Do some bodies need more carbs than others?

October 22, 2025 •

4 min read

The Dietary Guidelines for Americans recommend that carbohydrates make up 45% to 65% of total daily calories, yet this broad advice doesn't account for individual differences. This wide range exists because the question, "do some bodies need more carbs than others?", can be answered with a resounding yes, as factors like genetics, activity, and metabolic health play a crucial role.

Quick Summary

Carbohydrate requirements are not universal and vary significantly among individuals based on genetic factors, physical activity levels, and metabolic health. Adjusting intake according to personal needs is key for optimal energy and well-being. This personalization can improve insulin sensitivity and support health goals.

Key Points

Genetics Matter: Inherited genes can influence how efficiently your body metabolizes carbohydrates, affecting your tolerance and energy levels.
Activity Drives Needs: Physical activity level is a major determinant of carb requirements, with endurance athletes needing significantly more than sedentary individuals.
Insulin Sensitivity is Key: How responsive your cells are to insulin, which is affected by body fat and exercise, dictates how well you process carbohydrates.
Not One-Size-Fits-All: A personalized approach is crucial, as a broad dietary guideline may not be optimal for your unique metabolic profile.
Quality Over Quantity: Focusing on high-fiber, complex carbohydrates from whole foods is beneficial for most people, regardless of their total intake.
Self-Monitoring is Powerful: Tracking your body's response to carbohydrate intake can help you determine your personal tolerance and optimal consumption levels.

The Scientific Basis for Varying Carbohydrate Needs

Individual metabolic responses to carbohydrates are far from uniform, meaning the amount of carbohydrates a person needs can differ dramatically from the next. The body's primary function for carbohydrates is to break them down into glucose, the main fuel source for energy. However, how efficiently and quickly a person uses, stores, or clears this glucose is influenced by a complex interplay of genetic, lifestyle, and physiological factors.

Genetic Predisposition and Metabolism

Your genetic makeup plays a foundational role in determining your carbohydrate tolerance. While rare inherited metabolic disorders can severely impair carbohydrate breakdown, subtle genetic variants can also impact metabolism.

FTO Gene Variants: Studies have linked specific variants of the FTO (fat mass and obesity-associated) gene to differing responses to dietary macronutrients. Some individuals with certain FTO variants may experience better weight management outcomes on lower-carb diets.
FGF21 Gene Variants: This gene encodes a protein that regulates carbohydrate metabolism and energy use. Genetic variations in FGF21 can lead to distinct carbohydrate tolerances, influencing whether someone benefits more from a lower-carb or higher-carb diet for weight loss.
Enzyme Efficiency: Variations in genes like SI (sucrase-isomaltase) can affect the digestive system's ability to break down carbohydrates, potentially leading to gastrointestinal distress with high-carb intake.

Physical Activity and Energy Demands

Physical activity level is one of the most significant determinants of carbohydrate needs. As the body's primary fuel during moderate to high-intensity exercise, glycogen stores must be replenished, necessitating higher carbohydrate intake for active individuals.

Endurance Athletes: Marathon runners or triathletes performing intense training for multiple hours per day require very high carbohydrate intake to fuel performance and recovery. Their consistent activity enhances insulin sensitivity, allowing them to process large quantities of carbs efficiently.
Sedentary Individuals: In contrast, someone with a very low activity level does not deplete glycogen stores rapidly and, therefore, has much lower carbohydrate requirements. Excess carbs consumed by a sedentary person are more likely to be stored as fat, especially if insulin sensitivity is low.

Insulin Sensitivity and Body Composition

Insulin is the hormone that helps cells absorb glucose from the bloodstream. Insulin sensitivity, or how well cells respond to insulin, varies from person to person and is affected by body composition.

High Insulin Sensitivity: A lean, physically active person typically has high insulin sensitivity. Their cells readily respond to insulin signals, allowing them to handle a higher carbohydrate load effectively and use glucose for energy rather than storing it as fat.
Insulin Resistance: In contrast, overweight or sedentary individuals, or those with genetic predispositions, may develop insulin resistance, a precursor to type 2 diabetes. Their cells are less responsive to insulin, meaning blood sugar levels remain elevated longer after a high-carb meal, which can be detrimental to health.

Comparison of Carbohydrate Needs


Factor	Sedentary Person	Endurance Athlete	Insulin-Resistant Individual
Activity Level	Minimal or low intensity (e.g., walking)	High intensity, >1 hour/day (e.g., running)	Low to moderate
Energy Demand	Low to moderate	Very High	Variable, often lower
Insulin Sensitivity	Lower, potentially resistant	High	Low (Insulin Resistant)
Carb Requirements	Lower end (e.g., 3-5 g/kg/day or ~45% total calories)	Higher end (e.g., 6-12 g/kg/day or >65% total calories)	Cautious approach, focusing on low GI carbs
Carb Source Focus	Complex, high-fiber carbs to maintain stable blood sugar	Mixed, including refined carbs for quick energy pre/intra-workout	Complex, high-fiber, low glycemic index carbs

Practical Steps for Personalized Carb Intake

Determining your specific carbohydrate needs is a process of observation and adjustment. There is no one-size-fits-all formula, but these steps can help guide you.

Assess Your Activity Level: Use guidelines from organizations like the British Dietetic Association to match your activity level with recommended grams of carbs per kilogram of body weight.
Monitor Your Response: Pay close attention to how you feel after meals. Fatigue, cravings, or energy crashes after eating carbs can be a sign you're consuming too much, or the wrong type.
Track Your Intake: Use a food diary or app to monitor your carbohydrate intake and its effect on your energy levels and weight over a few days. The USDA's Food Composition Database can be a helpful tool for finding carbohydrate content in foods.
Prioritize High-Quality Carbs: Focus on complex carbs from whole foods and limit refined grains and added sugars.
- Best Sources: Fruits, vegetables, whole grains, legumes, and beans.
- Limit: Sugary drinks, cakes, white bread, and refined pasta.
Consider Professional Guidance: Consulting with a registered dietitian nutritionist (RDN) or certified diabetes care and education specialist (CDCES) can provide tailored medical nutrition therapy, especially for those with conditions like diabetes.

Conclusion: A Personalized, Not Standardized, Approach

Ultimately, the idea that every body has the same carbohydrate needs is a myth. The latest nutritional science confirms that factors from our genetics to our daily physical exertion create a unique metabolic picture for each person. By understanding these individual differences, you can move away from rigid, standardized diets and towards a personalized approach that optimizes energy, supports health goals, and improves overall well-being. Focusing on high-quality, complex carbohydrates and adjusting intake based on activity and metabolic response is the most effective strategy for anyone looking to fine-tune their diet. Finding your ideal intake requires self-awareness and patience, but the long-term benefits are substantial. For further information on insulin action and diet, consider reviewing the comprehensive article on the topic in The Journal of Nutrition.

Frequently Asked Questions

Carbohydrate tolerance refers to your body's ability to effectively process and clear glucose from the bloodstream after eating carbs. It is closely related to insulin sensitivity, or how well your cells respond to insulin.

Yes, your carbohydrate needs can change. Factors like age, changes in physical activity level, weight fluctuations, and shifts in metabolic health (like developing insulin resistance) can all alter your body's requirements over time.

Genetic variations can affect enzymes and regulatory proteins involved in digestion and glucose handling. For example, some gene variants influence insulin sensitivity and how efficiently the body uses carbohydrates versus storing them as fat.

Yes, active people use carbohydrates more rapidly and efficiently. Intense exercise depletes the glycogen stores in muscles, creating a greater demand for carbohydrate replenishment. This increased demand is why athletes require a higher carb intake.

For someone with lower carb tolerance or insulin resistance, a reduced carbohydrate intake can be beneficial for managing blood sugar levels and weight. However, the focus should be on high-quality carbohydrates and monitoring your individual response.

Listen to your body. Experiencing sustained energy, stable mood, and good athletic performance on your current intake suggests it's working. However, persistent fatigue, mood swings, or blood sugar crashes after meals could indicate an imbalance in your carb consumption.

No, carb counting is not necessary for everyone, but it can be a useful tool, especially for those managing conditions like diabetes. For most people, focusing on high-quality carbohydrate sources and listening to your body's signals is a sufficient approach.