with the absence of carbs in the diet.
Even though glucose is required for survival, your body has a backup plan.
How the Body Makes Glucose Without Carbs
Your body can produce glucose through a process called gluconeogenesis — literally “making new glucose.”
It can do this using:
- Lactate
- Certain amino acids from protein
- Glycerol from fat breakdown
This ensures that glucose-dependent tissues are never left without fuel — even if dietary carbs are low or absent.
This doesn’t mean carbs are useless.
It means your body is adaptable.
The Practical Takeaway
Carbohydrates are:
- Your most efficient fuel for high-intensity work
- Non-essential, but extremely useful
- Best used strategically, not mindlessly
For athletes:
- Use carbs to support training demands
- Choose whole-food sources when possible
- Avoid relying on ultra-processed sugars for daily fuel
Like everything else in nutrition, carbs aren’t good or bad — they’re a tool.
Use the right tool, in the right amount, for the right job.
Next up, we’ll zoom out and tie all of this together so you can actually apply it without overthinking every meal.
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