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Calorie restriction (caloric restriction or energy restriction) is a dietary regimen that reduces intake of energy from caloric foods & beverages without incurring malnutrition. "Reduce" can be defined relative to the subject's previous intake before intentionally restricting food or beverage consumption, or relative to an average person of similar body type. Calorie restriction is typically adopted intentionally to reduce
body weight Human body weight is a person's mass or weight. Strictly speaking, body weight is the measurement of weight without items located on the person. Practically though, body weight may be measured with clothes on, but without shoes or heavy accessor ...
. It is recommended as a possible regimen by US dietary guidelines and scientific societies for body weight control.


Health effects


Recommendations

Caloric intake control, and reduction for overweight individuals, is recommended by US dietary guidelines and science-based societies. Calorie restriction is recommended for people with diabetes and prediabetes, in combination with physical exercise and a weight loss goal of 5-15% for diabetes and 7-10% for prediabetes to prevent progression to diabetes. and mild calorie restriction may be beneficial for pregnant women to reduce weight gain (without weight loss) and reduce perinatal risks for both the mother and child. For overweight or obese individuals, calorie restriction may improve health through weight loss, although a gradual weight regain of per year may occur.


Risks of malnutrition

The term "calorie restriction" as used in the study of aging refers to dietary regimens that reduce calorie intake without incurring malnutrition. If a restricted diet is not designed to include essential nutrients, malnutrition may result in serious deleterious effects, as shown in the
Minnesota Starvation Experiment The Minnesota Starvation Experiment, also known as the Minnesota Semi-Starvation Experiment, the Minnesota Starvation-Recovery Experiment and the Starvation Study, was a clinical study performed at the University of Minnesota between November 19, 1 ...
. This study was conducted during World War II on a group of lean men, who restricted their calorie intake by 45% for six months and composed roughly 77% of their diet with carbohydrates.Keys A, Brozek J, Henschels A & Mickelsen O & Taylor H. The Biology of Human Starvation, 1950. University of Minnesota Press, Minneapolis As expected, this malnutrition resulted in metabolic adaptations, such as decreased body fat, improved lipid profile, and decreased resting heart rate. The experiment also caused negative effects, such as
anemia Anemia or anaemia (British English) is a blood disorder in which the blood has a reduced ability to carry oxygen due to a lower than normal number of red blood cells, or a reduction in the amount of hemoglobin. When anemia comes on slowly, t ...
, edema,
muscle wasting Muscle atrophy is the loss of skeletal muscle mass. It can be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system. Muscle atrophy leads to muscle weakness ...
,
weakness Weakness is a symptom of a number of different conditions. The causes are many and can be divided into conditions that have true or perceived muscle weakness. True muscle weakness is a primary symptom of a variety of skeletal muscle diseases, i ...
, dizziness, irritability, lethargy, and depression. Typical low-calorie diets may not supply sufficient nutrient intake that is typically included in a calorie restriction diet.


Side effects

People losing weight during calorie restriction risk developing side effects, such as
cold sensitivity Cold sensitivity or cold intolerance is unusual discomfort felt by some people when in a cool environment. There is much variation in the sensitivity to cold experienced by different people, with some putting on many layers of clothing while other ...
,
menstrual irregularities Irregular menstruation is a menstrual disorder whose manifestations include irregular cycle lengths as well as metrorrhagia (vaginal bleeding between expected periods). The possible causes of irregular menstruation may vary. The common factors of ...
, infertility, or hormonal changes.


Research


Humans

Decreasing
caloric intake The calorie is a unit of energy. For historical reasons, two main definitions of "calorie" are in wide use. The large calorie, food calorie, or kilogram calorie was originally defined as the amount of heat needed to raise the temperature of on ...
by 20-30%, while fulfilling nutrient requirements, has been found to remedy diseases of aging, including cancer, cardiovascular disease, dementia, and diabetes in humans, and result in an average loss of in body weight, but because of the long lifespan of humans, evidence that caloric restriction could prevent age-related disease in humans is still emerging. While calorie restriction has beneficial effects, especially in relation to weight and fat loss, the precise amount of calorie intake and associated fat mass for optimal health in humans is not known. It is conceivable that even moderate amounts of calorie restriction might have harmful effects on certain population groups, such as lean people with low body fat.


Non-human primates

A calorie restriction study started in 1987 by the
National Institute on Aging The National Institute on Aging (NIA) is a division of the U.S. National Institutes of Health (NIH), located in Bethesda, Maryland. The NIA itself is headquartered in Baltimore, Maryland. The NIA leads a broad scientific effort to understand the ...
showed that calorie restriction did not extend years of life or reduce age-related deaths in non-obese rhesus macaques. It did improve certain measures of health, however. These results were publicized as being different from the Wisconsin rhesus macaque calorie restriction study, which also started in 1987 and showed an increase in the lifespan of rhesus macaques following calorie restriction. In a 2017 report on rhesus monkeys, caloric restriction in the presence of adequate nutrition was effective in delaying the effects of aging. Older age of onset, female sex, lower body weight and fat mass, reduced food intake, diet quality, and lower fasting blood glucose levels were factors associated with fewer disorders of aging and with improved survival rates. Specifically, reduced food intake was beneficial in adult and older primates, but not in younger monkeys. The study indicated that caloric restriction provided health benefits with fewer age-related disorders in elderly monkeys and, because rhesus monkeys are genetically similar to humans, the benefits and mechanisms of caloric restriction may apply to human health during aging.


Life extension

According to scientific reviews, accumulating data suggests dietary restriction (DR) – mainly intermittent fasting and caloric restriction – results in many of the same beneficial changes in adult humans as in studied organisms, potentially increasing health- and lifespan beyond the benefits of healthy body weight. Which protocols of and combinations (e.g. see
caloric restriction mimetic Calorie restriction mimetics (CRM), also known as energy restriction mimetics, are a hypothetical class of dietary supplements or drug candidates that would, in principle, mimic the substantial anti-aging effects that calorie restriction (CR) has o ...
and
AMPK AMPK may refer to: * AMP-activated protein kinase 5' AMP-activated protein kinase or AMPK or 5' adenosine monophosphate-activated protein kinase is an enzyme (EC 2.7.11.31) that plays a role in cellular energy homeostasis, largely to activate gl ...
) with DR are effective or most effective in humans is largely unknown and is being actively researched. A geroscience field of " precision nutrigeroscience" is proposed that also considers the potential need for adjustments of nutritional interventions per individual (e.g. due to differences in genetics and age). The mechanisms of these effects include
autophagy Autophagy (or autophagocytosis; from the Ancient Greek , , meaning "self-devouring" and , , meaning "hollow") is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent r ...
and a decline in
inflammaging Inflammaging (also known as inflamm-aging or inflamm-ageing) is a chronic, sterile low-grade inflammation that develops with advanced age, in the absence of overt infection, and may contribute to clinical manifestations of other age-related patho ...
. Intermittent fasting refers to periods with intervals during which no food but only e.g. water and tea/coffee are ingested – such as a period of daily time-restricted eating with a window of 8 to 12 hours for any caloric intake – and could be combined with overall caloric restriction and variants of the Mediterranean diet which usually has benefits of long-term cardiovascular health and longevity.


Activity levels

Calorie restriction preserves muscle tissue in nonhuman primates and rodents. Mechanisms include reduced muscle cell
apoptosis Apoptosis (from grc, ἀπόπτωσις, apóptōsis, 'falling off') is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes (morphology) and death. These changes includ ...
and inflammation; protection against or adaptation to age-related mitochondrial abnormalities; and preserved muscle
stem cell In multicellular organisms, stem cells are undifferentiated or partially differentiated cells that can differentiate into various types of cells and proliferate indefinitely to produce more of the same stem cell. They are the earliest type of ...
function. Muscle tissue grows when stimulated, so it has been suggested that the calorie-restricted test animals exercised more than their companions on higher calories, perhaps because animals enter a foraging state during calorie restriction. However, studies show that overall activity levels are no higher in calorie restriction than
ad libitum In music and other performing arts, the phrase (; from Latin for 'at one's pleasure' or 'as you desire'), often shortened to "ad lib" (as an adjective or adverb) or "ad-lib" (as a verb or noun), refers to various forms of improvisation. The r ...
animals in youth. Laboratory rodents placed on a calorie restriction diet tend to exhibit increased activity levels (particularly when provided with exercise equipment) at feeding time. Monkeys undergoing calorie restriction also appear more restless immediately before and after meals.


Sirtuin-mediated mechanism

Preliminary research indicates that sirtuins are activated by fasting and serve as "energy sensors" during metabolism. Sirtuins, specifically Sir2 (found in yeast) have been implicated in the aging of yeast, and are a class of
highly conserved In evolutionary biology, conserved sequences are identical or similar sequences in nucleic acids ( DNA and RNA) or proteins across species ( orthologous sequences), or within a genome ( paralogous sequences), or between donor and receptor taxa ( ...
, NAD+-dependent
histone deacetylase Histone deacetylases (, HDAC) are a class of enzymes that remove acetyl groups (O=C-CH3) from an ε-N-acetyl lysine amino acid on a histone, allowing the histones to wrap the DNA more tightly. This is important because DNA is wrapped around his ...
enzymes. Sir2 homologs have been identified in a wide range of organisms from bacteria to humans.


Hormesis

Some research has pointed toward hormesis as an explanation for the benefits of caloric restriction, representing beneficial actions linked to a low-intensity biological stressor such as reduced calorie intake. As a potential role for caloric restriction, the diet imposes a low-intensity biological stress on the organism, eliciting a defensive response that may help protect it against the disorders of aging. In other words, caloric restriction places the organism in a defensive state so that it can survive adversity.


Intensive care

, current clinical guidelines recommend that hospitals ensure that the patients get fed with 80–100% of energy expenditure, the normocaloric feeding. A systematic review investigated whether people in hospitals' intensive care units have different outcomes with normocaloric feeding or hypocaloric feeding, and found no difference. However, a comment criticized the inadequate control of protein intake, and raised concerns that hypocaloric feeding safety should be further assessed with underweight critically ill people.


See also

*
CR Society International The CR Society International (or CRSI) is a Non-profit organization, nonprofit 501(c)(3) organization that was previously known as the CR Society or Calorie Restriction Society. In 1994, Brian M. Delaney, Lisa Walford, and Roy Walford, along with ...
* Fasting * Intermittent fasting * List of diets * Luigi Cornaro *
Mitohormesis Hormesis is a characteristic of many biological processes, namely a biphasic or triphasic response to exposure to increasing amounts of a substance or condition. Within the hormetic zone, the biological response to low exposures to toxins and othe ...
* Okinawa diet * Very low calorie diet


References


Bibliography

* * {{DEFAULTSORT:Calorie Restriction Diets Eating behaviors Life extension Senescence