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. 2023 Apr 17;9(3):e70. doi: 10.1192/bjo.2023.36

Table 1.

Operational definitions: low carbohydrate and ketogenic diets (LC/KD)

Term Abbreviation Carbohydrate content, g/day and/or % daily intake of a nominal 2000 kcal diet Comment
Moderate carbohydrate diet 300–400 g or 26–45% Western-pattern diets typically contain over 300 g carbohydrate/day
Low carbohydrate diet LC, LCD <130 g or <26%
Very low carbohydrate diet VLCD <30 g (some define 25–50 g) or <10% Leads to nutritional ketosis if maintained beyond 4–7 days
Ketogenic diet KD Fat:carbohydrate:protein ratio calculated on an individual basis for children with epilepsy High fat and very low carbohydrate: a ketogenic diet usually refers to the strict nutritional intervention for medication-resistant paediatric epilepsy17,18 (although the term is used more widely now). First described in 1921.19 Paediatric application requires specialist neurological and dietetic monitoring. Protein restricted: gluconeogenesis reduces ketosis. Diet modified according to child's weight and growth. Response rates are significant: at 3 months 55% are seizure-free and 85% have reduced seizures.17 Two types of ketogenic diet:20
  1. ‘traditional’ ketogenic diet: strictly ultra-low carbohydrate, minimal protein intake, sufficient for growth; intense monitoring, vitamin, and mineral supplementation:
    1. classic ketogenic diet‘3:1’ and ‘4:1’ diets (ratio of fat to carbohydrate + protein)
    2. medium-chain triglycerides (MCTs) (1970s): better absorption and ketone yield, allowing less fat, more carbohydrate and protein
  2. Modified ketogenic diet: less restrictive, better adherence, equal efficacy:
    1. modified Atkins diet (MAD) 2003:21 carbohydrate <10 g/day child, <20 g/day adult, excluding fibre; protein allowed freely
    2. low glycaemic index treatment (LGIT) 2002:22 carbohydrate 40–60 g/day, restricted to foods with a glycaemic index <50, including fibre; normal amount of protein
Keto-adaptation After Phinney:23 metabolic switch from carbohydrate to ketones as primary fuel source, stabilising over several weeks
Ketones β-hydroxybutyrate (β-HB), acetoacetate, acetone
Ketosis Presence of circulating ketones β-HB 0.5–3.0 mmol/l; physiological response to starvation or carbohydrate reduction (‘nutritional ketosis’)
Ketoacidosis Distinct from nutritional ketosis: ketoacidosis defined as β-HB >20 mmol/l in the context of acutely destabilised type 1 diabetes, with severe hyperglycaemia and acidosis
Low carbohydrate high fat diet LCHF May be ketogenic (carbohydrates <25–50 g/day) or non-ketogenic (130–50 g/day); similar to the modified Atkins diet (MAD)21
Low carbohydrate ketogenic diet LCKD, KLCHF The terms LCHF, KLCHF, LC/KD and ketogenic diet have some overlap and may appear interchangeably in the literature

Source: modified from Accurso et al.32