Carbohydrates might be the most debated macronutrient in fitness.
High carb.
Low carb.
No carb.
“Carbs for performance.”
“Carbs are ruining your metabolism.”
And now, a new paper has added more fuel to the fire.
Recently, a narrative review was published examining carbohydrate intake, exercise metabolism, and physical performance. It reviewed over 100 studies spanning more than 100 years of research.
This paper, combined with what I’ve learned from coaching, physiology, and seeing real people respond very differently to carbs, pushed me to revisit and refine my thinking on carbohydrate intake.
This article breaks down:
• What the paper actually found
• Why it’s already being misinterpreted
• How carbs really fit into performance and body composition
• And what to do if you feel like you “don’t handle carbs well”
What this paper actually reviewed
This was a narrative review, not a new intervention study.
A narrative review summarizes existing research rather than producing new data. That means it can be useful for perspective and hypothesis generation, but it’s still influenced by study selection, interpretation, and context.
The population examined was primarily athletes, especially endurance athletes. That’s important because athletes operate under very different physiological demands than the general population.
Still, some of the insights are worth discussing more broadly.
The five main conclusions from the review
1. Carb loading may be overemphasized
Traditional sports nutrition guidelines often recommend very high carbohydrate intakes for long-duration activity, sometimes 60–90 grams per hour during training or competition.
That can push daily carbohydrate intake over 1,000 grams per day for some athletes.
The authors argue that research has historically overemphasized:
• Muscle glycogen levels
• Carbohydrate oxidation rates
While these metrics do not consistently predict performance outcomes.
In other words, having more stored carbs or burning more carbs does not always equal better performance.
2. Sustaining brain energy appears to matter more than glycogen
According to the review, the strongest predictor of performance was maintaining brain energy availability, not simply maximizing muscle glycogen.
Brain energy can come from multiple sources:
• Glucose
• Ketones
• Lactate
Across more than 160 performance studies, carbohydrate ingestion improved outcomes primarily when blood glucose dropped significantly in the placebo group. When glucose remained stable, carb ingestion often provided little or no additional benefit.
This suggests the key issue isn’t “high carbs vs low carbs,” but rather avoiding a drop in blood glucose that compromises brain function and perceived effort.
This also explains why ketogenic or lower-carb athletes can still perform well when glucose is adequately maintained through other mechanisms.
3. Very high carb intake may increase glycogen breakdown and suppress fat oxidation
Another interesting finding was that higher carbohydrate intake during exercise can:
• Accelerate glycogen breakdown
• Suppress fat oxidation
This contradicts the common marketing claim that high carb fueling “spares glycogen.”
Interestingly, better fat oxidation has been associated with improved endurance performance in several studies.
This doesn’t mean carbs are bad. It means more carbs isn’t always better, especially when metabolic flexibility is poor.
4. High-carb sports nutrition environments may create metabolic stress
One of the most controversial points in the review was the suggestion that very high carbohydrate intakes may contribute to pre-diabetic markers in some athletes.
The authors note that current sports nutrition strategies can create a metabolic environment resembling diabetes during exercise:
• Elevated insulin
• Suppressed fat oxidation
• Greater reliance on glucose
• Accelerated glycogen depletion
The key takeaway here is not that carbs cause diabetes.
It’s that athletes are not metabolically invincible, and genetic predisposition, recovery quality, stress load, and diet quality still matter.
5. Ketogenic athletes can still “bonk”
Another important clarification.
Athletes on ketogenic diets can still experience performance crashes if blood glucose drops too low. Ketones alone are not always sufficient to fully support brain energy during prolonged or intense efforts.
Interestingly, both high-carb and low-carb athletes benefited from small, targeted carbohydrate doses around 10 grams per hour during exercise lasting longer than 60 minutes.
After adaptation, ketogenic and high-carb athletes performed similarly, provided brain energy was supported.
Again, the theme repeats.
This isn’t about extremes.
It’s about fuel availability and flexibility.
Why this paper is already being misused
This paper will likely fuel more arguments:
High-carb advocates dismissing it.
Low-carb advocates weaponizing it.
Both sides are missing the point.
Carbohydrates are the most individual macronutrient.
Protein needs are relatively predictable.
Fat has a minimum requirement.
Carbohydrates exist on a massive spectrum.
What works well for one person may be completely wrong for another.
What actually determines your ideal carb intake
There is no universal “right” amount of carbohydrates. Intake should be based on multiple interacting factors.
Training load and activity
Higher training volume and overall movement generally increase carbohydrate needs.
But that doesn’t automatically mean very high carb intake is required for everyone who trains hard. Metabolic flexibility, recovery, and body composition still matter.
Body composition, not just body fat
People with more muscle mass tend to tolerate and utilize carbohydrates better because muscle is a major glucose sink.
Individuals with higher body fat and lower muscle mass often do better initially with lower to moderate carbohydrate intake, especially during fat loss phases.
Individual response and genetics/Metabolic health matter
Some people are genetically more predisposed to insulin resistance and dysregulated glucose control.
The worse your metabolic health, the less helpful extremely high carbohydrate intake tends to be.
In these cases, blood work can be informative:
- Fasting glucose
Ideal / functional
• ~75–90 mg/dL
• Low 90s can still be fine in very muscular or highly stressed individuals
Yellow flags
• Consistently 95–99 mg/dL
• Especially if paired with poor sleep, high stress, or low activity
Red flags
• 100+ mg/dL fasting (especially repeatedly)
Context matters here. Elevated fasting glucose can reflect stress physiology and poor recovery, not just carbs.
- Fasting insulin
This is one of the most important markers.
Ideal / functional
• ~2–6 µIU/mL
• Under ~5 is generally a good sign of insulin sensitivity
Yellow flags
• 7–10 µIU/mL
Red flags
• 10+ µIU/mL
• Especially if glucose is also elevated
High insulin with “normal” glucose often means the body is working harder than it should to maintain blood sugar.
- Hemoglobin A1C
Represents ~3 months average glucose exposure.
Ideal / functional
• ~4.8–5.2%
Yellow flags
• 5.3–5.6%
Often shows early glucose dysregulation, stress load, or poor sleep
Red flags
• 5.7%+ (prediabetes range)
Important nuance:
You can see A1C creep up even in active people if recovery, sleep, or fueling timing is poor.
If these markers are suboptimal, very high carbohydrate intake may not be the best strategy even if activity levels are high at the moment. The goal would be to get these numbers in line first.
Nutrition phase
Fat loss phases generally involve lower carbohydrate intake to create a calorie deficit.
Muscle-building phases often require higher carbohydrate intake to support training and recovery.
But even here, fats can sometimes be increased instead of carbs depending on individual response.
What you’ve been doing recently
Always high-carb?
A lower-carb phase may improve metabolic flexibility.
Always low-carb?
Strategic higher-carb days or phases may improve carbohydrate oxidation.
Being able to use both fuels matters.
Rethinking carbs for lifters over 30
One area where my thinking has changed the most is carbohydrate needs for recreational lifters.
If you lift 3–6 days per week, do some cardio, and stay moderately active, you likely do not need massive carb intakes all the time.
If you feel like you need huge amounts of carbs just to get through a basic lifting session, that’s often a sign that something else needs attention:
• Carb quality
• Metabolic flexibility
• Sleep and recovery
• Stress load
• Conditioning base
Carbs support performance, but dependency on constant carb intake is usually a symptom, not a requirement.
Carb source matters more than most people think
If most of your carbs come from ultra-processed foods, the issue isn’t carbohydrates.
It’s diet quality.
Whole-food carbohydrate sources are harder to overeat, improve satiety, and support metabolic health far better than gels, refined snacks, and liquid carbs used excessively outside of endurance contexts.
How to improve your ability to handle carbohydrates
If carbs make you feel bloated, sluggish, or stall fat loss, the answer is rarely “cut carbs forever.”
The goal is improving how your body handles them.
Build muscle
Muscle is your largest glucose sink.
More muscle equals more places to store carbs.
You don’t need to gain a lot of weight to build muscle, but intentional resistance training matters.
Move after meals
Post-meal walking or light activity significantly improves blood glucose control and digestion.
Meals plus movement beat meals alone.
Improve your conditioning base
Low to moderate intensity conditioning 2 times per week improves carbohydrate utilization and insulin sensitivity.
You don’t need to crush HIIT sessions constantly. Too much intensity can backfire by increasing stress load.
Manage stress and recovery
High resting heart rate and low HRV are associated with reduced insulin sensitivity.
Better recovery, smarter training volume, and lower overall stress improve carb tolerance.
Dial in circadian rhythm and sleep
Morning sunlight
Consistent sleep and wake times
Less blue light at night
Smarter caffeine timing
Circadian alignment plays a major role in carbohydrate metabolism.
Time carbs intelligently
More carbs earlier in the day and around training often work better than large late-night carb loads, unless you are very lean or dieting aggressively.
Include occasional high-intensity intervals
One higher-intensity session per week can improve glucose uptake and metabolic flexibility when used appropriately.
Improve carb quality
Focus on fiber-rich, slower-digesting sources:
• Potatoes and sweet potatoes
• Oats
• Beans and lentils
• Fruits and berries
Ultra-processed carbs should be minimized outside of specific performance needs.
Get leaner if needed
You don’t need to be shredded.
But moving toward roughly:
• 10–20% body fat for men
• 20–30% body fat for women
Improves insulin sensitivity and carb handling for most people.
This often requires a temporary lower-carb phase to get there.
Periodically spend time in lower-energy states
You shouldn’t diet or go low-carb year-round.
But intentional periods of lower energy or lower carb intake can improve fuel utilization long-term, especially for people who are always eating high carb.
Titrate carbs gradually
If you’ve been very low carb, don’t jump from 50 grams to 300 grams overnight.
Increase slowly.
Assess response.
Adjust.
Magnesium matters
Magnesium plays a role in carbohydrate metabolism and insulin sensitivity.
Most people are deficient.
Supplementation has been shown to improve fasting glucose, insulin levels, and insulin sensitivity markers.
A few final considerations
Menstrual cycle phase can influence carb tolerance, especially during the luteal phase.
Short-term weight gain after eating carbs is usually water and glycogen, not fat.
And most importantly:
There is no single carbohydrate prescription that works for everyone.
Takeaway
Carbohydrates are not the enemy.
They’re also not magic.
They are a tool.
Your job is not to pick a side in the carb debate.
Your job is to figure out what your body actually responds to, in the context of your training, lifestyle, recovery, and metabolic health.
That’s exactly what I help clients do inside my one-on-one coaching and the Performance Recomp Method.
