Calorie restriction (caloric restriction or energy restriction) is a dietary regimen that reduces intake of energy from caloric foods & beverages without incurring

malnutrition Malnutrition occurs when an organism gets too few or too many nutrients, resulting in health problems. Specifically, it is "a deficiency, excess, or imbalance of energy, protein and other nutrients" which adversely affects the body's tissues ...

. "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. 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 Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level (hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

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

. 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. This study was conducted during

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...

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, ...

edema Edema, also spelled oedema, and also known as fluid retention, dropsy, hydropsy and swelling, is the build-up of fluid in the body's tissue. Most commonly, the legs or arms are affected. Symptoms may include skin which feels tight, the area ma ...

, muscle wasting,

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 Dizziness is an imprecise term that can refer to a sense of disorientation in space, vertigo, or lightheadedness. It can also refer to disequilibrium or a non-specific feeling, such as giddiness or foolishness. Dizziness is a common medical ...

, irritability,

lethargy Lethargy is a state of tiredness, sleepiness, weariness, fatigue, sluggishness or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overwor ...

, 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 effect In medicine, a side effect is an effect, whether therapeutic or adverse, that is secondary to the one intended; although the term is predominantly employed to describe adverse effects, it can also apply to beneficial, but unintended, consequence ...

s, 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,

infertility Infertility is the inability of a person, animal or plant to reproduce by natural means. It is usually not the natural state of a healthy adult, except notably among certain eusocial species (mostly haplodiploid insects). It is the normal st ...

, or hormonal changes.

Research

Humans

Decreasing caloric intake 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 showed that calorie restriction did not extend years of life or reduce age-related deaths in non-obese

rhesus macaque The rhesus macaque (''Macaca mulatta''), colloquially rhesus monkey, is a species of Old World monkey. There are between six and nine recognised subspecies that are split between two groups, the Chinese-derived and the Indian-derived. Generally b ...

s. 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 Fasting is the abstention from eating and sometimes drinking. From a purely physiological context, "fasting" may refer to the metabolic status of a person who has not eaten overnight (see " Breakfast"), or to the metabolic state achieved after co ...

blood glucose Glycaemia, also known as blood sugar level, blood sugar concentration, or blood glucose level is the measure of glucose concentrated in the blood of humans or other animals. Approximately 4 grams of glucose, a simple sugar, is present in the bl ...

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 review A review article is an article that summarizes the current state of understanding on a topic within a certain discipline. A review article is generally considered a secondary source since it may analyze and discuss the method and conclusions ...

s, 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 and AMPK) with DR are effective or most effective in humans is largely unknown and is being actively researched. A

geroscience Gerontology ( ) is the study of the social, cultural, psychological, cognitive, and biological aspects of aging. The word was coined by Ilya Ilyich Mechnikov in 1903, from the Greek , ''geron'', "old man" and , ''-logia'', "study of". The fiel ...

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 re ...

and a decline in inflammaging. 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 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 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

sirtuin Sirtuins are a family of signaling proteins involved in metabolic regulation. They are ancient in animal evolution and appear to possess a highly conserved structure throughout all kingdoms of life. Chemically, sirtuins are a class of proteins ...

s are activated by fasting and serve as "energy sensors" during

metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run c ...

. 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 h ...

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

s. 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.

References

Bibliography

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