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, oftentimes the body weights of animals who experience nutritional restriction will 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 where it does not ever reach normal weight. Usually in animals, complete recovery from

carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ma ...

and

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

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

human Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

s, other species of

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...

reptile Reptiles, as most commonly defined are the animals in the class Reptilia ( ), a paraphyletic grouping comprising all sauropsids except birds. Living reptiles comprise turtles, crocodilians, squamates (lizards and snakes) and rhynchocephalians ( ...

fish Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

s (especially

grass Poaceae () or Gramineae () is a large and nearly ubiquitous family of monocotyledonous flowering plants commonly known as grasses. It includes the cereal grasses, bamboos and the grasses of natural grassland and species cultivated in lawns an ...

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

sapling In botany, a tree is a perennial plant with an elongated stem, or trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondary growth, plants that are ...

s),

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

microbe A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s, pigs, 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, Anisoptera, but are smaller and have slimmer bodies. Most species fold the wings along ...

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.

Mechanism

In animals,

homeostatic In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) 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 i ...

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 Basal metabolic rate (BMR) is the rate of energy expenditure per unit time by endothermic animals at rest. It is reported in energy units per unit time ranging from watt (joule/second) to ml O2/min or joule per hour per kg body mass J/(h·kg). Pro ...

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 h ...

(GH) are increased by the

pituitary gland In vertebrate anatomy, the pituitary gland, or hypophysis, is an endocrine gland, about the size of a chickpea and weighing, on average, in humans. It is a protrusion off the bottom of the hypothalamus at the base of the brain. The ...

, 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 acids Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha am ...

are released from muscle cells and catabolic hormones circulate to initiate

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

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, often referred to simply as anorexia, is an eating disorder characterized by low weight, food restriction, body image disturbance, fear of gaining weight, and an overpowering desire to be thin. ''Anorexia'' is a term of Gr ...

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 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