Human Metabolism & Energy Balance
Metabolism is the sum of all chemical processes that keep the body functioning. It is best understood as energy in vs energy out, commonly described by Total Daily Energy Expenditure (TDEE).
TDEE Includes:
Basal Metabolic Rate (BMR): Energy required to maintain basic bodily functions at rest (~60-70%)
Thermic Effect of Food (TEF): Energy used to digest and process food (~10%)
Physical Activity:
EAT: Planned exercise
NEAT: Non-Exercise Activity Thermogenesis. Everyday movement, such as standing or fidgeting.
Glucose Regulation & Insulin
When carbohydrates are consumed, blood glucose rises. The pancreas releases insulin, which helps move glucose into cells for energy.
Insulin resistance occurs when cells respond poorly to insulin, leading to prolonged elevations in blood glucose. Over time, this is associated with metabolic conditions such as pre-diabetes and type 2 diabetes.
Rapid glucose spikes may be followed by sharp drops, which can contribute to fatigue and cravings.
Glycemic Index (GI) and Glycemic Load (GL)
The glycemic Index (GI) describes how quickly a food raises blood glucose, while glycemic load (GL) also accounts for the amount consumed, offering a more practical view of overall glucose impact. Individual responses vary based on factors such as insulin sensitivity and meal composition.
Examples often cited for context include:
Higher GI/GL: White bread, sugary drinks, refined grains
Lower GI/GL: Non-starchy vegetables, legumes, whole grains
Macronutrients: How the Body Uses Fuel
Carbohydrates (4 kcal/g)
Primary energy source
Broken down into glucose
Directly impact blood glucose
Common intake range: 45-65% of calories
Protein (4 kcal/g)
Builds and repairs tissue
Broken into amino acids
Minimal impact on blood glucose
Common intake range: 15-35% of calories
Fat (9 kcal/g)
Energy storage and cell function
No direct glucose impact
Slows digestion of carbohydrates
Common intake range: 20-35%
Digestion & Nutrient Absorption
Digestion begins in the mouth and continues through the gastrointestinal tract, with most nutrient absorption occurring in the small intestine.
Meals containing fiber, protein, and fat generally digest more slowly and are associated with more gradual glucose responses.
Chronic Conditions Influenced by Nutrition
Nutrition influences many metabolic conditions by affecting blood glucose regulation, inflammation, and cardiovascular risk. While care is individualized and guided by healthcare providers, research highlights shared metabolic patterns across these conditions.
Diabetes and Pre-Diabetes
These conditions involve impaired blood glucose regulation, most often due to insulin resistance, where cells respond less effectively to insulin and blood sugar remains elevated.
Common nutritional themes include:
Prioritizing lower glycemic load (GL) foods to reduce glucose spikes
Distributing carbohydrate intake more evenly throughout the day
Using light activity, such as waling after meals, to support insulin sensitivity.
Cardiovascular Disease (CVD) and Hypertension
Cardiovascular disease affects the heart and blood vessels, with hypertension serving as a major risk factor. According to the American Heart Association, nutrition influences cholesterol levels, blood pressure, and overall vascular health.
Common nutritional themes:
Increasing fiber to support cholesterol management
Emphasizing unsaturated fats, including omega-3s
Managing sodium intake to help regulate blood pressure
Metabolic Syndrome, Obesity, and PCOS
These conditions are closely related and frequently share insulin resistance as an underlying factor.
Metabolic Syndrome: A cluster of risk factors that significantly increases the risk of type 2 diabetes and cardiovascular disease
Obesity: Excess fat, which can worsen insulin resistance and inflammation
PCOS: A hormonal condition often associated with pronounced insulin resistance
Low Energy and Fatigue: Often linked to glucose variability or inefficient nutrient utilization
Common nutritional themes include:
Improving insulin sensitivity through lower-GL eating patterns
Increasing protein and fiber to support metabolic stability
Encouraging consistent daily movement, particularly NEAT
Closing Note
This article is intended to support general understanding of nutrition and metabolic concepts based on current scientific research and public health guidance. It is not a substitute for medical advice, diagnosis, or treatment. Interpretation of health data and nutritional strategies should always be guided by qualified healthcare professionals.
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