Report of the IDECG Working Group on lower and upper limits of carbohydrate and fat intake DM Bier 1 , JT Brosnan 2 , JP Flatt 3 , RW Hanson 4 , W Heird 5 , MK Hellerstein 6 , E Je Âquier 7 , S Kalhan 8 , B Koletzko 9 , I Macdonald 10 , O Owen 11 and R Uauy 12 1 Children's Nutrition Research Center, Baylor College of Medicine, Houston, TX; USA; 2 Department of Biochemistry, Memorial University of Newfoundland, St. John's, Canada; 3 Department of Biochemistry, University of Massachusetts Medical School, Worcester, MA, USA; 4 Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA; 5 Department of Pediatrics, Baylor College of Medicine, Houston, TX; USA; 6 Department of Nutritional Sciences, University of California at Berkeley, Berkeley, CA, USA; 7 Institute of Physiology, University of Lausanne, Lausanne, Switzerland; 8 Center for Metabolism and Nutrition, and Department of Pediatrics, Case Western Reserve University School of Medicine, Cleveland, Ohio, USA; 9 Division of Metabolic Disorders and Nutrition, Kinderklinik and Kinderpoliklinik, Ludwig-Maximilians-University of Munich, Mu Ènchen, Germany; 10 School of Biomedical Sciences, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, UK; 11 Spring Mill Road, Gladwyne, PA, USA; 12 Institute of Nutrition and Food Technology (INTA), University of Chile, Santiago, Chile Carbohydrate intakes The theoretical minimal level of carbohydrate (CHO) intake is zero, but CHO is a universal fuel for all cells, the cheapest source of dietary energy, and also the source of plant ®ber. In addition, the complete absence of dietary CHO entails the breakdown of fat to supply energy (gly- cerol as a gluconeogenic substrate, and ketone bodies as an alternative fuel for the central nervous system (CNS)), resulting in symptomatic ketosis. Data in childhood are unavailable, but ketosis in adults can be prevented by a daily CHO intake of about 50 g. This value appears to approximate the quantity of glucose required to satisfy minimal glucose needs of the CNS and during starvation. The Group therefore concluded that the theoretical mini- mum intake of zero should not be recommended as a practical minimum. For the de®nition of the lower limit of carbohydrate intake the following set of assumptions were made: 1. Estimates are based on the assumption that energy and protein intakes are adequate. 2. Only absorbable non-alcohol CHO are taken into con- sideration. 3. The CHO must come from a variety of sources. 4. The minimum level of CHO intake must be adequate to maintain an appropriate body weight and composition in adults and allow for adequate growth and development in children; ideally it should minimize protein carbon use for gluconeogenesis. 5. It should be compatible with food preferences, commu- nity needs, religious rites and other societal factors. 6. It should meet requirements that are based on calculations of irreversible carbon loss in brain metabolism, allowing for the uncertainty of available data. It is assumed that at ages above 3 ± 4 y the adult irreversible oxidation rate applies. Under these assumptions about 100 g of glucose=d are irreversibly oxidized by the brain from the age of 3 ± 4 y onward. However, this excludes recycled carbon, gluco- neogenic carbon, for example, from glycerol, and it does not account for glucose used by other non-CNS tissues. For example, in the adult, muscle and other non-CNS account for an additional 20 ± 30 g of glucose daily. For this reason a safety margin of 50 g=d is arbitrarily added to the value of 100 g=d and the practical minimal CHO intake set at 150 g=d beyond the ages of 3 ± 4 y. This can then be expressed as a fraction of the total daily energy requirement that should be provided as absorbable CHO. The balance of the diet has to be supplied by protein and lipids. Too much of the latter could contribute to the risk of cardiovascular disease, obesity and insulin resistance. This minimal CHO requirement should therefore not be taken as an optimal recommendation from a public health point of view. Special populations:  From the age of 0 ± 3 y there is a rapid increase in brain size and irreversible glucose oxidation, amounting to about 25% of total energy expenditure. Allowing for the same safety factors as mentioned for adults, we arrive at a recommendation that at least a third of dietary energy should be supplied from CHO.  In individuals with signi®cant risk factors for cardiovas- cular disease the relation of CHO to fat intake may have to be different than that of a general population.  A small fraction of individuals engaged in sustained endurance activities at 60% of maximum oxygen consump- tion (VO 2 max) are likely to require a high CHO intake. With regard to the upper limit of CHO intake, the basic assumptions include the following: 1. Those made for the low CHO intake. 2. There is no intrinsic upper limit to the oxidation of CHO. However, while the body is highly ef®cient in matching CHO oxidation to intake, it should be recog- nized that increased fat deposition can occur at a level of CHO intake exceeding energy expenditure. 3. Additionally, account must be made of the need to supply other essential nutrients, fatty acids, amino acids, vitamins (including fat-soluble vitamins) and various micronutrients, which may be de®cient in Correspondence: IDECG Secretariat, c=o Nestle  Foundation, POB 581, 1001 Lausanne, Switzerland. European Journal of Clinical Nutrition (1999) 53, Suppl 1, S177±S178 ß 1999 Stockton Press. All rights reserved 0954±3007/99 $12.00 http://www.stockton-press.co.uk/ejcn