Compensatory growth, known as catch-up growth and compensatory gain, is an accelerated growth of an organism following a period of slowed development, particularly as a result of

nutrient A nutrient is a substance used by an organism to survive, grow and reproduce. The requirement for dietary nutrient intake applies to animals, plants, fungi and protists. Nutrients can be incorporated into cells for metabolic purposes or excret ...

deprivation. The growth may be with respect to weight or length (or height in humans). For example, the body weights of animals who experience nutritional restriction will often over time become similar to those of animals who did not experience such stress. It is possible for high compensatory growth rates to result in overcompensation, where the organism exceeds normal weight and often has excessive fat deposition. An organism can recover to normal weight without additional time. Sometimes when the nutrient restriction is severe, the growth period is extended to reach the normal weight. If the nutrient restriction is severe enough, the organism may have permanent

stunted growth Stunted growth, also known as stunting or linear growth failure, is defined as impaired growth and development manifested by low height-for-age. Stunted growth is often caused by malnutrition, and can also be caused by Endogeny (biology), endogeno ...

where it does not ever reach normal weight. Usually in animals, complete recovery from

carbohydrate A carbohydrate () is a biomolecule composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The typical hydrogen-to-oxygen atomic ratio is 2:1, analogous to that of water, and is represented by the empirical formula (where ''m'' and ''n'' ...

and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

restriction occurs. Compensatory growth has been observed in a number of organisms including

human Humans (''Homo sapiens'') or modern humans are the most common and widespread species of primate, and the last surviving species of the genus ''Homo''. They are Hominidae, great apes characterized by their Prehistory of nakedness and clothing ...

s, other species of

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

fish A fish (: fish or fishes) is an aquatic animal, aquatic, Anamniotes, anamniotic, gill-bearing vertebrate animal with swimming fish fin, fins and craniate, a hard skull, but lacking limb (anatomy), limbs with digit (anatomy), digits. Fish can ...

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s (especially

grass Poaceae ( ), also called Gramineae ( ), is a large and nearly ubiquitous family (biology), family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos, the grasses of natural grassland and spe ...

es and young tree

seedling A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...

s and saplings),

fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...

microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

pig The pig (''Sus domesticus''), also called swine (: swine) or hog, is an omnivorous, domesticated, even-toed, hoofed mammal. It is named the domestic pig when distinguishing it from other members of the genus '' Sus''. Some authorities cons ...

s, and

damselflies Damselflies are flying insects of the suborder Zygoptera in the order Odonata. They are similar to dragonflies (which constitute the other odonatan suborder, Epiprocta) but are usually smaller and have slimmer bodies. Most species fold the win ...

History

In 1911, Hans Aron performed the earliest study of growth after periods of undernourishment. He underfed a dog and found that it still had the capacity to rapidly gain weight, though it did not reach the final weight of a dog that was fed normally. In 1915, Osborne and Mendel were the first to demonstrate that rats fed after growth restriction had an accelerated growth rate. In 1945, Brody developed the idea of "homoestasis of growth" in the book ''Bioenergetics and Growth''. In 1955, Verle Bohman was the first to use the term "compensatory growth" in an article pertaining to

beef cattle Beef cattle are cattle raised for meat production (as distinguished from dairy cattle, used for milk (production)). The meat of mature or almost mature cattle is mostly known as beef. In beef production there are three main stages: cow-calf opera ...

Mechanism

In animals,

homeostatic In biology, homeostasis (British also homoeostasis; ) is the state of steady internal physical and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and includes many variables, su ...

and homeorhetic processes are involved in the abnormally high growth rates. Homeostatic processes usually affect compensatory growth in the short term, whereas homeorhetic processes usually have a long-term effect. First, during nutrient starvation, a reduction of basal metabolism takes place. The gut tissues are the first tissues to be reduced in weight and activity. Then, during the realimentation (re-feeding) phase, an increase in feeding enables more dietary protein and energy to be contributed for tissue growth instead of basal metabolism. The gut tissues are the first to increase in weight, followed by muscle tissue and finally adipose tissue. The exact biological mechanisms for compensatory growth remain poorly understood. However, it is known that during the restriction period, levels of

growth hormone Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...

(GH) are increased by the

pituitary gland The pituitary gland or hypophysis is an endocrine gland in vertebrates. In humans, the pituitary gland is located at the base of the human brain, brain, protruding off the bottom of the hypothalamus. The pituitary gland and the hypothalamus contr ...

, while the number of GH receptors decrease. There is a decrease in insulin-like growth factor (IGF-1) as well. When this restriction is severe,

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s are released from muscle cells and catabolic hormones circulate to initiate

gluconeogenesis Gluconeogenesis (GNG) is a metabolic pathway that results in the biosynthesis of glucose from certain non-carbohydrate carbon substrates. It is a ubiquitous process, present in plants, animals, fungi, bacteria, and other microorganisms. In verte ...

processes. Then, when compensation begins, the GH levels continue to remain high while insulin levels spike, allowing the GH to be used for growth processes. At first, lean muscle is built, but after a few weeks of refeeding, fat begins to accumulate on the organism. IGF-1 and thyroid hormones, on the other hand, approach normal levels much sooner. This may be why animals often have increased fat deposition after a period of refeeding.

Effects of compensatory growth

Compensatory growth in an organism can have impacts on the organism's behavior and muscle development. These changes can occur during or after the period of compensation, and can lead to changes in behavior, movement, and body composition. During compensation, animals may experience changes in food intake, body composition (increased fat and lessened muscle), metabolism, and the endocrine system. Animals undergoing compensatory growth have been seen to have impaired muscle development after regrowth, which leads to impairments in locomotion and escape movements. Behavioral impacts such as increased risk-taking and aggression have also been seen, both during and after regrowth. Animals often have impaired movement due to lessened muscle development, yet they have been observed taking time during feeding, despite the risks of extended time spent eating. Brown trout ('' Salmon trutta)'' who have been treated with growth hormone after a period of deprivation have been observed to increase their growth rate but decrease their anti-predator responses, such as swimming in waters more accessible by predators. Increased aggression and decreased sexual displays have also been seen in animals undergoing compensatory growth.

Studies of growth in anorexic human patients

Anorexia nervosa Anorexia nervosa (AN), often referred to simply as anorexia, is an eating disorder characterized by Calorie restriction, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. Individuals wit ...

can have serious implications if its duration and severity are significant and if onset occurs before the completion of growth, pubertal maturation or prior to attaining peak bone mass. Both height gain and pubertal development are dependent on the release of growth hormone and gonadotrophins (LH and FSH) from the pituitary gland. Suppression of gonadotropins in patients with anorexia nervosa has been frequently documented. In some cases, especially where onset is pre-pubertal, physical consequences such as stunted growth and pubertal delay are usually fully reversible. Height potential is normally preserved if the duration and severity of anorexia nervosa are not significant and/or if the illness is accompanied with delayed bone age (especially prior to a bone age of approximately 15 years), as hypogonadism may negate the deleterious effects of undernutrition on stature by allowing for a longer duration of growth compared to controls. In such cases, appropriate early treatment can preserve height potential and may even help to increase it in some post-anorexic subjects due to the aforementioned reasons in addition to factors such as long-term reduced estrogen-producing

adipose tissue Adipose tissue (also known as body fat or simply fat) is a loose connective tissue composed mostly of adipocytes. It also contains the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, Blood vessel, vascular endothel ...

levels compared to premorbid levels.

Factors affecting compensatory growth

In 1960, Wilson and Osborne outlined six factors that could affect compensatory growth in a review article. The importance of each, some, or all of these factors is not well understood. These factors are as follows: * The nature of the restricted diet * The degree of severity of undernutrition * The duration of the period of undernutrition * The stage of development at the commencement of undernutrition * The relative rate of maturity of the species * The pattern of re-alimenation Animal factors that can affect compensatory growth may include the maturity level and fat proportion of the animal at the time of nutrient deprivation, the genotype, the gender, and the metabolic changes. The stage of development of the animal when the nutrient restriction occurs greatly affects its body composition.

References