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Calorie Restriction

Calorie restriction (caloric restriction or energy restriction) is a dietary regimen that reduces the energy intake from caloric foods & beverages without incurring malnutrition. Over the last half-century, there has been a surge in research interest in aging and the progression of age-related diseases. The effect of diet on longevity and age-related disease has been a particularly active area of research. Calorie restriction, also known as dietary restriction, is a frequently demonstrated topic within the field of aging; to significantly increase lifespan and reduce age-related disease. Even though many model organisms have consistently displayed favorable responses to calorie restriction, it remains unclear if calorie restriction will extend human lifespan.

The History of Calorie Restriction

In human history, involuntary instances of calorie restriction aren't unusual. Only a handful of these events did not result in malnutrition. This was a result of many government's enforced food restriction with sufficient consumption of essential nutritionally dense foods.

World War I & World War II

Denmark was a neutral nation during World War I, but the conflict continued to have an impact there, particularly in terms of food shortages. During World War I, the men and women of Denmark were forced to cut back on food consumption for two years. Given that Denmark was reliant on imported food throughout the war, many of the nations that produced the food had to put the needs of their citizens first. A significant amount of food supplies were also taken by German forces, who also occupied parts of Denmark, for their own use. Throughout the two-year food shortage, many families created well-planned and satisfactory meals consisting of whole-grain cereals, vegetables, and milk. The unintended caloric restriction experiment resulted in a 34% reduction in death rates. In a similar manner, during World War II, the citizens of Oslo were subjected to a forced 20% calorie restriction without malnutrition (for example, appropriate consumption of fresh vegetables, potatoes, fish, and whole cereals) for approximately 4 years.

The Centenarians of Okinawa

On the lovely island of Okinawa, which is situated 640 kilometers south of Japan's main island, a natural caloric restriction experiment was conducted. In Okinawa, it is estimated that 50 out of every 100,000 people are 100 years of age or older, which is 4-5 times higher than the average for all industrialized nations. Okinawan residents' mortality rates from ischemic heart disease and cancer (including prostate, colon, breast, and lymphoma) were significantly lower than those of the average mainland Japanese and US population. Okinawans lived longer lives on average and at their maximum potential in 1995 (average 83.8 years, maximum 104.9 years), when compared to mainland Japanese residents (82.3 years, 101.1 years), and Americans living in the USA. (78.9 years, 101.3 years). According to studies looking into Okinawan adults' eating habits, they consumed 40% fewer calories than the average adult in the United States, and 17% fewer calories than the average adult in Japan . It's important to note that the lower energy intake was not entirely attributable to the older populations' overeating (energy intake exceeding energy requirements). According to the Harris-Benedict energy requirements equation, Okinawans are thought to have a 10-15% energy intake deficit. The Okinawan diet is also said to be high in fresh fruits, vegetables, sweet potatoes, soy, and fish, and low in protein (9% of calories). Unfortunately, as a result of an increase in fast food restaurants introduced by US soldiers in the 1960s, Okinawans' eating habits have grown more Westernized, which has led to a rise in body mass index and mortality. In 2010, the average lifespan difference between Okinawan newborns and those on the Japanese mainland had vanished, but it remained higher for Okinawans 65 and older.

Research Results

More research, both in humans and in experimental animals, is required to fully understand the connections between single nutrient modifications, calorie restrictions, and regular exercise in the prevention of CVD, cancer, cognitive impairment/dementia, inflammatory diseases, sarcopenia, and immune senescence. Currently, there is a lack of adequately controlled long-term studies examining the impact of calorie restriction in humans. Although caloric restriction has the advantage of slowing down the reduction of muscle mass with age, the initial reduction of mass may be substantial and have an effect on a person's strength and endurance.

Minnesota Starvation Experiment

The groundbreaking "Minnesota Starvation Experiment" by Ancel Keys, describes the physical and psychological effects of extreme calorie restriction in a clinical experiment. 32 young and lean 24-year-old pacifists were carefully observed under a 40% reduction in energy intake for 6 months. The study was designed to mimic dietary conditions during World War II. Participants could only eat 1800 kcal per day, but were required to walk 5 km per day and burn off 3000 kcal. The men lost about 25% of their body weight by the end of the study, of which 67% was fat mass and 17% fat-free mass. The quality of the diet was insufficient to accurately represent the diet during war due to the inadequate consumption of protein, and a lack of fruits and vegetables. Despite the fact that this study was of extreme calorie restriction, it was not representative of true calorie-restrictive diets, which adhere to intake guidelines for macro and micro-nutrients. Chronic weakness, decreased aerobic capacity, and excruciatingly painful lower limb edema was caused by the malnourished calorie restrictive diet Severe emotional distress, confusion, apathy, depression, hysteria, hypochondriasis, suicidal thoughts, and loss of sex drive were among the abnormal psychological behaviors that became apparent by six weeks.

Non-Human Primates

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Health Effects

Calorie restriction has numerous health advantages for mammals, including a decline in age-related diseases like cancer. Despite the so-called "magic" of calorie restriction, there may be a number of health issues with this intervention in humans that might not be relevant to, or have an impact on, the lives of experimental animals but may be in humans. It is unknown at this time whether or not a calorie-restrictive diet reduces aging and increases the maximum lifespan in humans. Nevertheless, research on people who have engaged in long-term caloric restrictions without experiencing malnutrition shows that calorie restrictions oppose aging-related changes in myocardial stiffness and autonomic function.

Side Effects

Weakened Muscle Mass

It is hypothesized that having strong muscles in middle age may prevent people from becoming disabled in old age by giving them a bigger safety margin higher than the threshold of disability. Surgery and acute illness are two instances in which physical degeneration can happen. Functional disability is a legitimate concern in such circumstances given the already low muscle mass and muscle reserve resulting from a calorie restrictive lifestyle. Another "side effect" of calorie restriction is a slower rate of wound healing.Reduced collagen biosynthesis and cellular proliferation are linked to caloric restriction. Impaired wound healing may be caused by changes in growth factors, hormones, and other mitogen levels brought on by dietary restrictions.

The Risk of Malnutrition

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