European Journal of Cardiovascular Medicine

Carbohydrates are the principal and most rapidly utilized source of energy for the human body. In a typical Indian diet — especially a mixed meal rich in cereals, pulses, and vegetables — carbohydrates form 60–70% of daily caloric intake. The digestion, absorption, and utilization of these carbohydrates is a complex yet well-orchestrated process, and the body’s metabolic balance depends on a steady supply of glucose.

In diabetic individuals, carbohydrate metabolism is profoundly influenced by insulin availability and sensitivity. Moreover, drastic carbohydrate restriction — while often attempted for glycemic control — may produce dangerous metabolic consequences, including the precipitation of diabetic ketoacidosis (DKA) in insulin-deficient states.

1. Evolutionary Adoption of Glucose as the Universal Fuel

• From unicellular organisms to multicellular humans, glucose has remained the universal
• metabolic fuel. Early prokaryotes used primitive glycolytic pathways (Embden–Meyerhof)
• before oxygen appeared. Glucose offered thermodynamic  stability, cytoplasmic  safety, and
• the highest ATP yield per carbon atom, making it evolution’s preferred substrate. The
• conservation of glycolytic enzymes like hexokinase, PFK, and pyruvate kinase across species
• highlights the ancient biochemical legacy of glucose utilization.
• Carbohydrates are the principal and most rapidly utilized source of energy for the human body.

• Organ-wise Obligatory Glucose Requirement Organ / Tissue Approximate Daily Glucose Requirement Organ / Tissue Approximate Daily Glucose Requirement (g/day)
• Brain (neurons, glial cells )-> 120
• Skeletal muscle (resting) 40–>50
• Erythrocytes (RBCs)-> 30
• Kidneys 15–>20
• Liver ->20–25
• Cardiac muscle-> 10
• Other tissues (intestine, immune cells,endothelium )->10
• Total Human Requirement ≈ 220–250
• In diabetic individuals, carbohydrate metabolism is profoundly influenced by insulin
• availability and sensitivity. Moreover, drastic carbohydrate restriction — while often
• attempted for glycemic control — may produce dangerous metabolic consequences, including the precipitation of diabetic ketoacidosis (DKA) in insulin-deficient states.

Carbohydrate Metabolism from Eating to Glucose Appearance in Blood

1. Stepwise Process in a Normal Healthy Adult

2. Key Characteristics of Indian Diet Digestion

- Cooking method: Gelatinizes starch, making it easier to digest and absorb.
- Rice vs. roti: White rice digests faster; whole wheat chapati digests slower due to fiber.
- Pulses/dal: Protein + soluble fiber slow digestion and blunt glucose spikes.
- Added sugar: Absorbed rapidly, raising glucose within minutes.

Physiological Necessity of Dietary Carbohydrate

1. Obligatory Glucose-Dependent Tissues

2. Minimum Carbohydrate Requirement

• WHO & ICMR recommend ≥130 g/day of digestible carbohydrate in adults to meet the brain’s minimal glucose needs in the fed state.
  - In diabetes, carbohydrate should be from low-glycemic-index, fiber-rich sources to maintain stable glucose.

1. Physiological Necessity of Dietary Carbohydrate

CONSEQUENCES OF SEVERE OR TOTAL CARBOHYDRATE RESTRICTION

1. Acute Phase (First 24–48 hours)

• Liver glycogen depleted within 24 hrs.
• Gluconeogenesis increases (muscle protein breakdown, glycerol mobilization).
• Insulin secretion falls further; glucagon and counter-regulatory hormones rise.

2. Adaptation Phase (3–14 days)

• Ketone bodies supply up to 70% of brain energy.
• Persistent gluconeogenesis to supply obligate glucose users.
• Increased nitrogen loss → muscle wasting.

3. Chronic Zero-Carb State

• Loss of lean body mass.
• Micronutrient deficiencies.
• Altered gut microbiota.
• In insulin-deficient diabetics → high risk of pathological ketoacidosis.

1. Mechanism of Carbohydrate Restriction-Induced DKA in Diabetes
2. Pathway

• Low/no carbohydrate intake in an insulin-deficient diabetic → further decreases
• circulating insulin levels.
• Elevated glucagon, cortisol, catecholamines → stimulate uncontrolled lipolysis.
• Free fatty acids flood the liver → β-oxidation → excessive ketone body production.
• No adequate insulin to suppress ketogenesis → metabolic acidosis.

2. Clinical Sequence

a.Carb restriction → fall in insulin → rise in counter-regulatory hormones.

1. Massive lipolysis → FFA to liver.
2. Accelerated ketogenesis.
3. Ketone accumulation + dehydration → DKA.
4. Infection as a Secondary Trigger

• Infection increases insulin resistance and counter-regulatory hormones, worsening
•  
• But without the carbohydrate restriction + insulin deficiency base, many infections cause

only hyperglycemia, not DKA.

Clinical Implications

• Never remove all carbohydrates from a diabetic’s diet, even during illness.
• Maintain at least 100–130 g/day of low-GI carbs.
• In patients on SGLT2 inhibitors, avoid prolonged fasting or very-low-carb diets due to risk
• of euglycemic DKA.
• Educate patients that carbohydrate restriction is not a cure; in insulin-deficient states it is a potential trigger for DKA.

Obligatory Glucose Requirement

• The obligatory glucose requirement, often cited as 130–150 g/day, represents the minimal
• quantity of glucose needed to sustain the metabolic functions of the human brain, red blood
• cells, and certain glucose-dependent tissues. However, this figure applies to a resting,
• fasting, sedentary state and does not reflect the physiological demand of real-life working
• adults, especially in tropical environments such as India where physical exertion, heat
• stress, and mental activity substantially increase glucose oxidation.

2. Concept of Obligatory Glucose Requirement

The concept stems from the minimum glucose oxidation necessary to meet energy requirements of tissues that depend almost exclusively on glucose:

Table 1.

• Obligatory Glucose Requirement by Organ/Tissue
• Tissue / Organ Average Daily Requirement in gm / Remarks
• Brainà 110–120g àPrimary consumer forneuronal ATP generation
• Red Blood Cellsà 20–30g àAnaerobic glycolysis, nomitochondria
• Renal medulla / Retina /Testes à10–20g àGlucose-dependent due to low oxidative capacity
• Total obligatory baseline ≈ 130–150 g/day (bare minimum to prevent ketosis and maintain function).

3. Increment with Physical and Mental Work

In real-world conditions, humans rarely remain at rest. Even light office or household work

imposes additional muscular and neural demands, increasing glucose turnover and hepatic

glycogen cycling.

Table 2.

Incremental Glucose Requirement by Activity Level

Activity Level-- Additional GlucoseOxidation (g/day)--Total Requirement

Sedentary / Resting —> 130–150g –>Baseline requirement

Light work (office,teaching, clinical duties) à+30–70g à180–220 -Brain and mild ,muscular tone

Moderate work(walking 2–3 km/day, household chores)à+70–100g à220–280 àMuscle glucose oxidation  , cori cycle

Heavy work (manual labour,farming, sports)--+150–250-- 280–350—>Continuous muscular

contraction and activities. lactate recycling

4. Metabolic Substitution and Limitations

While fatty acids and ketones can partially replace glucose during starvation, this adaptation is neither efficient nor sustainable for normal working life. The brain still needs ≥100 g/day, muscles initially use glucose before switching to β-oxidation, and kidneys/liver perform ATP-expensive gluconeogenesis. Intake of just  130 g/day forces protein catabolism, fatigue, and dehydration.

5. Implications in Diabetes Management

Maintaining adequate carbohydrate intake supports stable endogenous insulin rhythm, reduces counter-regulatory hormone activation, improves hydration and prevents

hypoglycemia-induced rebound hyperglycemia. Thus, excessive restriction can worsen control.

6. Practical Recommendations

Table 3.

Practical Carbohydrate Requirements Category/. Ideal Total Carbohydrate /Glucose Intake/Remarks

Sedentary / Resting adults 130–150 g/day  ->/Minimum for CNS and RBC metabolism

Light to moderate work 180–250 g/day->/ Optimal for cognitive and muscular activity

Heavy physical work 250–>350 g/day ->Matches 2,400–3,000kcal/day energyexpenditure

Below 130 g/day/ Inadequate /Triggers gluconeogenesis, dehydration, fatigue

Above 350 g/day /Excess /May exceed utilization, leading to hyperglycemia

7. Summary

The 130 g/day figure is the minimal obligatory, not optimal daily requirement. For Indian

working adults, 200–250 g/day maintains stability, mental clarity, and safe glycemic

control. Adequate hydration is essential.

Carbohydrates are not merely a source of calories; they are essential for the functioning of specific tissues and for maintaining metabolic balance. In diabetic patients — particularly those with insulin deficiency — excessive restriction of dietary carbohydrates can be dangerous, potentially precipitating DKA even without infection. A balanced intake of low- GI carbohydrates, adequate hydration, and tailored insulin therapy remain the safest and

most physiological approach.

“In insulin-deficient diabetes, carbohydrate deprivation is not a cure — it is the spark that

can ignite diabetic ketoacidosis.”

— Prof. Dr. Aditya Bikram Mishra

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